VVR noise

[bepone]

if using this schematic, this is better

Plan18W_0V_bon.png

[ChopSauce]

Fine, tons of thanks...

I see the point in connecting the grounds for the power section (I think I saw xtian did it this way) but I don't catch the upper left red arrow...
(There's no such derivation on my schematic anyway... )

EDIT: what does "TBD" stands for?

[bepone]

these resistors in yellow belong to output section, and need to be firsly grounded there (below cathode capacitor)
TBD to be discussed a lot of theory there about grounding to the chassis, essential is to ground input jack to the chassis short way, so there must be point of the grounding to the chassis for the start,

[ChopSauce]

Thanks for your consideration - again!

Do you recommend grounding the first reservoir cap with (the rest &) the pre-amp, through the physical connection to the chassis for the input jack?

That never worked for me, nor does it seem to be a common practice amongst amp builders on this forum.

I do separate pre- and power-amp grounds at the very least.

With the VVR, there seem to be an additional problem I'll have to investigate.

[martin manning]

First and most important is to connect the reservoir capacitor negative directly to the power transformer center tap or bridge rectifier ground, and that should be located at the power amp end of the chassis. Some other circuit grounds can be made at that point, such as bias supply and filament winding center tap, but the input and preamp grounds are best made on the opposite end of the chassis near the input jack. For general theory of grounding, I recommend a read of this article: http://www.valvewizard.co.uk/Grounding.html

[ChopSauce]

On a related matter, where would you advise that would be best to ground the 1M input grid leak resistor



after the input coupling cap:

- right at V1 socket ;

- with the cathode (R,k) for V1 ;

- or with the input jack (as depicted above)...

First and most important is to connect the reservoir capacitor negative directly to the power transformer center tap or bridge rectifier ground...

I did that, also connecting the VVR ground to it. That was an improvement but still there is some noise from the input, that I would like to take care of - hence the question above -

[martin manning]

On a related matter, where would you advise that would be best to ground the 1M input grid leak resistor

Grounding that 1Meg at the input jacks should be fine. Is your remaining hum at all VVR settings or more noticeable at low voltage settings? If it's at low voltage settings you might try adding a blocking cap to the second stage.

[ChopSauce]

Thx Martin, but it's not like hum now. It looks like that was solved a few moves ago.

It is sounding perfectly with the VVR down. The grid leak resistor have been grounded with the input jack - as you wrote - and I already put an additional coupling cap before V2a grid, NB.

Still have some remanent light scratchiness, though.

Other than that I could read something about the VVR being possibly to close to the AC input,..

EDIT: I can confirm. Having AC close to the VVR can be a significant source of noise. I managed to take AC as far away as possible and this made a difference. Next move - if any - would be to shield the VVR, I guess.