want to mod JCM800 (2210), more gain needed

[BeëlzeM]

How did this one turn out for you? It sounds good, but I'm concerned about the overall gain lost, I quite need the gain, worth trying it?:

R3 (10k) to 2k7, also remove D1 bypassing cathode and use 0.68uF cap to bypass R3. removing D1 lowers gain quite a bit, but overdrive ‘feels’ more valve-like and natural/organic, it does however take some sizzle from the tone and need to re-EQ amp to compensate for treble loss (though a cathode bypass cap would most likely take care of that). Lowering cathode resistor (R3) to 2k2 increased gain, but not a mental amount like expected. Have added 0.68uF cap across cathode resistor, added more gain and snarl in hi-mids. The diode and 10k still had more more overall gain, though the tone was more ‘transistory’.

[HTH]

How did this one turn out for you? It sounds good, but I'm concerned about the overall gain lost, I quite need the gain, worth trying it?:

the tone was much better, but some gain was lost, however this was more than made up when I added the extra gain stage that was removed from the clean channel and used in the boost channel.

the extra gain stage mod is not really something I can give a 'join the dots' explanation of, you either know how to do it or you don't. that said, I've attached the schematic to this thread with some alterations showing what you need to do.

if you can get the extra gain stage working, come back and I'll give you some extra mods to get a bit more from the amp.

btw, how old are the valves in the amp? - you said that the bass was muddy. even BEFORE the mods, the 2210 I modded wasn't muddy UNLESS the gain was below 10 (but I doubt you're using less than full gain, right?)

[BeëlzeM]

Right, my preamp tubes are maybe 2 months old Tung-sols.

My powertubes are KT77's at the moment which I threw in a couple of days ago, since the old tubes went bad and took my 5watt screen grid resistors with them. So I replaced those and put in some new KT77's.

I don't know how to add the extra gain stage. So I shoud pass on that?

The schematic you attached seems pretty doable, but does that include adding the gain stage or is that just to improve the clean channel?

How much better and how much more gain will the amp have with all this working? Will it require a lot of work after the gain stage is added?

[HTH]

The schematic you attached seems pretty doable, but does that include adding the gain stage or is that just to improve the clean channel?

it includes the mod you already did where you modded the clean channel. the gain stage you bypassed in the clean channel is used for the boost channel - look at the schematic I've modded compared to the stock one.

How much better and how much more gain will the amp have with all this working? Will it require a lot of work after the gain stage is added?

easily enough gain to do Sepultura. once the extra stage is added, you'll only need a few tweaks really. I would remove all the clipping diodes though.

[BeëlzeM]

Removing all the diode clipping. Is that just clipping out W005, D6 and D1? No replacement?

About the schematic, I just want to make it clear in my head. VR1 is the clean channel pot, and stock the green wire went from there to V2a. I have to wire that to V2b (the green wire in your modified schematic).

The orange and red wires aren't clear for me yet:

Orange:
There went an orange wire from VR4a to V1b. I have to wire that orange wire from that line at VR4a to V2a.

Red:
I have to wire the red wire (is there a wire like that stock?) from V1b, to V2-something (where?)

What about the green wire that went stock to V2, the one I should have taped up?

Any pin numbers you can give me, or more indications?
-------------------------------------------------------------
In the end, it would be wired like this, right?:
V1a - First gain stage for both normal and boost channel
V1b - Second gain stage for boost channel

V2a - Third gain stage for boost channel
V2b - Second gain stage for normal channel

V3a - Fourth gain stage for boost channel
V3b - Reverb drive

V4a - Reverb recovery
V4b - Final gain stage for entire pre amp

V5 - PI
-------------------------------------------------------------
Another question:
I have done most of the tweaks you recommended me in the first place, practically the whole list of mods you gave me. This is all good when I decide I want to add the gain stage? I'm about the do the resonance-control as well.

Sorry for asking a lot , I'm just planning it all out and making sure I'm doing it right. The work after the mod, those are just a few extra tweaks?

[BeëlzeM]

Ah some better looking in the chassis as well cleared most of it up. The wiring shouldn't be too difficult and I'll do that. Curious how it will turn out.

But still about removing all the diode clipping. Is that just clipping out W005, D6 and D1? Nothing else? Or should I leave W005 in?

And the last thing. What would I need to tweak after the rewiring? Not much? Would be cool to hear what that should be. Will the difference be that big with the 4th stage?

Tubelayout would be like in my previous post then right?

Thanks

[HTH]

But still about removing all the diode clipping. Is that just clipping out W005, D6 and D1? Nothing else? Or should I leave W005 in?

yes, remove all those diodes.

And the last thing. What would I need to tweak after the rewiring? Not much? Would be cool to hear what that should be. Will the difference be that big with the 4th stage?

Tubelayout would be like in my previous post then right?

Thanks

have a look at other high-gain schematics and get an idea of how they're biasing the various gain stages, it's not rocket science (I understand it to some degree afterall, ha ha). use 100k plate, 1k5 cathode with a 1uF bypass cap then a 22nF cap from the plate and you won't go far wrong.

[BeëlzeM]

Alright, I will clip those diodes out.

Do I see it right I have to swap out these marked components? So R14 to 100k, R13 to 1k5 with a uF cap across it, and C13 is already 22nF?



to:



That's how it's done?

[HTH]

yes, that all sounds fine - good luck

[BeëlzeM]

Alright, I've got it all in. Wired it all.

When I turn on the amp (standby on), it's all fine, everything warms up. But when I turn standby off (play mode), it starts a high whistle kind of sound with some noise on the background. The whistle gets lower every second though.

I've done the normal tweaking, the added gain stage on the boost channel, and the resonance pot.

Any help on this one? I'm allmost finished...

EDIT:
I've removed the resonance pot and wired the purple wire back to where it was. Still the whistle sound that starts high and gets lower right away. Anything I might have soldered/wired wrong?




Here's what I've done all in all:

- short C1 (0.047uF) with a wire
- R4 (100k) to 220k
- clip out R12 (220k)
- short out C39 (0.047uF) with a wire
- clip out C20 (0.002uF)
- bypass R25 (1K5) with a 10uF cap
- clip R46 (1k5)
- R43 (470 ohm) to 820ohm
- R41 (330k) to 1M
- R44 (120k) to 1M
- C32 (0.022uF) to 0.047uF
- C34 (0.022uF) to 0.047uF
- R47 (100k) to 47k
- C18 (22uF) to 10uF

I did the rewiring on the preamp sockets for the added gainstage. Plus:
- R13 (10k) to 2k2
- bypass R13 with .68uF cap
- R14 to 100k
- clipped out D1, D6 and soldered out DB1 (diodebridge with number W005)

There is quite a bit of hum. And when I turn my master volume up the hum increases. The gain is fine until I turn it past maybe 6 or 7, then this very loud whistle comes in and when playing an open chord the sound kind of fades away into this buzzing sound. Also, the overdrive is pretty muffled and very heavy on the bass end. With an overdrive pedal and my EQ the sound is better, but it then is a bit on the bright side. I still can't turn my gain over 7 or my amp starts going crazy with this whistle sound that gets lower in tone immediately. It's not just gain whistle/buzz, I've never heard this before really.

The resonance control didn't do all that much, I can't really hear the difference with the 4700pf cap there. Something wrong?

My sound isn't really that tight as I want it to be. It's quite flabby and farty in the bass end, and still pretty high in the treble. The tone sounds somewhat muffled and not very clear where it should be. Could I change the cathode resistor and cathode bypass cap in the added gain stage? I don't really know what to do now, I'm not satisfied yet and the whistle on hi-gain is something I definately need to get rid of.

[HTH]

the whistle will be because of all the gain going on - you should use shielded cable for the grid connections (the green wires).

as for the tone, I can't say why your amp sounds like that - could be your speakers, the guitar, pickups, cables, the way you have the amp EQ'd, the amp might need some general maintenance anyway (recap etc...) - hard to say.

for tighter low end, use 2k7 and 0.68uF on the cathodes.

[BeëlzeM]

the whistle will be because of all the gain going on - you should use shielded cable for the grid connections (the green wires).

as for the tone, I can't say why your amp sounds like that - could be your speakers, the guitar, pickups, cables, the way you have the amp EQ'd, the amp might need some general maintenance anyway (recap etc...) - hard to say.

for tighter low end, use 2k7 and 0.68uF on the cathodes.

Hey man, thanks for your reply.

I'll get some shielded wires for the grids. What I did was I just use the stock wires and soldered them to the other pins. Shielded helps alot?

I'm using a pretty normal setup, active EMG equipped guitar, modded BOSS SD-1 to boost and an MXR 10 band EQ after it. Amp eq is something like bass 7, mid 7, treble 5. The filter caps are brand new JJ's I put in there a few weeks ago. Cab is just a 1960A cab with G12T-75's.

I'll try that cathode combination as well. The bass is just a bit loose and sounds unbalanced compared to the rest of the sound. The overdrive isn't really round. I don't really want more bass, I kinda want it to be tighter and more agressive and matching with the rest of the sound.

[tlsaudio]

@BeëlzeM
Sorry to respond to an old thread but was thinking of doing this to my 2210. How did it turn out and did you get the volume issue figured out? Which mods did you end up using?
Thanks,
Terry

[tlsaudio]

Sorry to bump an old thread but I was thinking of doing the same mods to my 2210, which mods did you end up keeping and did you ever get all the issues fixed with your amp? How do you think the amp sounds now?
Thanks for any info,
-T

[BeëlzeM]

Sorry to bump an old thread but I was thinking of doing the same mods to my 2210, which mods did you end up keeping and did you ever get all the issues fixed with your amp? How do you think the amp sounds now?
Thanks for any info,
-T

Wow, this is super old. Haha. It's that I have e-mail notifications turned on otherwise I wouldn't have noticed this.

Anyways. After this whole debacle I've just completely rebuilt my 2205 to a hotrodded 2204 with an extra triode. Took everything out and started from scratch since I wasn't satisfied with what I had. I first started learning a whole lot about amps and building.

You can read all about it here:
NAD! Finally completed my hotrodded JCM 800 2204 build

Cheers