M15mk1 - More bass and gain on channel 2

Luigi

Hello,
I've just achieved a successful M15mk1 build.

Although, I noticed a lack of bass freqs on channel 2, at least regarding my tastes.

Then, I've looked at JCM800 and JTM schematics and I've seen that, in the first gain stage, the cathode capacitor (680 nF) is a bit small respect the 820 Ohm resistor. Probably, to match the response of original Marshall, a 2,2uF capacitor is needed.

Moreover, to get a bit more gain, I'm also thinking about adding a cathode capacitor to the second stage.

Do you have some advice about these points?

Regards,
Luigi

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Clipfishcarsten

Hi Luigi,

What you're planning to do is nothing new, especially when it comes to "pumping up" marshall-style amps. It's a common and easy way to make old JCM800s and JTMs sound "bigger" with increasing the capacitors on different stages.
As the two channels are entirely separated on the M15, you're not running the risk of making the first channel sound "bloated" when using higher cathode capacitors in the second channel. 2,2uF could be reasonable value there. But keep in mind that a cap that is too big can make the bass response "flub out" at higher volume levels and reduce the tightness of the overall tone. Maybe that's why a smaller cap (680nF) is in there by default.

Regards,
CfC

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