Best place to kill hiss

[ampedup]

My sunn clone is sounding pretty good but has some very high frequency hiss. Is there a good spot in the circuit to kill it without killing tone?http://www.4tubes.com/SCHEMATICS/BY-BRA ... /2000s.gif

[Jana]

Roll your tubes and select the quietest one you can find for V1.

Replace the 1M resistor that goes from the wiper of the treble and the grid of V2 (pin 8 ) with a 1M pot. This will also help tame your touchy volume control issue.

edited to make is say pin 8 instead of pin

[Roe]

the v1 grid resistor contributes greatly to hiss. Try a small value of a 1-2w metal film resistor

[ampedup]

Roll your tubes and select the quietest one you can find for V1.

Replace the 1M resistor that goes from the wiper of the treble and the grid of V2 (pin 8 ) with a 1M pot. This will also help tame your touchy volume control issue.)

So lowering the value of the 1 meg off the treble will help the touchy volume and tame hiss? Interesting, thanks.

[Cliff Schecht]

Best place to kill hiss

I take it out to the backyard.

[tubeswell]

Yep - use 2W metal film resistors on all the plate resistors and grid leak resistors. In fact use metal film resistors all round.

[Merlinb]

So lowering the value of the 1 meg off the treble will help the touchy volume and tame hiss? Interesting, thanks.

It may help the volume pot issue, but it won't tame hiss (except by reducing the overall volume of everything). The input grid stoppers are usually the dominant source of hiss, and reducing them to perhaps 10k is a good start. The input grid leak could also be increased to a more conventional 1Meg, which would improve the signal-noise ration.

[ampedup]

If I'm understanding you, you are saying increase the 150k on the voltage divider to 1 meg? Wouldn't this make the input kind of hot for modern basses?

[tubeswell]

He's saying the signal-noise ratio on V1 needs to be as much signal and as least noise as you can get, because it doesn't get any easier to maintain that ratio as you get further down the signal chain.

You can always attenuate the subsequent gain stages, and the first gain stage shouldn't clip of its own accord even if its fully bypassed (unless you are driving it with an already amplified signal - like a pedal of some sort or active p-ups)

[ampedup]

since this circuit is a voltage divider input is it still a good idea to decrease the grid stopper to 10k? Is it still a grid stopper in this case?

[ampedup]

was this circuit designed with the voltage divider because of the multiple inputs? since I'm just using one input would it be better to do away with the divider and use a 1meg with a 10k stopper?

[ampedup]

I put a 10k/470k on the input. I can't really tell any difference.