We have music with no hum but terrible hisssss
You need to check the PSU for oscillations (you need a 100Mhz scope for that).
currently i´m adding a million solderpoints in the signalpath for a input imp. switch..
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
about the grounding, i made a simple psu with one trafo per channel (but just 4 diodes, not 8 like in the drawing from FdW.
In the first attempt i had terrrible noise and a little hum.
As a provisory i connected the grounds from the chinchplugs together and the tonarm mass goes there.
on the board the grounding is to the input and the power ground. like this it is ok for now (but shurely totally wrong).
measurements will follow. Most critical value seems op amp at pin 6 its 3.5 Volts at one channel. and i cannot say anything about oscillation. you don´t hear it, right? maybe i can carry it to a doctor.
In the first attempt i had terrrible noise and a little hum.
As a provisory i connected the grounds from the chinchplugs together and the tonarm mass goes there.
on the board the grounding is to the input and the power ground. like this it is ok for now (but shurely totally wrong).
measurements will follow. Most critical value seems op amp at pin 6 its 3.5 Volts at one channel. and i cannot say anything about oscillation. you don´t hear it, right? maybe i can carry it to a doctor.
Shame on me. I used the trimmer so badly that I really got negative voltage on plus caps. Again shame on me!!!!Now the voltage is -0,698V on the upper resitor block (going down to vminus) and +0,697V at the lower one (going up to vplus). Me think it´s alright now.
But now another problem. I start up a soundcheck. Everything alright but there was a little fizz in voices. So I recheck the riaa area. I have 33.3nF at one bench (horizontal bench) (matched very good
) but on the other (vertical) bench (what shall be 11.1nF) is 25,4nF . so I desolder the 2 caps and there are still 25,4nF.I looked on the shematic and this could not be. There are only the R18c (Neumann) and C2a and C2b that go to Vriaa. Right? That would mean ground to VRIAA is Capacity of 25,4nF.
Thanks
Please explain better what you are measuring. Vertical ? Horizontal ?
You can not get a good measurement of the caps in the riaa filter once they are soldered. The only thing you can have is an idea of the matching between channels.
Did you measure the caps before you installed them ?
Beware of styroflex... these can change values with heat during soldering.
I meaned the vertical bench of 11,1nF Riaa (where 2 caps can go in) and the 33,3nF Bech where 6 Caps may go in. The 6Caps bench measured 33,3nF and the bench of 2 meausured 25,4nF without caps.
Yes I measured 11,1nF with 2 caps. I used the wima red caps from GB.
another one is up and running ; )
thanks to all for circuitdesign-, pcb-making, partsdistribution helpdesking around and so on.
stefan
No thanks, I'm happy to see it working