WD Pre3 rebuild - different resistor or capacitor advice?

[tomtidswell]

Dear All,

Back on the forum again, as I had my first Pre3 problem (after 13+ years of continuous use), with valve rustle on one channel despite replacement valves. Strangely the problem came on after 10 minutes use (or so) and the problem not obvious from bench testing voltages on the Pre3.

In discussion with Matthew, I have purchased the updated Pre3 and PSU3 boards + components and in the process of replacement. PSU3 is now complete, tested and working fine.

Before I rebuild the Pre3 board, I would be interested to know if anyone has found using different resistors and output stage capacitor (C1/2, replacing the Soniqs SAX 0.1microF) is worthwhile. I have searched the forum and can't find reference to this previously.

Matthew has kindly sent a pack of carbon film and metal film to try out, so I do have these options, but also was looking at the AudioNote tantalum resistors (on Hi-Fi Collective website).

As a final note, before the Pre3 went, I had tested it against a ~£13k pre-amp at one of the central West London Hi-Fi shops. There was no reason to let go of the Pre3, even in standard form.

[bob orbell]

I have answered questions to the like before and your best course of action is a better PSU, power resistors by Mills bring an improvement as will Shottky diodes in the HV section and low ESR power capacitors but ultimately a regulated PSU, HT and LT will bring the out the best, by the way, carbon resistors are a anachronism, their noise and tolerance are poor, but do make useful grid stoppers. Bob

[BOONDI]

For c1/c2 you could try some russian pio or teflon types from fleabay. I think you will struggle at the sensible price range to get much better than the sax you already have. As for resistors, zfoil for anything in the signal path, but again, they are expensive. Also, my experience of ruskie postal service is slow slow slow. Im with bob re the carbons, noisy and capable of sonic mush/hiss. If you want a vintage sound then by all means use them in signal path......

[John Caswell]

I think that there is some confusion here over carbon resistors.
Matthew sent carbon film resistors (MRS25 or equivalent) which are a totally different thing to the basic homogenous carbon resistors, and are perfectly suitable for Phono 2/3. Apart from the front end resistors where I use bulk foil the rest of my Phono 3 is carbon film resistors.
I have some severe doubts over the reliability of Paper in Oil capacitors. I am finding them to be electrically leaky after some years. Not sure about the Russian PIO types but the Teflon types should be fine.
I must disagree with Bob over regulated supplies, they are not the be all and end all. My Phono PSU is valve rectified HT and SS rectified heaters. Sounds B Good to me. But as usual you pays your money.....

John

[Richard]

Hi Tom, the Soniqs caps are already the upgrade option on the standard orange drop polyesters and I like them and found them a nice balance. By all means try a different "flavour" but no-one can really tell you what's best as ears taste and systems are so different. There are small differences in sound with different capacitor and resistor types but really you've already answered your own question with that comparison at the London dealer.

The rustling however will be an electrical issue and may be from the Pre3 or PSU3. You've changed valves so after 13 years I'd change the electrolytic caps, starting with Pre3 bypass caps C2/3 in particular.

[tomtidswell]

Dear All,

Thanks for the advice.

Richard: I have replaced all caps in the PSU, put in the new (updated) board and new components (as easier than soldering de-soldered components). On the scope no visible ripple on the HT voltage when unloaded (nothing visible above 0.5V which is around 0.1%, DC offset too high to be able to assess noise less than this). A very good point about the London dealer comparison.

The next step is to replace the input HT supply cap on the Pre3 and install the new board with new components (John: thanks for pointing out the quality of the carbon resistors that Matthew sent out). Matthew prefers the carbons, so I may well go for these (if doing comparisons, I will need to ask Matthew for another board!). Agree with Boondi that new flavours of capicitors appear expensive. I'll stick with the Soniqs SAX as have lived with these for the last 13/14 years or so.

Bob - thanks for your advice about the PSU regulated supply, it may be one step too far at present as I would be keen to get the Pre3 up and running again soon (I have looked at your recommendation of the Glass-ware kit regulated supply, but may be a bit complex for me to follow).

As a final note, I was really glad Andy Grove designed the kit with the balanced output as this has been put to good use over the last year driving a second hand Audio Research 75SE - which takes balanced inputs only; the other output drives the headphone amps.

Cheers, Tom

[BOONDI]

Side note. Re noise in resistors.
https://www.google.com/url?q=https:/...eovSLCyf4tYO0P

Old pio from russia were built to survive the apocalypse. Just be sure to buy tested ones. Matched set even better. Bulk foil resistors the way to go though expensive if used indiscriminately, with no thought to the benefit they bring.

Also on the subject of caps, there is a bit of a thing on the net about bypassing output caps such as your sax with much smaller and therefore much cheaper, higher priced "Hand rolled by nymphetes in the Himalayas" types. Suggest using between 1 /20 th and 1/100 th the value you are bypassing. This is said to bring some of the flavour of the high end caps into your sound.

I have not tried it yet but I am awaiting some teflons to give it a try. Like I said, ruskie post is slow....