Intentional Impedance Mismatch
Kerry Maxwell
Was perusing the web page for Germino amps ( www.germino.com ) and
noticed a suggestion of a *fun thing for folks to try* with their
Masonette combo was impedance mismatching ( i.e. amp selector set to 8
ohms, speaker load = 4 ohms). I promptly fired up my Rivera Quiana and
set the amp selector to 16 ohms (the actual speaker load being 8 ohms).
I also found that the FAQ for this group has LV suggesting just such an
arrangement (set your amp selector for the maximum load available). With
the limited testing I have done at fairly low volumes, I really like the
change in amp response. I have not rebiased the amp, and I am wondering
if the perceived change is essentially just the tubes running *hotter*?
Should I rebias if I plan to leave it this way? Will that negate the
increase in responsiveness I find now? Is a slight decrease in tube
life, my main worry?
Kerry M
Phil Allison
"Kerry Maxwell" <kma...@earthlink.net> wrote in message
news:XViva.65284$ey1.5...@newsread1.prod.itd.earthlink.net...
** Doing this usually results in the amp delivering about half its
rated power and can easily lead to severe tube overheating and sudden
failure.
It all depends how loud and long you play it like that.
............ Phil
Lord Valve
Kerry Maxwell wrote:
> Should be the name of my band, but really...
>
> Was perusing the web page for Germino amps ( www.germino.com ) and
> noticed a suggestion of a *fun thing for folks to try* with their
> Masonette combo was impedance mismatching ( i.e. amp selector set to 8
> ohms, speaker load = 4 ohms). I promptly fired up my Rivera Quiana and
> set the amp selector to 16 ohms (the actual speaker load being 8 ohms).
> I also found that the FAQ for this group has LV suggesting just such an
> arrangement (set your amp selector for the maximum load available).
You've misinterpreted what I said. What I said was that if you
have a choice, it's better to use the entire secondary in the
OPT to couple power to the load. This means that if you're
wiring a 412 box up for your Marshall tube head, and you have
four 16-ohm speakers, the best choice is to wire the box for
16 ohms instead of 4, since the Marshall head offers you the
option (via the impedance selector) of setting the output at
4-, 8-, or 16 ohms. I've also said that if you *must* run a tube
amp into a load it isn't designed/set for, it's better for the mismatch
to be in a downward direction, i.e., amp set for 16 driving an
8-ohm load. Assuming the amp has decent iron in the output.
stage, all you'll do is wear your power tubes out a bit faster.
Remember, however, that a transformer-coupled output
stage can only deliver the amp's rated power to the correct
load; any mismatch (in either direction) will result in a loss
of RMS output power. I'd stay away from upward mismatches,
since they sometimes induce a condition known as "flyback,"
which can fry output tubes, the sockets they're in, and worse.
Lord Valve
American
John King
In the early '80s, Peavey actually printed speaker impedance mismatch
instructions in user manuals for some of their hybrid/tube amps.
I know it was in the manual for the Classic Chorus I bought new about
1982. I have since searched the Peavey site, and none of the manuals
they reprint show this recommendation, so... I recount it to the best
of my recollection:
The Classic chorus has two speaker outputs, 8 and 4 ohm. The default
setting is to plug the two paralleled 8 ohm speakers (4 ohm total), into
the 4 ohm jack. However, by plugging the internal speakers into the 8
ohm jack, the power tubes will reach saturation at a lower volume level
(a sound that is desirable to some players). It should be noted that
doing this causes stress on the output transformer, and decrease tube life
somewhat. There will be a reduction in overall volume and headroom with the
load mismatched.
If at an engagement you find yourself playing with the volume AND master
volume at extremely high levels, it is advisable to move the speaker plug
back to the 4 ohm jack, at least for the duration of that engagement.
(The wording, and order of sentences may not be correct, but all this info,
including the warnings, was contained in the owners manual.)
Now, in my experience with three years of rehearsal and gigs with the Classic
Chorus, I followed my own common sense and decided that; if the volume level
at a gig was likely to have me turn the volume, and master volume, up past a
cumulative value of 14, it was time to swap the speaker plug. This worked
like a charm, and the original tubes lasted for the three years I used the
amp. (fairly heavily) The amp served me well for a few hundred rehearsals/
gigs, without ANY service whatsoever.
Now, having said all that; NOT ALL AMPS LIKE TO BE FORCED INTO A MISMATCH!
Recently, I had a 1969 Sunn Solarus, and decided to try the old speaker load
mismatch trick on it. The options were 8 and 16 ohms on the amp. I used
the 16 ohm jack to plug into either an 8 ohm single 12" cabinet, or an
8 ohm 4-10" cabinet. It sounded like crap with either cabinet when mismatched,
and made sizzling, crackeling noises too! In my imagination, the noises I was
hearing were a socket trying to arc out from the flyback induced by the load
mismatch.
Switching to the correct transformer/speaker load and it was just fine
(except for being DAMN LOUD when the good tube saturation finally set in).
So... as with many things, each case must be considered on its own merits.
There is not a solid, absolute rule in this one, just rule of thumb, and
common sense.
Just my 2ข... YMMV,
John King
Kerry Maxwell
news:3EBDD273...@ix.netcom.com...
I guess what I'm getting at is, why do I like what I hear, is it all in
my mind, and is there a better way to get it? As I mentioned, I have
just fooled around at low volumes with switching the impedance selector
from the *correct* 8 ohms to 16 ohms. It seems like the amp becomes
slightly more *responsive*. A loss of RMS power is not tragic if it
sounds good, but frying my tubes ( NOS Philips 7581A from LV ) when
there is a *better way* would be. Is there any correlation with the
reason Derek Trucks likes Pyle Driver speakers in his Super Reverb?
Trying to figure it all out
Kerry M
Jim Anable
> my mind, and is there a better way to get it?
Maybe because you are running more current through the tubes and saturating
them at a lower power level.
> As I mentioned, I have
> just fooled around at low volumes with switching the impedance selector
> from the *correct* 8 ohms to 16 ohms. It seems like the amp becomes
> slightly more *responsive*. A loss of RMS power is not tragic if it
> sounds good, but frying my tubes ( NOS Philips 7581A from LV )
Those may not be the best tubes to be intentionally stressing. I'll bet
they can handle it, but they will wear out faster.
Rich Koerner
Kerry, it's not a good idea to be mismatching at all!!!!!!!
Some amps can take it, and some won't.
Why, is the question I always ask.
Why is it when the owner of the amp finds they have MORE amp than they
need, they resort to all these half bakes ideas for the lowering of the
performance at great RISK!!!!!!!!!!!!!!!!!!
Why some players grab up 100 watt amps, when a 40 watt one will do the
job just fine.
Or, like the guy that called me up a while ago, and wanted to know if
there was a way to lower the wattage of his 100 watt JCM 800 to 25 watts
so he could play in the house and not kill the family.
I asked if the JCM 800 was his gigging amp. He said, it was a hobby,
and had no interest in being in a band.
I told him that this situation was a little like having a top fuel
dragster to go food shopping.
It's a little overkill, wouldn't you all think!!!!!!!!!!!!!!!!!!!!
He said he wanted THAT sound from the old days of Cream and Hendrix.
From THAT point on in the conversation, he didn't like anything I had to
say, because it didn't fit his program.
So, here you go again.
The WRONG amp for the job, and we ARE going to MAKE It Fit The Program,
Even If It BLOWS UP trying!!!!!!!!!
By God, I don't give a SHIT what Rich
Says!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I'm going to put a TRANNY TOASTER on it, and I'll even MISMATCH it in
the process too!!!!!!!!!!!!!!!!!!!!
<thinking>
Yeah, that's what is going through their minds when I tell 'em the right
thing to do.
And,... most musicians are short on smarts, and big on stubborn for
getting things their way.
<thinking>
I keep telling them, it's easier to keep 'em out of getting into
trouble, than it is for me to get them out of it when they have gotten
themselves up to their eyeballs in Big Time TROUBLE.
Like fried sockets, fried tubes, and fried Trannys too!!!!!
For a 100 JCM 800, it gets expensive real quick!!!!!!!!!!!!!!!!!
<thinking>
Hey, don't take my advice, and you will wind up repairing an amp that
was problem free at the get go.
Well, I guess the only problem the amp had, was it had the WRONG owner
looking after it's well being!!!!!!
<thinking>
I'm getting a little tired watching amp abuse, by people who should not
own them!!!!!!!!!!!!!
Here, want to see what smoked sockets look like from a
mismatch!!!!!!!!!!!!!!!!!!!!!!!
http://timeelect.com/test/Socket-5.jpg
That happened in a micro-second.
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers
John Templeton
Okay, I chopped out a bit of the post because I'm familiar with the content.
But I'm real curious about what advice you gave this guy. Did you have
something in mind that the fella could use to get the sound he wanted?
--
John
"If you dont know where you're going, any road will take you there."
-George Harrison
SNIP>
> He said he wanted THAT sound from the old days of Cream and Hendrix.
>
> From THAT point on in the conversation, he didn't like anything I had to
> say, because it didn't fit his program.
More snippage
Rich Koerner
John Templeton wrote:
>
> Okay, I chopped out a bit of the post because I'm familiar with the content.
> But I'm real curious about what advice you gave this guy. Did you have
> something in mind that the fella could use to get the sound he wanted?
> --
> John
Here's the short form as best as I can remember of what went down on the
phone John.
First, he wanted to nail certain songs like the recordings. Well that's
fine providing you are picking out songs that were recorded in the
studio. But, when you want to reproduce the sounds of the LIVE
recordings of Cream and Hendrix, it a whole different ball game.
Recording tracks in the studio is in itself, a whole different world of
sonics and technology, when compared to the live guitar sound sonics
recorded in the live venue.
BOTH, the gear and the intended applications, are worlds appart.
<sidebar>
BTW, the one thing did I offered, was to change his JCM 800 into a
JMP/JTM to bring him more in line to what was used by both Jimi and
Eric.
<to continue>
I told him, if he wanted to nail the hendrix tone EXACTLY, as was done
live with a pair of Marshall Stacks on the edge of blowing up, with all
the BIG venue created sonics in the living room of a house with a small
amp,... was impossible, and It Can't Be Done.
Well, unless he was willing to make some sonic tradeoffs, which he was
not willing to do, this is a sure low volume impossiblity. He just
would not make any tradeoffs or compromises.
For an example, for his intro of Foxy Lady, there is no way to start the
tune with the opening note, going in feedback and hitting the proper
harmonic at a lower volume, than the threshold of what is required for
the sonic energy, from the speakers in the air, to reach and infulence
the guitar strings, thus creating the feedback, and proper harmonic in
the first place.
Without that, it ain't going to happen!!!!!!!!!!!!!!!!!!!!!!!!!
I told him to try starting Foxy with what he had at high and then
lowering the volumes, to understand what is happening, and why. If he
could find some point where he was close to the threshold, at a volume
close to what would be OK to him, I could maybe help him out with a
small mod to the amp, and the guitar.
Somewhere in the time line of the phone conversation, I remember he said
he was using two 12 cab with a pair of celestion 75's, and was having
trouble starting Foxy as it was. I suggested putting the cab on a chair
to get it more in line with the guitar strings, back up agaist the cab,
as it would help kick things off, and maybe then, he could lower the
volume some what to start Foxy.
Then, for the live Cream stuff at Albert Hall, it is what it
was!!!!!!!!!!!!!!!!!!!!!!!!
Again, you have the case of a pair of Marshall stacks hauling ass *in*
the "sweet" spot with a Gibson and its humbuckers. A Les Paul is close,
but it ain't going to do what a 335 does exactly. They are different
animals.
When that Gibson, SG or 335, is in the full up Marshall JMP/JTM *sweet
spot*, you have what Clapton had going on at Albert Hall. Those
Marshall's had no master volume, and they were not operating at
livingroom playing level at the time Clapton was doing his thing.
The MAGIC of those old Marshalls stacks only happens ONE WAY.
It's called LOUD!!!!!!!!!
Freaking LOUD, in a BIG Venue LOUD!!!!!!!!!!!!!!!!!!!!
Those amps are for BIG ROOMS only!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Not a livingroom, in a house!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I said, ACCEPT IT!!!!!!!!!!
He couldn't, and wouldn't buy it.
He said there has to be a way.
There has to be some mod you can do to my 800.
I told him, ANY mod I do to Lower The Volume, WILL not produce what you
want exactly, and you are not going to be a happy camper. It won't be
exactly, what you are looking for.
Then, I said go to GC or Sam Ash, and try out some small Mesa Boogies
for starters.
Try some SG's or 335's though them for the Cream stuff, and maybe trade
the Les Paul in for the one that worked out the best.
Maybe, even try out some of the lowered wattage Marshalls too.
He didn't like that suggestion either.
So, at that point, I said I had to get back to work, and Good Luck.
Never heard from hin again.
<thinking>
I think I can tell you one thing for sure about now.
With the first tricked up 100 watt Marshall JCM 800 that walks in here
now, I'll remember this post and wonder if that amp belonged to the
person on the phone with me that day.
Fried tube sockets, worn out output tubes, and/or a sickly output tranny
would be all it would take.
Lectrkbluz
LV...I have a Fender Tone Master Head into the matching 16 ohm cabinet. Fender
recommends, in the owner's manual, dropping the impedence setting on the head
(Hi, Mid, Lo) to emulate the tone of an overdriven amp at lower volume levels.
The head has a huge OT. It seems that in your above statement that it is OK to
do what Fender recommends for the Tone Master, but you also seem to imply that
it is better to run, say an 8 ohm amp, into a 4 ohm load, as would be the case
in running an extension cab. I am a little confused by your response. I am
not sure if I can do what Fender recommends (16 ohm cab with head set for 4 or
8 ohms) using say my Marshall 50 watt Plexi reissue without burning up the OT
or power tubes. BTW, thanks for the new catalogs. Lots of good stuff.
Chuck.
Subject: Re: Intentional Impedance Mismatch
From: Lord Valve <detr...@ix.netcom.com>
Date: Sat, 10 May 2003 22:32:52 -0600
Kerry Maxwell
>
> You've misinterpreted what I said. What I said was that if you
> have a choice, it's better to use the entire secondary in the
> OPT to couple power to the load. This means that if you're
> wiring a 412 box up for your Marshall tube head, and you have
> four 16-ohm speakers, the best choice is to wire the box for
> 16 ohms instead of 4, since the Marshall head offers you the
> option (via the impedance selector) of setting the output at
> 4-, 8-, or 16 ohms. I've also said that if you *must* run a tube
> amp into a load it isn't designed/set for, it's better for the
mismatch
> to be in a downward direction, i.e., amp set for 16 driving an
> 8-ohm load. Assuming the amp has decent iron in the output.
> stage, all you'll do is wear your power tubes out a bit faster.
> Remember, however, that a transformer-coupled output
> stage can only deliver the amp's rated power to the correct
> load; any mismatch (in either direction) will result in a loss
> of RMS output power. I'd stay away from upward mismatches,
> since they sometimes induce a condition known as "flyback,"
> which can fry output tubes, the sockets they're in, and worse.
>
OK, I've decided against using an impedance mismatch on my Rivera Quiana
as part of my *signature tone* ;) but am now thinking of replacing the
two 16 ohm V30s wired in parallel with two 8 ohm speakers wired in
series. I would then be using the 16 ohm tap on the amp, but what other
sonic gremlins would I be unleashing by running speakers in series vs.
parallel?
Kerry M
Lectrkbluz
LV...I have a Fender Tone Master Head into the matching 16 ohm cabinet. Fender
recommends, in the owner's manual, dropping the impedence setting on the head
(Hi, Mid, Lo) to emulate the tone of an overdriven amp at lower volume levels.
The head has a huge OT. It seems that in your above statement that it is OK to
do what Fender recommends for the Tone Master, but you also seem to imply that
it is better to run, say an 8 ohm amp, into a 4 ohm load, as would be the case
in running an extension cab. I am a little confused by your response. I am
not sure if I can do what Fender recommends (16 ohm cab with head set for 4 or
8 ohms) using say my Marshall 50 watt Plexi reissue without burning up the OT
or power tubes. BTW, thanks for the new catalogs. Lots of good stuff.
Chuck.
Subject: Re: Intentional Impedance Mismatch
From: Lord Valve <detr...@ix.netcom.com>
Date: Sat, 10 May 2003 22:32:52 -0600
Kerry Maxwell wrote: