Can multiple output transformer taps be used at the same time?
Mr X
My tube amp has seperate 4, 8, and 16 Ohm taps from the output
transformer. I have two 2x12 cabinets. one is 16 ohms and the other
is 8 ohms. I want to use both cabinets at the same time. Can I plug
them both into the amp and still match the impedence? Would plugging
the 8 ohm cab into the 4 ohm out and the 16 ohm cab into the 8 ohm out
cause any problems?
thanks
RoccaforteAmps
on your transformer
at the same time
you'll short the transformer,
and have very little output.
I would use the 8 ohm tap
on your amp to run
both a 16+8 ohm cab,
the 8 ohm cab will be louder
because of its lower resistance.
Doug
Chris Mohrbacher
> If you use two taps
> on your transformer
> at the same time
> you'll short the transformer,
> and have very little output.
Not with my Sovtek.
--- Chris
Chris Mohrbacher
What kind of amp is it?
--- Chris
The Prof
wow what a question!!
That just may work, but I don't know if it would be a match.... You
can allways look at the problem in terms of current... The secondary
would have a part of the winding that is shareing current into both
speakers, and one part that would not. All that means is that the
transformer would not be running efficiantly, and may even saturate on
that part of the coil.
As an electrical problem - if the source impedance of the amp was
really low, the voltage could be measured at each tap, and the load
would take power according to ohms law just as you can figure power in
your house using the electrical companys 120-240 volt transformer on
the street. Your stove, for example, is placing multiple loads at the
same time on taps on this transformer.
However - you are presenting an example where the amps impedance is
only half of each load that you are planning, therefor the voltage
will drop considerably.
I don't have time now, but it would be fun to plot this out...
Mr X
Sovtek MIG 100H
Ken Gilbert
> here's my problem :
> My tube amp has seperate 4, 8, and 16 Ohm taps from the output
> transformer. I have two 2x12 cabinets. one is 16 ohms and the other
> is 8 ohms. I want to use both cabinets at the same time. Can I plug
> them both into the amp and still match the impedence?
yes, you can.
> Would plugging
> the 8 ohm cab into the 4 ohm out and the 16 ohm cab into the 8 ohm out
> cause any problems?
> thanks
that's exactly what you have to do. the 8r load on the 4r tap will
cause a reflected load of 2x what the "rated" primary Z is. the 16r
load on the 8r tap will have exactly the same effect. the two 2x
loads in parallel will present the expected primary Z to the tubes.
the only caveat is that you will have "extra" current flowing through
the portion of the 2ndnary winding that is common to both output
circuits. i don't expect there to be any problem here though--i've
run OPTs with shorted 2ndaries to no ill effect... the finite rp of
the driving tubes limit the current to a reasonable value.
ken
Tony Hwang
Just simply how about parallelling those two cabs and hook it up at 4
Ohms.
Pretty close match. 1/(1/16 + 1/8) = 5.33333
IMO, this is better way than that.
Tony
Miles O'Neal
Could you plug two 8 ohm speaker cabs into a multi-tapped
OT by putting one between common and the 8 ohm tap, and the
other between the 8 ohm tap and the 16 ohm tap? I know you
could just plug 'em in parallel into the 4 ohm tap, but this
seems like it would make better use of the tranny, for better
response, etc. How well would this work?
Jim Anable
I think it is a BAD idea. I don't know of any OPTs with individual secondary
windings, they just have taps. In that situation, you are running more current
through parts of the secondary than it was designed for. Even if you had
isolated secondaries, it would put major changes on the primary side of the
OPT. Like purposely running a lower impedance (which may not cause a problem,
but might stress the power tubes).
Beyond all of this, many amps are wired so that you get the lowest impedance
that you plug in to. Okay, I know that is confusing, but follow me...
On my Peavey Classic 60/60 tube power amp, for example: There is a 16 ohm, 8
ohm and 4 ohm jack. The individual jack components are the same type as an
input jack on an amp (normally closed switch to ground), the ones that
automatically short the tip to ground when you pull the plug. They use these
jacks to wire them so that they choose the lowest impedance tap on the
secondary. Plug in both the 16 and the 8 ohm jacks, and you are getting only
the 8 ohm winding. Plug in all three, and you are getting three jacks in
parallel to your 4 ohm winding.
...so, if I were to plug one speaker into my 8 ohm jack, and a second one into
my 4 ohm jack, I'm really getting two cabs in parallel on my 4 ohm tap. NOT one
cab on my 8 ohm winding and another on my 4 ohm winding.
Jim Anable
I am NOT a tech, but I don't see a problem with this one (phase the speakers
right, of course). My guess is that the amp wouldn't know the difference
between this and two speakers in series, connected to the 16 ohm tap. This
assumes the normal OPT construction of one continuous secondary with taps.
Am I missing something?
Randall Aiken
No. Strange as it may sound, the impedance between the 8 and 16 ohms
taps is not 8 ohms, it is 1.37 ohms. You'll get the wrong reflected
primary impedance if you drive one speaker from the 8 ohm tap to common
and the other from the 16 ohm tap to the 8 ohm tap.
Randall Aiken
Aiken Amplification
sco...@sbcglobal.net
says...
So can you connect a 2-ohm load there, and get a match?
__
Steve
.
sco...@sbcglobal.net
attorney.com says...
...
> I think it is a BAD idea. I don't know of any OPTs with individual secondary
> windings, they just have taps.
Witness the mighty 400PS! Multiple secondary windings.
__
Steve
.
Ken Gilbert
> taps is not 8 ohms, it is 1.37 ohms. You'll get the wrong reflected
> primary impedance if you drive one speaker from the 8 ohm tap to common
> and the other from the 16 ohm tap to the 8 ohm tap.
... you COULD however use the common to 4r tap as one "half" and the
4r to 16r winding as the other. those two connections have the same #
of turns, therefore same impedance, 4r. in fact, with 8r loads on
each, you would present the proper primary impedance.
ken
Ken Gilbert
> Hi,
> Just simply how about parallelling those two cabs and hook it up at 4
> Ohms.
> Pretty close match. 1/(1/16 + 1/8) = 5.33333
> IMO, this is better way than that.
> Tony
well, you run into the issue that roccaforte noted, in that the cab
with lower impedance will draw a correspondingly and
disproportionately larger portion of the total output power.
therefore those speakers will likely break up and distort long before
the others. it would probably work just fine, but the other method,
while complex, presents an equal power dissipation in each
load--technically a more elegant solution.
ken
Chris Mohrbacher
>
> Sovtek MIG 100H
Great! Got one myself. The jacks on that amp don't have any funny internal switching; they're simply connected to their own separate
taps on the output transformer. Therefore, you can do exactly as you asked, namely;
plug your 8-ohm cab into the 4-ohm outlet
AND
plug your 16-ohm cab into the 8-ohm outlet
and the electrical result will be...
the amp's power will be split equally between the two cabs,
and the amp (specifically, the output tubes) will see exactly the right load they need.
The other Sovteks (Mig 50, Mig 50H, Mig 60 and Mig 100) are wired the same way, so the same applies to them. Kind of a handy
feature.
-- Chris
Chris Mohrbacher
"Ken Gilbert" <ride...@ride.ri.net> wrote in message news:582a152f.02071...@posting.google.com...
> ri...@harlanjberk.com (Mr X) wrote in message news:<91abbf93.02071...@posting.google.com>...
> > here's my problem :
> > My tube amp has seperate 4, 8, and 16 Ohm taps from the output
> > transformer. I have two 2x12 cabinets. one is 16 ohms and the other
> > is 8 ohms. I want to use both cabinets at the same time. Can I plug
> > them both into the amp and still match the impedence?
>
> yes, you can.
>
> > Would plugging
> > the 8 ohm cab into the 4 ohm out and the 16 ohm cab into the 8 ohm out
> > cause any problems?
> > thanks
>
> that's exactly what you have to do. the 8r load on the 4r tap will
> cause a reflected load of 2x what the "rated" primary Z is. the 16r
> load on the 8r tap will have exactly the same effect. the two 2x
> loads in parallel will present the expected primary Z to the tubes.
That's a good way to put it.
> the only caveat is that you will have "extra" current flowing through
> the portion of the 2ndnary winding that is common to both output
> circuits.
I don't think so... Remember, each load is drawing less than "normal" to start with, which includes the common portion of the
winding. I think it all adds up to the same thing in the end.
--- Chris
Chris Mohrbacher
"Miles O'Neal" <m...@rru.com> wrote in message news:GziZ8.2002$kj.5...@dca1-nnrp2.news.algx.net...
Actually, the 8-ohm tap isn't halfway (measured by # of windings) between ground and the 16-ohm tap... it's more like 71%
(square-root of 1/2). That means the windings between the 8 and 16 ohm taps will match a load of... get ready for this... 1.37
ohms... BUT if you actually connected a 1.37-ohm load across these two points, the windings in between wouldn't be very happy with
the corresponding high current demanded of them. Not a good idea.
You might be wondering... what *is* the "halfway" point on a 16-ohm secondary? Turns out it's... the 4-ohm tap. Which means the
"other" half of the windings (between the 4-ohm tap and the 16-ohm "top") is *also* a "4-ohm" output. But again, it's not a good
idea to connect a 4-ohm load there, because that part of the winding might be made with smaller wire (in order to save space), since
those windings normally only have to supply the kind of current needed by a 16-ohm load, i.e. not as much.
--- Chris
Chris Mohrbacher
<sco...@sbcglobal.net> wrote in message news:MPG.179fbead7...@news.dallas.sbcglobal.net...
Theoretically yes, but the current requirements will be way more than those particular windings are designed for... probably
resulting in smoke if you push it.
-- Chris
Jim Anable
That's right! And I knew that, just forgot.
Jim Anable
Why? Is this because the the length of each winding gets longer towards the
outside of the xformer?
Jim Anable
The Prof
No.... but if you had 2 - 4 ohm speakers, you could put one on the 4
ohm tap, and the other between the 4 and 16 ohm tap.
Ain't electronics weird?
It's because you have to square the turns to get the Z.
The Prof
>Miles O'Neal wrote:
>>
>> I just had a weird thought...
>>
>> Could you plug two 8 ohm speaker cabs into a multi-tapped
>> OT by putting one between common and the 8 ohm tap, and the
>> other between the 8 ohm tap and the 16 ohm tap? I know you
>> could just plug 'em in parallel into the 4 ohm tap, but this
>> seems like it would make better use of the tranny, for better
>> response, etc. How well would this work?
>
>I am NOT a tech, but I don't see a problem with this one (phase the speakers
>right, of course).
this connection is only about 2 ohms impedance, not 8.
>
>Am I missing something?
Yes, the square root of the Z ratio!
JJ Tash
Marshall at one time made a amp that not only had
the normal 4/8/16 taps, but a balanced 600 tap(s)
OFF the output transformer sec side. I always thought
that was a nifty idea, maybe giving a little of the MoJo
from the OT/output stages. Let me check my records
to see wha amp did it..
...................ok...here it is..3 of them...... :
4001 (15 wt combo)
2000 ( 6 6550's !!!)
2001 ( 8 6550's !!!!!!!!!!!!!!!!!!!)
J Tash
(new pix going online today)
Ever changing Amp pix at: http://jjt24.tripod.com
houston
attorney.com says...
Not 'zackly... I got out the old physics book and found:
Equation for transfer of resistance to an AC voltage
through a transformer is:
Rp = ((Np/Ns)^2)Rs
(R=resistance, N=turns, p=primary, s=secondary)
so it's a square-law thing... first let's make a 100ohm to
10ohm transformer, with 50 turns on the primary:
100 = X*10
so X is 10. Square root of 10 is 3.16, so the
ratio inside the parenthesis has to equal 3.16. With 50
primary turns, the secondary has
50/3.16 = 15.8 turns
Now do the same thing, but for a 5ohm tap:
100=X*5, X=20, sqrt20=4.47, 50/4.47=11.2 turns
The difference between the turns is 15.8-11.2 = 4.6 turns
Across that 4.6 turns, the secondary sees:
100/((50/4.6)^2) = 0.85ohms
which is 8.5% of the full 10ohm secondary. Does this jibe with
the 1.37ohm figure given above?
(16/1.37)*100 = 8.6% voila! (or viola! as meils used to say).
__
Steve
.
Dave Curtis
I was going to say something similar, but I knew
someone could explain it better...
Thanks, Randall.
Dave
Rich Koerner
Two considerations:
1. The exact configuration of what is actually being hooked up to the
secondary winding.
Assuming equal (same make and model) speakers of different voice coil
impedances used by the cabinets.
As speakers are more a current device, it WILL BE the *individual*
speakers that pull more current will produce the higher SPL.
This being, either by the nature of the actual wiring configuration
used, and/or specific voice coil winding impedance the output signal
finds.
2. The manner it is hooked up to the secondary winding.
Likewise, the specific windings, and/or taps used with the reflected
impedance loading placed on the tubes attached to the primary winding
WILL Effect the manner of which the tubes load up on the primary
winding.
For the maximum no loss performance yield, proper loading principals
must be at the forefront of considerations.
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
Chris Mohrbacher
> >On Wed, 17 Jul 2002 18:20:22 GMT, m...@rru.com (Miles O'Neal) wrote:
>
> >I just had a weird thought...
> >
> >Could you plug two 8 ohm speaker cabs into a multi-tapped
> >OT by putting one between common and the 8 ohm tap, and the
> >other between the 8 ohm tap and the 16 ohm tap? I know you
> >could just plug 'em in parallel into the 4 ohm tap, but this
> >seems like it would make better use of the tranny, for better
> >response, etc. How well would this work?
>
> No.... but if you had 2 - 4 ohm speakers, you could put one on the 4
> ohm tap, and the other between the 4 and 16 ohm tap.
... and if you did that then each speaker would get an equal share of the power, however you'd wind up with the equivalent of
connecting an 8-ohm speaker to the 16-ohm tap. Probably not quite what you had in mind.
-- Chris
The Prof
Yes of course you are right - I was just showing how weird the Z is in
reality rather then how it looks, the centertap of a 16 ohm tranny
being 4 ohms.
At least it wouldn't harm the amp, and the entire winding gets to be
used. You would even get a match at higher frequencies as the spk Z
rises!!
But all Miles had to do is put the 2 - 8ohm spks in series on the 16
ohm tap, and ignore the 8.
hmmm what would you get if you put 2 eights like that, but tied the
center to the 4 ohm tap - which is the center of the trannie?
Center of load to center of trannie? hmmmmm
Miles O'Neal
|But all Miles had to do is put the 2 - 8ohm spks in series on the 16
|ohm tap, and ignore the 8.
Unless one doesn't want to wire them in series.
Besides, the whole point wasn't "Gee, how can I
use these speakers", it was, "what if..."? You
know, that HP thang.
|hmmm what would you get if you put 2 eights like that, but tied the
|center to the 4 ohm tap - which is the center of the trannie?
Well, that *was* the idea, and about five
other people already pointed out that the
4 ohm tap was the center. 8^)
So, you'd use two 4 ohm speakers like that,
instead of two 8 ohm speakers. But that
means... Yossarian, where are you?
Chris Mohrbacher
Not much would happen there... those two points kinda see eye to eye.
-- Chris
The Prof
>The Prof <flin...@NONONOvideotron.ca> wrote:
>|But all Miles had to do is put the 2 - 8ohm spks in series on the 16
>|ohm tap, and ignore the 8.
>
>Unless one doesn't want to wire them in series.
>Besides, the whole point wasn't "Gee, how can I
>use these speakers", it was, "what if..."? You
>know, that HP thang.
Ya I know - it's just a thread...
>|hmmm what would you get if you put 2 eights like that, but tied the
>|center to the 4 ohm tap - which is the center of the trannie?
>
>Well, that *was* the idea, and about five
>other people already pointed out that the
>4 ohm tap was the center. 8^)
wow I'm missing most of those posts!! Time to get a new provider...
>So, you'd use two 4 ohm speakers like that,
>instead of two 8 ohm speakers. But that
>means... Yossarian, where are you?
No - I would put 2 eights in series across the 16 - the 4 ohm tap is
the center of the trannie and could be put to the center point of the
speakers, but wouldn't serve any purpose. Using 4s would throw off the
load value.
So going back to the beginning of this thread (if I can remember it)
An 8 ohm speaker could be placed on the 4 ohm tap, and another 8 ohm
from the 4ohm tap to the 16 ohm tap... You can't use the 8ohm tap.
This sounds weird but because we're using twice the load, we need
twice the impedance. I said 4 in an earlier post but I was only
discussing the center point, I didn't take into account the total Z. I
was thinking along the lines of putting a single speaker in either
place and getting a match of impedance for 1 speaker...
I hope this is all cleared up now!!!