#34 mod sounds awful...

[alfi27]

Hey guys,

I recently started accepting other people's amps for modding, after working on my own for a few years. My first job was a '77 JMP with a Friedman style mod not too long ago, and I also did a Vintage Modern for the same guy quite recently. Yesterday I got a 2203x in for a #34 mod, which is a mod I have never done in its entirety before, but as I had the official schematic posted by Santiago on hand I expected it to be piece of cake - well, as you might have guessed, it wasn't. I played it for a bit before I got started so I knew what the starting point was, and it sounded absolutely killer - made me wonder why he wanted me to mess with it in the first place. Then I did the mod (see the schematic attached, only difference is 0.68uF presence), and my Les Paul with treble and presence at zero sounded like a Strat bridge single coil into a stock JCM800 with a treble booster pedal and treble and presence on 10... At first I tried to avoid the hot shield by using a 50pF between grid and plate, that sounded really meh and actually not bright enough - I removed it and installed an actual hot shield, and that's when things got stupid bright. The input cable is a 12" coaxial, which I understand is longer than what is recommended, but even with that length I didn't hear a massive difference between the hot shield being connected and disconnected.

The amp will also get 6550 tubes and a PPIMV, waiting for the tubes to arrive so I'm tempted to not do anything else before that - just a slight problem that the owner wanted clips of the mod with both EL34s and 6550s... I have sort of narrowed the issue down to the 100nF cathode bypass, I took it all back to stock and added one thing at a time. The 470nF 3rd stage cathode bypass and 2200pF treble peaker bypass were both great, and the 100nF worked fine when I did a partial bypass (10k in series with the cap). But that led to a different problem - too little gain. What's even more weird than all this, is that when I first started out modding I did something to my old 2204 that ended up sounding incredibly close to the #34, or at least what I would expect it to sound like - the notes I found said it was just a 0.68uF presence and 3rd stage bypass, and 10k and 0.1uF in parallel with the 10k cathode. When I tried this on the 2203x it didn't sound anywhere near that, I made a clip of it so I'm not going by memory - so there might be something else going on, will do a full inspection of the amp.

Finally, just a short-ish rant that you can feel very free to skip: Why on earth would someone take an already bright amp, and make it even brighter? Just the fact that you have to run treble and presence at zero and crank the master up to 8 (which is what Slash does as well), as well as the (potentially) dangerous hot shielded input wire strikes me as a horribly designed circuit honestly. Although I am a big Slash fan and I like his tone, surely there's got to be a better way of getting that tone - at the very least without running treble and presence at zero... From what I understand the #36 circuit was designed to get a similar tone/amount of gain without running master at 8, so that's one step in the right direction at least.

Cheers guys, and sorry for the rant, haha!

IMG_4600.JPG

[Roe]

shouldn't the 150k be across the volum pot while the 1nf bright cap remains as across the viper and input of the pot?

[Thermionic/EL-34]

Frank Levi never seemed to have a problem.

Conversely his mods were in demand and he was doing them before anyone else except for maybe Randall Smith.

[Littlewyan]

Dave Friedman worked on the #34 amp and he himself said it was a ridiculously bright amp. What speakers are you testing it through?

https://www.youtube.com/watch?v=y4_3CSZkVHU&t=1s

Here is that amp through a Marshall 1960B cab, which I think has G12T-75 speakers.

[alfi27]

Dave Friedman worked on the #34 amp and he himself said it was a ridiculously bright amp. What speakers are you testing it through?

https://www.youtube.com/watch?v=y4_3CSZkVHU&t=1s

Here is that amp through a Marshall 1960B cab, which I think has G12T-75 speakers.

Pretty sure Slash uses V30s almost exclusively, but maybe it's not his cab. I'm using a Suhr Reactive Load with Ownhammer Greenback IRs - the GNR pack, I know Slash didn't record Chinese Democracy but still pretty cool that it's made from that speaker. I do try different IRs occasionally, but that one is a good benchmark. It also makes it possible to run master at 8 relatively painless.

Regarding that video, it sounds absolutely killer as well and nothing like the amp I'm working on. The one I'm working on with the official #34 mod is so bright it's painful, it sounds broken plain and simple. I'll see if I can get a short clip made, so you know what I mean. Cheers

[Roe]

he recorded with G12Ms and the #34 on UYI.

a stock 2203 sounds as bright as the #34 imho

[Thermionic/EL-34]

Welcome to 100 watt Marshall 101.
Some of you guys seem like you've never heard one or something IDK maybe you havent how old are you ?

That was almost 40 years ago or was.

It was Frank Levi who worked for SIR & re-wired all the SIR amps including the famous ones.
Caswell seems to get the glory for some reason.

As for the Marshall AFD money-grab amp Santigo Alverez is a friend of mine & an outstanding Engineer.
The Marshall AFD amp is what it is & has some cool features but hardly resembles any of the SIR amps in circuitry or looks.

Slash was all jacked up on Booze & Smack and even admits he doesn't even remember what amp he used [its on video].
You need to separate fact from fiction & internet myths.

He must have liked the amp enough to steal it cuz he did.

SIR ended up stealing it back and those amps have disappered.

[alfi27]

he recorded with G12Ms and the #34 on UYI.

a stock 2203 sounds as bright as the #34 imho

The #34 is more about the high mids I guess, but the 0.1uF cathode bypass in particular adds a LOT of high end content as well. As does the 0.47uF cathode bypass and 2200pF treble peaker, a single 220pF plate bypass won't counter for all that. I checked out the schematics for the SL-5 just for fun, not quite comparable because it doesn't have a phase inverter but that one also has a 10k in series with the 0.1uF (though after it, and not before).

This is the closest I've been able to get so far, it doesn't sound bad but the high end is a bit grainy/plastic'y and maybe not bright enough. I'm tempted to just tell the owner that I won't be able to make a comparison clip, and put the whole thing on hold until the 6550s arrive.
https://www.dropbox.com/s/91kmm5k7nyp24 ... 1.mp3?dl=0

[Roe]

he recorded with G12Ms and the #34 on UYI.

a stock 2203 sounds as bright as the #34 imho

The #34 is more about the high mids I guess, but the 0.1uF cathode bypass in particular adds a LOT of high end content as well. As does the 0.47uF cathode bypass and 2200pF treble peaker, a single 220pF plate bypass won't counter for all that. I checked out the schematics for the SL-5 just for fun, not quite comparable because it doesn't have a phase inverter but that one also has a 10k in series with the 0.1uF (though after it, and not before).

This is the closest I've been able to get so far, it doesn't sound bad but the high end is a bit grainy/plastic'y and maybe not bright enough. I'm tempted to just tell the owner that I won't be able to make a comparison clip, and put the whole thing on hold until the 6550s arrive.
https://www.dropbox.com/s/91kmm5k7nyp24 ... 1.mp3?dl=0

the 2203 is brighter than #34 due to:
- the 150k resistor on 34
- the 220p snubber
- the 2n2 peaker
- more gain and compression gives a thicker, tone with more harmonic content
But #34 is brighter because of
- the partially bypassed cathodes, although this boost low mids and high bass, not just higher frequencies

[Littlewyan]

Slash's main speaker is the Vintage 30, but in that video he was using G12T-75s.

To be honest the amp sounds pretty killer in that clip you posted and in the same ballpark as the amp in the clip I posted! LIke I said, it's a bright amp! Watch some other clips on Youtube of it with Vintage 30s.

And just a side note, what are the EL34s biased to? 70%?

[Thermionic/EL-34]

Slash's main speaker is the Vintage 30, but in that video he was using G12T-75s.

To be honest the amp sounds pretty killer in that clip you posted and in the same ballpark as the amp in the clip I posted! LIke I said, it's a bright amp! Watch some other clips on Youtube of it with Vintage 30s.

And just a side note, what are the EL34s biased to? 70%?

Tubes in the Levi #34 supposedly were 6550's.
But unless you're a 40 year old fly on SIR's wall who knows ?


The guy above was a hot mess back then & no help.

[Roe]

Slash's main speaker is the Vintage 30

it has been for a long time but UYI was G12M. AFD seems to have been G12-80 but we don't really know

[Littlewyan]

Slash's main speaker is the Vintage 30

it has been for a long time but UYI was G12M. AFD seems to have been G12-80 but we don't really know

That’s interesting, I didn’t know that! Thinking about it, he used the Jubilee amps live and those speaker cabs came with Vintage 30s. So perhaps it started out as only a live thing.

Just listened to the clip again and I still think it sounds great. Sounds like the UYI tone to me, or in the same ballpark.

[alfi27]

the 2203 is brighter than #34 due to:
- the 150k resistor on 34
- the 220p snubber
- the 2n2 peaker
- more gain and compression gives a thicker, tone with more harmonic content
But #34 is brighter because of
- the partially bypassed cathodes, although this boost low mids and high bass, not just higher frequencies

The 150k thins out (or what some would call "tightens") the tone, at least that's what it did when I put the ground side on an alligator clip. The 2n2 peaker also adds mostly high-center mid content - again, from what I was hearing when taking it in and out. But if you are right, then something is definitely off (which I'm fairly convinced there is, anyway).

That’s interesting, I didn’t know that! Thinking about it, he used the Jubilee amps live and those speaker cabs came with Vintage 30s. So perhaps it started out as only a live thing.

Just listened to the clip again and I still think it sounds great. Sounds like the UYI tone to me, or in the same ballpark.

Cheers man, it doesn't sound bad but it's closer to the stock 2203 and I don't want the owner to get the amp back and feel like it wasn't worth it...

Here are a couple of clips, I have been in touch with Jay Linton who seems like a bit of an expert on this mod, and he said the hot shield is the key (he also claims that EL34s don't do this mod justice). So I put the hot shield back in with the correct length (8" ish) and made a clip, the only thing differing from the official #34 is a 470pF plate bypass instead of 220pF.

Stock 2203: https://www.dropbox.com/s/fx0tcv3vs0ai2 ... k.mp3?dl=0
Official #34: https://www.dropbox.com/s/hb12qemi8scue ... 2.mp3?dl=0
Tweaked #34: https://www.dropbox.com/s/91kmm5k7nyp24 ... 1.mp3?dl=0
My personal '81 2204 with a simplified #34: https://www.dropbox.com/s/svpnv1bfbwikc ... 0.wav?dl=0

The clip with my 2204 is exactly the tone I think about when I think #34. The official #34 clip needs to be heard on a good listening medium to really hear what I'm talking about, on my iPhone speaker it sounded pretty good but on any decent speaker or headphones you can hear it's stupid bright... It's with treble and presence at zero as well, compared to treble and presence at 5 on the stock clip so it's *definitely* brighter than stock. It almost seems like the hot shield isn't doing its job, but how can that be? It's a RG174 coaxial cable, shield goes to pin 6 and the core goes through a 33k to pin 7 at the tube socket. Not exactly rocket science...

[Littlewyan]

The official clip sounds good, although slightly too hairy. Tweaked sounds best, more control in the sound I think.

Did you have the Treble and Presence on 0 in the tweaked clip?