100pF cap — V1 pins 6 and 8

[Bad Brain]

Does anyone know why ceriatone and other 2203 clones add this? I don't see it in the Marshall schematics. Is it voicing or stability or something else?

 

[FourT6and2]

Low pass filter to help prevent parasitic oscillation.

*no AI was used in this response

 

[Bad Brain]

Are we talking ultrasonic oscillations? Why doesn't Marshall spec it?

 

[Floyd Eye]

Wow. How’s it going dude ?

 

[Bad Brain]

Hey Floyd... Thanks for the shout out! Doing well, playing a lot lately, fine-tuning gear...

 

[glpg80]

Are we talking ultrasonic oscillations? Why doesn't Marshall spec it?

Because unfortunately Marshall’s too busy figuring out what shirt or keychain or other consumerism garbage people will buy next to boost their profit margin.

It will help tubes last longer not allowing inaudible oscillations to occur and helps keep the frequencies of interest well within the audible range. Stability is the primary reason though and they should be kept and not removed.

 

[Bad Brain]

Stability is the primary reason though and they should be kept and not removed.

Is it possible that I can hear a difference--a touch more clarity/sparkle with it removed?

I don't have an oscilloscope but if it checked out I assume no risk to tubes, etc?

 

[glpg80]

Is it possible that I can hear a difference--a touch more clarity/sparkle with it removed?

I don't have an oscilloscope but if it checked out I assume no risk to tubes, etc?

I mean I’ll be completely honest with you - there is an actual audible difference because it forms not just a low pass filter with the output to next stage, but also an RC resonant tank circuit that varies its response with frequency that does reach all the way down to audible upper mid frequency ranges. You’re not going to notice it in the low end or low mids but certainly noticeable everywhere else. Everything is a trade, however it doesn’t do any good to amplify frequencies the wiring and layout can’t support. It sets the stability of the amplifier and is not something you should go messing with unless you have the experience to do so.

There’s no risk to tubes and they’ll be much happier with it there than without. If anything you’ll notice a better bass response because the response time of the triode is also improved since it doesn’t have high frequency garbage to shunt to ground.

 

[FourT6and2]

100pF in this position forms a cutoff at 40KHz...

Can you hear it? No. Does it make the tubes/amp happier? Yes. So sure... on some level, the amp is no longer waisting energy dealing with those high frequency oscillations. And that means the amp runs more efficiently. That eventually trickles down to affect how the amp responds and feels and sounds, but it's not like you will actually hear it if you A/B the amp with and without the cap.

Theoroetically, a guitar amp might be better off only dealing with and amplifing the exact frequencies you can hear and the guitar and the speakers can reproduce. Everything above and below that range is wasted energy. In theory. Why waste energy sending a 40KHz signal to the speakers? In many cases, HF parasitic oscillation in certain parts of the circuit are what cause red-plating. So it's best to reign them in where you can.

 

[Floyd Eye]

Hey Floyd... Thanks for the shout out! Doing well, playing a lot lately, fine-tuning gear...

Good to see you man. I missed you. Glad to hear you’re playing a lot.