Solved hum problem. Can anyone tell me why?

[fabiomayo]

fabio,
Here is a build log of a guy who built a SLO clone and he did it real meticulously...looks real purty. I just built a SLO and mine doesn't look as good but it's def a cool way to wire the tubes. Keep in mind that the tube sockets are 'clocked' such that everything lines up...you even have to use certain sockets (Fender-type if the mounts are like the SLO chassis).

That's one marvelous piece of work. Thanks!

[Fischerman]

I will say, the SLO and the Dumble are completley different animals.

You mean I won't be able to get Robben-tone with my SLO?

[bluesfendermanblues]

a SLO has a serious mid cut in its entire tone. A Dumble has a pronounced midtone spectrum...its tone controls are almost bass-mid, mid-mid and treble-mid.

So no RF tone in a SLO

[Fischerman]

Yea, I was just kidding bluesfendermanblues. But FWIW, the SLO isn't mid-scooped although it can be dialed in that way. It's def a totally different tone than an ODS though.

[cornel moldovan]

I HAD THE SAME HUM PROBLEM , UNTIL I REMOVED THE NEGATIVE POLE OF THE RELAYS SUPPLY, AWAY FROM THE AMP CHASSIS .IT HAS TO BE COMPLETELY SEPARATED . OTHERWISE THEY WILL INTERFERE WITH THE SIGNAL PATH . THE SWICHING GROUND HAS NOTHING IN COMMON WITH THE SIGNAL PATH, AND MUST BE TOTALLY REMOVED FROM THE AMP'S GROUND. IF THE HUM STILL REMAINS PUT A MATCHED PAIR OF POWER TUBES IN YOUR AMP , AND TWEAK THE BIAS..IN THE LAST CASE CHECK THE SHIELDED CABLES NOT TO BE GROUNDED AT BOTH EXTREMITIES. [/u][/i][/b]

[heisthl]

If you're using a LFB on V1B make sure to put some distance between it and the input side of the tube.
Re the relay supply - A lot of people isolate the relay supply ground but I've always lumped it in with the main filter ground and ran a wire from there to the swiches and/or footswitch jack. Never had a hum problem yet (knock wood). I NEVER use the preamp ground/pot bus bar ground for relay switching.

[novosibir]

Fabio, is the hum gone with a guitar plugged into the input?

If so, then simply ground the switch contact at the tip of the input jack, so that the input is grounded, when no guitar cord is plugged in!

On your photo I neither can see a cable there, nor a solder joint

Larry

[fabiomayo]

Thanks for the tips, novosibir.

I have to check the jack input wiring... There may be a mistake there

In any case, the hum problem is MUCH better now.

FWIW, I had the relay supply ground completely isolated but that ]resulted in incredibly loud noise. Grounding the relay supply near
the main PT ground solved the problem...

[Tdale]

fabio,
Here is a build log of a guy who built a SLO clone and he did it real meticulously...looks real purty. I just built a SLO and mine doesn't look as good but it's def a cool way to wire the tubes. Keep in mind that the tube sockets are 'clocked' such that everything lines up...you even have to use certain sockets (Fender-type if the mounts are like the SLO chassis).

How come the paralell heat leads, that are not twiested, doesn't hum? Isn't that what we have learned, that twisted cables don't hum and paralell cabels do?

Looks really good, but why does it work?

Tommy

[Fischerman]

Tommy,
It actually doesn't matter in the power section because it all gets cancelled out anyway. On the preamp tubes it does matter and to be honest I probably won't ever do the preamp like that again. If the preamp wires all 'approach' the socket from above and you put those non-twisted heater wires on the floor (like the SLO) it's not so bad. But I do like the power tubes done that way...so far.

The SLO has two gain stage/cathode follower pairs and high-ish voltages...that's kind of stressful on those preamp tubes and also creates some noise because the cathodes are over 200vdc. I elevated the heaters to ~45vdc in my SLO to knock down the hum as much as possible without going DC (it def made a diff). I can't really say if or how much not twisting the preamp heater wires contributed to the low level hum I had...that's the way Soldano does it. It might not be necessary in an amp that 'runs' differently (like an ODS).

[novosibir]

I have to check the jack input wiring... There may be a mistake there

Larry

[novosibir]

I have to check the jack input wiring... There may be a mistake there

Larry

Fabio?

Faaabioooh!

Faaaaaaaaabiiiiioooooooohmaaaaaaaaajoooooooooooooh !!!




Have you already checked for a mistake?

Larry

[fabiomayo]

Sorry for not getting back earlier, novosibir.

I haven't been inside the amp for quite some time. New job is taking up my whole time... I'm hardly even playing theses days...

Anyway, the noise does not go away when plugged in. Keep in mind that the noise is much better now and the amp is sounding good... I had good trimmer settings but decided to tinker around without measuring and could never find that 'sweet spot' once again...

[heisthl]

I just ran into a hum problem that was solved by adding additional filtering to the relay supply.