Brigth cap, question?

[Rod]

Hello!

Need some help here, i want to reduce the brightness of a amp, what will be the best option, of the foloowing two options?



1 - Reduce the brigth cap value from 470pf to 150fp, has seen in the schematic bellow
i have tried this option and it seems that the amp lost the bottom end tightness.




2- IF i add the the a grid stopper resistor of 470k,before the second gain stage like in the shematic bellow, will it reduce the overall brigthness, and keep the bottom end tight?

[eschertron]

most of your brightness is due to the .002u cap that parallels the 470k resistor in the schem you show. Marshall makes that 470p, about 1/4 the value of your amp's cap. The 470p 'bright' cap (the one you mention) paralleled with the volume will only have an effect at low volumes. My advice is to play with values for both until you get a control that works for you. I've done a bit o' that in one of my amps. It took a few tries, but I like it now!

[alexradium]

Hello!

Need some help here, i want to reduce the brightness of a amp, what will be the best option, of the foloowing two options?



1 - Reduce the brigth cap value from 470pf to 150fp, has seen in the schematic bellow
i have tried this option and it seems that the amp lost the bottom end tightness.

[ATTACH=CONFIG]57929[/ATTACH]


2- IF i add the the a grid stopper resistor of 470k,before the second gain stage like in the shematic bellow, will it reduce the overall brigthness, and keep the bottom end tight?

[ATTACH=CONFIG]57927[/ATTACH]

put that 470k in series with the bright cap

[Rod]

I have tried the second option with the grid stopper resistance of 470k after the brigth cap and this optioni makes the amp less brighter, not harsh at all, a little more darker in a good way , i think that this is a better design. I will try other values instead the 470K, to see what i get.

[Helmholtz]

A bright cap doesn't influence bass response.

[Rod]

A bright cap doesn't influence bass response.

It does influence the bass responce, in the schematic of option 1 i can clearly ear less tight bass responce and more bass overall, if i reduce the value from 470pf to 150pf.

[The Dude]

I think what you might be hearing is less attack on the notes (high frequency) and your ear is interpreting it as "less tight bass response". Further, I think you're interpreting less treble (changing the cap value) as "more bass overall", which is sort of the same thing. There is no way a small value cap like that, in that circuit, can effect bass response. Perhaps you made too much of a value change for the sound you're looking for.

[Helmholtz]

It does influence the bass responce, in the schematic of option 1 i can clearly ear less tight bass responce and more bass overall, if i reduce the value from 470pf to 150pf.

Problem is that it is not clear what "tight bass" means in terms of frequency response.

Circuit analysis allows to calculate (or simulate) high pass and low pass frequency responses and the bright cap is part of a high pass filter that doesn't affect low frequency amplitudes.
In your option 1 schematic the 470p bright cap only boosts frequencies above 700Hz or higher depending on vol pot setting. Replacing with a 150p bright cap shifts the start of the boost to frequencies above 2kHz.