Search found 11748 matches

by Nick
Wed Jul 17, 2019 3:43 pm
Forum: Everyones Projects
Topic: Small Push-Pull Amp.
Replies: 17
Views: 286

Re: Small Push-Pull Amp.

Ali Tait wrote:
Wed Jul 17, 2019 3:26 pm
I remember liking that EL34 PP Nick made for one Owston.
I had to think, do you mean the one I made using Collins output transformers and the sowter interstage phase splitter?

Still have most of that somewhere.
by Nick
Wed Jul 17, 2019 11:00 am
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

Nothing is a simple resistance. Certainly not a heated wire. But remember the part that matters is not the hefty heater power, its the tiny fragile audio signal that has to coexist in the same circuit.
by Nick
Mon Jul 15, 2019 8:51 am
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

Nuts! You'd convinced me with the space charge scenario! :) I can't think why a different part of the DC supply might sound different though? Well, if its regulated, one end will be the emitter of a transistor, the other the ground or a sense resistor for the supply. Remember Mark found that he cou...
by Nick
Sun Jul 14, 2019 7:43 pm
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

1000v, 80ma, -100v on the grid is not a bad operating point.
by Nick
Sun Jul 14, 2019 9:55 am
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

Had another one of those "Are we looking in the wrong direction" moments. While most DC supplies may be floating, I don’t thing they are balanced. At least not from the perspective of the audio signal path. So the fact that causing the signal to exit from one or the other end may well make a differe...
by Nick
Sat Jul 13, 2019 10:28 pm
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

I don’t know, I could imagine one end of the filament may sound different to the other, not because of the filament voltage, but physically, they may be different. I don’t; know, so can't say. The cause of the effect may not be the one that’s expected, or it may be, reality can be tricky.
by Nick
Sat Jul 13, 2019 9:13 pm
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

I've always thought, perhaps erroneously, that hum pots were used with AC filaments to find the "balance" point across the filament potential difference where the hum was minimum. Yes, thats what they do, but what I never found was a explanation of how they do it. I'm not sure why a hum pot or pair...
by Nick
Sat Jul 13, 2019 7:03 pm
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

Its based on a mathematical analysis of how the centre tap works I did some years ago (there is a copy of the maths somewhere on here). As to if there is any noise , don't know. the odd thing is, its hard to find a explanation how a hum pot works, so I worked out my own answer to that and its applic...
by Nick
Sat Jul 13, 2019 4:59 pm
Forum: Everyones Projects
Topic: GM70 PP
Replies: 35
Views: 528

Re: GM70 PP

I have argued that a centre tap with DC will help reduce any residual noise. But I think it practice its not worth doing and may be worst as you are adding extra resistors in the circuit.
by Nick
Sat Jul 13, 2019 11:31 am
Forum: General Vinyl
Topic: Technics Sp10 Woes
Replies: 99
Views: 9805

Re: Technics Sp10 Woes

Yep maybe also check for a short somewhere. Trace back from the gate if that meet and see if the pulse appears.
by Nick
Fri Jul 12, 2019 8:47 am
Forum: General Vinyl
Topic: Technics Sp10 Woes
Replies: 99
Views: 9805

Re: Technics Sp10 Woes

Yep, though TBH, I would just get a replacement and replace it.
by Nick
Wed Jul 10, 2019 11:48 pm
Forum: General Vinyl
Topic: Technics Sp10 Woes
Replies: 99
Views: 9805

Re: Technics Sp10 Woes

Yes, its the sample and hold that implements the phase lock. the pulse samples the ramp at the position it is at the time, and that held value is then used to provide the phase lock signal to the turntable.
by Nick
Wed Jul 10, 2019 1:18 pm
Forum: General Vinyl
Topic: Technics Sp10 Woes
Replies: 99
Views: 9805

Re: Technics Sp10 Woes

THat would point to a short somewhere or a fault somewhere around the sample and hold area and R186. Maybe a failed TR151.
by Nick
Wed Jul 10, 2019 1:17 am
Forum: General Vinyl
Topic: Technics Sp10 Woes
Replies: 99
Views: 9805

Re: Technics Sp10 Woes

The correct setting is in the service manual. Show us what you are getting.
by Nick
Tue Jul 09, 2019 11:04 pm
Forum: General Vinyl
Topic: Technics Sp10 Woes
Replies: 99
Views: 9805

Re: Technics Sp10 Woes

Was about to congratulate you till I realised it was Neal showing what the trace should look like.

I wondered if you had a different scope :-)