Volume control hiss/white noise

[kanderson70]

So I took an old Peavey Bandit combo, gutted it, and built a Matchless Lightning into the chassis. The amp actually sounds really good EXCEPT...
The louder I turn up the volume, the louder the hiss and white noise becomes. Its really annoying. Things I've tried to reduce it:
Reflow solder joints
Check for missing grounds
Replace tubes
Reroute the shielded wires to outer edges of chassis
Chopstick for loose connections

The noise is persistent with or without a guitar plugged in.

What would you guys suggest I check next? Any help is greatly appreciated!

[xtian]

The troubleshooting steps you mention are all good ones...if what you're trying to solve is hum or buzz. But you describe hiss and white noise, which can sometimes be lessened with better component choices. Can you post a photo of your turret board?

Is the amp silent with the Master at zero? What about with the Master at 10, but the Volume at zero?

[Stevem]

None of the things you posted up about other then trying out different tubes will be the cause of a hiss issue !

The source of you hiss is way more then likely a bad resistor.

To narrow down where this might be yank out the first preamp tube, if the hiss gets greatly reduced then just shotgun it and replace all the plate load, cathode and the resistor on the input jack with 1 watt metal film type resistors.

If the hiss is still there big time when you yank out that first tube then replace all of those same resistors that deal with the next 2 tubes.

This all being said, seeing as your volume control is only dealing with the signal outout from your first preamp tube, that makes me say that the resistor issue is there in the circuit around that tube.

In that same vein I would triple check that you have the right value resistors in place that deal with the function of that first tube.

The higher value plate load resistor than what's called for will kick up the gain a lot, and with that excess gain comes hiss!

This should all cost less then 10 bucks!

[pdf64]

Any series resistance with the input, eg input mixer / grid stopper, typically has the greatest potential for being the noisiest resistor in an amp.

[kanderson70]

The troubleshooting steps you mention are all good ones...if what you're trying to solve is hum or buzz. But you describe hiss and white noise, which can sometimes be lessened with better component choices. Can you post a photo of your turret board?

Is the amp silent with the Master at zero? What about with the Master at 10, but the Volume at zero?

Thanks for your reply xtian. Yes the amp is silent with master at zero and volume at zero with master on 10.
Here's a pic of the rats nest.

[kanderson70]

None of the things you posted up about other then trying out different tubes will be the cause of a hiss issue !

The source of you hiss is way more then likely a bad resistor.

To narrow down where this might be yank out the first preamp tube, if the hiss gets greatly reduced then just shotgun it and replace all the plate load, cathode and the resistor on the input jack with 1 watt metal film type resistors.

If the hiss is still there big time when you yank out that first tube then replace all of those same resistors that deal with the next 2 tubes.

This all being said, seeing as your volume control is only dealing with the signal outout from your first preamp tube, that makes me say that the resistor issue is there in the circuit around that tube.

In that same vein I would triple check that you have the right value resistors in place that deal with the function of that first tube.

The higher value plate load resistor than what's called for will kick up the gain a lot, and with that excess gain comes hiss!

This should all cost less then 10 bucks!

Thanks Stevem! I tried the yanking out V1 and that did remove the hiss, so I will try your suggestion although am using 1 watt metal oxide resistors throughout. Maybe it's just a bad one...

[kanderson70]

Any series resistance with the input, eg input mixer / grid stopper, typically has the greatest potential for being the noisiest resistor in an amp.

Thanks pdf64!

[thetragichero]

i generally use 1-2w metal oxide throughout but the 1M to ground and 68k/33k first stage grid resistors i use metal film. these are likely the noisiest resistors in the amp

[Phil_S]

The cheapest and simplest thing to do is to replace all of the plate load resistors with 1W or 2W metal oxide. It won't take you very long and it is worth a try.

I built an Express deviant that has too much hiss. This was the recommended solution. I just never got around to it, so, regrettably, I have nothing useful to report.

[Colossal]

The cheapest and simplest thing to do is to replace all of the plate load resistors with 1W or 2W metal oxide

I think you mean metal film

[kanderson70]

UPDATE: Hiss is under control now. Thanks for all your replies in helping me pinpoint it.

I had a bad 1M metal oxide resistor on the inputs and when I replaced it, that helped a lot with the noise but the hiss was still present. Next step was to replace the two 68K 1 watt resistors, but I didn't have any metal film. So I took a stab in the dark with 1W Carbon Film. Yep. That did it. The hiss is still present but not to the extent it was earlier. I wouldn't have guessed carbon film would have made that much difference, but it did! Thanks for all your help fellas! you guys saved me literally weeks of messing around with this stupid problem. Now I can button it up and finish making it presentable.

[Phil_S]

Colossal:
The quote function is not working for me. I think your correction is on the mark, but I not think I mis-remember the advice I was given. Anyhow, it was quite literally years ago and there is no mileage in chasing it down. Thanks for weighing it. I'll get some metal film resistors when I get to that work. I'm planning to retire at the end of the calendar year. This is one of the many things on my long list of things to do.

[Roe]

Metal oxide is noisy, only carbon comp is worse.

[thetragichero]

not that i consider everything the guy says as gospel but aiken lists metal oxide between metal and carbon films: https://www.aikenamps.com/index.php/res ... -it-matter
if you include the fact that metal oxide resistors can easily come in at 2 or 3w ratings (even 5w aren't that big) helping to mitigate thermal noise
not looking to argue just interested in expanding my knowledge

[Roe]

not that i consider everything the guy says as gospel but aiken lists metal oxide between metal and carbon films: https://www.aikenamps.com/index.php/res ... -it-matter
if you include the fact that metal oxide resistors can easily come in at 2 or 3w ratings (even 5w aren't that big) helping to mitigate thermal noise
not looking to argue just interested in expanding my knowledge

For a different view, (and figures), see http://www.valvewizard.co.uk/Book1.html