Sending my 2204 clone for some mods, looking for some suggestions

Sorry if this is too close to some other threads, but I didn’t want to hijack and rather start a new.

I have a Mojotone 800 kit that my father-in-law built for me and I’m planning on taking it to a tech to spice it up. It already has a PPIMV, so really I am looking for some more gain and perhaps more control over tightness and bass.

I don’t trust myself with electronics, so I have only tested a few things.Using alligator clips I have found that I really dig the sound of the amp with a 2.5k resistor on the R6 (I tried this with a total of 4 10ks in parallel), but only when the amp is boosted with my OD808. In the end, I may ask for a rotary switch to be installed so I can go from stock, to 5k, to 2.7-2.5k.

However, is there any way I can get the tightness from the boost with some changes to the amp?

Also, what would you recommend in terms of a resonance control?

since this is a home brew build that I Intend to keep for eternity, I’m okay with drilling and installing switches/pots for the sake of flexibility.
Thanks!
 

rm5153

Member
I would contact David Hopkins on this site and send your amp to him. He will make your JCM800 clone into something really special. Lots of his work can be found on YouTube under the Hopkins Pandora mod. I have a JCM800 reissue that he did and it is killer. I don't know what he charges as the amp I got was purchased with the mods already incorporated.
 

fusedbrain

Well-known member
Lots of good techs out there doing their high gain mods to 800's.
Hopkins and the Monomyth guy are 2 that frequent this forum and do quality work.
May not be necessary to go down that road and spend the $$ just yet though.
If your father in law built the amp, and is willing to spend 45 minutes making some adjustments, try this:
*** Note: This is not my design or idea, but has been proven to sound very good***
A few guys on here will know what this is :LOL: :LOL: :LOL:
Modded Jcm800 preamp.png

Changing the first coupling cap to 2.2nf will tighten the amp up.
Addding the 3.3k + .68uf to the 10k gives you 2.5k bypassed with the cap for more gain.
Adding the 220k to ground at the same time keeps everything tight and under control, as the 3.3k // .680uf is adding a lot of gain.
You can swap out the gain pot for a 1meg with a DPDT switch on the back to do this switching, or drill and add a switch.
*****Note that the switch contacts for the resistor / cap combo should be wired between the 10k and the top of the R+C, with the bottom of the R+C connected to ground. If you wire it as shown, by switching the ground connection, it will pop.
The 22uf on the 3rd cathode beefs things up and the 470pf on the cathode follower kills some ice-pick and will add a touch of compression.
Add a resonance control and you're done.
$20 worth of parts and a little bit of time.
 
Lots of good techs out there doing their high gain mods to 800's.
Hopkins and the Monomyth guy are 2 that frequent this forum and do quality work.
May not be necessary to go down that road and spend the $$ just yet though.
If your father in law built the amp, and is willing to spend 45 minutes making some adjustments, try this:
*** Note: This is not my design or idea, but has been proven to sound very good***
A few guys on here will know what this is :LOL: :LOL: :LOL:
View attachment 66393
Changing the first coupling cap to 2.2nf will tighten the amp up.
Addding the 3.3k + .68uf to the 10k gives you 2.5k bypassed with the cap for more gain.
Adding the 220k to ground at the same time keeps everything tight and under control, as the 3.3k // .680uf is adding a lot of gain.
You can swap out the gain pot for a 1meg with a DPDT switch on the back to do this switching, or drill and add a switch.
*****Note that the switch contacts for the resistor / cap combo should be wired between the 10k and the top of the R+C, with the bottom of the R+C connected to ground. If you wire it as shown, by switching the ground connection, it will pop.
The 22uf on the 3rd cathode beefs things up and the 470pf on the cathode follower kills some ice-pick and will add a touch of compression.
Add a resonance control and you're done.
$20 worth of parts and a little bit of time.

Thanks a ton for these suggestions!

I am probably just going to take the amp to a local tech who has a cheap bench fee.
Is it okay if I print off your schematic and notes and give them to him?

Also, for the resonance control does the usual 1meg audio pot + 4.7nF cap do the trick?
 

fusedbrain

Well-known member
Thanks a ton for these suggestions!

I am probably just going to take the amp to a local tech who has a cheap bench fee.
Is it okay if I print off your schematic and notes and give them to him?

Also, for the resonance control does the usual 1meg audio pot + 4.7nF cap do the trick?
No problem & yes. :D
Should also mention that it will still sound 800-ish. Just bigger and meaner.
If you want to maintain the general vibe of an 800, then cool.
If you are looking for something completely different, then maybe talk to Hopkins or Monomyth.
But I'm getting the sense that you just want to kick your 800 in the nutz a little bit :LOL: :LOL: :LOL:
 
Last edited:
No problem & yes. :D
Should also mention that it will still sound 800-ish. Just bigger and meaner.
If you want to maintain the general vibe of an 800, then cool.
If you are looking for something completely different, then maybe talk to Hopkins or Monomyth.
But I'm getting the sense that you just want to kick your 800 in the nutz a little bit :LOL: :LOL: :LOL:
Yep def want to keep the 800 character, just give it more balls!

Last question: what should the voltage be on the 470pF?
 

burger

New member
Lots of good techs out there doing their high gain mods to 800's.
Hopkins and the Monomyth guy are 2 that frequent this forum and do quality work.
May not be necessary to go down that road and spend the $$ just yet though.
If your father in law built the amp, and is willing to spend 45 minutes making some adjustments, try this:
*** Note: This is not my design or idea, but has been proven to sound very good***
A few guys on here will know what this is :LOL: :LOL: :LOL:
View attachment 66393
Changing the first coupling cap to 2.2nf will tighten the amp up.
Addding the 3.3k + .68uf to the 10k gives you 2.5k bypassed with the cap for more gain.
Adding the 220k to ground at the same time keeps everything tight and under control, as the 3.3k // .680uf is adding a lot of gain.
You can swap out the gain pot for a 1meg with a DPDT switch on the back to do this switching, or drill and add a switch.
*****Note that the switch contacts for the resistor / cap combo should be wired between the 10k and the top of the R+C, with the bottom of the R+C connected to ground. If you wire it as shown, by switching the ground connection, it will pop.
The 22uf on the 3rd cathode beefs things up and the 470pf on the cathode follower kills some ice-pick and will add a touch of compression.
Add a resonance control and you're done.
$20 worth of parts and a little bit of time.

I just posted a DIY guide for making these mods to your 2203/2204 JMP/JCM800...

 
Have you thought about using a pedal out front? There are so many that will do what you want.... like the VFE standout, Dragon etc.

Here is a bone stock 1980 Marshall 2203. One pedal out front (I can’t remember which one). Tons of gain and tightness. Amp has 6550’s in it.
I may have to pick up the dragon in the classifieds. This sounds really amazing and tight!
 
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