New D'Lite-ish 6V6 powered up, and making noise.

[Colossal]

Dave,

As we discussed, a single point for grounding for the entire relay system is the way to go. Usually this can be done at the footswitch jack so that it is well away from the preamp star ground. The only thing, IIRC, from our discussion that is attached to the relay ground plane from the preamp is that one 4M7 switch-pop resistor from the Mid Boost.

If you have a scope, you could look for crossover distortion in your output section.

[Duble]

Grab your chopstick and start tapping if you don't have a scope. More than likely something is getting rattled at high volume causing some sort of transient noise/distortion. You might try these things, and tiding up your lead dress.

Twisting your heaters.
Follow ODS lead dress on Plate & Cathode wires.
Grounding the Input Coax at the V1 Grid terminal strip.
Grounding your Preamp filtering and PI at input star ground.
Grounding Power tube filtering between Power tubes.
Grounding Speaker outputs with OT Common at Power Tube ground.
Grounding Bias Supply and Main Filters by AC Power Ground.
Presence control ground by FX Loop Ground.

To each their own of course, but I've found all these little things can make a huge difference in stopping transient noise at high volume levels.

Adding star grounding points to these locations in the chassis will make a more finite connection. I've found it's not enough to just depend on the jacks physical tightening to the chassis. They can become lose even with a locking washer.

[martin manning]

Most especially make sure power supply ground connections and solder joints are solid.

[deiseldave]

Wow! Thanks for all the help. I did as instructed, and separated the grounds. Now relay/footswitch system is grounded at the PT bolt nearest Power and STDBY switch. The grounds for PAB bass an mids are going to the romex buss right between the bass and mid pots, the OD ground is now tied to the VI preamp board ground where the V1 cathode bypass caps are grounded. I hadn't read Colossal Dave's post about the 4.7M mid boost resistor, until I had already made the changes. So, at this time, the 4.7M mid-boost is grounded at input jack star ground. Is that a problem.
Seems like the univibe-ish oscillation has gotten a lot better. Now its what I'm thinking is crossover distortion. I captured and posted a simple sound clip of that. It happens with or without OD or boost. The sound clip is with no OD or boost. Everything at 12:00 and increasing the master, until the noise appears.
I also captured voltages, and attached them. Thanks again, everyone.

[deiseldave]

Grab your chopstick and start tapping if you don't have a scope. More than likely something is getting rattled at high volume causing some sort of transient noise/distortion. You might try these things, and tiding up your lead dress.

Twisting your heaters.
Follow ODS lead dress on Plate & Cathode wires.
Grounding the Input Coax at the V1 Grid terminal strip.
Grounding your Preamp filtering and PI at input star ground.
Grounding Power tube filtering between Power tubes.
Grounding Speaker outputs with OT Common at Power Tube ground.
Grounding Bias Supply and Main Filters by AC Power Ground.
Presence control ground by FX Loop Ground.

To each their own of course, but I've found all these little things can make a huge difference in stopping transient noise at high volume levels.

Adding star grounding points to these locations in the chassis will make a more finite connection. I've found it's not enough to just depend on the jacks physical tightening to the chassis. They can become lose even with a locking washer.

Thanks Duble. Looks like I have a few variances from what you posted. I will itemize the differences, and maybe you can tell me if what I actually did is a problem, or just a difference. BTW, I have "chop-sticked" several times, and didn't have anything jump out at me. So, on to your list.

Twisting your heaters. - I tried the suspended straight heater buss on this build, and elevated the CT about 75V. The amp is real quiet as far as hum goes.
Follow ODS lead dress on Plate & Cathode wires. - I think I did it the way the layout was (as best I could with the differences in the JudyBox donor chassis). Do you see anything wrong in those runs in my pic?
Grounding the Input Coax at the V1 Grid terminal strip. - I grounded the shielding at the input jack, and no shield connection at the other end. Wrong? Or, not a big deal?
Grounding your Preamp filtering and PI at input star ground. - Didn't do this. Per the layouts I used, I have a star for preamp filters, and PI filter just in front of the power supply filter board.
Grounding Power tube filtering between Power tubes. - I used a 50uf X 50uf cap can to make use of the unused tube rectifier hole. Per (how I interpreted) Randall Aiken's grounding tutorial, I have the HT center tap going to the cap can negative pole, and then a short piece of 16ga going from the neg pole, to a star at one of the cap can mounting lugs. Is this a problem?
Grounding Speaker outputs with OT Common at Power Tube ground. - Ok, this I don't have like you said, and that sounds like a problem. What I have is OT Primary CT terminated at +Pole of first filter cap, OT secondary ground going to isolated speaker jack grounds, with no other connection back to power amp filter ground.
Grounding Bias Supply and Main Filters by AC Power Ground. - I have the bias supply grounded along with the relay system at the PT lug nearest the On and Stdby switches, and the main filters grounded at cap can lug near AC safety ground.
Presence control ground by FX Loop Ground. - I don't think I understand this. On the layout's that I used, the presence pot was grounded at the end of the ground bus that terminates at input jack star point, and is suspended above the pots in front. I didn't see a ground on the FX loop. Are you talking about the coax shield from the FX loop? If so, I grounded that on the buss suspended above pots.

Seems like I have several things that are not as you recommend. Can you tell me which are the most critical to change? If so, I will do those, and see if it helps. If it doesn't I will move on to some of the less critical ones.
Thanks a ton for the help. Dave

[deiseldave]

I noticed the sound clip isn't working. Do I need to convert it to a different format? Thanks.

[splgeo]

sound slip worked for me. it sounds like a bad solder joint or a micro-phonic tube

[martin manning]

OT secondary ground going to isolated speaker jack grounds, with no other connection back to power amp filter ground.

Ground the OT secondary at the power tube ground or at the speaker jacks. You need to ground the secondary to the chassis to get the NFB voltage reference.

Everything else sounds ok.

[deiseldave]

OT secondary ground going to isolated speaker jack grounds, with no other connection back to power amp filter ground.

Ground the OT secondary at the power tube ground or at the speaker jacks. You need to ground the secondary to the chassis to get the NFB voltage reference.

Everything else sounds ok.

Thanks Martin. I will make that connection first thing in the morning.

[M Fowler]

That most definitely sounded like a missed solder joint or bad solder joint.

Look carefully and I bet you find one joint without solder or poorly looking.

[norburybrook]

I chased an intermittent noise on my Bluesmaster for a coup0le of months before I eventually tracked it down to a slightly loose socket on either the send or return FX loop!!!!!! In the interim I'd replaced the heater wiring, reflowed every solder joint on the valve sockets and boards.


Have you swapped valves for known good ones? Always a good start



Marcus

[Duble]

Thanks Duble. Looks like I have a few variances from what you posted. I will itemize the differences, and maybe you can tell me if what I actually did is a problem, or just a difference. BTW, I have "chop-sticked" several times, and didn't have anything jump out at me. So, on to your list. Thanks a ton for the help. Dave

I think although your amp is based upon a D'lite, it might give you some insight to have a look into the original example. If you look at any Moss built Brown Note's you'll see all his amps are pretty much dressed like an actual ODS.

On the flip side, if it's quiet and sounds good then roll with it.

I agree with Martin, everything looks fine except the OT Grounding.

[deiseldave]

Seriously bumming. Did massive cleanup work on the amp, and now when I switch on Standby with volume and master completely turned down, I get a loud squeal. Here is the work I did.
1) Ran a ground from PI and Preamp filter star to sleeve of output jacks. From Randall Aiken's grounding tutorial "Note that there still must be a return path to the rest of the circuit if the amp uses global negative feedback. This should be in the form of a wire from the sleeve connection of the output jack to the preamp ground point where the phase inverter common connections are grounded (or wherever the global feedback is returned)."
While I had the chassis pulled, I figured I would fix some other issues, clean up the lead dress, etc.

Repaced the (2) big honkin' 22M resistors on V1B with some newly received mil-spec resistors. Made lead dress look more like layout.

Replaced experimental 100K rear panel mounted OD trim pot with onboard 100K trimmer to get back in line with original layout.

Replaced crappy Power and Stdby switches that came with the donor chassis with some NKK S2A's. I mistakenly ordered SPDT instead of SPST. But didn't see this as a reason to not use them. Am I wrong?

Cleaned up too long transformer AC wires, twisted AC wires that were not already twisted together.

Re-soldered all filter grounds...

What would cause a squeal with volumes turned all the way down?

I'm trying to improve, and making things worse...

Thanks for any help - Dave.

[martin manning]

You probably just need to swap the OT primary leads. You are now getting the effect of the FB loop with the OT secondary grounded, and the oscillation is all in the power amp from the speaker output to the PI, so the volume controls have no authority over it.

[deiseldave]

Ahh. Thank you! I lifted that ground, and squeal went away. I will swap the OT Primary leads, tie the ground back down, and report back. Thank you so much!