Remove cathode bypass cap?

edo

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I’ve beed consjdering to experiment with this mod on one of my real ac30’s, and was curious whether I can mimic this mod within the axe to get an idea of the result.. if so, how?
 
Ouch, good question! I found the following info on an ac30 mods post/forum, and was curious to esperiment for myself (although I should add that I have no evidence this is true, that’s why I wanted to hear what it sounds like!):

“Removal of Top Boost Cathode Bypass cap
This is the U2 mod - the Edge's amp doesn't have this cap and it makes for tighter bass, more headroom/lower gain on the TB channel.
(kinda nice to put on a switch)”

Any clue?
 
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It should be C9 in an AC30CC2 or C18 in a AC30C2 according to the info I found. My feeling is that we cannot "disable" it in the Amp settings until Cliff adds a switch for it like for the Bright Cap...
 
Yeah, I read how it’s done on a real amp, I was asking if it can be done one the amp model!
 
So really you’re asking Cliff if he has a C9/C18 equivalent in the model and if so can he put a bypass option on it. That’s a nice idea.
 
So really you’re asking Cliff if he has a C9/C18 equivalent in the model and if so can he put a bypass option on it. That’s a nice idea.
Lol, of course not! I’m just asking if the axe has a parameter to tweak and mimic this mod!
 
Yeah, I read how it’s done on a real amp, I was asking if it can be done one the amp model!

Interesting mod., I hadn’t heard of it before. I had quite a few JMI mods. done by Lyle on my AC30, not sure if he did that one. I’ll have to check my notes and look into it.
 
Lol, of course not! I’m just asking if the axe has a parameter to tweak and mimic this mod!
You’ve misunderstood my English. It’s exactly what your asking, remove the simulated C9/C18 from the modelled circuit with bypass/switch.
 
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You’ve misunderstood my English. It’s exactly what your asking, remove the simulated C9/C18 from the modelled circuit with bypass/switch.

Or something along the line of “you can turn parameter X to 0 to simulate this”!
 
I think the question is what does that cap do
Does removing it make the amp
Darker smoother less compressed?

I know Cliff has mentioned he does not like the way the cathode is implemented in the AC30 and recommended turning down the power tube hardness to get rid of some of the undesirable artifacts and harshness
 
I think the question is what does that cap do
Does removing it make the amp
Darker smoother less compressed?

I know Cliff has mentioned he does not like the way the cathode is implemented in the AC30 and recommended turning down the power tube hardness to get rid of some of the undesirable artifacts and harshness
It simply increases the gain. Reduce Input Trim to simulate removing it. Without doing the math I'd guess probably down to around 0.5.

The power tube hardness is unrelated to this. This is on the preamp gain stage. A capacitor in parallel with the cathode resistor increases the gain. If it's a large value (which it is in this case) it increases the gain equally at all frequencies. If it's a small value it increases the gain at higher frequencies. Therefore you can simulate removing the cap by simply turning down the Input Trim.
 
It simply increases the gain. Reduce Input Trim to simulate removing it. Without doing the math I'd guess probably down to around 0.5.

The power tube hardness is unrelated to this. This is on the preamp gain stage. A capacitor in parallel with the cathode resistor increases the gain. If it's a large value (which it is in this case) it increases the gain equally at all frequencies. If it's a small value it increases the gain at higher frequencies. Therefore you can simulate removing the cap by simply turning down the Input Trim.

And does this yield tighter bass, like the mod description suggests?
 
And does this yield tighter bass, like the mod description suggests?
No. Lowering the Input Trim isn't exactly the same since removing the cap increases the negative feedback but I can't imagine it would make that big a difference.
 
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No. Lowering the Input Trim isn't exactly the same since removing the cap increases the negative feedback but I can't imagine it would make that big a difference.

Does that apply on a non negative feedback amp type (eg ac30)?
 
Does that apply on a non negative feedback amp type (eg ac30)?

That's power amp. Cathode bypass (unless we're talking about cathode-bias power tubes bypass cap, which I've never really ever seen omitted) is a preamp thing.
 
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