Ground scheme

[Salas]

P.S. Remember that input jack must be isolated from chassis.

 

[nkg]

I am also building this amplifer the extra cap you suggested from the anode load resistor to ground, is 20uf as used by the type 76 valve acceptable.
Many thanks
Nigel

 

[athos56]

Is it 20uf? A value wasn't listed so I didn't add it. I wonder what it would change? I have a little work to do still, my hum balance pots are all wrong, i acidently got 50k ohm pots not 50ohm so I'm waiting for the mail man to bring me the rest... If a value on that cap is determined let me know. Thanks

 

[lquintas]

This extra cap only changes the value of the 50 uf cap in the power supply circuit, because they are in paralell. Is it necessary? Thanks

 

[nkg]

Question for Athos 56

I'm still a few weeks from finishing my amp just curious as how far off you are from finishing your amp maybe compare notes.
Nigel

 

[bibster]

Think of currents running downstream. We start at the top with the supply (being careful not to break into a high ripple current loop). We then cascade down, with successive stages dumping less and less current in until we reach the earth/safety ground.

This is what I needed to 'get it'... Thanks Sy!
I'm finishing my aikido now, based on JB's 5687 board.

Few related Q's though:
My RCA's grounds are 'bussed' per IN and OUT (1 bus each thus)
Should I link these two busses, and go with one wire to the Aikido PCB? If yes, then: Which of the many Gnd's on the pcb? (2 on the IN side, 2 on the OUT side)
Or should I rather put the OUT bus on the OUT side and the IN bus on the IN side?
Or should I link them one by one to the gnd bus? (I think so...)
Than: Where to go from ground bus to earth (PE, wall plug green/yellow) NOTE: My chassis is 100% wood (For the moment being) Well.. 99% wood, 0,8% glue, 0,2% paint
Should I pick a point 'further downstream' (cf. Sy's analogy) than the RCA's

So far, I thought of this bus like this:

CT---PSU C's----PSU regulator board ---Heater PSU Ground Ref.--- Aikido PCB 'ground' conn.----INPUT RCA's-----Output RCA's------diode/resistor/capacitor network to PE
(The two PSU C's are connected together, thus only one ground wire, the volume control's GND to the same spot is the input RCA's)
Does anyone GET this, and Is it 'the way to go'?
(See attached image file)

Paul

PS: Could this BUS be a piece of 2.5mm2 stripped copper, and could it make a nice(?) long (?) sightseeing tour underneath my chassis?

 

[SY]

If you're using the Aikido PCB, make use of the very nice ground connections that John provides; his grounding is star rather than the bus grounding I was talking about before.

In my build using John's board, the power supply return was connected to the board star, the input commons were separate for each channel (but all input jack commons connected together within a channel) and returned to the board Input Ground, as was the bottom of the volume control pot. The twisted pair output leads were connected to the respective output Cx and GND terminals on the board. The R/C/diode network was connected between the star ground and the safety (earth) ground on the board, and a thick wire was run from the board's safety ground to where the green wire from the IEC socket was attached to the chassis. All input and output jacks were isolated from the chassis.

One other thing: when looking at spectra of the output noise, I found that it was worthwhile to trim the resistor divider that provides the nulling signal. The null is a pretty sharp one, and given the tolerance in tube mu...

 

[bibster]

Thank you Sy,

So I'll make a PSU star (CT, C's, heater and HT regulator boards), run that to the GND connection on the board.
The output RCA's commons are allready bussed together (L+R and all 6 inputs together) so I'll run 1 wire to one of the input gnd connections, using the other for the vol.pot.
Same for the outputs: I'll use either of of the provided gnd's. (Or put some cat5 TP and thus use both...)

I'm not whether too use the board's safety gnd, as the board is attached to some wooden case... Well, It doesn't harm, does it? If I decide to add some shielding later...

Thanks, Paul