Deluxe Reverb AB763 Grounding Scheme

[mikepukmel]

After lots of reading, I got the idea, mostly that the cathode wiring should be routed first to the filter cap that feeds the plate for that tube. Something like:




But what to do from there? I have a big mess of ground wires running all over the place, and that can't be helping.

In the original amps, there's only one wire leading from the negative side of all the filter caps feeding tubes (power, pi, reverb, tremolo, preamp) and one wire from the reservior caps. they are grounded to the chassis very far apart. i think that's one of my main screwups, trying to route them all to a 'star'.

Is it really so bad to have the preamp grounded to the chassis on one side, and the power stuff on the other side?

[mac dillard]

This works. https://el34world.com/charts/grounds.htm Me, I use a variation of that where I separate the pre amp from the power end...Don't solder buss to the back of the pots. Just run a buss wire and pick up all of the pre and ground that on a terminal right at the input jacks. The power end on a terminal close to the 1st filter cap and a separate terminal for the incoming mains ground wire. Works for me.

[mikepukmel]

This works. https://el34world.com/charts/grounds.htm Me, I use a variation of that where I separate the pre amp from the power end...Don't solder buss to the back of the pots. Just run a buss wire and pick up all of the pre and ground that on a terminal right at the input jacks. The power end on a terminal close to the 1st filter cap and a separate terminal for the incoming mains ground wire. Works for me.

Cool, thanks for the link and tips Mac!!

[Randall]

Flying a copper bus wire is the way to go. As mac says, don't connect it to the pots backs, all grounds from pots and preamps go to bus, as well as the pre and PI (C and D) filter caps, and then the bus gets grounded close to the input jacks. The B+ and screen caps get grounded with the PT at B+ side of the board. Bias is grounded at a PT bolt, power tubes grounded right at socket side (consider using a 1 ohm resistor for this). I've done two this way, and they are quiet as church mice.

[mikepukmel]

Flying a copper bus wire is the way to go. As mac says, don't connect it to the pots backs, all grounds from pots and preamps go to bus, as well as the pre and PI (C and D) filter caps, and then the bus gets grounded close to the input jacks. The B+ and screen caps get grounded with the PT at B+ side of the board. Bias is grounded at a PT bolt, power tubes grounded right at socket side (consider using a 1 ohm resistor for this). I've done two this way, and they are quiet as church mice.

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Thanks for the info Randall, and thanks for the photo.

[mikepukmel]

Beautiful wiring, Randall.

[mikepukmel]

Huge improvement, thanks for the suggestions.

[Tom Phillips]

...As mentioned elsewhere, what I can't fix:
- The reverb driver tube is fed from the dirty end of the power supply, first filter cap node. But the reverb driver tube's bypass cap and resistor are grounded to the same point where the second preamp tube is grounded. This can't be good.

The stock reverb driver power supply node is not really that “dirty” for the guitar amp application. Keep in mind that the reverb driver is actually a class A power amp. It is similar to the output stage of a small practice amp such as a Fender Champ. In the stock Fender circuit the high voltage supply is fed from the second node of the power supply. A C-L-C filter network and the same PS node that supplies the power tube screens. This is much better filtering than used in the output stage of a Champ. (The primary reason that stock Champs hum is because the power amp has only one stage of filtering and the single ended power amp doesn’t cancel the hum like a push-pull stage does) As you showed on the red lined schematic in post #26 you modified the circuitry to add an additional filter stage before the reverb driver so your amp has a C-L-C-R-C filter network feeding the reverb driver. I think the ripple is very low and certainly clean enough for the reverb driver circuit. One problem I see with your implementation is that you grounded your added cap to the same node as the reservoir cap. That is certainly the dirtiest node in the power supply. I don’t know where, or if, you moved that ground connection during your last rework. A good spot for that ground would be with the 12AT7 reverb driver cathode resistor ground.

...I ordered a turret staking tool, will try to put one more turret in and move the reverb driver's bypass to a separate wire and run that over to where the first filter cap negative lead is attached to the chassis.

Don’t put it there. The power transformer high voltage winding center tap is the only connection that should share that point. We know that the Fender grounding scheme is not ideal but it works OK for a low gain guitar amp. Fender grounded the reverb driver cathode resistor to a spot between the Normal channel bass control and the “Vibrato” channel input jack. Since your amp layout is significantly different you can experiment to find a better location as follows. Free up the negative end of the filter cap you added for your reverb driver power node. Then use a long clip lead or length of wire to temporarily connect it to various ground points in your amp. Pick the permanent connection point based on the lowest hum you achieve. There is also learning value in discovering which point is the worst and which points are the same. Since you have a unique wiring layout and ground buss in your amp you will probably find that your best point is different than that which works best for someone else

...Maybe last thing to do, move the ground for the bias board away from the "dirty signal" ground lug...

Definitely and maybe not the last thing to do. However, if the hum is under control and the amp sounds good it’s time to play guitar. When the noise picked up by the guitar pickups swamps out the noise floor in the guitar amp you are good to go.

Cheers,
Tom

[mikepukmel]

Hi Tom,

Thank you very much for taking the time to write up all of the detail. Reading, re-reading and digesting now. I think I understand most of what you've written!
I took the extra filter can and dropping resistor out, to see if it was the cause of some of the noise, but would like to put it back in a better place, and grounded more correctly than it was. With your suggestions, I think I understand what that is. Can't wait till next weekend to do a little more incremental improvement! This is such way cool stuff.
And of course, hopefully wife and son will have some place to go so I can up the practice volume a little.
Best Regards,
Mike

[mikepukmel]

Re guitar noise swamping ... yeah, exactly what is happening now. I have a G&L strat looking thing with 3 single coil pickups that looove the fluorescent/CCF lights and something else in the house someplace. I have to turn around slowly until I can find a null point, and not move around too much while practicing.

[Zozobra]

I'm sure you're already covered but I've always subscribed to the ground schemes laid out in Merlin Blencowe's books/site and I've built some childishly high gain amps that have been surprisingly quiet. I tend to put grounds to the stage they are feeding wherever I can but sometimes it's better to compromise on this to keep ground paths short. I do, however, sit and draw layouts in different styles just for fun when I'm bored though. This weeks procrastination has been the Framus Cobra on eyelet in the style of the SLOclone turret layout.

[mikepukmel]

I'm sure you're already covered but I've always subscribed to the ground schemes laid out in Merlin Blencowe's books/site and I've built some childishly high gain amps that have been surprisingly quiet. I tend to put grounds to the stage they are feeding wherever I can but sometimes it's better to compromise on this to keep ground paths short. I do, however, sit and draw layouts in different styles just for fun when I'm bored though. This weeks procrastination has been the Framus Cobra on eyelet in the style of the SLOclone turret layout.

Thanks Zozobra, yeah, Ive been through Aiken's doc and have read Merlin's book. I think the last screw up I have to fix is related to input jacks. Think I did something stupid there.

Im writing a book. "How to make your amp howl". I believe I have figured out every wiring combination to make the amp hum nicely. Would love to see photos, etc from your Framus, when you get going.