JMP 2204 Doesn't Clean Up

TexasMedic

Member
Messages
107
So I have an '81 2204 I just converted to EL34s. Killer amp, definitely nails a wide range of tones. I'm used to playing a Super Lead and riding my volume (50s wiring) and when I roll down I usually don't lose highs. But on the JMP it gets sort of muddy and dark when I roll the guitar volume down. Is this a 50 watt thing? Or input resistor issue? Maybe the Super Lead having more headroom has something to do with it I don't know. Any advice?

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Rod

Tone is Paramount
Gold Supporting Member
Messages
24,736
Yes, the Super Lead has a lot more headroom....but you should be able to get similar tones with more compression from the 50...... some of us use the low input for better cleans then use a few cool overdrive pedals for leads... muddy and dark.... hum.. are the EL34’s biased to 70% ect? And were the screen grid resistors changed? Love your cat;)
 

pdf64

Member
Messages
8,922
Try turning the gain down and the master vol up, and adjust the tone controls to suit (suggest to try turning the treble and mids down, presence up); maxxing the gain effectively bypasses its bright cap, which would lose you that early treble boost.
Whereas SLs have a massive bright cap, often 5nF.
To make the guitar vol control usable, it's best to get the treble boost in as early as feasible, well before the clipping stages, so the controls can then be set to minimise treble further added down the line.
The 470pF bright cap on 2204 should help to do that, but only if the volume control it's associated with is turned down some.
If you are setting the amp's master vol to overdrive the power amp, then setting the presence control high, by reducing the degree of negative feedback, should favour lower harmonics and also make the transition into overdrive smoother.

Turning the guitar's tone control down some can help too; with 50s wiring, if it's set for the Clapton 'bloom' at full volume, the guitar will get much brighter as the volume is turned down.
 
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TexasMedic

Member
Messages
107
Yes, the Super Lead has a lot more headroom....but you should be able to get similar tones with more compression from the 50...... some of us use the low input for better cleans then use a few cool overdrive pedals for leads... muddy and dark.... hum.. are the EL34’s biased to 70% ect? And were the screen grid resistors changed? Love your cat;)
Yeah they're at 70% at 113v. They're actually 6CA7's but they're in range. My heaters are in range too. I haven't touched the grid resistors, it also does not have grid stoppers. With guitar volume on 10 it's very bright like it should be, it just doesn't clean up like the SL. Probably too much gain.
 
Messages
550
Try turning the gain down and the master vol up, and adjust the tone controls to suit (suggest to try turning the treble and mids down, presence up); maxxing the gain effectively bypasses its bright cap, which would lose you that early treble boost.
Whereas SLs have a massive bright cap, often 5nF.
To make the guitar vol control usable, it's best to get the treble boost in as early as feasible, well before the clipping stages, so the controls can then be set to minimise treble further added down the line.
The 470pF bright cap on 2204 should help to do that, but only if the volume control it's associated with is turned down some.
If you are setting the amp's master vol to overdrive the power amp, then setting the presence control high, by reducing the degree of negative feedback, should favour lower harmonics and also make the transition into overdrive smoother.

Turning the guitar's tone control down some can help too; with 50s wiring, if it's set for the Clapton 'bloom' at full volume, the guitar will get much brighter as the volume is turned down.

Absolutely! I'm with pdf64 on this. I used to have an early JCM800 and ran the gain down near 3 or 4 with the MV up. Very cool clean tones are to be had with the guitar volume down a bit, and they are easily pushed into glorious gobs of overdrive and distortion with the twist of the knob and a goooooose from a Boss SD-1. I miss that amp, but it was a combo and I couldn't carry it without injuring myself.
 

TexasMedic

Member
Messages
107
Absolutely! I'm with pdf64 on this. I used to have an early JCM800 and ran the gain down near 3 or 4 with the MV up. Very cool clean tones are to be had with the guitar volume down a bit, and they are easily pushed into glorious gobs of overdrive and distortion with the twist of the knob and a goooooose from a Boss SD-1. I miss that amp, but it was a combo and I couldn't carry it without injuring myself.
DS-1's are so good with the 22 circuits, way better than a tube screamer. Yeah running the gain high just is too much to clean up with the knob but in my opinion that beats any boost from a pedal!
 
Messages
550
DS-1's are so good with the 22 circuits, way better than a tube screamer. Yeah running the gain high just is too much to clean up with the knob but in my opinion that beats any boost from a pedal!

I agree, but it's a fine line if you want a "clean" sound without readjusting at the amp. I live under the old adage: "you can add dirt, but you can't add clean".
 

TexasMedic

Member
Messages
107
I agree, but it's a fine line if you want a "clean" sound without readjusting at the amp. I live under the old adage: "you can add dirt, but you can't add clean".
I agree. I think there is a happy medium at the amp that gives you a nice drive that can clean up with rolling back the guitar volume and be pushed for a lead tone.
 

JJman

Member
Messages
994
Loosing highs while rolling the volume down is a common thing and depends on the pickups, pots, bypass caps (all in the guitar) and the load the amp's input places on the guitar. Amp wattage and amps tone controls and headroom and 98% of the circuit are not related to the specific phenomenon described. A bad 1st tube can place DC on the guitar which could do bad things too.
 




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