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

[deiseldave]

We have ignition. Sounds pretty good, so far… Whew! That was pretty complex for only my second build. There were a few times there when I thought I might've bitten off more than I could chew. Mounted in a 1X12 combo cab today loaded with an Eminence GB128 (What I had on hand). Still need to complete the footswitch, faceplate, etc.
Much thanks to Dave at Colossal Amps. He really came through for me. Also, I got a lot out of Structo's D-Lite journey, and many others. It's so awesome to have this site as a resource. Thank you all so much.
I had to go through a bunch of tubes. After trying nearly 30 tubes in V3, I never did find a PI tube that would allow me to adjust the PI trimmer anywhere close to 0V between the bias test points (as I interpret the Ampeg method). I tried the method of trying to get 30VAC on grid of 6V6’s, and couldn’t get that to balance either, before running out of PI trim POT adjustment. So, I just settled for 20mv balance, and 6V hotter on input side of the PI. Sounds good. I’m not getting any magical “bloom” like people have suggested…
The only issue I have that concerns me, is kind of minor, and what I am guessing is a little crossover distortion. It is only when I am really loud (input and master passed noon), in overdrive, or boosted. Certain notes will get a garbley buzz at their peak, and some seem to do a sort of univibey thing. I have some of that with my Plexi6v6 also. I hate it.
Does that sound like crossover distortion symptoms to any of you? Any ideas of how to fix it? Thanks.

[xtian]

Great job!

(Can I call you Dave?)

What's your power section bias?

[lord preset]

I had a similar issue with a Small Special build. Separating the PS grounds for the power amp and preamp filter caps did the trick in that case.

https://tubeamparchive.com/viewtopic.ph ... highlight=

[deiseldave]

Great job!

(Can I call you Dave?)

What's your power section bias?

Thanks Xtian. Dave is fine. The bias measured at test points a little over 23mv.

I had a similar issue with a Small Special build. Separating the PS grounds for the power amp and preamp filter caps did the trick in that case.

Thanks Lord Preset. However, I already have those separate.

[deiseldave]

I had a similar issue with a Small Special build. Separating the PS grounds for the power amp and preamp filter caps did the trick in that case.

https://tubeamparchive.com/viewtopic.ph ... highlight=

I followed the D'lite "Tweaked" layout and scheme for grounding. The only deviations are heater elevation, and on the relays for PAB and OD, instead of running separate ground wires for the signal grounds, I jumpered them to the onboard ground eyelet, and then ran just one ground wire from the relay system to the star ground by the input jack. Could that be it?

[martin manning]

On the Tweaked D'Lite schematic I'm looking at I see only one ground on the relay contacts related to the guitar signal, and that is just to ground the OD input in clean mode. The grounds to energize the coils can be tied together, but I would take that to the relay power supply ground, along with the ground from the footswitch jack, which should be an isolated type.

[M Fowler]

You might have to reduce that 820R PI bias resistor to increase voltage closer to 35v per side with about 55v at the PI bias resistor.

[deiseldave]

On the Tweaked D'Lite schematic I'm looking at I see only one ground on the relay contacts related to the guitar signal, and that is just to ground the OD input in clean mode. The grounds to energize the coils can be tied together, but I would take that to the relay power supply ground, along with the ground from the footswitch jack, which should be an isolated type.

Thank's Martin. Your threads were a huge help to me. Thanks for everything you do on this forum.
So, I deviated on PAB based on this thread https://tubeamparchive.com/viewtopic.ph ... 9&start=15
I put 500k trimmers for bass and mids on the PAB board just like Angelodp. I also added a mid-boost relay.
I will open up the amp, and make a separate ground for the relay/footswitch system power supply ground, (near power supply board) and run the signal grounds that get switched by PAB and OD to a separate star ground point. Would you recommend the star point near input jack, preamp board ground points, or rail above pots? Thanks again. - Dave

[deiseldave]

You might have to reduce that 820R PI bias resistor to increase voltage closer to 35v per side with about 55v at the PI bias resistor.

Thanks M Fowler. When I open the amp back up, I will measure those voltages, and see where I am. Just to be clear, we are talking about DC, right. I got all caught up with the PI trimmer adjustments yesterday, and one of the threads was talking about adjusting to 30VAC at the 6V6 grids. Sorry if that is a stupid question. Just wanting to be clear. Thanks again.

[martin manning]

On real Dumbles the footswitch and relay supply are grounded at their own star near the relay transformer, thus keeping relay ground currents off the chassis. That means a wire runs from the FS jack along the back and then forward to the front corner.

[deiseldave]

On real Dumbles the footswitch and relay supply are grounded at their own star near the relay transformer, thus keeping relay ground currents off the chassis. That means a wire runs from the FS jack along the back and then forward to the front corner.

The idea of getting in to solder on the footswitch DIN connector is stressing me out. Can I just run the footswitch/relay system ground to a transformer lug towards the front of the amp? That sounds more do-able.
I have (5) wires going from the relays to the footswitch jack. System Ground, +5V, Mid Switch lead, OD switch lead, and PAB switch lead.
Thanks, Martin.

[martin manning]

Do you have a ground wire already soldered from the DIN jack to the back panel switches? You could run the ground from a switch lug. As far as the star location, somewhere close to the front-right corner is probably fine.

[deiseldave]

Do you have a ground wire already soldered from the DIN jack to the back panel switches? You could run the ground from a switch lug. As far as the star location, somewhere close to the front-right corner is probably fine.

Martin - Thanks. I don't have any back panel switches. The DIN ground pin goes to the mid boost relay board's 0V eyelet, and the DIN's B+ pin goes to the +5VDC eyelet on the same relay board. Mid boost relay is the relay closest to the input jack. Then the only connection to chassis from the entire relay system is currently connected to the star closest to the input.
It is going to be invasive surgery to split out the relay system grounds and the PAB & OD signal grounds, so, I'm looking for an easier yet functional way to do it.
Unless someone convinces me otherwise, my plan is to:
Remove all onboard relay jumpers that go from a switched signal path to onboard ground.
Reconnect those switched signal paths to their nearest preamp ground point.
Remove the connection from relay system ground to input jack star point.
Make a new star ground connection from the front PT bolt closest to the power switch to the nearest relay board ground.
That connection to the PT bolt would be the only connection from the entire relay/footswitch system, and the switched signal ground paths would go to preamp ground zone.
That would be the least amount of surgery. Sound OK?

[martin manning]

Yes, that sounds good- single ground point for the relay coils to the chassis away from the input ground is the key. Will this cure your buzz? Maybe and maybe not, but it might end up with lower noise.

[deiseldave]

Yes, that sounds good- single ground point for the relay coils to the chassis away from the input ground is the key. Will this cure your buzz? Maybe and maybe not, but it might end up with lower noise.

Martin - Thanks. As it is, the amp is dead quiet. The quietest amp I think I have ever heard (in person). I just have a strange effect happening when I am at really high gain, and loud. It is an oscillation of notes higher on the neck sounds like tremelo mixed with univibe, and some notes get a garbled sound at the peak of them. But only when the amp is really pushed. At low gain and moderate gain. It really sounds nice.
I will change the relay grounding thing, and see if the high gain oscillation effect goes away. If not, at least the relay grounding can be eliminated as the cause, and I will sleep better at night knowing better grounding practice was deployed. Thanks again - Dave.