Ceriatone Chupacabra mods

peterc52

Well-known member
I know this has been talked about a ton. But can’t seem to find the informative treads.

I’ve just bought back a Chupa I built a couple of years ago and want to start experimenting with it. What’s your favorite mods?

I know that @scottosan and @FourT6and2 had dived deep into this. Others?

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What do you want out of it sonically?

There are a ton of mods but doing mods without an end goal in sight is a long dark expensive deep path you want to try to avoid unless you just want to experiment or have to do so lol
 
Looks like a passive effects loop - you can certainly upgrade that with a Ceriatone board and power it off the B+. I say Ceriatone board because the jack spacing won't fit a Metro or Mojo loop unless you widen it out 1/2". There's also room for adding another preamp tube/additional gain stage.
Adjustable NFB is never really a bad idea with amps geared towards that sort of voicing.

But like what was said above, depends on what you're wanting to get out of it.
 
Looks like a passive effects loop - you can certainly upgrade that with a Ceriatone board and power it off the B+. I say Ceriatone board because the jack spacing won't fit a Metro or Mojo loop unless you widen it out 1/2". There's also room for adding another preamp tube/additional gain stage.
Adjustable NFB is never really a bad idea with amps geared towards that sort of voicing.

But like what was said above, depends on what you're wanting to get out of it.
Good idea! I’ll order a ceriatone loop! I have a headfirst loop thats going into my 2203 too :)

I had a Cameron ocean at some point which was a bit towards a Mesa. Would love to try going that way
 
Yeah depends on what you want out of it. I'd say, in general, add the missing 10K B+ dropper if you haven't already. Change slope resistor to 33K. Change NFB resistor to 47K. Change depth cap to 2200pf or 3300pF. Lower V1a plate resistor to 220k and 100k in series or just a 330k will do. Change first two cathode stages to 0.68uF/2.7K. Lots of other things I would personally do, but those are the basics.

Basically... put it back to stock Marshall values haha
 
Yeah depends on what you want out of it. I'd say, in general, add the missing 10K B+ dropper if you haven't already. Change slope resistor to 33K. Change NFB resistor to 47K. Change depth cap to 2200pf or 3300pF. Lower V1a plate resistor to 220k and 100k in series or just a 330k will do. Change first two cathode stages to 0.68uF/2.7K. Lots of other things I would personally do, but those are the basics.

Basically... put it back to stock Marshall values haha
Thank you!! I know you know them well :)
 
This is what’s missing right? Layout from a 2203 :)
 

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Yeah depends on what you want out of it. I'd say, in general, add the missing 10K B+ dropper if you haven't already. Change slope resistor to 33K. Change NFB resistor to 47K. Change depth cap to 2200pf or 3300pF. Lower V1a plate resistor to 220k and 100k in series or just a 330k will do. Change first two cathode stages to 0.68uF/2.7K. Lots of other things I would personally do, but those are the basics.

Basically... put it back to stock Marshall values haha
I going to try to learn some this time. I had no problem following a layout but didn’t learn much :/

Slope resistor is the one before the 2 0.022uf going to treble and middle right?

And v1a plate resistor is on pin 1 farthest from transformers?
 
I going to try to learn some this time. I had no problem following a layout but didn’t learn much :/

Slope resistor is the one before the 2 0.022uf going to treble and middle right?

And v1a plate resistor is on pin 1 farthest from transformers?
These are all basically the same as what Jason has in his video. Great minds think alike.
 
This is what’s missing right? Layout from a 2203 :)

Hard to tell from that photo. But the b+ dropper is the one right after the PI node. It goes between the PI node and the first half of the preamp filter cap. It's mentioned in that video above. I think I was the first person to notice Ceriatone left it out years ago. I emailed Nik about it and his response was along the lines of "it doesn't matter, that resistor doesn't do anything." In reality, he just copied a bad schematic he found on the internet and left out that resistor because the schematic omitted it by mistake.

That resistor is needed to decouple each stage of the amp and provide proper filtering.
 
I going to try to learn some this time. I had no problem following a layout but didn’t learn much :/

Slope resistor is the one before the 2 0.022uf going to treble and middle right?

And v1a plate resistor is on pin 1 farthest from transformers?

Yep, you got it.
 
These are all basically the same as what Jason has in his video. Great minds think alike.

Yeah, they're all very common mods. Been around for 40 years.

There are a bunch of other things I would personally do to mod these amps, but that gets into secret sauce territory haha. I'd say just experiment a bunch until you find stuff that sounds good. Learn what each component does to change the sound of the amp and start experimenting. Check out the schems/layouts of the other amps as well for ideas.

In terms of voicing, I think Marshall really got it right the first time. 2.7k/.68uF cathodes in first two stages to keep things punchy and tight, don't goose the first plate too much. You want at least 160v on V1a plate, if not more. V1b input grid resistor could come down in value too. But then you gotta adjust all the crap on those gain pots and swap the order of those first two coupling caps as well.

Mods don't exist in a vacuum. When you change one thing here, you gotta change another thing over there to work with it.
 
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Yeah depends on what you want out of it. I'd say, in general, add the missing 10K B+ dropper if you haven't already. Change slope resistor to 33K. Change NFB resistor to 47K. Change depth cap to 2200pf or 3300pF. Lower V1a plate resistor to 220k and 100k in series or just a 330k will do. Change first two cathode stages to 0.68uF/2.7K. Lots of other things I would personally do, but those are the basics.

Basically... put it back to stock Marshall values haha
Agreed. I’d lose that pussy trim setup as well.

I’d also mess with the clipping options.
 
I keep the stock 68k in my 74 Marshall. I find it trims the highs and keeps things touch sensitive.

I agree with all of the above - I have a stock first stage cathode setup 2.7k//0.68uF.
 
Agreed. I’d lose that pussy trim setup as well.

I’d also mess with the clipping options.

Yeah, just replace the trimmer with a 470k resistor and put it right on the board like in most Marshalls. That frees up the hole in the chassis for something else. I put a 6-position rotary there with a bunch of clipping options.

Could also swap out the "feel" resistor that's on that push/pull with a pot to make the feel control variable (*cough* Fortin *cough*).
 
Yeah, just replace the trimmer with a 470k resistor and put it right on the board like in most Marshalls. That frees up the hole in the chassis for something else. I put a 6-position rotary there with a bunch of clipping options.

Could also swap out the "feel" resistor that's on that push/pull with a pot to make the feel control variable (*cough* Fortin *cough*).
I see you have removed the bright switches entirely. Do you not have any bright caps on? Or just hardwired one?
 
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