Marshall sound?

Ghandi · September 20, 2004, 12:09:11 PM

Hi!
I have a question what the parallel combination of the 470K resistor and the 470pF capacitor in the Marshall preamps and also in the BSIAB2 is doing?
Any ideas? What is this contributing to the marschall sound?
LP- HP- filtering?

Thanks

cd · September 20, 2004, 12:37:15 PM

HP. High frequencies see the cap as a short, so they pass through unattenuated.

Steben · September 21, 2004, 03:24:00 AM

Quote from: GhandiHi!
I have a question what the parallel combination of the 470K resistor and the 470pF capacitor in the Marshall preamps and also in the BSIAB2 is doing?
Any ideas? What is this contributing to the marschall sound?
LP- HP- filtering?

Thanks

It's a kind of passive treble booster circuit.

cd · September 21, 2004, 08:52:10 AM

Oh yeah, it contributes the ear piercing brightness (without low end mud) that Marshalls were famous for (up to the 800s).

Ghandi · May 04, 2005, 07:56:20 AM

Ok, back to an old thread!
I just have two questions leaved.
Would be very kind if you guys could help me out.

Is the fq-respons (of the 470Kll470pF combination) independent of the setting/value of the resistor before to ground, in most cases the 1M Vol. control?

If I want to reduce the resistance of the parallel cap resistor combination and keep the fq-respons the same,
for example:
470K/47=10K
and
470pF*47=22.09nF
would this be right?

vanhansen · May 04, 2005, 10:14:55 AM

Just remove the cap and leave the resistor as-is. This was a very common mod on the JCM800's to remove the brightness.

Ghandi · May 04, 2005, 11:06:07 AM

Yeah,
But the problem is that I want the brightness!

I want that trick for an effect where I have the 10K resistor in the signal path.

My problem is that I'm not really sure if the mathematics are right?

vanhansen · May 04, 2005, 01:15:22 PM

What trick is that? I guess I don't know what you are trying to accomplish.

WGTP · May 04, 2005, 01:17:27 PM

I think this is an excellent location to "voice" your distortions. If you double one, Half the other to maintaine the same freqency response, but raise or lower the amount of signal going to the next stage.

1M/220pf
470k/470pf
220k/.001uf

etc. 470k/470pf = 720Hz

Raising the resistor will lower gain but increase treble
Lowering the resistor will increase gain and bass

Within limits.

Good place for a 1 or 2 meg pot

News:

Marshall sound?