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Old 4th May 2008, 03:02 PM   #1
regal is offline regal  United States
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Default SRPP Powersupply, replace R with choke ?

Please see this power supply.

Would it make sense to replace the CRC resistor with a 10H choke ?:

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Old 4th May 2008, 03:27 PM   #2
SY is offline SY  United States
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Are you having hum issues that you've traced to ripple at the regulator outputs?
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Old 4th May 2008, 03:50 PM   #3
regal is offline regal  United States
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I am having a slight hum at high volumes playing a silence track. For a tube DAC its pretty good, actually less hiss than my solid state DAC, but I do think the hum could be audible playing music.
If it was hiss I could live with it, but hum is a little more noticeable.

I don't have a scope, so not sure how to determine if the hum is the PS or the inductors in the analog stage picking up EMI.
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Old 4th May 2008, 09:14 PM   #4
euro21 is offline euro21  Hungary
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Default Is this Lite Audio DAC?

Mods of my Lite DAC-50 (PCM63P-K DAC, 6922 SRPP):

- HEXFRED diodes in rectifying stages;
- 5H choke in HV stage (C-L-C);
- Power supply bypass capacitors (MKP10);
- NOS Tesla E88CC in SRPP;
- ClarityCap coupling capacitors
- Coupling capacitor bypass by 0.1uF VCap (teflon);

and the best:
- I/V resistor change to Sowter 8347 transformer (1:18, 2K0 Caddock resistor in secondary).
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Old 4th May 2008, 10:16 PM   #5
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Hi,

You must determine if the hum is from the supply, otherwise a choke won't help.

The hum could be induced through the heaters, stray magnetic fields or even ground noise.

Cheers!
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Old 4th May 2008, 10:51 PM   #6
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Tell us more about the amp in question. It's much more likely that you're getting noise through the filaments, but that can depend a bit. If you can get ahold of a scope, I'd peek at that B+ line and see how it looks before you go in there and tear it up.
-Paul
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Old 5th May 2008, 01:20 PM   #7
regal is offline regal  United States
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Default Re: Is this Lite Audio DAC?

Quote:
[i]and the best:
- I/V resistor change to Sowter 8347 transformer (1:18, 2K0 Caddock resistor in secondary). [/B]

How does that work with the 2K0 in the secondary. The load the DAC sees is what 2000/(18*18)= 6 ohms?

But what is the Vp-p before the SRRP? is it 4mA*6*18=0.432V
Then 0.432V * 16 (gain) = 7Vp-p = ~ 2.4Vrms ?

Any caps or filtering before the SRPP ?
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Old 5th May 2008, 02:04 PM   #8
euro21 is offline euro21  Hungary
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Yes, ~ 2.4Vrms.

There are no filtering, only Sowter transformer as "bandpass" filter (like attachement).

Kill all filter in Lite DAC SRPP ( remove 0.22mH*2, 473pF), remove I/V resistor (100 ohm), and grid resistor (470 ohm).
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Old 5th May 2008, 02:21 PM   #9
regal is offline regal  United States
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Thanks I had been kicking around the Sowter idea for months, but they are so expensive.


with the attachment there is some filtering caps added as well a a small resistor on the primary side R4,R5,R6 & C6.

Did you add all this or just go with the 2K0 on the secondary?
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Old 5th May 2008, 02:39 PM   #10
euro21 is offline euro21  Hungary
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R6-C5 only neccessary if above 18-20 Khz are small bump in freq. curve.

Some idea suggest real I/V resistor (primary side), some recommend resistors both side, some only on secondary side.

For me the best result: resistor only on secondary, no other filter.
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