Comparing battery-powered phono pre-amps, from RS ($$) to ASR ($$$$) ... and beyond!

derek92994

derek92994

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I decided to beef up the capacitors in the Rat Shack Pre. Used whatever was in stock from previous projects, nothing too exotic but better than average caps, mainly panasonic. Not really knowing what I was doing here are the changes:

C11 25v/100uf to 16v/470uf (the Rat shack pre that 3D got has a 16v cap instead of 25v for the pre's sourced here in Oz)
C1/C2 50v/1uf to 50v/33uf
C13/C10 16v/10uf to 16v/100uf
C5/C6 25v/47uf to 25v/100uf

Pre before changing caps:
06F244A5-4578-4403-A6E5-A1DE150B02BF.jpeg


Pre after changing caps:

ED997863-8D23-4E65-A660-DF7A23DD5223.jpeg

The original stock caps seem to be made by Jackcon, I have never heard of them. Reviews on the web mainly lean towards saying they are cheap/hit and miss to outright crap.

E2B9399F-06B5-40F8-8E21-C22A9CA0A6F7.jpeg

Did a couple of recordings from vinyl, used Dire Straits "Heavy Fuel" from the On Every Street LP. I prefer the sound of the upgraded caps, its not a night and day difference, but its there. There are also other components to be upgraded like resistors, transistors, metal film caps etc.

Dropbox Link, recorded at 24bit/96khz PCM/Wav format (Click to download, try not to use the dropbox player, I suspect it might compress the audio, dropbox download button should be around the top left of the screen):

New Caps

Old Caps

Keen to hear your thoughts on the differences. Also welcome opinions on the cap values used and what effect they may have on the audio.
 
J!m

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Just did a quick search of "C1740" on Mouser and did not find those... I am inclined to think TI makes a much quieter replacement 40 years later...
 
J!m

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And on the subject of transistors- with the phono preamp Wyn designed, he was able to drive noise down furthr by paralleling the op amps on the first gain stage. There might be something there, running parallel transistors in this thing... (but I'm not the right guy to design that circuit).

Do we have a schematic? Can someone put it into SPICE and tinker with it? Joe?
 
derek92994

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laatsch55 said:
Darcy, a lot of those caps zee frequency dependent except the big values I believe...
Meaning if they are not part of the power supply, and are in the signal path I wouldn't mess with the UF number...
Click to expand...
Good advice, thanks Lee. When I order high end caps, will stick to original values except the power cap which has been boosted from 100uf to 470uf. Always Learning!
 
laatsch55

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Coolness....
Joe could tell us if any other of the electros were involved in the power supply, I certainly can't...
 
derek92994

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Ok, so far cap grade can be improved and power cap boosted.
I assume 2SC1740 can be replaced with the low noise version.
What about the brown looking cap things in C9 and C12? (47pf), what voltage are they? Can they be replaced with Wima Caps? I might just have some.
In terms of resistors, should they ALL be upgraded to metal film or just the ones in the audio path? in this case there is just 2 of those.
 
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