JCM 800 2210 VOLUME MOD NEEDED

hotguit

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Hi
I'm modding a bit my JCM 800 2210.
I lift the diodes gain stage for a pure tube drive.
I've heard about a buffer mod to fix the problem but i found nothing on the web.
Nobody has a good mod for its terrible lead channel volume?. I have to run it maxed to have a decent and not flubby tone.
Any idea?
Thank you
Peter
 
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XTRXTR

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There isn't a diode gain stage in a 2210
There is an IC transistor array to control the channel switching from a foot switch
 

hotguit

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there is a diode gain stage in a 2210, there is...
Here it is
The transistor switching is not involved in gain stages; it only switches (badly) channels.
Cheers.
 

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Spanngitter

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There is multiple Versions of the 2210 out there, they differ in the Diode clipping Stage, in Channel Switching (Transistor vs logic IC) and a few more small points.
I had multiple 22xx here for repair and fluppy tone usually denotes the requirement of a Cap Job, checking all the GND connections as the used black oxide washers do rust over time and degrade the GND and a proper Bias adjustment...and so far the majority of them sounded great again after that, no need to mod on the circuit.
 

XTRXTR

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Well I'll be a...buckeyed mule. I missed it. apologies.

I figured to see what they did in the original 2205 circa '81-'82 with a DCCF driving the diodes from V2 in the boost channel section.
1652267144997.png
I didn't see the square box w005.
 

hotguit

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There is multiple Versions of the 2210 out there, they differ in the Diode clipping Stage, in Channel Switching (Transistor vs logic IC) and a few more small points.
I had multiple 22xx here for repair and fluppy tone usually denotes the requirement of a Cap Job, checking all the GND connections as the used black oxide washers do rust over time and degrade the GND and a proper Bias adjustment...and so far the majority of them sounded great again after that, no need to mod on the circuit.
I had repaired and modded many amps, from SLP to JCM. i really do not like how stock 2210s sound.
It is a matter of taste i think...
Have you ever pointed your attention over the volume? Any idea how to fix it?
Thank you
Peter
 

thetragichero

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maybe off topic but i saw "diode gain stage" and wondered how-in-the-hell one would arrange a bunch of diodes to get more signal out than in (kinda need either another p-type or n-type region)
 

Pete Farrington

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i really do not like how stock 2210s sound.
It is a matter of taste i think...
Have you ever pointed your attention over the volume? Any idea how to fix it?
As there are completely different versions (eg Oct 81 above, Mar 87) of the same model #, it would be beneficial to identify your specific amp schematic, with a link preferably.
 
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hotguit

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it is an 87 limited edition with green tolex.
Same schem as a 1987 jcm 800 2210 dual channel
Schem attached; talking about VR5
Peter
 

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Tatzmann

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I did a simple switchable cap mod on
my 1988 2205. Its 95% sounding and
feeling like my 2203 now. Found the mod
somewhere on here.

This amp doesnt really need mods, it
needs to be run loud to sound good.

I didnt like it stock for ACDC, but for 80s
Metal it was damn good stock, crank the
bass, lower the mids and up the highs as
much as you need to pop through...oh and run
it LOUD, otherwise this amp is a letdown.

Its not a bedroom amp kiddos. I wouldnt
butcher it, but you will, i guess.
 

XTRXTR

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If you're lifting the diodes anyway that takes them out of circuit, right.
So the previous tube stage V1b cathode could be modified for a hot bias at R3. I've been experimenting with LEDs on V1 both cathodes of my 2204. In any case you could lower the 10K to about 2k to get a hot bias. I have a 1.5 Vf red LED there at the moment. 10K gets you about 2.8VDC, 2k gets you about 1.6Vdc, You could jumper a piggyback 130k on the 470k load resistor to bring it down to about 100k. It should act like a cold clipper biased hot. If its too hot increase the cathode resistor or use a green LED 1.8Vf.

I have a switch I'm working on that will give me options of 3.7,2.7 and 1.5 VDC each from different color LEDs. Gives me super clean, to regular to awesome overdrive.

The LED keeps the low frequencies in play or use a 2kR with a fairly large bypass cap.

Then use the 1mlog as your volume and remove the VR5 out of circuit. IOW VR4B wiper to where the VR5 wiper is. You will have to remove the R3 10kR and diode but You may be able to test the rest with a few jumpers and see what you get.

Just spit ballin
 
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hotguit

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Then use the 1mlog as your volume and remove the VR5 out of circuit. IOW VR4B wiper to where the VR5 wiper is. You will have to remove the R3 10kR and diode but You may be able to test the rest with a few jumpers and see what you get.

Thank you
The amp is not stock. R3 is actually a 1K/1uF combo. I just replaced some value according to GOLUB SE Lead specs (i'll post value asap)
But... why do i have to remove R3? The one i have to replace with a red or green led?
And What does IOW VR4B mean?
Thank you
 

XTRXTR

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IOW = In other words, internet short language

Low volume problems can also be due to the contact point at the return input jack. Clean that with some deoxit and work a plug in there 10 or 20 times.

I figured you would have to remove R3 to get an LED or a 2kR with a .68uF or higher cap in its place. 1k is very low, an LED won't really change anything compared to that. You might be getting a fizzy type noise out of that.

What is the B+ voltage on that 470k load resistor?
Didn't realize you had modified from the schematic. Try a 200k piggyback on the load resistor R7 - 470k//200k = 140k-ish since the cathode is so low it may give you more gain. And then jumper the VR4b wiper to where the VR5 wiper is, you may have volume control issues doing this as one will affect the other. You could leave VR5 at full hi and allow VR4b to control the actual volume or disconnect VR5 wiper from circuit, I think this is a PCB mounted volume correct? So, disconnecting may not be so easy.
 
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hotguit

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Hi
My 2210 dist channel now is like the schem attached. (M. G. SE LEAD reverse engineering schem - from an original thing)
Great tone but needs any refining touch...
 

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  • SELEAD HOT (2).JPG
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