K&K Audio Rakk Dac

[luvdunhill]

Marc,

The transformer I need for the Aleph clone is 2 x 55-60V secondaries (and probably something to do a 5Vdc supply off of for input selector/volume control ala Dantimax or TwistedPear, etc.). I was looking at vt4c, but only see the custom 50VA and 100VA, of which I would probably want the 100VA one. They are somewhat unclear, as they have a statement

but then provide pricing quantities of 1-3, etc. which would seem to indicate that I could order 1?

Regarding your last statement, I ran across this thread today which I found rather illuminating... particularly around the middle of it (p5 or so, p8 is interesting ).

yes, you can order just one. I've ordered 4-5 custom R-Cores from vt4c. In fact, I'm using a pair of custom R-Cores in my preamp 96 VCT @ 50VA each. It will take a month or so though, and to that point I'd hurry in order to avoid the usual delays around Chinese New Year. One thing, is they are pretty conservative on their VA ratings and for custom work they'll give you around 80% of the total theoretical VA rating to work with.

If you go the Dantimax route, look at the Standby2 for 5v out (or maybe use a rigged up e24), I'm using it to power some things as well as providing switched power, which is very convenient.

Also, there's another guy selling R-cores on Ebay, analog888 that might have something in stock you can use. He can get things custom wound as well, but I have no experience there.

[Pars]

I didn't see anything in analog888's listings, nor any offer for custom values. DIY Gene also sells R-cores on ebay:

50W R Core Transformer,115V//230V, for Preamp,DAC/R26-x - eBay (item 260307179697 end time Nov-27-08 05:34:16 PST)

R26-42 0-50-55X2

would work, although it is 50VA, which I guess would be more than enough. I had heard the same thing as you were telling me though that going up a bit on the xfrmr rating could sound better. He has some 100VA, but nothing with the right secondaries. Plus, this was the guy that was doing the clone amps (and probably still is), so I'm not sure I want to deal with him.

[Pars]

I took another look, and also checked some of the other suppliers you recommended Marc.

DIYGene has a 100VA R-core, and one of the secondary choices is:

R80-34 (30-20-0-20-30)X2(1A).0-15 X2(1A).0-9 (1A)

I would guess that the 30-20-0-20-30 windings would work as 60V windings from the ends? Or am I mistaken? Anything I would need to be concerned about as far as ground for the preamp goes, etc? I don't think so but thought I'd check.

Also, Marc, was it your impression that these R-core trannys that you have used are light on their specification (i.e., a 50VA isn't really 50VA, etc.) I got a bit confused reading your impressions of these.

Thanks,

Chris

[luvdunhill]

I took another look, and also checked some of the other suppliers you recommended Marc.

DIYGene has a 100VA R-core, and one of the secondary choices is:

R80-34 (30-20-0-20-30)X2(1A).0-15 X2(1A).0-9 (1A)

I would guess that the 30-20-0-20-30 windings would work as 60V windings from the ends? Or am I mistaken? Anything I would need to be concerned about as far as ground for the preamp goes, etc? I don't think so but thought I'd check.

Also, Marc, was it your impression that these R-core trannys that you have used are light on their specification (i.e., a 50VA isn't really 50VA, etc.) I got a bit confused reading your impressions of these.

Thanks,

Chris

Well, what I meant was if you ask for a custom transformer that is 50VA and you would like 50V @ 1A they push back and say, what about 50V @ 0.8A. I'm not sure if they are ensuring 20% headroom, or if they run conservatively. That's a good question.

As for 60VAC, yeah that will work. Just tuck the center tap and other taps out of the way somewhere. As long as you don't need to parallel the two windings, you should be fine. I'm actually having problems with an R-Core right now due to paralleling the secondaries is causing the transformer to short. I'm not sure if it's a defect or what.. I hope to get to the bottom of this tonite and will keep you posted.

[luvdunhill]

Well, what I meant was if you ask for a custom transformer that is 50VA and you would like 50V @ 1A they push back and say, what about 50V @ 0.8A. I'm not sure if they are ensuring 20% headroom, or if they run conservatively. That's a good question.

As for 60VAC, yeah that will work. Just tuck the center tap and other taps out of the way somewhere. As long as you don't need to parallel the two windings, you should be fine. I'm actually having problems with an R-Core right now due to paralleling the secondaries is causing the transformer to blow 3A fuses with nothing on the secondaries. I'm not sure if it's a defect or what.. I hope to get to the bottom of this tonite and will keep you posted.

[Pars]

Thanks Marc. I wouldn't need to parallel the secondaries, but have dual supplies, so one secondary per supply (channel). I may just use a 102VA Hammond 186F120 instead.

Regarding the transformer you are having problems with: have you tried reversing one set of secondary connections? If that doesn't do it, I don't know. Could be a defect, but I'm not the most knowledgeable on transformers either.

[luvdunhill]

Regarding the transformer you are having problems with: have you tried reversing one set of secondary connections? If that doesn't do it, I don't know. Could be a defect, but I'm not the most knowledgeable on transformers either.

yup, this is exactly what I'm going to try tonite, as well as not paralleling the secondaries. I'll try these two things with and without a 100k resistor or so to provide some sort of load. I almost didn't fuse the primary side, as I have a fuse on the power supply board... glad I decided to do this, and a reminder that this is always a good idea!

[philodox]

The output stage in my CD player is pretty near identical to the passive one on that site. Sounds good to me.