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Old 26th January 2013, 04:20 PM   #1271
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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 donīt hear it, right? maybe i can carry it to a doctor.
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Old 26th January 2013, 04:36 PM   #1272
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keith if you have one traffo shared across both boards it will hum.
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Old 26th January 2013, 05:29 PM   #1273
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Originally Posted by hesener View Post
If this were true, the input voltage should be around -4.5V (the VBE of the PNPs and the 3.8V)



If this were true, the input voltage should be around -4.1V (the VBE of the NPNs minus the 4.8V).

Now, both of above conditions could happen at the same time, but only at a input voltage of e.g. -4.3V or so. It takes an odd combination of issues for that to happen....

could you please check R1 and R1b (the 10k resistor and the input offset trimmer), if they are not short-circuited or causing a short to a negative voltage somehow?

and, can you please check the collector - emitter voltages of the PNPs? That should be around 13V.

And, just for completeness, please measure the voltage on both ends of R5 (82 Ohms) just to see if the current source is operating correctly....

No worries, we'll get there....

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 itīs 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.

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Old 26th January 2013, 05:58 PM   #1274
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by sq225917 View Post
keith if you have one traffo shared across both boards it will hum.
Well not really, it can be done with only one trafo.
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Old 26th January 2013, 06:02 PM   #1275
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by Libby123 View Post
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.
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.
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Old 26th January 2013, 06:19 PM   #1276
Marra is offline Marra  United Kingdom
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The sound is now hum free; turns out I had forgotten to connect the centre connector on the caps to ground.The Paradise sounds pretty good to my ears and should sound even better when I go dual mono with seperate supplies.
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Old 26th January 2013, 06:21 PM   #1277
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Old 26th January 2013, 06:47 PM   #1278
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Originally Posted by RCruz View Post
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.
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Old 26th January 2013, 07:30 PM   #1279
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you can not measure them after soldering in place.... The whole riaa circuit acts as a complex filter.

Give me the real measurements before soldering... including riaa resistors.
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Old 26th January 2013, 07:40 PM   #1280
FdW is offline FdW  Netherlands
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Originally Posted by noelectrix View Post
another one is up and running ; )
Click the image to open in full size.

thanks to all for circuitdesign-, pcb-making, partsdistribution helpdesking around and so on.

stefan
No thanks, I'm happy to see it working
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