What Makes An Audio Op Amp An Audio Op Amp?
Abby Brown
What characteristics of an audio op-amp distinguish it from
other op amps? Which of those are most desirable for a high
quality circuit? Obviously, it needs appropriate bandwidth.
What isn't important? If AC coupled is DC behavior relevant?
Just curious. I have made a few simple audio circuits as a
hobby. In the past I've selected whatever was locally available
listed as an audio op-amp.
Thanks,
Gary
Vladimir Vassilevsky
Abby Brown wrote:
> Hi,
>
> What characteristics of an audio op-amp distinguish it from
> other op amps?
Audio opamp = a very cheap yet not extremely bad opamp.
> Which of those are most desirable for a high
> quality circuit?
Inexpensiveness.
> Obviously, it needs appropriate bandwidth.
Slew rate ~ 1 V/V, reasonably low noise.
> What isn't important?
Nothing is very important.
> If AC coupled is DC behavior relevant?
Depends.
> Just curious. I have made a few simple audio circuits as a
> hobby. In the past I've selected whatever was locally available
> listed as an audio op-amp.
Now try some other opamps. There won't be any difference except for
pathological cases.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Bill Sloman
Mainly, the capacity to drive relatively low impedance loads. The
standard loudspeaker looks quite like an 8-ohm resistor, and regular
integrated circuit op amps aren't designed to drive resistance that
low.
Bob Widlar's LM12 integrated circuit amplifier is an exception, but it
doesn't seem to have been cheap enough - or sufficiently easy to heat-
sink - to take the audio world by storm.
Class-D switching power amplifiers are more efficient, so they don't
require as much heat-sink area to survive when delivering useful
amounts of power to audio speakers (which aren't all that efficient at
converting electrical power into acoustic power) but they can have a
tendency to mix the switching frequency with the music signals that
they are amplifying, which has given them a bad name in the audio
community.
--
Bill Sloman, Nijmegen
Spehro Pefhany
4558s are acceptable for many audio applications. Two op-amps in an
8-pin package for under a dime in reasonable quantity.
John Larkin
<abby...@charter.net> wrote:
>Hi,
>
>What characteristics of an audio op-amp distinguish it from
>other op amps?
Superstition, mostly. Some really bad opamps are popular because
people think they sound good.
Which of those are most desirable for a high
>quality circuit? Obviously, it needs appropriate bandwidth.
>What isn't important? If AC coupled is DC behavior relevant?
>
>Just curious. I have made a few simple audio circuits as a
>hobby. In the past I've selected whatever was locally available
>listed as an audio op-amp.
Just don't use LM324 types. They have visible distortion at 60 Hz.
John
Gz
It's not clear if it's just interstage opamps or driver.. Stability,
noise, on off stability, circuitry involved can dictate bipolar or
not.
Greg
Raveninghorde
<abby...@charter.net> wrote:
The NE5532 was always a popular audio op amp as, unlike a lot of other
op amps, it does not under go phase reversal of the output signal when
overloaded.
From memory it was also specifed to drive 600 ohms.
Mark Fergerson
dnRA_JaBkWYjTn...@supernews.com:
I want to help, but you left out some important information. I don't
know your level of "formal" education so I'll hit a few high points.
Please don't feel insulted.
An amplifier is basically just a device with gain (can amplify a
signal) to which is added a feedback path to "feed back" some of the
output to the input. That signal adds to or subtracts from the signal to
be amplified, roughly setting the gain factor.
Different kinds of gain elements and feedback topologies give "good
results" (adequate values of gain, linearity, noise, etc.) at various
frequencies. Audio means signals in the frequency range humans can hear;
optimistically, 20 Hz to 20 kHz.
Operational amplifiers were intended to be one-size-fits-all devices
that you can hang components onto to make pretty much any kind of active
circuit element. They were invented to stand in for linear and nonlinear
amplifiers, integrators, differentiators, and other bits of analog
computers. With them you can damn near anything from fake inductors to a
sort of tunnel diode.
Hence an "audio op amp" is simply one that provides "good results" at
audio frequencies. You have to define what "good" means in your specific
situation, though, which is why there's more than one kind of opamp out
there.
(OK, I left out some details.) ;>)
Now, about the "important information" you left out. What fidelity do
you require? What's your load? How much power and heat are you willing
to handle?
Answer those questions, find opamp data sheets, decide where you're
willing to compromise, select.
Depending on your answers, a 741 could be adequate (not likely, but
still) or you might be forced to give up on opamps entirely and think
vacuum tubes instead.
Mark L. Fergerson
Glenn Gundlach
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
<snip>
>
> Just don't use LM324 types. They have visible distortion at 60 Hz.
>
> John
They're not even good as 14 pin thumbtacks.
G²
Glenn Gundlach
>
> >Thanks,
> >Gary
>
> The NE5532 was always a popular audio op amp as, unlike a lot of
other
> op amps, it does not under go phase reversal of the output signal
when
> overloaded.
>
> From memory it was also specifed to drive 600 ohms.
Most audio you hear has gone through an army of 5532s.
G²
John Larkin
But, somehow, passing them through one more tube produces "stunning"
improvements in "musicality" or "macrodynamics" or something.
John
NT
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Thu, 7 Jul 2011 10:38:45 -0400, "Abby Brown"
>
I love 324s, theyre cheaper than taking a dump. Distortion depends a
lot on how theyre loaded, not that theyre ever quality performers.
NT
Jim Thompson
Once upon a time they were the least expensive thing around. For low
distortion you simply bled enough output DC current to make it
class-A. Larkin wouldn't know that in spite of me mentioning it
dozens of times here.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Raveninghorde
>G�
Back when I made audio/video kit, pre DVD, for studios we did indeed
use the NE5532s by the bucket full.
Another advantage of the NE5532 for audio is that it has an abs max
+/-22V supplies compared to the more normal +/-18V or for the
LM358/LM324 +/-16V. This allows one to design with more head room on
the signal.
Jamie
Yup. I guess lack of shoot through on the cross over would do that!
Jamie
Jamie
if memory serves, aren't those equivalent to the 741 ?
Jamie
Phil Allison
"Vladimir Vassilevsky"
>
> Abby Brown wrote:
>>
>> What characteristics of an audio op-amp distinguish it from other op
>> amps?
>
> Audio opamp = a very cheap yet not extremely bad opamp.
** What absolute BOLLOCKS !!!
Piss off to hell - you stupid jerk.
.... Phil
Gz
Faster, very similar to 4136's quads.
Greg
Phil Allison
"Bill Slowman"
>
> What characteristics of an audio op-amp distinguish it from
> other op amps? Which of those are most desirable for a high
> quality circuit? Obviously, it needs appropriate bandwidth.
> What isn't important? If AC coupled is DC behavior relevant?
>
> Just curious. I have made a few simple audio circuits as a
> hobby. In the past I've selected whatever was locally available
> listed as an audio op-amp.
Mainly, the capacity to drive relatively low impedance loads.
** Huh ???
Read the friggin question !!!
.... Phil
Phil Allison
"Jamie the Radio Ham jerk "
>> 4558s are acceptable for many audio applications. Two op-amps in an
>> 8-pin package for under a dime in reasonable quantity.
>>
> if memory serves, aren't those equivalent to the 741 ?
** No.
Look it up - fool.
.... Phil
Gz
I thought he was making a turntable preamplifier.
Greg
Jamie
I think has a 1458 on my mind..
Jamie
Gz
Opa132's were pretty good, bidet.
National now has some rather spectacular chips at least specs look
good.
Greg
Phil Allison
"Abby Brown"
** Particular devices are referred to as "audio op-amps " for the simple
reason that they are most commonly found being used in audio equipment.
Q. What op-amps do audio designers like to use ?
A. Ones that can economically replace discrete transistor, small signal
audio circuits with equivalent or better performance.
Back in the late 1960s, when general purpose op-amps like the 741 and 301A
became available at low enough cost, audio designers pounced on them for the
reason given above.
The next step in reducing board area and circuit cost was by employing dual
and quad op-amps like the 4558 and 4136 - which were intended to be used in
audio circuits.
The game is all about cost and often the op-amps used have performance
characteristics way beyond what is strictly needed for processing audio
signals.
.... Phil
k...@att.bizzzzzzzzzzzz
The LM833 is still our go-to high-voltage opamp.
Bill Sloman
> On Thu, 7 Jul 2011 10:38:45 -0400, "Abby Brown"
>
The fact that it has a typical input noise voltage of 5nV per root Hz
(worst case 6nV) at 1kHz also played a part.
There are plenty of lower noise op amps around, but the NE5532 was
cheap and available in volume.
--
Bill Sloman, Nijmegen
Dirk Bruere at NeoPax
Probably the 742 ie with 2 per pack, as opposed to the 744 etc
--
Dirk
http://www.neopax.com/technomage/ - My new book - Magick and Technology
Bill Sloman
> "BillSlowman"
Hi Phil. Nice to hear from you. I'm in Sydney at the moment - we
should get together for coffee.
According to the Sydney Morning Herald, "Bill's" (no relation) serves
the best coffee in Sydney, and it's on Liverpool Street in
Darlinghurst, five minutes walk from where I'm living. It's a bit
noisy for anybody who makes the money in audio, but "The Bunker" -
which is a block closer along Liverpool Street - is much quieter, and
teh coffee is almost as good.
Send me an e-mail at bill....@ieee.org ...
--
Bill Sloman, Darlinghurst (at the moment)
Phil Allison
"Dirk Bruere at NeoPax"
Phil Allison wrote:
"Jamie the Radio Ham jerk"
>
>>
>>>> 4558s are acceptable for many audio applications. Two op-amps in an
>>>> 8-pin package for under a dime in reasonable quantity.
>>>>
>>> if memory serves, aren't those equivalent to the 741 ?
>>
>>
>> ** No.
>>
>> Look it up - fool.
>
>
** The dual of the 741 is the LM747 - in 14 pin DIL.
http://www.national.com/ds/LM/LM747.pdf
Or in 8 pin DIL the LM1458
http://www.national.com/ds/LM/LM1458.pdf
The quad 741 is the LM148 - also in 14 pin DIL.
http://www.national.com/ds/LM/LM148.pdf
.... Phil
Jan Panteltje
Gundlach <stra...@yahoo.com> wrote in
<57c5509b-0a5d-48fe...@m10g2000yqd.googlegroups.com>:
I disagree, I have used them a lot, not for audio mind you.
Seems to work great in my thermocouple setup, and in my fluxgate compass.
http://panteltje.com/panteltje/pic/th_pic/
http://panteltje.com/panteltje/pic/mag_pic/
George Herold
wrote:
What do you mean by high-voltage? The supply voltage? +/- 18V
doesn't seem that high? (I'd love an opamp that worked with maybe 50
or 60 volts of supply, without having to use an expensive Apex part.)
George H.
John Larkin
OPA552.
John
George Herold
>
> - Show quoted text -
Thanks,
k...@att.bizzzzzzzzzzzz
wrote:
>On Jul 7, 8:37 pm, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
>wrote:
>> On Thu, 7 Jul 2011 16:44:01 -0700 (PDT), Gz <ze...@comcast.net> wrote:
>> >I was using some lm833's in the 80's. Like an up graded 1458.
>> >Opa132's were pretty good, bidet.
>> >National now has some rather spectacular chips at least specs look
>> >good.
>>
>> The LM833 is still our go-to high-voltage opamp.
>
>What do you mean by high-voltage?
Anything above 5V. ;-) That generally means 24-30V.
>The supply voltage? +/- 18V doesn't seem that high?
It is when you have to boost to get there. When almost everything else is
3.3V or 5V, 30V is *high*. ;-)
>(I'd love an opamp that worked with maybe 50
>or 60 volts of supply, without having to use an expensive Apex part.)
Use the trick Larkin has shown here a few times, with the FETs driven from
bias networks in the power leads.
John Larkin
If you cascode that, you can go to +-500 volt rails from a low-voltage
opamp.
And there's my ought-to-be-famous HV opamp circuit...
ftp://jjlarkin.lmi.net/HVamp.JPG
John
k...@att.bizzzzzzzzzzzz
But where does FB go? ;-)
John Larkin
<k...@att.bizzzzzzzzzzzz> wrote:
Wherever you like. It's an opamp.
Cool thing is that the rails don't have to be +-200. They could be -50
and +350, or +2000 and +2400.
John
George Herold
wrote:
> On Fri, 8 Jul 2011 08:36:35 -0700 (PDT), George Herold <gher...@teachspin.com>
Hmm, I thought I needed BJT's in the power leads. I thought it was a
current gain circuit.
George H.
George Herold
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 08 Jul 2011 18:06:35 -0500, "k...@att.bizzzzzzzzzzzz"
>
>
>
>
>
> <k...@att.bizzzzzzzzzzzz> wrote:
> >wrote:
>
> >>On Jul 7, 8:37 pm, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
> >>wrote:
> >>> On Thu, 7 Jul 2011 16:44:01 -0700 (PDT), Gz <ze...@comcast.net> wrote:
> >>> >I was using some lm833's in the 80's. Like an up graded 1458.
> >>> >Opa132's were pretty good, bidet.
> >>> >National now has some rather spectacular chips at least specs look
> >>> >good.
>
> >>> The LM833 is still our go-to high-voltage opamp.
>
> >>What do you mean by high-voltage?
>
> >Anything above 5V. ;-) That generally means 24-30V.
>
> >>The supply voltage? +/- 18V doesn't seem that high?
>
> >It is when you have to boost to get there. When almost everything else is
> >3.3V or 5V, 30V is *high*. ;-)
>
> >>(I'd love an opamp that worked with maybe 50
> >>or 60 volts of supply, without having to use an expensive Apex part.)
>
> >Use the trick Larkin has shown here a few times, with the FETs driven from
> >bias networks in the power leads.
>
> If you cascode that, you can go to +-500 volt rails from a low-voltage
> opamp.
>
> And there's my ought-to-be-famous HV opamp circuit...
>
> ftp://jjlarkin.lmi.net/HVamp.JPG
>
>
> - Show quoted text -
That's Great! It's a current 'gain' thing again. I could do with a
fairly low time constant, does the FB take care of the cross over
distortion?
George H.
George Herold
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 08 Jul 2011 18:41:14 -0500, "k...@att.bizzzzzzzzzzzz"
>
>
>
>
>
> <k...@att.bizzzzzzzzzzzz> wrote:
> >On Fri, 08 Jul 2011 16:36:25 -0700, John Larkin
> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> >>On Fri, 08 Jul 2011 18:06:35 -0500, "k...@att.bizzzzzzzzzzzz"
> >><k...@att.bizzzzzzzzzzzz> wrote:
>
>
> - Show quoted text -
OK now I need an opamp with low idle current. (did you already
recommend one?)
George H.
k...@att.bizzzzzzzzzzzz
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
But it has to feed back to the difference amplifier. How?
>Cool thing is that the rails don't have to be +-200. They could be -50
>and +350, or +2000 and +2400.
...just like an opamp. ;-)
k...@att.bizzzzzzzzzzzz
wrote:
>On Jul 8, 8:20 pm, John Larkin
Define "low".
k...@att.bizzzzzzzzzzzz
wrote:
>On Jul 8, 7:06 pm, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
Nope. FETs work as the amplifier, too.
>I thought it was a current gain circuit.
That too. ;-)
John Larkin
<k...@att.bizzzzzzzzzzzz> wrote:
Resistors?
John
John Larkin
The Iq of the opamp keeps both optos on a little all the time, so it's
class AB, mild crossover distortion. But sure, it needs feedback to be
linear. The opamp is an integrator, so DC error is nill.
This is good for biasing physics-type things, like electrodes in
vacuum and such. I first used it to set the voltages in a
microchannel-plate delay-line imager for a weird instrument.
If the domiant compensation pole is a biggish cap to ground from the
output, that hardens it against arcs and such and obviously makes it
capacitive-load tolerant. It's easy to make it short-circuit
protected, too.
Think kilohertz, not megahertz.
Another circuit I like is
ftp://jjlarkin.lmi.net/Opto_Totem.JPG
which is a pair of optoisolators working totem-pole. It behaves like
cmos, in that there's zero static power consumption on the isolated
side.
Optoisolators are great as long as you don't use them the way they
were intended.
John
John Larkin
<k...@att.bizzzzzzzzzzzz> wrote:
Mosfets have decently high current gain.
John
Phil Hobbs
(Of course one can't always be sure of the sign.)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net
k...@att.bizzzzzzzzzzzz
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
Kinda defeats the purpose of the isolators.
k...@att.bizzzzzzzzzzzz
Beat me to it. ;-)
John Larkin
<k...@att.bizzzzzzzzzzzz> wrote:
>>>>>>And there's my ought-to-be-famous HV opamp circuit...
>>>>>>
>>>>>>ftp://jjlarkin.lmi.net/HVamp.JPG
>>>>>>
>>>>>
>>>>>But where does FB go? ;-)
>>>>
>>>>
>>>>Wherever you like. It's an opamp.
>>>
>>>But it has to feed back to the difference amplifier. How?
>>
>>Resistors?
>
>Kinda defeats the purpose of the isolators.
The isolators aren't there to be isolators. They are high-voltage gain
stages. Can you think of a simpler or cheaper way to get 400 volts p-p
swing?
John
Dirk Bruere at NeoPax
Glenn Gundlach
Web-Site.com> wrote:
> On Thu, 7 Jul 2011 11:52:08 -0700 (PDT), Glenn Gundlach
>
> <stratu...@yahoo.com> wrote:
> >On Jul 7, 8:08 am, John Larkin
> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> ><snip>
>
> > > Just don't use LM324 types. They have visible distortion at 60 Hz.
>
> > > John
>
> >They're not even good as 14 pin thumbtacks.
>
> >G²
>
low
> distortion you simply bled enough output DC current to make it
> class-A. Larkin wouldn't know that in spite of me mentioning it
> dozens of times here.
>
> ...Jim Thompson
> --
> | James E.Thompson, CTO | mens |
> | Analog Innovations, Inc. | et |
> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
> | Phoenix, Arizona 85048 Skype: Contacts Only | |
> | Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
> | E-mail Icon athttp://www.analog-innovations.com| 1962 |
>
> I love to cook with wine. Sometimes I even put it in the food.
Many years back ('78 or so) I was using opamp followers mixing
multiple frequency sawtooth (max freq 8.1KHz) in a heavily modified
Schober electronic organ. I was getting the strangest mixes I could
imagine and for an experiment swapped out all the LM324s with TL074s
and the problem vanished. My best explanation was output slew rate
limits caused some sort of back conduction through the input diff
pairs. Plausible ?
G²
Glenn Gundlach
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
<snip>
> >>ftp://jjlarkin.lmi.net/HVamp.JPG
>
> >But where does FB go? ;-)
>
> Wherever you like. It's an opamp.
>
> Cool thing is that the rails don't have to be +-200. They could be
-50
> and +350, or +2000 and +2400.
>
> John
Direct coupled electrostatic headphone amplifier?
G²
Simon S Aysdie
> Hi,
>
> What characteristics of an audio op-amp distinguish it from
> other op amps? Which of those are most desirable for a high
> quality circuit? Obviously, it needs appropriate bandwidth.
> What isn't important? If AC coupled is DC behavior relevant?
>
> Just curious. I have made a few simple audio circuits as a
> hobby. In the past I've selected whatever was locally available
> listed as an audio op-amp.
>
> Thanks,
> Gary
For "hi-fi" check out the data sheets for
TL072A "just good enough, and cheap" (Similar to LF351 & LF356 ?)
OPA2134 "a bit better"
Phil Hobbs
>
> OPA2134 "a bit better"
>
Besides adequately low noise and high drive, "audio" op amps usually
have crap input offsets.
Jim Thompson
<pcdhSpamM...@electrooptical.net> wrote:
>Simon S Aysdie wrote:
>> On Jul 7, 7:38 am, "Abby Brown"<abbybr...@charter.net> wrote:
>>> Hi,
>>>
>>> What characteristics of an audio op-amp distinguish it from
>>> other op amps? Which of those are most desirable for a high
>>> quality circuit? Obviously, it needs appropriate bandwidth.
>>> What isn't important? If AC coupled is DC behavior relevant?
>>>
>>> Just curious. I have made a few simple audio circuits as a
>>> hobby. In the past I've selected whatever was locally available
>>> listed as an audio op-amp.
>>>
>>> Thanks,
>>> Gary
>>
>> For "hi-fi" check out the data sheets for
>>
>> TL072A "just good enough, and cheap" (Similar to LF351& LF356 ?)
>>
>> OPA2134 "a bit better"
>>
>
>Besides adequately low noise and high drive, "audio" op amps usually
>have crap input offsets.
>
>Cheers
>
>Phil Hobbs
Like it matters with audio and DC-centering loops ?:-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Phil Hobbs
> On Sat, 09 Jul 2011 16:05:28 -0400, Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
>> Simon S Aysdie wrote:
>>> On Jul 7, 7:38 am, "Abby Brown"<abbybr...@charter.net> wrote:
>>>> Hi,
>>>>
>>>> What characteristics of an audio op-amp distinguish it from
>>>> other op amps? Which of those are most desirable for a high
>>>> quality circuit? Obviously, it needs appropriate bandwidth.
>>>> What isn't important? If AC coupled is DC behavior relevant?
>>>>
>>>> Just curious. I have made a few simple audio circuits as a
>>>> hobby. In the past I've selected whatever was locally available
>>>> listed as an audio op-amp.
>>>>
>>>> Thanks,
>>>> Gary
>>>
>>> For "hi-fi" check out the data sheets for
>>>
>>> TL072A "just good enough, and cheap" (Similar to LF351& LF356 ?)
>>>
>>> OPA2134 "a bit better"
>>>
>>
>> Besides adequately low noise and high drive, "audio" op amps usually
>> have crap input offsets.
>>
>> Cheers
>>
>> Phil Hobbs
>
> Like it matters with audio and DC-centering loops ?:-)
>
> ...Jim Thompson
Of course. It saves a few pennies, and nobody cares, so why not?
Jim Thompson
<pcdhSpamM...@electrooptical.net> wrote:
I doubt that it saves pennies, just substantially safer to compensate
the loop if you don't overdo the open loop gain.
upsid...@downunder.com
Has anyone actually used tubes and optoisolators in the same design ?
Jamie
You worry too much! :)
Just apply a couple of small bypass caps at the OP-AMP rails. That
will should give you a little shoot through while it's switching over..
P.S.
I noticed that the output there is not going to be symmetrical, but
who cares about .7 volts verses .2 when you're dealing 200 volts.
Jamie
John Larkin
The place for a cap is between the opamp supply pins.
If you want more opto quiescent current, to push it more class A, add
a resistor there as well. But in real life, with a little luck, the
opamp supply current provides the quiescent optotransistor bias.
>
> P.S.
> I noticed that the output there is not going to be symmetrical, but
>who cares about .7 volts verses .2 when you're dealing 200 volts.
Why is it asymmetric? The optos are identical.
John
John Larkin
<stra...@yahoo.com> wrote:
>G�
This circuit tends to be slow, and won't output much current. Adding
b-e resistors to the output transistors will speed it up some, at the
cost of CTR. This circuit is best for slow HV stuff, like biasing
electrodes.
Adding cascode transistors would help speed a lot, but that wrecks the
nice simplicity.
Depletion mode mosfets might be interesting additions.
John
John Larkin
LM324's shared the bias current sources among all four sections. So
when one section railed or slew limited, it would collapse the current
sources and trash the other opamp sections. I tried using 324's as
comparators once, just once. Channel-channel interaction made it
unworkable. Crappy opamp design.
Bifet opamps, like LF347, make pretty good medium-slow comparators.
The other problem with LM324 (I emphasize LM, because I don't know if
anybody else's is better) is that a tiny amount of ESD diode current
in the negative direction, on any of the inputs, will spray charge all
over the chip and do all sorts of nasty things. Did I mention that
this is a crappy opamp?
Thompson is long on strutting and short on facts. I discovered the
trick of loading the output to reduce crossover distortion, but my fix
was to buy a better opamp. HC4046 charge pump, ditto.
John
Phil Hobbs
The 4046 phase detector problem isn't the same as the 324's. You don't
have to turn off the pulldown, you just need to nudge the output
slightly one way or the other. That's a minor wart as opposed to a
fundamental design flaw like the LM324's bias problem (which I didn't
know about--I've never tried doing anything much with 324s).
The metal-gate 4046 is an excellent part otherwise. The HC4046, now,
_that_'s a botch. They took a nice 1000:1 VCO design, which was quite
pretty in a small way, and turned it into a 10:1 VCO that simply quits
if its control voltage gets too low. If you try building a fancy loop
with that, you're in for a surprise. I occasionally use the HC part for
its phase detector, but never for its oscillator.
Jim Thompson
<pcdhSpamM...@electrooptical.net> wrote:
>John Larkin wrote:
>> On Sat, 9 Jul 2011 12:25:02 -0700 (PDT), Glenn Gundlach
>> <stra...@yahoo.com> wrote:
>>
>>> On Jul 7, 1:28 pm, Jim Thompson<To-Email-Use-The-Envelope-I...@On-My-
>>> Web-Site.com> wrote:
>>>> On Thu, 7 Jul 2011 11:52:08 -0700 (PDT), Glenn Gundlach
>>>>
>>>> <stratu...@yahoo.com> wrote:
>>>>> On Jul 7, 8:08 am, John Larkin
>>>>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>>>> <snip>
>>>>
>>>>>> Just don't use LM324 types. They have visible distortion at 60 Hz.
>>>>
>>>>>> John
>>>>
>>>>> They're not even good as 14 pin thumbtacks.
>>>>
>>>>> G²
>>>>
>>>> Once upon a time they were the least expensive thing around. For
>>> low
>>>> distortion you simply bled enough output DC current to make it
>>>> class-A. Larkin wouldn't know that in spite of me mentioning it
>>>> dozens of times here.
>>>>
>>>> ...Jim Thompson
>>>> --
[snip]
>>>
>>> Many years back ('78 or so) I was using opamp followers mixing
>>> multiple frequency sawtooth (max freq 8.1KHz) in a heavily modified
>>> Schober electronic organ. I was getting the strangest mixes I could
>>> imagine and for an experiment swapped out all the LM324s with TL074s
>>> and the problem vanished. My best explanation was output slew rate
>>> limits caused some sort of back conduction through the input diff
>>> pairs. Plausible ?
>>>
>>> G²
>>
>> LM324's shared the bias current sources among all four sections. So
>> when one section railed or slew limited, it would collapse the current
>> sources and trash the other opamp sections. I tried using 324's as
>> comparators once, just once. Channel-channel interaction made it
>> unworkable. Crappy opamp design.
>>
>> Bifet opamps, like LF347, make pretty good medium-slow comparators.
>>
>> The other problem with LM324 (I emphasize LM, because I don't know if
>> anybody else's is better) is that a tiny amount of ESD diode current
>> in the negative direction, on any of the inputs, will spray charge all
>> over the chip and do all sorts of nasty things. Did I mention that
>> this is a crappy opamp?
>>
>> Thompson is long on strutting and short on facts. I discovered the
>> trick of loading the output to reduce crossover distortion, but my fix
>> was to buy a better opamp. HC4046 charge pump, ditto.
>>
>> John
Reporting from Long Island... bias behavior depended on brand. Whilst
at GenRad I banned Motorola 324's from the purchasing list.
>>
>
>The 4046 phase detector problem isn't the same as the 324's. You don't
>have to turn off the pulldown, you just need to nudge the output
>slightly one way or the other. That's a minor wart as opposed to a
>fundamental design flaw like the LM324's bias problem (which I didn't
>know about--I've never tried doing anything much with 324s).
>
>The metal-gate 4046 is an excellent part otherwise. The HC4046, now,
>_that_'s a botch. They took a nice 1000:1 VCO design, which was quite
>pretty in a small way, and turned it into a 10:1 VCO that simply quits
>if its control voltage gets too low. If you try building a fancy loop
>with that, you're in for a surprise. I occasionally use the HC part for
>its phase detector, but never for its oscillator.
>
>Cheers
>
>Phil Hobbs
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
josephkk
<dirk....@gmail.com> wrote:
>On 08/07/2011 00:52, Phil Allison wrote:
>> "Jamie the Radio Ham jerk"
>>
>>
>>>> 4558s are acceptable for many audio applications. Two op-amps in an
>>>> 8-pin package for under a dime in reasonable quantity.
>>>>
>>> if memory serves, aren't those equivalent to the 741 ?
>>
>>
>> ** No.
>>
>> Look it up - fool.
>>
>>
>> .... Phil
>
>Probably the 742 ie with 2 per pack, as opposed to the 744 etc
The dual 741 was the 747, not 741.
Jamie
sure the optos are, but you're using a emitter follower on the high
side and common emitter on the lower side. The low side is going to be
closer t0 its -200 volts than will be the +200 side.
That's my observation. Just something I noticed, but like I stated
before, at 200 volts, who is going to worry?
Jamie
josephkk
>On Fri, 08 Jul 2011 18:06:35 -0500, "k...@att.bizzzzzzzzzzzz"
><k...@att.bizzzzzzzzzzzz> wrote:
>
>>On Fri, 8 Jul 2011 08:36:35 -0700 (PDT), George Herold <ghe...@teachspin.com>
>>wrote:
>>
>>>On Jul 7, 8:37 pm, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
>>>wrote:
>>>> On Thu, 7 Jul 2011 16:44:01 -0700 (PDT), Gz <ze...@comcast.net> wrote:
>>>> >I was using some lm833's in the 80's. Like an up graded 1458.
>>>> >Opa132's were pretty good, bidet.
>>>> >National now has some rather spectacular chips at least specs look
>>>> >good.
>>>>
>>>> The LM833 is still our go-to high-voltage opamp.
>>>
>>>What do you mean by high-voltage?
>>
>>Anything above 5V. ;-) That generally means 24-30V.
>>
>>>The supply voltage? +/- 18V doesn't seem that high?
>>
>>It is when you have to boost to get there. When almost everything else is
>>3.3V or 5V, 30V is *high*. ;-)
>>
>>>(I'd love an opamp that worked with maybe 50
>>>or 60 volts of supply, without having to use an expensive Apex part.)
>>
>>Use the trick Larkin has shown here a few times, with the FETs driven from
>>bias networks in the power leads.
>
>If you cascode that, you can go to +-500 volt rails from a low-voltage
>opamp.
>
>And there's my ought-to-be-famous HV opamp circuit...
>
>ftp://jjlarkin.lmi.net/HVamp.JPG
>
>
>John
Just one thing, where do you get the output transistors?
??-/
Jim Thompson
Alas! Always the reality question ;-)
John Larkin
<pcdhSpamM...@electrooptical.net> wrote:
Well, both have a deadband in their transfer functions, and both
benefit from a resistor to ground, and both are dumb designs.
We use a phase detector that we sort of invented... I did the outside
stuff and Rob did the FPGA insides.
ftp://jjlarkin.lmi.net/Phase_Detector.jpg
The UP and DN pulses are hard FPGA outputs, not tri-state. Rob managed
to overlap them a bit so there's no deadband. This also has a mode
where it works as a delta-sigma DAC (with U4 on) so we can
tune/calibrate the crystal oscillator when it's not being phase locked
to an external reference.
John
John Larkin
I don't see that. Neither transistor knows what mode it's being used
in. It just turns on.
John
John Larkin
They are part of the optocouplers.
John
Phil Hobbs
That's the Motorola approach, used e.g. in the MC145152. That produces
more reference frequency sidebands and requires more parts, but doesn't
have a deadband.
John Walliker
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> And there's my ought-to-be-famous HV opamp circuit...
>
> ftp://jjlarkin.lmi.net/HVamp.JPG
>
>
Putting LEDs in the power rails of an op-amp is a neat trick. I first
came across it in the Burr Brown 3650 and 3652 optically coupled
isolation amplifiers. The data sheet is dated 1976. These hybrid
devices have a pair of optical cavities, each containing an led and
two matched photodiodes. One LED is in series with each of the power
rails of an op-amp and one photodiode from each cavity is used to
close the feedback loop of the driving op-amp. There is a load
resistor from that op-amp output to ground. The isolated receive side
uses the other photodiode from each optical cavity in conjunction with
another op-amp.. There is no feedback across the isolation barrier,
but the overal performance was excellent in its day.
The data sheet carefully disguises the details I described above, but
I once dismantled a broken one to discover how it really worked.
John
John Larkin
Good grief! He doesn't get it! Astonishing.
John
Rich Grise
> Hi,
>
> What characteristics of an audio op-amp distinguish it from
> other op amps?
Usage.
Hope This Helps!
Rich
whit3rd
> On Sun, 10 Jul 2011 13:30:38 -0400, Phil Hobbs
>
>
> >John Larkin wrote:
> >> LM324 ... Crappy opamp design.
>... a deadband in their transfer functions
The deadband in the transfer function is a good thing, though,
when your application is battery powered. The output, while good
for 20 mA when you need it, takes less power in the 'deadband'.
LM324 has less than half the quiescent dissipation of the contemporary
LM348, with otherwise similar specs.
LM358, most people know, is a dual amplifier variant of LM324, and
is just as deadbanded. It's similarly power-stingy.
George Herold
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 8 Jul 2011 18:46:17 -0700 (PDT), George Herold
> >> On Fri, 08 Jul 2011 18:06:35 -0500, "k...@att.bizzzzzzzzzzzz"
>
> >> <k...@att.bizzzzzzzzzzzz> wrote:
> >> >wrote:
>
> >> >>On Jul 7, 8:37 pm, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
> >> >>wrote:
> >> >>> On Thu, 7 Jul 2011 16:44:01 -0700 (PDT), Gz <ze...@comcast.net> wrote:
> >> >>> >I was using some lm833's in the 80's. Like an up graded 1458.
> >> >>> >Opa132's were pretty good, bidet.
> >> >>> >National now has some rather spectacular chips at least specs look
> >> >>> >good.
>
> >> >>> The LM833 is still our go-to high-voltage opamp.
>
> >> >>What do you mean by high-voltage?
>
> >> >Anything above 5V. ;-) That generally means 24-30V.
>
> >> >>The supply voltage? +/- 18V doesn't seem that high?
>
> >> >It is when you have to boost to get there. When almost everything else is
> >> >3.3V or 5V, 30V is *high*. ;-)
>
> >> >>(I'd love an opamp that worked with maybe 50
> >> >>or 60 volts of supply, without having to use an expensive Apex part.)
>
> >> >Use the trick Larkin has shown here a few times, with the FETs driven from
> >> >bias networks in the power leads.
>
> >> If you cascode that, you can go to +-500 volt rails from a low-voltage
> >> opamp.
>
> >> And there's my ought-to-be-famous HV opamp circuit...
>
> >>ftp://jjlarkin.lmi.net/HVamp.JPG
>
>
> >> - Show quoted text -
>
> >That's Great! It's a current 'gain' thing again. I could do with a
> >fairly low time constant, does the FB take care of the cross over
> >distortion?
>
> >George H.
>
> class AB, mild crossover distortion. But sure, it needs feedback to be
> linear. The opamp is an integrator, so DC error is nill.
>
> This is good for biasing physics-type things, like electrodes in
> vacuum and such. I first used it to set the voltages in a
> microchannel-plate delay-line imager for a weird instrument.
>
> If the domiant compensation pole is a biggish cap to ground from the
> output, that hardens it against arcs and such and obviously makes it
> capacitive-load tolerant. It's easy to make it short-circuit
> protected, too.
>
> Think kilohertz, not megahertz.
>
> Another circuit I like is
>
> ftp://jjlarkin.lmi.net/Opto_Totem.JPG
>
> which is a pair of optoisolators working totem-pole. It behaves like
> cmos, in that there's zero static power consumption on the isolated
> side.
>
> Optoisolators are great as long as you don't use them the way they
> were intended.
>
> John- Hide quoted text -
>
> - Show quoted text -
That's cool too thanks.
I guess the future circuit I have in mind is a replacemnt for a
stacked piezo drive. ~ 100V diffrential drive at frequencies up to
10kHz, or so.... maybe faster if I make other things lighter. At the
moment this is done with a linear supply and a ~$50 Apex opamp. We
bought a bunch of the linear ~150VDC supplies, when those run out,
we'll have to do something else.
George H.
George Herold
I love the opa134 and 2134. (I want to keep pushing it so someone
else will buy it my ~100/year is not enough.)
George H.
George Herold
Web-Site.com> wrote:
> On Sat, 09 Jul 2011 17:06:16 -0400, Phil Hobbs
>
>
>
>
>
> <pcdhSpamMeSensel...@electrooptical.net> wrote:
> >Jim Thompson wrote:
> >> On Sat, 09 Jul 2011 16:05:28 -0400, Phil Hobbs
Sorry, silly question.
The open loop gain helps reduce input offset voltage?
George H.
>
> ...Jim Thompson
> --
> | James E.Thompson, CTO | mens |
> | Analog Innovations, Inc. | et |
> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
> | Phoenix, Arizona 85048 Skype: Contacts Only | |
> | Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
> | E-mail Icon athttp://www.analog-innovations.com| 1962 |
>
> I love to cook with wine. Sometimes I even put it in the food.- Hide quoted text -
Jim Thompson
Indirectly. The mirror structure that helps overall circuit balance
(and offset) also raises loop gain... thus a double-edged sword.
>
>George H.
>>
>> � � � � � � � � � � � � � � � � � � � � ...Jim Thompson
[snip]
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Phil Allison
"Rich Grise"
>
> Abby Brown wrote:
>
>
>> What characteristics of an audio op-amp distinguish it from
>> other op amps?
>
> Usage.
** Seems to be a four day echo round here .....
... Phil
Rich Grise
Glenn
wrote:
> John Larkin wrote:
> > On Sat, 9 Jul 2011 12:25:02 -0700 (PDT), Glenn Gundlach
Hi!
Is 74HC9046 a lot better?:
http://www.lavryengineering.com/white_papers/jitter.pdf
Quote: "...
Special praise is in order for the designers of the latest
generation 74HC9046 at Philips Semiconductors. This device operates on
the same principles but overcomes the backlash, variable gain and
interaction with circuit capacity problems. The 74HC9046 utilizes a
switched current charge pump, with no dead zone.
...."
http://www.standardics.nxp.com/products/hc/pdf/74hct9046a.pdf
Do not know how much better 74HC7046 is to 74HC4046:
http://datasheet4u.com/html/7/4/H/74HC7046A_PhilipsSemiconductors.pdf.html
-
74HC9046 should be better than:
http://datasheet4u.com/html/4/0/4/4046B_PhilipsSemiconductors.pdf.html
http://datasheet4u.com/html/7/4/H/74HC4046_PhilipsSemiconductors.pdf.html
Glenn
josephkk
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
That is a bit evasive. How about some part numbers?
??-/
John Larkin
<joseph_...@sbcglobal.net> wrote:
The part number is on the schematic, in plain sight.
John
Phil Hobbs
Everyone makes the HC4046, though, and they're cheap. I regard the flat
spot as a minor wart (and a pitfall for the unwary), but it doesn't get
in my way. It isn't very big, for one thing, only a couple or three
nanoseconds wide; the problem is that the loop wants to servo right on
top of it, where it causes all sorts of evil behaviour. You add a
resistor to ground to make the loop servo with a very small phase
offset, and life gets better really fast.
The real issue with the HC4046 is the VCO : it stalls when the tuning
voltage gets below half a volt, and it's fairly horribly nonlinear:
df/dV varies as much as 5:1 with voltage, which will make frequency
compensating a PLL significantly harder.
Judging by Fig 23 on P.24 of the datasheet, the HCT9046 has the same
issues. According to Figures 18 through 23, the CD74HC7046 performs the
astounding feat of having a much worse VCO than the HC4046--it dies at
1V instead of 0.6V, and its linearity is about the ugliest thing I've
seen this week. The NXP 74HC7046's VCO nonlinearity is equally horrible
though different looking.
So for my money, there's no point in paying $3 for an 'improved' part
rather than 50 cents for the old one, when the flat spot can be fixed
with a $0.002 resistor to ground. I'd much prefer to spend the dough on
a decent oscillator.
John Larkin
ONLY a couple of nanoseconds wide?!!!
It's ONLY Niagra Falls.
It's ONLY the Grand Canyon.
John
Phil Hobbs
Sure, if one cycle corresponds with the continental US, that's about
right. You just have to set your PLL to run in Cincinnati instead of
Niagara. ;)
Jim Thompson
<joseph_...@sbcglobal.net> wrote:
Haven't you realized yet that Larkin is all bull-shit and no hat ;-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
John Larkin
This is such a simple, obvious circuit, and JT *still* doesn't get it.
Sad.
John
Michael A. Terrell
He doesn't want to cover his clown's fright wig with a hat?
--
It's easy to think outside the box, when you have a cutting torch.
lang...@fonz.dk
> On Sun, 10 Jul 2011 19:15:38 -0700, John Larkin
>
>
>
>
>
>
>
>
>
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> >On Sun, 10 Jul 2011 18:33:15 -0700, josephkk
> ><joseph_barr...@sbcglobal.net> wrote:
>
> >>On Fri, 08 Jul 2011 16:36:25 -0700, John Larkin
> >><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> >>>On Fri, 08 Jul 2011 18:06:35 -0500, "k...@att.bizzzzzzzzzzzz"
> >>><k...@att.bizzzzzzzzzzzz> wrote:
>
what's wrong with the part number on the schematic? moc8204s
-Lasse
RST Engineering
<To-Email-Use-Th...@On-My-Web-Site.com> wrote:
>
>Haven't you realized yet that Larkin is all bull-shit and no hat ;-)
>
> ...Jim Thompson
Jim, Jim, Jim. You really need that extra glass of wine tonight with
your meds.
Jim
John Larkin
JT has killfiled me, so you'd think he doesn't want to see my posts.
But he follows me around, peeping by proxy so he won't miss anything,
so naturally he gets confused.
Weird old git.
And he still doesn't understand a circuit with one opamp and two
optoisolators. I suppose you don't understand it either.
John
Phil Hobbs
BTW I just got an HP5372A Frequency and Time Interval Analyzer on eBay
for $389 plus $75 shipping. (Including $3500 for the jitter FFT option,
it was $34,000 in 1991, and it's still very useful.) The 5372A is just
the thing for spotting PLL hitter problems, among many other jobs, and
the FFT option will tell you right away if it's something like hum from
a too-small filter cap, or AM interference, or what. A remarkable gizmo
altogether, especially since it's basically a glorified time interval
counter.
The guy selling it showed screen shots of it failing POST, but to me it
looked like a backup battery failure, so I took a flyer on it. When it
arrived, it turned out that once I cleared the first POST error,
everything else worked flawlessly, and a new lithium-thionyl chloride
backup battery fixed it right up.
I used it today to measure the jitter of an HP 3325A, which was much
worse than I expected it to be--a few hundred picoseconds at 150 kHz,
even with a 7th order lowpass to get rid of the DDS jaggies.
This really is an amazing time to be buying test equipment.
John Larkin
<pcdhSpamM...@electrooptical.net> wrote:
We still use 5370Bs in some of our test stands. It's a TIC with 20 ps
LSB resolution. It's a remarkable design, and uses an 8-bit 6800
processor to do a lot of amazing math.
I have a herd of Tek 11801 scopes, the 40 GHz sampler, bought off
ebay. Often they are sold cheap, because they won't start up, and all
they need is batteries. Various models have jitters in the 1.2 to 3 ps
RMS range.
I'd love to do a 5370 TIC clone some day. SRS has one, but it's
mediocre. But it's hard to compete with ebay.
John
Phil Hobbs
I'd love a better two-channel FFT spectrum analyzer. I have an HP
35665A dynamic signal analyzer, which works great, but its autoranging
is fairly nasty and it only goes up to 50 kHz in two-channel mode.
However, it computes complex transfer functions, noise bandwidths,
harmonics, all that stuff. (It does have one bug, where the flat-top
window gives the wrong noise PSD due to an error computing its
bandwidth--irritating.)
Something similar that worked up to, say, 10 or 50 MHz would be one of
my favourite two or three instruments. (It would need to have much
better ground loop immunity than the 35665A, too.)
John Larkin
<pcdhSpamM...@electrooptical.net> wrote:
Seems to me that all one would need these days is a good
filter/digitizer, and let your PC do all the math. A small box could
be fully floating.
John
Phil Hobbs
Something like that would be terrific, except that almost any vendor I
could think of would insist on doing it in LabView, which sucks so big
it makes Washington DC look like a source term. ;)