Why does my 1977 2103 sound much better than my friend's 2203x?

[greengriff]

The difference is definitely not in my imagination. It's quite pronounced. Although the amps are in the same sonic ballpark, the 1977 amp sounds noticeably more 'alive' and 3 dimensional. I will have to pull the chassis of both amps and go through them component by component, but I'm pretty certain that the amp is original and unmodified. The only disturbed solder joints are the ones I did when replacing the bias supply filter caps and the main filter caps. One thing I did notice - and I've started a thread about it - is that the presence control does nothing that I can hear, whereas it definitely does on both my 88 2204 and my friend's 2203x.

[The Dude]

So, you've identified a potential problem with the amp in the presence circuit. I wouldn't expect a non-working amp to sound like a fully working amp. You may have answered your own question.

[nhbassguitar]

In my book, comparing two amps’ characters always begins with bench testing at several frequencies into identical dummy loads with scope connected, and saving the waveforms for visual comparison. Also pink noise testing.

The scope test is usually revealing. “Okay... Unit 1 at this power level is beginning to round off this 100 Hz waveform, but only at the bottom. Unit 2 isn't. And Unit 2 is showing a very high frequency ripple at 5 watts and above, starting at 1.5 KHz. Unit 1 isn't.” At least now you’ve got footprints in the dirt you can follow. Then you start probing each amp, working from downstream toward upstream, taking notes along the way. You’ll be shocked at what you find. In my opinion, using any other means to track down the real causes of why two amps sound different is nothing more than chasing after wind.

[greengriff]

Yes I agree. I don't have a scope though. The issue was touched on again in the presence control thread. Some tweaks made my old amp sound much more like the reissue.

[Gtr0]

Don't forget to check pot resistance and tapers.... one amp with a linear treble pot will sound much brighter than one with a log pot at the same settings if < 8 or so. This is many times the case in the master volume. Some people are tricked into believing their amp is better than yours because it appears much louder at the same setting (indicates a linear 1M master volume pot).

[pdf64]

Even then, a pot's conformance to its nominal taper is untoleranced, it could be anything and still be in spec, eg a lin pot labelled as audio couldn't be rejected on the basis of it being out of spec.
User's often seem to be under the impression that guitar amps are precision equipment, which results in some incorrect expectations, eg the same setting on different examples of the same amp model should sound exactly the same, setting a (master) vol to halfway results in half power output

[vintagekiki]

The difference is logical. Despite the same command settings, there will be a difference in sound for several reasons.

For beginning, 2104 amp is 50W and 2203 amp is 100W.
Both amps have different OT(different inductance)
Both amps have different tubes (types, operating hours ... ...)

How to compare two amps.
Amps are compared in the same conditions, clean, without any effect.
That is, the same guitar, the same melodic phrase on the guitar, the same cab, the same guitar and amp setup.
In both amp mark all tubes from 1, 2, 3, to n. In 2203 amp mount 2 power tubes.
After test the reference amp remove all tubes and mount them in the same order in the amp which is compared.
Now compare the difference in the same conditions.

[greengriff]

The comparison was between a 2103 and a 2203, which are (I believe - someone correct me if I'm wrong) schematically identical bar an extra capacitor on the mid control. As detailed somewhere else, modifying the presence control of one of the amps bought them much closer in sound. The rest of the difference is probably down to a panoply of component tolerances adding up to something more than the sum of the parts. An emergent property if you will. Either way, whatever the cause, the amp sounds great!

[vintagekiki]

As schematic is identical, passive components don't have effect on sound.
The difference in sound between a 2103 and a 2203 is due to the difference in the tubes that are in them (types, how long the tubes work ... ...)
If amp sounds great, why modify it?

[greengriff]

I swapped all the valves back and forth between the 2 amps, and whilst it made a small difference, the amps still didn't sound the same. I find it hard to believe that the difference in tolerances between a number of passive components couldn't add up to a change in tone. For example a capacitor that reads 10% lower than the correct spec is going to allow different frequencies to 'pass through' when compared to one that reads 10% high. I'm not saying that that is the actual reason one amp sounds better, but it would seem to be a plausible explanation. Maybe there's some small differences between how the transformers perform in the reissue vs the original as well? Who knows? It would be an interesting mystery to solve, but I lack the time, skills and motivation to carry out a component-by-component analysis.

[Chuck H]

As mentioned earlier...

Many components and all have spec tolerance. That's opportunity for a hundred tiny differences that can stack up. And that's not even considering variables like lead dress.

A scope and some bench testing to discover where significant differences in performance are would be the only real way to adjust one amp to sound more like another. Anything less at this point is just speculation.

I don't think the transformers are responsible. IMHE Marshall has done well by their reissues as iron goes. Also IMHE provided quality iron is chosen differences between transformers as it relates to tone is pretty small AND subjective. Differences rather than a better/worse equation.

Also inferred was that the reissue amp may be in ill repair. That should be sorted before anything else can be determined.

[Greg_L]

I'm kind of looking at it from the other side.....why would you expect them to sound the same? One is 40+ years old, the other is relatively brand new. I personally think Marshall has done a pretty dang good job with the 2203X. IMO it's by far the best of all their reissues compared to the originals. One thing that definitely does matter, and can be the difference, is the B+ voltage in the vintage models compared to new. Somewhere around 1979-1980 Marshall's PTs started kicking out much higher B+ voltage. This generally coincided with the cosmetic change from JMP to JCM 800. It's not unusual to find a late 70s JMP with something like 380 VDC on the power tube plates. Go forward a few years into the early 80s and those same amps had 450 VDC on the plates. That's one reason why even with the exact same circuit specs, the "JCM 800" versions sound brighter and more aggressive than the JMP era 2203s.

I know it's fun to dissect and compare supposedly similar amps, but let's be real. They're both great and the casual listener of music made with either of these tools couldn't care less about which is which.

[greengriff]

The 77 (once biased properly) was 445v on the anodes. The reissue was about the same. I agree with you that the reissue is a quality item. The thing that made the biggest difference to the tone (bringing them closer together) was modifying the presence circuits to be identical.

[Greg_L]

The 77 (once biased properly) was 445v on the anodes. The reissue was about the same. I agree with you that the reissue is a quality item. The thing that made the biggest difference to the tone (bringing them closer together) was modifying the presence circuits to be identical.

Ok cool. Is that the original PT in the 77? I have a 79 2204 that's all-original. I'm only getting about 390-400 Vdc at the plates.

[greengriff]

Yes it's the original factory PT. Is that level of anode voltage not normal for an amp of that era?