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Old 24th August 2010, 06:33 PM   #3001
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Yep, can't get this to work properly. I tried two PCM assembly's one with op-amps and decoupling components and one without. The result was the same with both - very low volume and loud hiss. I also tried Bill suggestion of removing the secondary resistor and also tried without resistors on primary leads.

The UTC's are basically unsuitable for current output DAC's. However the PCM1794 has higher output than the 1798 so might try that sometime. I will shelve the project until I can afford appropriate output transformers.

McGyver - out of interest, which transformers and tube stage did you use?

Cheers

Rich
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Old 24th August 2010, 06:37 PM   #3002
Ryssen is offline Ryssen  Sweden
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Quote:
Originally Posted by RichLund View Post
McGyver, that looks very nice.

I am trying the PCM1798 in my DAC now but have very low volume and hiss. It may be the UTC A-20's I am using, although I have them configured for 1:3 with 47R resistors on primaries and 510R across secondaries.

Did you remove the opamps under the PCM adapter? I think I may need them for adequate signal amplification. The spec calls for OPA2604 but I have some OPA2132 and OPA1642 I could try. I ordered blank adapter boards from snow and used some sample PCM1798 DAC chips. I have 56uF oscon and 10K resistor similar to your board in post #2854.

Any ideas?
How did you connect the 47R on Primary?Between primarys or primary to ground?
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Old 24th August 2010, 06:42 PM   #3003
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I should add that the DAC is sounding very good indeed with CS4398 chip following some extensive modifications recently.

I upgraded and separated the power rails for 5V and 3.3V digital rails and added VBE 'Regulator boosters' made on strip board to all supplies including the up-sampling module. I intend to try a PFM flea module for the sampling clock XO module and separate 3.3V regulator for the CS8421 sampling chip. I would also like to try a DIR9001 with a flea regulator supplying the onboard XO clock.

Some pics:

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Old 24th August 2010, 06:43 PM   #3004
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Quote:
Originally Posted by Ryssen View Post
How did you connect the 47R on Primary?Between primarys or primary to ground?
Ryssen I had 47R on each primary!

Was this wrong?
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Old 24th August 2010, 06:46 PM   #3005
McGyver is offline McGyver  Poland
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I used some Sowters 1:10 or so, but I don't have it any more and don't remember the symbol.
My tube stage is like this:
Attached Images
File Type: gif 6922_schematics.gif (4.7 KB, 146 views)

Last edited by McGyver; 24th August 2010 at 06:48 PM.
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Old 24th August 2010, 06:55 PM   #3006
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Quote:
Originally Posted by McGyver View Post
I used some Sowters 1:10 or so, but I don't have it any more and don't remember the symbol.
My tube stage is like this:
Thanks Mcgyver, the tube stage looks nice and simple. I could bravely attempt that sometime. Could you post some pics and component values. I really like your DAC case is it a Modushop?

I had considered Sowter, not least as they are in the UK, something like the 9762 model.

Cheers

Rich
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Old 24th August 2010, 06:57 PM   #3007
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Quote:
Originally Posted by McGyver View Post
I used some Sowters 1:10 or so, but I don't have it any more and don't remember the symbol.
My tube stage is like this:
Too complicated!
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Old 24th August 2010, 07:03 PM   #3008
McGyver is offline McGyver  Poland
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I'm going to test a circuit like this also:
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File Type: jpg 1798 stage.jpg (22.1 KB, 164 views)
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Old 24th August 2010, 07:04 PM   #3009
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Originally Posted by Bill Fuss View Post
Too complicated!
Yep, it uses more than three components... its out of my league!
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Old 24th August 2010, 07:08 PM   #3010
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Mcgyver, would you need separate power supplies for filament and heaters etc?
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