.1 cap on 1st preamp node
Moderators: pompeiisneaks, Colossal
.1 cap on 1st preamp node
I have the info somewhere but can't find it. I have seen schematics with a .1uf cap in parallel with the electrolytic on the 1st preamp triode. What is the purpose of this cap? Thanks
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Andy Le Blanc
- Posts: 2582
- Joined: Sat Dec 22, 2007 1:16 am
- Location: central Maine
Re: .1 cap on 1st preamp node
Its an voicing trick, you can put film and other cap types parallel with the
electrolytic's on both sides of the tube circuit, the cathode and plate sides.
It effects the detail and presentation on the top.
IE: There's this big blues JR mod out there on the net to get it to sound like a vox. Instead of
doing the entire mod ( a lot of cap replacement through the amp) you can
do the "one wire mod" in the tone stack, and then put a .02 cap on each side
of the first gain stage to tighten and brighten the response of the amp critically.
And ... get it to resemble a vox tone with a bit-O-wire and two caps.
Its fun to play with but you need to be careful, a guitar amp doesn't necessarily
need more detail, its not hi fi.
electrolytic's on both sides of the tube circuit, the cathode and plate sides.
It effects the detail and presentation on the top.
IE: There's this big blues JR mod out there on the net to get it to sound like a vox. Instead of
doing the entire mod ( a lot of cap replacement through the amp) you can
do the "one wire mod" in the tone stack, and then put a .02 cap on each side
of the first gain stage to tighten and brighten the response of the amp critically.
And ... get it to resemble a vox tone with a bit-O-wire and two caps.
Its fun to play with but you need to be careful, a guitar amp doesn't necessarily
need more detail, its not hi fi.
lazymaryamps
Re: .1 cap on 1st preamp node
To further Andy's comments, this is a carry over from Hi-fi. Elytic caps are far from ideal and suffer from ESR, or internal resistance. The poly caps are much "faster" or "transparent". A good place for them is paralleling the first filter cap after the diodes to reduce the diode "hash".
They do affect the tone, in my experience can quiet the amp and aslo brighten the tone. That being said, the vintage amps that we all know the tone of had elytic caps that were far from ideal.
They do affect the tone, in my experience can quiet the amp and aslo brighten the tone. That being said, the vintage amps that we all know the tone of had elytic caps that were far from ideal.
Re: .1 cap on 1st preamp node
Interesting.
I had heard of using the film caps on the electrolytics in the smoothing filters but not on the bypass caps.
May have to experiment with that on my 6V6 amp.
I had heard of using the film caps on the electrolytics in the smoothing filters but not on the bypass caps.
May have to experiment with that on my 6V6 amp.
Tom
Don't let that smoke out!
Don't let that smoke out!
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Andy Le Blanc
- Posts: 2582
- Joined: Sat Dec 22, 2007 1:16 am
- Location: central Maine
Re: .1 cap on 1st preamp node
Try scabbing on to ground, alternately and then together, a cap on the
cathode circuit of the first gain stage and the PS node that feeds the
plate resistor of the same stage. Use say a .1 400v poly then a .02.....
It works very well in a HI-FI pre to expose more detail.
You can also try using poly exclusively as cathode bypass, get a ripping
overdrive tone in a high gain affair. But... its to taste its easy to over do
with a guitar amp. Its very easy to scab into a circuit with clips.
cathode circuit of the first gain stage and the PS node that feeds the
plate resistor of the same stage. Use say a .1 400v poly then a .02.....
It works very well in a HI-FI pre to expose more detail.
You can also try using poly exclusively as cathode bypass, get a ripping
overdrive tone in a high gain affair. But... its to taste its easy to over do
with a guitar amp. Its very easy to scab into a circuit with clips.
lazymaryamps