Hum issue - please help

[fabiomayo]

Thanks, jelle.

I had already done that and the amp mutes, no hum (or guitar obviously).

I think shielding the preamp heater wires could help but I'm still suspicious
that the relay supply might be the culprit. I may try disconnecting it...

It's better now but I'd like to zero this issue before starting to tweak

[fabiomayo]

Thanks, jelle.

I had already done that with an alligator jumper. The amp mutes as a
result, no hum whatsoever (or guitar sound obviously).

The only other point in the preamp ckt where that happens is from the
output of the masters (clean or OD when in the respective mode).

I'm positive that shielding the preamp wires will help.
I'm still suspicious of the relay supply though. What do you think?


BTW, I updated the files to reflect recent changes (no Clean Master
bright cap and ground reference on relay power supply).

[jelle]

No, heaters look great IHMO.... just disconnect the relay supply ( both wires!)... reconnect the preamp to the pi and try again.

I have had one amp where the signal wires were very sensitive (read:hum) when they got close to the relay DC wires in the preamp. There could be ripple on those relay power supply wires.....

Good luck!

jelle

[jelle]

The amp of mine also had one filtercap (4700uf) in the relay supply just like yours. I suggest that you try to disconnect those relay supply wires. In case this is the cause I'd relocate the diodes, filtercaps and voltage regulator away from the B+ diodes (layout counts here too!) and add one or two filtercaps like some of the schematics here have.

Good luck.

jelle

[skyboltone]

Kinda jumpin in in the middle here. Sometimes it's not heaters and it's not filter caps and it's not other supplies like the relay supply. Sometimes it's just weird grounding. Aiken Amplification has excellent reading on grounding and as a first resort a person may want to take a good look at some of his ideas and see if any major no no's apply. I've noticed that a lot of hum that's accompanied by a higher pitched hiss is frequently related to cathode noise crossing over into the pre-amp. Make sure that the chassis carries no heavy ground loads and that everything associated with the power supplies for relays, power tubes, PI, and finally the pre section all ground in order to the right filter cap without any cross overs. Hum usually goes pretty silent.

Dan

[heisthl]

Last week I had a noticeable hum in the reverb stage of a new build. Grounding the grids in the stage reduced it but did not get rid of it. Grounding the PI entrance did get rid of it. Adding additional filtering to B+1 helped it but did not eliminate it. The scope showed me the hum on the recovery plates but it wasn't until I looked at the dropping string nodes with the scope that I found the biggest signal (hum), the node feeding the reverb stage was shorted to the red O.T. lead under the cap board. No hum after correction. Maybe I should quit cramming so much stuff in such a small space:

[jelle]

Kinda jumpin in in the middle here. Sometimes it's not heaters and it's not filter caps and it's not other supplies like the relay supply. Sometimes it's just weird grounding. Aiken Amplification has excellent reading on grounding and as a first resort a person may want to take a good look at some of his ideas and see if any major no no's apply. I've noticed that a lot of hum that's accompanied by a higher pitched hiss is frequently related to cathode noise crossing over into the pre-amp. Make sure that the chassis carries no heavy ground loads and that everything associated with the power supplies for relays, power tubes, PI, and finally the pre section all ground in order to the right filter cap without any cross overs. Hum usually goes pretty silent.

Dan

I agree with that but I wanted to excluce these other things first. We\ll get to that in case needed...

Jelle

[fabiomayo]

Hi, everyone.

Thanks so much for all the replies.

This weekend I put shielded wire from the heaters goingo from V3 to V2
and from V2 to V1. No change in noise.

I tried disconecting the 5v secondaries (from which the relay supply is
taken) and again, no change in noise...

heisthl, I'll check the OT leads but I'm positive all is well in that
department. I too should've used a bigger chassis

About grounding: I did read Aiken's text but I decided on using a ground
layout closer to Dumble's. I will try different groundings but it's already
in order, even though the B+5, B+4 and B+3 grounds are tied together
and grounded near input. I'll experiment with the cathodes.

Here's a few new info:

When I touch the chassis or plug in the guitar, noise dimishes considerably.

If I'm on the drive channel (PAB on) and have no guitar plugged in,
turning the input volume higher than 8 or 9 (scale from 0 to 10) gives
me a loud whistle sound.

Just in case you're wondering, the amp is playable. Clean channel has
little noise, drive channel is worse of course. Non hum-cancelling positions
on the guitar (like the P90 on the neck of my tele) is even worse. Still
I can play the amp in almost all settings without being too annoyed

[heisthl]

heisthl, I'll check the OT leads but I'm positive all is well in that
department. I too should've used a bigger chassis

I was kidding on the size - I did the small size on purpose - If you do it right there is no hums, squeals or noise of any kind. Keep working with it, you will get yours noise free.

[BobW]

Heisthl, Your RD-50 is a great build. After a few small mods to my RD-50 V1a/b stages, I may just leave it as is for now. It great for small clubs w/small stages.

[fabiomayo]

Hi, heisthl.

I did my chassis small on purpose too. To fit the layout of the former amp:
a 2x12" combo with controls on top (like a tweed amp).

That doesn't mean I'd do it again
(Probably would.... )

Thanks for the encouragement. I'll keep trying to make it better.

Anymore tips?

[Structo]

Are you sure your chassis ground is good and that you are getting a good ground through your outlet?

Also, I have chased noise in an amp before only to find out it was a extraneous noise source.
Fluorescent lights, motors, cell phones, etc.
You've probably thought about all that, just wanted to throw it out there.

[fabiomayo]

Thanks, Structo.

Here in Brazil the standard is two-pin outlets. Not a reliable energy source
either. It will oscilate more than 20v during the day. I have installed a
couple of ground bars over at the yard for things like computer and
guitar amps . They're grounding the outlets on two rooms in the
house. Through these outlets and at the same time, my other amps
sound dead quiet.

Grounding seems to be measuring ok but I do think I have not
done my best soldering them...