YAOB (yet another one-zero-two build)

[Structo]

What is the switch between the speaker jacks and loop jacks?

I also don't like the way the earth ground is wired off of the IEC.

You should use a larger gauge (16ga or so) wire and it should go to a screw and lock nut below the IEC.


Do you have a picture of your input jack wiring?

[aflynt]

So the problem has to be in the first stage. You did say the volume control effects the hum?

Does the hum go away when you turn the clean volume control to zero (fully counter clockwise)?

If you get a lead and short the wiper of the clean volume to ground does this effect the hum more than turning the control to zero?

I ask as I've had issues with dodgy Alpha pots.

The thing to work out is which triode is it coming from?

On the overdrive channel the clean volume control only changes the hum slightly. The hum is much quieter on clean than od.

I'll try the wiper thing next time I have the amp open.

-Aaron

[aflynt]

You might also double check your power tube heaters. With them being both green, it would be easy to accidently wire them out of phase....worth a quick look.

Thanks. I was extra careful of that when I wired it up and checked continuity multiple times.

-Aaron

[aflynt]

If the hum disappears with the PI tube pulled then it can't be coming from the power tubes. I don't like the look of the heater wires running up against the snubber caps on V2. Can you bend the caps out to put some distance between them and the heater wires?

I had the same thought about those gargantuan snubbers and tried moving them away, but the hum didn't change.

I did notice a reduction in hum when moving the heaters on V1 closer to the input side of the amp. Unfortunately it didn't really go away until I had the heaters touching the junction of the two 10 meg resistors on the input side terminal strip. It also got a bit quieter when I pushed the V1 heater leads down closer to the socket. I wound up twisting them a bit more closer to the socket connections. It seems slightly quieter now.

-Aaron

[aflynt]

What is the switch between the speaker jacks and loop jacks?

I also don't like the way the earth ground is wired off of the IEC.

You should use a larger gauge (16ga or so) wire and it should go to a screw and lock nut below the IEC.


Do you have a picture of your input jack wiring?

The switch is a LBFB defeat. I used the 18 AWG heater wire for the IEC ground. There's a lock washer under there but I'll replace that with a star one. I'll try to get a pic of the input wiring up soon.

-Aaron

[Structo]

Does switching the LNFB switch have any effect on the hum?

[aflynt]

Does switching the LNFB switch have any effect on the hum?

Nope.

-Aaron

[Mark]

The hum does go away in clean or overdrive if I remove V1.

On the overdrive channel the clean volume control only changes the hum slightly. The hum is much quieter on clean than od.

This is how I see it. If you can pull V1 and there isn't any hum, than the OD stage is probably okay.

You expect the hum to be louder when the OD is engaged as there is additional gain.

Have you tried shorting grid of V1 to ground (separately) to see if that has any effect on the problem?

I'd also remove the FET pre-amp from the problem too. Assuming it has a FET pre-amp of course.

[martin manning]

You might want to give something like this a go. Plug it into the return jack (which will disconnect the preamp from the power amp), and then follow the signal path from input to the send jack looking for the place where the hum appears. Of course, touch the tip to ground first to make sure that there is no hum from the PI and power stage. You can also plug it into another amp for more sensitivity, but mind the potentially high p-p voltage if you are feeding signal into the input of the amp under test.

[Mark]

That will work Martin, though gain may be an issue, The hum might not be heard if there isn't sufficient gain.

Like wise he could use a similar arrangement with the cap with a lead and an alligator clip to ground signal without trying to ground DC voltages.

[aflynt]

I haven't gotten to tracing through the circuit to find the hum yet. I did do some more tube rolling and found an unlabeled JJ ECC83S that when placed in V1 reduces the hum a whole lot. With that tube in place the hum is actually lower in volume than the hiss. I can deal with the nice even white noise of a few too many carbon comp resistors just fine.

Anyway. I've got the amp all buttoned up for an early afternoon job tomorrow. I'll continue the investigation tomorrow evening.

For the millionth time, thanks for all the help,
-Aaron

[aflynt]

Here are some images of the input wiring. With the JJ in V1, the hum is pretty much completely inaudible in a live situation, so fixing it has become somewhat lower priority. I did notice that after playing that outdoor job Sunday the amp now sounds much darker and smoother. I guess cranking the heck out of them for awhile must really expedite the break-in process.

[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]
[img764]http://www.aaronflynt.com/wp-content/up ... 24x764.jpg[/img]

-Aaron

[Structo]

Does your FET work?

[aflynt]

Does your FET work?

Yup. Works great. Kind of noisy, though. I think I overdid it a bit on carbon comps. Voltage-wise, the FET board goes from 21V/11V to 24V/12V on either side of the 10K depending on line voltage.

-Aaron

[aflynt]

For the sake of posterity, here are some clips of the amp with the D'Lator in clean and overdrive using a few different guitars.

http://soundcloud.com/aflynt/sets/overd ... ecial-with

-Aaron