More fun with grounding..

[Tonegeek]

The more I study grounding, the more confusing it becomes. Aiken seems to be saying that distributed capacitance is the way to go with the decoupling caps for the each section share the star for that section. All my caps are on a separate board, so that wont work for me and I dont see that working for any Dumble builder, unless you run a separate wire to each local star from each decoupling cap. This is a lot of wire across the chassis and it violates what Aiken says about separating ps grounds and signal grounds (unless he means you do not connect the local star to the buss- which makes a lot more sense - still it is a lot of wire).

Here is what I think would work and so I just need some validation: Buss bar on standoffs for pots and local star grounds, connected to chassis near the input jack. Power supply caps (all of them), power tube cathodes, and power tranny HV CT to the other end of the buss (furthest from the input jack). OT common to the isolated speaker jack shield, with small wire to neg feedback ground point nearest the PI ground on the buss.

The only issue i see is the small chance of ground loops between the local star and its corresponding decoupling supply cap. Anyone had issues with this?

One alternative (less desirable I think) to this arrangement is to use the tranny bolt, instead of the buss bar for the cap, ct and power tube cathode grounds. With that, you are carrying some ground return current across the chassis.


I don't really understand the theory behind floating the heaters, except somewhat in terms of electron attraction due to voltage differential/polarity, but how does that translate into hum? (gimme the short answer!) Basically, sHould I ground my heater ct or float it via Aiken? Guess I can wait and see on that until I hear it the first time.

I have read what most people say about grounding here, but want to hear from folks who have done what I am talking about and see if it worked for them, unless there is some major flaw in my scheme, in which case save me from myself!
thanks,
Whit

[drz400]

unless there is some major flaw in my scheme, in which case save me from myself!
thanks,
Whit

I have built an amp High gain with the Speaker jacks and PT ground then filter caps following one ground path with preamp decouple caps ground at points and ending at the input jack grounded to chassis.
The audio grounds follow another ground path and also meet separately at the input jack ground to chassis, So think like two busses with connections along the buss. I used 12VDC heaters on all the preamp tubes with a LM350K Steel regulator and 12.6VDC. That amp is 100% hum free even at full volume on master and gain and it has more gain that you could ever want, at least equal to a SLO100 and is still silent absolutely no hum. Floating the Heater CT to a positive voltage also helps but ONLY if the ground path is excellent, if it isnt it can get worse. DC heaters are the absolute best way to go for hum free on the heaters but it is more of a pain in the arse. However it can be the quickest way to remove hum very quickly, always works.

Even though I fully subscribe to the Aiken/London Power methods this first method worked Excellent and might be something easier for you to try.

[KT66]

DrZ400, would you mind posting the scematic or giving a complete description of the DC heater supply that you mentioned? I have a high gain amp that I built, it's a plexi with the Hoffman hot switch, and I have put alot of time into trying to reduce the noise and I am just not satisfied with the results. I have tried elevating the heater supply, but that just introduced a buzz into the amp. I have a ground buss that all of the preamp grounds are connected to, including the PS caps that feed the preamp at the appropriate spots along it, and the buss is grounded at the input side of the chassis. The power supply center tap, speaker jack, heater CT. EL34 cathodes, the PS caps that feed the OT center tap and the screens, and the bias supply are grounded at the same point near the PT. There is a 60Hz hum coming from the first gain stage that I assume is from the heater. I bought one of Funk's chassis to build an ODS, but I don't want to start it until I have mastered this grounding thing. I wish someone could tell me how to trouble shoot this issue. I thought I remember reading in the Dumble discussion about how to use a scope to find ground loops, but I can't remember where now. I think next I will try a hum balance pot, but if that fails I am stumped.

[Tonegeek]

There is a 60Hz hum coming from the first gain stage that I assume is from the heater.

My experience is limited in this area, but I have good trouble shooting skills and have read a lot about grounding.
I read on this site that you can use a lantern battery to power your heaters temporarily. This would definitely tell you if the heater is causing your issue. Might want to try it before building a DC supply for the heater. Also since you mentioned it is in the first tube, try shielded cable from the input jack (shield connected at one end only) and check the tube cover and socket for a solid connection to the chassis. I believe also that you could use a sensitive voltmeter to check for AC between your ground points (similar to using the scope). Try one probe on the local star point for the first tube and move the other around to other ground points, like the point where your buss connects to the chassis and the power supply star, etc. The voltage will be very small, if any (proportional to the volume of hum). Once you locate the voltage, it will require experimenting to fix. Also, there is no guarantee that the voltage may be causing your hum, but any voltage between ground points indicates resistance, so look at the connections and wire size, etc. Good luck.

[Tonegeek]

I have built an amp High gain with the Speaker jacks and PT ground then filter caps following one ground path with preamp decouple caps ground at points and ending at the input jack grounded to chassis.

Just to clarify:
I assume the ground connection point near the input is the only one to the chassis (other than the power cord ground wire)
I gather from your description that you connected all your supply caps to the same star point close to or on the OT common, and PT center tap.
I assume preamp decoupling caps mean the caps from tube cathode to ground. This makes perfect sense and is similar to what I want to try but with the Aiken version for the OT common going to the isolated speaker jack and on to the Feedback resistor\PI ground point. Correct me if I misread what you are saying as I am ready to wire my amp in the next day or so.

Part of my confusion from reading Aiken is that he seems to be talking about the supply caps grounding at the same point as the local star for each tube stage which would include the cathode caps, pot grounds, etc. I am guessing that this may not always be necessary although I think I see the logic behind it, espcially if your PS caps are on the main board.

[drz400]

I have built an amp High gain with the Speaker jacks and PT ground then filter caps following one ground path with preamp decouple caps ground at points and ending at the input jack grounded to chassis.

Just to clarify:
I assume the ground connection point near the input is the only one to the chassis (other than the power cord ground wire)

Correct

I gather from your description that you connected all your supply caps to the same star point close to or on the OT common, and PT center tap.

Yes to the begining of the buss near the power supply

I assume preamp decoupling caps mean the caps from tube cathode to ground.

Wrong, power supply caps for the preamp stages, the cathode caps and resistors I kept to that local buss

This makes perfect sense and is similar to what I want to try but with the Aiken version for the OT common going to the isolated speaker jack and on to the Feedback resistor\PI ground point.

Same thing I do but after it goes to the speaker jack it goes to the same point on the buss as the PT ground and each power tube ground also separately goes there. It would be better to take the OT ground it to the phase inverter ground if you have feedback but on this amp they were not that far apart and it didnt seem to matter.

Part of my confusion from reading Aiken is that he seems to be talking about the supply caps grounding at the same point as the local star for each tube stage which would include the cathode caps, pot grounds, etc. I am guessing that this may not always be necessary

That is the best way but I made this amp before I knew this and there is no possible way it could be more quiet so I was just pointing out that other variations work, if I was doing it from scratch I would follow TUT3 but I was pointing out an alternative if your supply caps are clumped more together.

although I think I see the logic behind it, espcially if your PS caps are on the main board.

Good luck!

[Tonegeek]

DRZ - I think I have got it. Thanks for taking the time to clarify. I have seen many of your posts on this forum and you must get tired of repeating yourself, but believe me, it helps to hear it over and over.

Tonight I will be mounting my pots, jacks, switches etc. to the chassis. I got my face plates on (it looks like an amp now!) I have already wired my heaters, (except the 6.3 V CT which I am trying to plan for in case I have to float it later for hum reduction). My boards are mostly populated except for values I will clip in for tweaking (like the treble bleed caps, etc.) I got a nice piece of brass welding rod about 16 or 14 guage for my buss bar. I can see the light at the tunnel's end now and can hardly wait to hear this amp. I planned this build to be very flexable (bypass switch for the on board dumbleator, EL34 or 6L6s, linking switch for switching OD and PAB simultaneously, dual external bias pots, test points, external access to HRM trim and tone stack). Some day I will post pix of how I did a couple of things (my relay board and OD stack access) that I have not seen done here before. Nothing earth shattering, just sort of interesting. I want to wait till I confirm these ideas really work so I don't embarass myself or more importantly lead anyone else done the wrong path!
whit