1979 vs 1977 JMP MK2 2203 comparison (video) - big difference in tone, how come?

[LPman]

I did an A/B comparison of my newly acquired 1979 JMP 2203 with one of my friends' 1977 one, they are exactly the same internally, identical transformers too. Exact same settings (volume and preamp both at 6, no attenuator - I almost gone deaf, blind and brain damaged - if I wasn't before). The volumes are equalized in the video but my '79 is about 15-20W louder than either his '77 or his '92 Super Lead!! My '79 has 500V on the plates which is pretty high (but heater voltage is spot-on 6.3V on the power tubes) so I suppose his amps are in the more usual 470 VDC range which would explain the volume difference, right? The other thing is they sound totally different as you can hear. My '79 is a fat beast but has a more dry and stiff feel, maybe not as gainy, while his '77 is thinner but kinda easier to play (if you listen to the last part where I try to fluidly palm mute on the low-E, the '77 runs more fluid where as the '79 is stiffer for the lack of a better word).

Does anyone know why these two amps are so different in tone and feel? Plate voltage difference / bias settings / something else? I like the thick fat overall tone of my '79 more but I would want the fluidity of the '77? Is that possible to tweak out of my amp somehow? Am I correct in thinking that I should bias my amp a little colder for that?

First black tolex one is my '79 (it's a mid 70s retolexed head cab) and the red one is his '77 (custom built head cab).

 

[stickyfinger]

When you say 15-20 watts louder how many dbs do you think? Should only be about 1 db.
Maybe its the bright caps and mixer caps, Ceramics usually are 20% and can measure all over the place.
Maybe its the pots. Can you adjust the black amp to get the same tone.
Black amps tubes are a bit microphonic.. maybe they are well worn compared to the red amps.
Maybe its the sum of parts and age but Im curious how close you can get them regardless of where the pots are set.

 

[V-man]

As relayed above, the tolerance on those parts led to significant differences between units (pot values are a prime example).

What should have been done was to dime out the EQ section (PBMT), then the input gain.

If the amps sound the same or significantly closer with all these 10s than when they were similarly-set in the 2-8 knob ranges, different pot value tolerances could be occurring, so mids on the ‘77 set at 5 for example, could only be registering at what 3 on the ‘79 would be due to the part tolerance difference.

 

[Pete Farrington]

Exact same settings (volume and preamp both at 6

That's absolutely meaningless.
The pots used for guitar amps are just cheapo.
Musicians seem to regard guitar amps as equivalent to calibrated laboratory instruments. But the polar opposite is actually the case.
The conformance of pot tapers to their intended nominal is untoleranced, it could be anything.
Literally a linear track could be fitted into a audio pot (and visa versa) yet nothing would be out of spec.

Even the overall end to end resistance of pot tracks has only historically been a 20% tolerance, and that's when new.
40+ years later you can't even expect that.

Film caps will also probably have been a 20% tolerance on actual value compared to nominal.

Then the vintage class 2 ceramic caps used here are again not compatible with the 'precision instrument' perception of what you are dealing with.
They have very poor value tolererance to nominal, and their actual value is greatly affected by temperature.

And then the tolerance and condition of the ecaps used in the bias and HT power supplies might be considered.

As per post 2 above, set the amps to be as close to each other in volume and tone as you can.
Then compare for subtle differences.

 

[LPman]

When you say 15-20 watts louder how many dbs do you think? Should only be about 1 db.
Maybe its the bright caps and mixer caps, Ceramics usually are 20% and can measure all over the place.
Maybe its the pots. Can you adjust the black amp to get the same tone.
Black amps tubes are a bit microphonic.. maybe they are well worn compared to the red amps.
Maybe its the sum of parts and age but Im curious how close you can get them regardless of where the pots are set.

You are correct, it was about a 1db difference when I equalized the volumes in sony vegas. The tubes are not microphonic in the '79, the reason you hear more squeel is because of the mentioned difference in volume and the unpotted Custombuckers being so close to that crazy loud amp. You can see that I had to twist into awkward positions to try to controll that as much as I could.

It's a great idea to crank all pots and redo it, should have thought about that, unfortunately we're 500 km apart so these comparisons are not so easy to organize.

 

[LPman]

That's absolutely meaningless.
The pots used for guitar amps are just cheapo.
Musicians seem to regard guitar amps as equivalent to calibrated laboratory instruments. But the polar opposite is actually the case.
The conformance of pot tapers to their intended nominal is untoleranced, it could be anything.
Literally a linear track could be fitted into a audio pot (and visa versa) yet nothing would be out of spec.

Even the overall end to end resistance of pot tracks has only historically been a 20% tolerance, and that's when new.
40+ years later you can't even expect that.

Film caps will also probably have been a 20% tolerance on actual value compared to nominal.

Then the vintage class 2 ceramic caps used here are again not compatible with the 'precision instrument' perception of what you are dealing with.
They have very poor value tolererance to nominal, and their actual value is greatly affected by temperature.

And then the tolerance and condition of the ecaps used in the bias and HT power supplies might be considered.

As per post 2 above, set the amps to be as close to each other in volume and tone as you can.
Then compare for subtle differences.

Do you think that the difference in pot taper is also the cause of the slightly different feel of these two amps (dryness / stiffness / fluidity). Btw, more or less all of the 2204 & 2203 and especially later JCM 800 amps I've played had this stiff and cold feel compared to 4 holers. They supposed to have more gain, yet even when I play drop tuned palm mute stuff, the notes jump out more easily, fluidly and heavily from the 4 holers. The MK2 / JCM series have a 'sticky' feel to me, like there is a latency in note response while the plexi amps react immediately. Hope it does make sense. It's really hard to descrbe these things. Do you know why is that and how to make these amps less dry?

Interestingly my '69 JMP 50 wired 2204-style had none of this quality. It reacted immediately to every touch on the guitar and the lows jumped off the fretboard like thunder strikes. With everything set to noon it sounded like a plexi. I really can't wrap my head around this and the techs I try to explain this are just scratching their heads. For once and for all it would be great to solve this mystery.

 

[TAZIN]

More than likely the difference is from a lot of little things adding up such as:
H.T. voltages
Valve types
Bias setting
Signal cap types ('77 Mullards & green chiklets vs '79 yellow 'lego' caps)
Component tolerances (transformers, potentiometers, resistors).

 

[Pete Farrington]

more or less all of the 2204 & 2203 and especially later JCM 800 amps I've played had this stiff and cold feel compared to 4 holers. They supposed to have more gain, yet even when I play drop tuned palm mute stuff, the notes jump out more easily, fluidly and heavily from the 4 holers.

The master volume is just a pot bunged in between the preamp output and power amp input.

From V2 onwards, a 2204 = 1987

With the master set halfway, there might only be 1/10 signal level being passed on from preamp to power amp, compared to a 4 holer.

The natural tendency of players though seems to be not to turn the master volume anywhere near full.
It's as if they're nervous of doing so?
WTF?

I suggest to set the master at / near full CW and reassess.

Interestingly my '69 JMP 50 wired 2204-style had none of this quality. It reacted immediately to every touch on the guitar and the lows jumped off the fretboard like thunder strikes. With everything set to noon it sounded like a plexi

Maybe its master volume was linear?
So set noon, compared to a master volume with a log / audio taper, there'd be 5x the signal level hitting the power amp. That's a good level, plenty to push the power amp hard, but not so much that things get turned inside out from being hit too hard.

To get the best from any amp, its controls need to be adjusted such that the power amp gets pushed at least to its sweet spot where it's making at least some contribution, perhaps beyond that.
Transfer gain from the preamp to the power amp, and allow your amp to breathe

 

[Matthews Guitars]

Component tolerances of 10 percent for EACH component can stack up to ENORMOUS variations between one example and another.

If you want amps to sound the same, measure and match components for same values.

 

[LPman]

The master volume is just a pot bunged in between the preamp output and power amp input.

From V2 onwards, a 2204 = 1987

With the master set halfway, there might only be 1/10 signal level being passed on from preamp to power amp, compared to a 4 holer.

The natural tendency of players though seems to be not to turn the master volume anywhere near full.
It's as if they're nervous of doing so?
WTF?

I suggest to set the master at / near full CW and reassess.



Maybe its master volume was linear?
So set noon, thered be 5x the signal level hitting the power amp.

To get the best from any amp, its controls need to be adjusted such that the power amp gets pushed at least to its sweet spot where it's making at least some contribution, perhaps beyond that.
Transfer gain from the preamp to the power amp, and allow your amp to breathe

I always set the master on every 2203/2204 to the point where the power section is cooking. To the highest sweet spot. If I turn them any higher, the amp farts out. With my current settings on this '79 (master and preamp on 5, the measured power is 110 watt so when I say cooking, I really mean it). When I still had my '69, I compared it to many 2204 and 2203 versions and also with 4 holers at equal volume levels and the conclusion has always been the same (not just for me but all of my friends present): the master versions feel dry /cold / stiff / sticky while the 4 holers has the immediate punch. I probably made a dozen threads about these observations on the forum. As I said, the only exception has been my '69. Maybe it had some kind of special master setup, altough I don't think so because everything reacted on it like on a usual 2204 (from preamp at 7 the bass boost turned on and so on).

Guys, no one else ever noticed this difference that I'm babbling about here ? Why do JMP MK2 amps feel dry and stiff compared to plexi style amps? Is there a solution to keep the master in these amps but make them similar in FEEL to the 4 holers? Master is already cranked as I said.

 

[boola1]

My '79 has 500V on the plates which is pretty high (but heater voltage is spot-on 6.3V on the power tubes) so I suppose his amps are in the more usual 470 VDC range which would explain the volume difference, right? The other thing is they sound totally different as you can hear. My '79 is a fat beast but has a more dry and stiff feel, maybe not as gainy, while his '77 is thinner but kinda easier to play (if you listen to the last part where I try to fluidly palm mute on the low-E, the '77 runs more fluid where as the '79 is stiffer for the lack of a better word).

The difference you describe in stiffness and volume is also how I'd describe the difference between 470 and 500.

I own 2 1987s with a similar difference in voltage. I have 2 Mesa Boogie Quads, 1 is wired for 240, the other for 230, same difference in feel between them.

 

[Purgasound]

I haven't measured every component in my '76 but all the 1M pots measure around 560K. That's a huge difference from what the spec should be. I always wondered why that amp sounds way off from my others and I decided to measure them on a whim.
That factor alone could make a large variation in tone between two different amplifiers that are supposed to be identical.
The tolerance on older potentiometers are really extreme compared to today and even modern pots still have a 20% tolerance.

Not to mention the bright caps, on some amps they can be pretty small like 100pF and others can be 4700pF. Major difference there. I think they sound best with a larger bright cap but put it on a switch so at lower preamp volume settings it can be removed from the circuit... I digress, I realize you're talking about 2203's and the bright cap thing is more of a variable on Superleads. They should have been fairly more consistent on the 2203's.

One last note, on my workbench I repaired three 2203's in the last month and all were from 1984. One of them had a stock 56K tone slope resistor while the others had 33K.

 

[stickyfinger]

Are the brands of pots different?
The 76 would have CTS and almost all the Nos ones I've bought measure lower (maybe 10% on average, I forget).
The 79 probably has the latter pots. Forget the manufacture name.

 

[79 2203]

I always set the master on every 2203/2204 to the point where the power section is cooking. To the highest sweet spot. If I turn them any higher, the amp farts out. With my current settings on this '79 (master and preamp on 5, the measured power is 110 watt so when I say cooking, I really mean it). When I still had my '69, I compared it to many 2204 and 2203 versions and also with 4 holers at equal volume levels and the conclusion has always been the same (not just for me but all of my friends present): the master versions feel dry /cold / stiff / sticky while the 4 holers has the immediate punch. I probably made a dozen threads about these observations on the forum. As I said, the only exception has been my '69. Maybe it had some kind of special master setup, altough I don't think so because everything reacted on it like on a usual 2204 (from preamp at 7 the bass boost turned on and so on).

Guys, no one else ever noticed this difference that I'm babbling about here ? Why do JMP MK2 amps feel dry and stiff compared to plexi style amps? Is there a solution to keep the master in these amps but make them similar in FEEL to the 4 holers? Master is already cranked as I said.

I told you when you were considering buying the 79 2203 that they are great amps but will never sound, and especially feel, like a 4 holer. Everything you’ve described here about the differences is 100% correct, so keep the 2203 and celebrate it for what it is(like I do with my 79 2203) and in the meantime search for a STOCK Plexi/early Metalpanel 4 holer and some Pulsonics, and you’ll have THE sound.

 

[playloud]

Why do JMP MK2 amps feel dry and stiff compared to plexi style amps?

To a first approximation, it's the cold clipper. No amount of control setting/channel selecting can avoid that.

1dB is hardly worth talking about.

 

[Purgasound]

No one is really pushing the PI's in 2203's like they have to in Superleads to get that overdrive.

 

[Eigen]

I've had a 77 2203 for some time now and my memory is a bit rusty, but when I first got it and was reading up on its I seem to recall reading that the 77 JMPs 2203/1959's had a unique PT, that was only installed in that year, the T3836 (which replaced the earlier T3556), that quickly changed to the more common T4074. (went and checked my notes)

That could be a source of the difference in power, but as others have said, its most likely just a difference in the sweep of the MV pot, there can be a huge variation between identical pots. Also the 77 would most likely be loaded with mustards and green chicklets, while the 79 would have the red legos, maybe that's attenuating the signal a bit?

Also the power tubes could have a huge impact depending on how they are biased on a 2203 and also depending on how worn they are.

Either way, both sound great.

 

[jlinde1973]

Ya my 85 is the same way. Rather stiff and dry. Not sweet like the 4 holer. Great amp but no plexi. I think the 2203/4 excell at punchy bar chords and rhythm stuff. Nothing beats them at that. The 4 holers much sweeter at lead and single note and neck pickup stuff. The 100k neg feedback resistor on 2203 contributes to the stiff dryness im sure.

 

[jlinde1973]

Forgot to add mine is the high voltage later PCB mounted pot version. I think the higher preamp voltage will give it a stiffer feel. Some people raise the drop resistors to lower the voltage for better feel. I'm leaving mine stock for better resale Incase I want to sell it for another 4 holer.

 

[william vogel]

Ya my 85 is the same way. Rather stiff and dry. Not sweet like the 4 holer. Great amp but no plexi. I think the 2203/4 excell at punchy bar chords and rhythm stuff. Nothing beats them at that. The 4 holers much sweeter at lead and single note and neck pickup stuff. The 100k neg feedback resistor on 2203 contributes to the stiff dryness im sure.

The reduction of NFB by a 100k resistor vs a 47k actually makes the amp more touchy and responsive up until the point of power tube clipping. I don’t know how you adjust your volume level but NFB actually makes an amp more sterile and clean while the feedback loop is maintaining clean sine. Amps that have no feedback or minimal amounts are more touch sensitive and responsive. By adjusting your amp to have more NFB with a parallel resistor across your 100k you can easily increase the signal level within the loop and see for yourself. Adding a 100k will nearly double the loop signal and a 47k will give even greater effect. You have to understand though that once the output section begins to clip, that the feedback loop injects harmonic content into a “clean” signal in the phase inverter cathode circuit. The massive amount of differential between signals causes a gain increase for all frequencies that aren’t in the original signal. Some perceive this effect as the amplifier being more sensitive feeling but in reality the amplifier has less linearity and would have a much more responsive feel with the deletion of the NFB loop altogether. The downside of removing the loop is the loss of the presence control but the amp with no NFB is brighter because the presence control is actually attenuating the frequencies until the control is turned full clockwise
So the moral of the story is that if you like touch sensitivity and you run the presence up at a high level, you’d probably enjoy the feel and sound of minimal or no NFB.