Ceriatone Chupacabra mods

  • Thread starter Thread starter peterc52
  • Start date Start date
FourT6and2 said:
Nope lol. Ceriatone left out a 10K B+ dropping resistor. There should be one between the PI and V2. The one you circled is between V2 and V1. These resistors separate each section of the amp so they each get their own filtering. Without it, you have multiple stages sharing the same filter cap.

It's fine if you like that sound/feel. But if it were me, I would install it.
Have a look at one of their superlead layouts and you'll see it: https://ceriatone.com/wp-content/uploads/2016/08/Plexi50BassCeriatone.jpg

Just make sure you get the connections right, so if you do it... really pay attention to how it's wired.
Click to expand...
Damn. I will!
 
FourT6and2 said:
Nope lol. Ceriatone left out a 10K B+ dropping resistor. There should be one between the PI and V2. The one you circled is between V2 and V1. These resistors separate each section of the amp so they each get their own filtering. Without it, you have multiple stages sharing the same filter cap.

It's fine if you like that sound/feel. But if it were me, I would install it.
Have a look at one of their superlead layouts and you'll see it: https://ceriatone.com/wp-content/uploads/2016/08/Plexi50BassCeriatone.jpg

Just make sure you get the connections right, so if you do it... really pay attention to how it's wired.
Click to expand...
That haven’t updated the circuit still?

What does it do to the sound?

IMG_9870.png
 
peterc52 said:
That haven’t updated the circuit still?

What does it do to the sound?

View attachment 376103
Click to expand...

Correct. They haven't updated their circuit. I had a chat about this with Ceriatone years ago. But he wasn't interested in fixing it. You gotta realize that they don't design these circuits. They just copy them from schematics posted to forums. Those schematics are drawn by users who blueprint various amps they own or have seen. This particular amp is most likely a clone of a Fortin Jose mod that is in turn, a variation on a Cameron mod. So you've got a few moments where information can get lost in translation. Cameron —> Fortin —> forum member who drew up schematic —> Ceriatone. Sometimes key details like this get lost along the way. Schematics have mistakes, etc. Ceriatone wasn't interested in fixing this at the time. Maybe they have now, who knows.

Without a 10K resistor between the PI B+ node and the left side of that cap (as it's drawn in THIS layout), the PI and V2b (cathode follower) are sharing the same filtering. It's not "bad", per se. But it's not what many would choose to do in an amp like this, that is supposed to be a "hot rodded", higher-gain JCM800. Amp will be a little looser, flubbier, rounder sounding, and more squish/sag.

Adding that resistor will give each stage it's own independent filtering. This provides each stage with it's own reservoir of smoother DC/B+. So the amp will be a little tighter, faster attack, less sag, etc.
 
FourT6and2 said:
Correct. They haven't updated their circuit. I had a chat about this with Ceriatone years ago. But he wasn't interested in fixing it. You gotta realize that they don't design these circuits. They just copy them from schematics posted to forums. Those schematics are drawn by users who blueprint various amps they own or have seen. This particular amp is most likely a clone of a Fortin Jose mod that is in turn, a variation on a Cameron mod. So you've got a few moments where information can get lost in translation. Cameron —> Fortin —> forum member who drew up schematic —> Ceriatone. Sometimes key details like this get lost along the way. Schematics have mistakes, etc. Ceriatone wasn't interested in fixing this at the time. Maybe they have now, who knows.

Without a 10K resistor between the PI B+ node and the left side of that cap (as it's drawn in THIS layout), the PI and V2b (cathode follower) are sharing the same filtering. It's not "bad", per se. But it's not what many would choose to do in an amp like this, that is supposed to be a "hot rodded", higher-gain JCM800. Amp will be a little looser, flubbier, rounder sounding, and more squish/sag.

Adding that resistor will give each stage it's own independent filtering. This provides each stage with it's own reservoir of smoother DC/B+. So the amp will be a little tighter, faster attack, less sag, etc.
Click to expand...
Thanks for the explanation!
 
FourT6and2 said:
Nope lol. Ceriatone left out a 10K B+ dropping resistor. There should be one between the PI and V2. The one you circled is between V2 and V1. These resistors separate each section of the amp so they each get their own filtering. Without it, you have multiple stages sharing the same filter cap.

It's fine if you like that sound/feel. But if it were me, I would install it.
Have a look at one of their superlead layouts and you'll see it: https://ceriatone.com/wp-content/uploads/2016/08/Plexi50BassCeriatone.jpg

Just make sure you get the connections right, so if you do it... really pay attention to how it's wired.
Click to expand...
Good catch!!!!
 
FourT6and2 said:
Did you remove the connection under the board? And did you make sure the connection from the other half of that cap to V1 node is correct?
Click to expand...
When I added the 10k the voltage dropped to 155 v on V1a. Damn
 
peterc52 said:
When I added the 10k the voltage dropped to 155 v on V1a. Damn
Click to expand...

Yeah, that'll happen. The only things you can do are:

1. PT with higher voltages.
2. Lower first/main B+ dropper(s). If you have a 10K + 10K or 10K + 8K2 or a single 10K, you can lower the values slightly.
3. Lower V1a plate resistor value slightly. If it's 470K, go with 330K. If it's 330K, try a 300K, etc.
4. Or just don't worry about it.
 
peterc52 said:
When I added the 10k the voltage dropped to 155 v on V1a. Damn
Click to expand...
FourT6and2 said:
Yeah, that'll happen. The only things you can do are:

1. PT with higher voltages.
2. Lower first/main B+ dropper(s). If you have a 10K + 10K or 10K + 8K2 or a single 10K, you can lower the values slightly.
3. Lower V1a plate resistor value slightly. If it's 470K, go with 330K. If it's 330K, try a 300K, etc.
4. Or just don't worry about it.
Click to expand...
Sorry, a little late to the party here, but good thread so far......
You are generally stuck with whatever B+ and screen voltage your PT and choke give you,
so what I typically do when looking at voltages in Marshall style builds is start by targeting 345-360 volts at the PI node. The dropping resistors from the screens to the PI can be any combo of 6.8k, 8.2k, 10k etc.. to get the target voltage at the PI.
Next I check the cathode follower to make sure I'm not exceeding about 180-190v. This will prevent you running into issues with some 12ax7s that can't handle too high a voltage difference between the cathode and the heaters. Standard 10k is usually ok here, but check.
Then I go to the plate on V1a and adjust voltage there to get a tone and feel I like by adjusting the dropper from the cathode follower and / or the plate resistor. A 10k dropper is usually ok, and then plate resistor to taste. I usually gravitate to around 170-175v, but it can be whatever you like within reason. If you really dig a 330k / 470k plate, then lower the dropper. The dropping resistor and the filter cap create a low pass filter on the b+ line, sending any ac ripple to ground.
If the cap is 32uf or bigger, you could probably lower the dropper all the way to 4.7k without an issue if you want to. 4.7k and 50uf will remove any ac ripple above 0.6hz.
Personally, I hate the soft, squishy sound and feel of extra large plate resistors in high gain amps, but that's just me.
Let us know how you make out with the amp!
 
fusedbrain said:
Sorry, a little late to the party here, but good thread so far......
You are generally stuck with whatever B+ and screen voltage your PT and choke give you,
so what I typically do when looking at voltages in Marshall style builds is start by targeting 345-360 volts at the PI node. The dropping resistors from the screens to the PI can be any combo of 6.8k, 8.2k, 10k etc.. to get the target voltage at the PI.
Next I check the cathode follower to make sure I'm not exceeding about 180-190v. This will prevent you running into issues with some 12ax7s that can't handle too high a voltage difference between the cathode and the heaters. Standard 10k is usually ok here, but check.
Then I go to the plate on V1a and adjust voltage there to get a tone and feel I like by adjusting the dropper from the cathode follower and / or the plate resistor. A 10k dropper is usually ok, and then plate resistor to taste. I usually gravitate to around 170-175v, but it can be whatever you like within reason. If you really dig a 330k / 470k plate, then lower the dropper. The dropping resistor and the filter cap create a low pass filter on the b+ line, sending any ac ripple to ground.
If the cap is 32uf or bigger, you could probably lower the dropper all the way to 4.7k without an issue if you want to. 4.7k and 50uf will remove any ac ripple above 0.6hz.
Personally, I hate the soft, squishy sound and feel of extra large plate resistors in high gain amps, but that's just me.
Let us know how you make out with the amp!
Click to expand...

Solid info!

Checking the CF voltage is a good idea. And for anybody else reading this that doesn't know, there's another way around that if the cathode-heater differential is too high (elevated heaters—I'm sure you know). But that might be getting too far into the weeds for OP. And historically, production amp designers didn't worry about it because tubes were stronger and could take the punishment back then. Definitely try to avoid modern long-plate 12AX7s in the CF in an amp like this.

I'm with you... I also don't like super large plate resistors. I think it's sort of a low-hanging-fruit trick to get more gain/distortion that leads to other problems. It'll work to a point, but I think in an amp like this, 330K is the highest total resistance I'd want on V1a. Ideally, I'd look toward other options to get more gain/distortion.
 
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