Pin1 ground of an octal

[surfsup]

A question on this. Currently i have a long lead from pin 1 to the ground bus on the other side of the circuit board. The lead runs up and over the board.

Would there be a possible ground loop problem if I ran this lead very short to a terminal ring on the octal socket mounting bolt right there on the chassis next to the pin? Or is this a no-no.

I ask becuase I see a lot of builds with grounds running down right next to the socket.

[selloutrr]

it's typically ran the shortest distance to chassis ground. not to say some botique builds don't use a "special" grounding path for "$mojo".

You should be just fine soldering it directly to the chassis or a grounding lug under a bolt. It's worked on fender builds since the 50's.

[iknowjohnny]

yeah, i bolt mine to the chassis right between the sockets. I have some hum lately after messing with some things, but till now the 2+ year old build (fairly high gain) has been quieter than most marshalls i've owned.

[surfsup]

Okay interesting. As I have been learning over the last couple months through this HO build I have come up with an idea for a new grounding scheme for my amp. I have a proposal for you guys for 5 ground lead changes that I think follow a two star ground pattern, one for the preamp/inputjack and one for the PowerSupply PS side.

Here are two photos, the first one with the PS changes (forgot to put in there a dedicated ground for the green long lead at the lower left bolt) and the second showing the ground at the preamp/input that would not change. Do you think my proposal would be better?

[img1000]http://chicagocadcam.com/ChrisHahn/POW_NEW.jpg[/img]

[img1000]http://chicagocadcam.com/ChrisHahn/PRE.jpg[/img]

[Alexo]

Ehh whatever you decide to do, only make one change at a time and test the amp after each change!

[selloutrr]

Does the amp have a high noise floor as is?

[Firestorm]

Technically, the safety ground/earth ground should go straight to chassis (as you have it) and nothing else should be connected there. Its sole purpose is to prevent voltage on the chassis in case of a short. Pick another point where you can tie your power amp grounds, where the leads will be short and simple.

[surfsup]

Ehh whatever you decide to do, only make one change at a time and test the amp after each change!

Well in this change of the grounding scheme, I am thinking its all or nothing?

Does the amp have a high noise floor as is?

No, only when stuff gets about 75% to max do I start noticeably hearing the hiss and very slight high pitched oscillation.

Technically, the safety ground/earth ground should go straight to chassis (as you have it) and nothing else should be connected there.

I see in many rocket builds the PT is grounded to the Earth ground. I saw some that had the full PS ground leads grounded there with the OT/speaker ground, but I also see some with a third chassis ground and some with a fourth:

1) Mains with PT
2) PS at the tube rectifier bolt
3) Pots grounded to a chassis ground near the pots
4) input ground

I read at aikenamps a two star ground is the best. So for my amp, if I leave the Earth ground alone, and leave the input/preamp ground leads alone, I could ground the PS all to a "third chassis ground"? Like the bolt at the top right of the extra noval socket on the right that will be removed soon? the YLW/RED lead from the PT is kinda short now.

[Alexo]

only when stuff gets about 75% to max do I start noticeably hearing the hiss and very slight high pitched oscillation.

Doesn't sound like something grounding will fix, ime. The hiss could just be standard "tube noise" or resistor noise. The oscillation could be lead dress, could even be a microphonic tube if your amp is close enough to the speaker, or even microphonic pickups.

[surfsup]

alexo, okay. Maybe I'll just leave well enough alone on this one. Or maybe I'll post a clip of the amp after this weekend. The grandparents are going to pick up my kid for the weekend so I'll be able to be a kid again.

[selloutrr]

i second Alexo

It's probably not going to get any better moving the ground.

what you are hearing it's pretty common in most amps.

you might benefit from a mil spec version of the preamp tube, or one tested for low noise, and microphonics.

keep in mind 75% of full volume is pretty good!

[surfsup]

"keep in mind 75% of full volume is pretty good!"

Really? Okay, can accept that. I just keep reading posts about how quiet people's amp builds are and think, hey, mine should be quieter than this...