New build issue w/ HRM OD (solved)

[Bob-I]

Weird.
I have the same issue with my d'lator.
If I turn the return pot all the way down it buzzes badly.
I figured it was a bad pot since I used the cheap Alpha's on it.

Haven't looked much more into it because it works fine otherwise.

Not likely a bad pot, there are millions of those Alpha's out there in production and homebuilds working fine.

More likely that when you bring the pot to 0, grounding whatever it's grounding, it's also creating a ground loop in the process.

I had this happen on a TrainWreck Rocket like build. I reworked the ground schema, moving many of the board grounds to the back of the pots and the problem went away.

[mlp-mx6]

Here are some pics

Pot shot

Full board

HRM & PI, showing the built-in D'lator

Fender pre and ODS pre. Note my ancient black Sprague cap (marked .00025 uF!). I bought this back when I lived in Richmond, VA at a VERY old electronics store downtown that closed before we left there in 1999. They had LOTS of old stuff. I wish I had known what a treasure trove that store likely was.

[mlp-mx6]

No, the buzz is NOT solved. @#$@#@!!

It has nothing to do with the OD master now. But when I switch to the Dumble side (either clean or OD, with OD louder (naturally)) the buzz is there. All I have to do to get rid of the buzz is turn on the built-in D'lator send bright switch. I am completely stumped and mystified.

I cannot for the life of me understand why turning on the BRIGHT on the D'lator send would kill the buzz.

Any ideas at all? I'm nearing my wit's end.

[Bob-I]

No, the buzz is NOT solved. @#$@#@!!

It has nothing to do with the OD master now. But when I switch to the Dumble side (either clean or OD, with OD louder (naturally)) the buzz is there. All I have to do to get rid of the buzz is turn on the built-in D'lator send bright switch. I am completely stumped and mystified.

I cannot for the life of me understand why turning on the BRIGHT on the D'lator send would kill the buzz.

Any ideas at all? I'm nearing my wit's end.

My guess is that it's not actually killing it, but sending it to ground.

I'd start in the Dulator. First disconnect the send and return and hard wire the amp with out it. At least you can narrow it down that way.

[erwin_ve]

I see you have few bright switches? If so ; if you all disengage them, is there also a buzz?

[rob@tele]

What about your relay power supply? Is it from a separate transformer or did you use the heater taps?

[mlp-mx6]

My guess is that it's not actually killing it, but sending it to ground.

I'd start in the Dulator. First disconnect the send and return and hard wire the amp with out it. At least you can narrow it down that way.

Bob, that is what I cannot quite wrap my head around. How is engaging a bright switch affecting ground at all?

However, you post a great idea. I will do that. Thanks.

[mlp-mx6]

I see you have few bright switches? If so ; if you all disengage them, is there also a buzz?

There is only one bright switch on the ODS side. The other switches are R/J, PAB, and mid-boost. The built-in D'lator has a bright switch on each pot as per the schematic. Only the D'lator send bright switch makes a difference.

[mlp-mx6]

What about your relay power supply? Is it from a separate transformer or did you use the heater taps?

I used a separate xfmr (Radio Shack). However, I am thinking about totally rebuilding the switching as well. If the D'lator isolation is not fruitful I'll go there next.

[Tonegeek]

What about your relay power supply? Is it from a separate transformer or did you use the heater taps?

I used a separate xfmr (Radio Shack). However, I am thinking about totally rebuilding the switching as well. If the D'lator isolation is not fruitful I'll go there next.

+1 on bypassing the d'lator. If it is the d'lator causing the hum, try the thing I mentioned ealier with adding a bit of reistance to the dlator input (right ahead of the .05 cap).

Doubt its the relay causing the buzz but to check -
Try tieing the DC ground of the relay circuit to the amps main ground buss bar (or separate the two if it is connected). My amps usually require them be tied together or it hums.

[mlp-mx6]

I removed the D'lator tube and clipped a test lead from the relay output to the PI input and the buzz is gone.

Thanks for helping me isolate (further) where the issue is. Now, to SOLVE it!

Regards,
Michael

[Bob-I]

My guess is that it's not actually killing it, but sending it to ground.

I'd start in the Dulator. First disconnect the send and return and hard wire the amp with out it. At least you can narrow it down that way.

Bob, that is what I cannot quite wrap my head around. How is engaging a bright switch affecting ground at all?

However, you post a great idea. I will do that. Thanks.

Yea, you're right, it was late and I was thinking treble bleed...

At least you know it's in the Dulator now. How about some pics of the offending area.

[mlp-mx6]

I'm almost ready to declare victory.

I moved a wire.

The shielded wire from the output of the master relay to the input of the D'lator. At this point, I actually think the problem was an oscillation.

I'll play with it a bit more, but I'm definitely happier than I was. And the amp is fun. It likes to sing in HRM mode (though very differently than my non-HRM, which I still prefer), the ODS clean is nice, and the Fender clean is bright and sparkly.

We'll see - but I'm hopeful.