SP 12 SE

[Gepetto]

Seems like a large left/right gain imbalance in the phono section Lee if both have 3mV in and one has 460mV out and the other has over a volt.

 

[speakerman1]

Lee

I know it is a ground loop. Can we daisy chain the grds. Like faceplate, PCBs, and trans? Just thinking out load. Run them to the IEC grd.? Or what do you think?

Larry

You should really try thinking out "Loud" thinking out "Load" might hurt.

LOL Depends on my frame of mind.

Larry

 

[laatsch55]

Yes Joe there was. There is also pots to balance the gain on the phono board itself.
Well I've outputted over 3 volts and no more power supply problems , and it's been on and testing for a good 4 hours.

 

[mlucitt]

Was it the commode diode?

 

[laatsch55]

In a tuber it would Pentridiode.

 

[laatsch55]

here's how this was grounded-------

Left channel, all inputs except phono
All inputs grounded at RCA jacks---then to--selector switch, no grounds , in or out---then to---tape/source switch, no grounds in or out---then to----left gain switch, grounded in and out, ---then to---Volume pot, grounded in BUT not out to board, ---then out of board to RCA out jacks---out of board grounded -rca out jacks not grounded.

 

[laatsch55]

Right channel, all inputs but phono.
All inputs grounded at RCA jacks, ---then to---selector switch, no grounds in or out,---then to--- Tape/source switch, no grounds in or out----then to ----right gain switch, grounded in and out, ---then to-----volume pot, grounded going in and out to board, grounded on in to board, grounded coming out of board and grounded at the RCA out jack.

 

[laatsch55]

Here's the latest. The top grfaph in each one was before I grounded the ungrounded runs from the volume pot onward. The bottom is the result afterward.

 

[Gepetto]

Hmmm...

 

[laatsch55]

Hmmmm???????

 

[laatsch55]

I might add gain was cut to a little less than 1 volt and it sounds,..............,.bad. A lot of microphony and tapping the chassis bottom causes a lot of spurious random stuff.

 

[speakerman1]

What are the tube numbers?

Larry

 

[speakerman1]

FFFFF. I got the numbers. Have to look in my stash of tubes. FFFFFF When I get the tubes or I will send the tester to you. We may have thrown to much at them. Didn't have tubes in my budget. Now to play CC roulette. FFFFF. I'll ship the tester tomorrow. Just to make sure. FFFFFFFF

 

[ksrigg]

You could send the pre to Roy and let him sort it out. He designed the thing...he could then send it to Lee for testing and then on to you. I just hate to see Lee hitting his head against a wall, and Roy has had to get the HUM out of several of them as I have read. I know he wouldnt' mind finding the source of the probalems...plus I know Lee doesn't LOVE tube gear in the first place..

 

[Skratch]

Men, I have had issues in the past on ST-70 upgrades from VTA

 

[laatsch55]

Sutton----I would learn only that I couldn't finish it if I sent it off. I am the kinda guy that may look pitiful when I'm hitting my head against the wll----till it gets personal----and it's persopnal now. I will die before I give up on this. That's how most of the problems are conquered in the oilfield, we just wear the M&^%$# F&^$$^%^& down!!
I'm weird like that.

 

[laatsch55]

Larrt----What's up with the FFFFFFFFFFF's??


Oh , and Sutton----- If I still have my sense of humor the project is safe from obliteration.
It's not that I don't love tube gear, a guy I love asked me to build it and I told him I could ergo-I will die tryin.

Old School Bud.

 

[laatsch55]

Besides it was all worth it to see a "Hmmmmm" out of Joe, that was precious!!

 

[laatsch55]

And--- one more thing. Pre-amps are very unforgiving of shoddy wire placement and induced everything to begin with. Valuable lessons before we scratch build the "Monster"--it's all good.

 

[speakerman1]

The FFFFs are my happy dance. LOL I didn't think to put some cheaper tubes in to test it. Or to test the tubes I bought. Oh well. It is all good now. I'm smiling.

Larry