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Old 1st May 2009, 05:29 PM   #3401
BigE is online now BigE  Canada
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Thank you Peter,

I think I am beginning to understand why there is a large cap on the output of the 8V regulator.

EDIT: a) Motor speed control could be affected by the performance of the 8V supply. b) Noise could pass through the secondary regulator without some sort of filtering of the 8V rail -- but 1000 uF is too big for that -- still thinking about that one...
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Old 1st May 2009, 06:59 PM   #3402
okapi is offline okapi  United States
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a large cap at the output of a voltage regulator serves to lower the output impedance of the regulator. One byproduct of reduced output impedance is an improved transient response. It will also help with ripple rejection, but there is not much ripple left after the input cap and the regulator.
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Old 1st May 2009, 07:05 PM   #3403
BigE is online now BigE  Canada
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Thanks okapi!

Have you or has anyone tried bypassing the caps on the output side with smaller caps? like a 4.7 or 10uF bypassing the 1000uf?

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Old 1st May 2009, 08:50 PM   #3404
BigE is online now BigE  Canada
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There is no snubber capacitor across the transformer primaries?
Has a snubber been attempted?

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Old 1st May 2009, 09:14 PM   #3405
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I am allergic to snubbers
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Old 1st May 2009, 11:00 PM   #3406
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I just completed building all-in-one player and it sounds surprisingly good. Seems like getting rid of digital interconnect has advantages.
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Old 1st May 2009, 11:06 PM   #3407
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I used series 300R Riken at transport's output and 75R Caddock at the DAC (input shunt). Hard wired connection is approx 3" long.
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Old 2nd May 2009, 09:11 AM   #3408
jitter is offline jitter  Netherlands
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Quote:
Originally posted by okapi
a large cap at the output of a voltage regulator serves to lower the output impedance of the regulator. One byproduct of reduced output impedance is an improved transient response. It will also help with ripple rejection, but there is not much ripple left after the input cap and the regulator.
You might get away with a smaller capacity if you use a lower ESR cap.

To explain this: the company I work for is an OEM of industrial electronics. The power amp of a measuring device we produce for a client has shunt regulated PSU's. Sometimes we have to use an electrolytic cap in a key position where a certain Wima cap is preferred but not available on short notice. The Wima cap (I think an MKS) has a much smaller capacitance than the substitute elco. I presume this has something to do with ESR.
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Old 2nd May 2009, 12:18 PM   #3409
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i recieved my dac today, i opted for the toroidal transformer that came with it. Its has a +8v and a 0 which i presume is the only connection i need to make to the dac board if I am bypassing the opamps.

It also has a +13v, 0, -13V winding. I am making the psu from the pdf file on page 2 of this thread. Do you think it is possible to use the +13 0 -13V windings to power the cd player? is there any benefit of making the cd player in the same unit as the dac?

I bought a +12 0 -12 toroidal from RS spares for £15, but i am thinking i could take this back if i can use the spare windings from the dac transformer.

cheers stuart
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Old 2nd May 2009, 10:57 PM   #3410
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by surfstu
i recieved my dac today, i opted for the toroidal transformer that came with it. Its has a +8v and a 0 which i presume is the only connection i need to make to the dac board if I am bypassing the opamps.

It also has a +13v, 0, -13V winding. I am making the psu from the pdf file on page 2 of this thread. Do you think it is possible to use the +13 0 -13V windings to power the cd player? is there any benefit of making the cd player in the same unit as the dac?

I bought a +12 0 -12 toroidal from RS spares for £15, but i am thinking i could take this back if i can use the spare windings from the dac transformer.

cheers stuart
Toroids provide relatively little HF noise isolation between their primaries and secondaries, and even less between secondaries in a lot of cases. I think you would want to keep the supplies entirely separate right down to the transformers in order to reduce the likelihood of noise injected from one supply to the other. The motors in the transport are noisy and also draw relatively large currents during seek, etc.

Also transformers have AC outputs, not the dc ones you seem to imply via the use of +/- symbols. AC transformers are generally specified without polarity. Examples based on yours would be 8V or 0-8V and 26VCT or 13-0-13 volts, etc. Other conventions also apply, but polarity does not.
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