oneplustwo Aleph X build thread

[dimkasta]

Holly crap.... that thing looks amazingly huge
Can you throw something in there for size reference? Like a CD or something?

[oneplustwo]

Yes, it is. See post #41 for reference: oneplustwo Aleph X build thread

[oneplustwo]

A few more pics in progress.

MOSFETs mounted on the heat sink and daughter board:


Soldering the wires was a pain. The holes in the board are way too big for the 14GA wire I'm using.

Similar issue with the main board:


Rough layout of where things will go. I ended up mounting the PSU board on the heat sink itself to get it out of the way.


QUESTION: My transformers have 4 secondaries where I only need 2. I believe I'm supposed to just wire 2 pairs in parallel to the PSU board, correct? The wires are also super beefy, at least 12GA... I'm going to have to solder the pairs together and down gauge to get them to fit in the board.

[gl]

I assume from your post that the secondaries are all the same voltage and that two secondaries will supply sufficient current for the amplifier.

Even if that's the case I would use the other two secondaries as well. The only reasonable way to do this is to use a separate rectifier bridge (or bridges) for the two extra windings and parallel these with the outputs of the existing bridge or bridges.

Don't parallel the secondaries directly.

Graeme

[oneplustwo]

Hmm, I had not considered not being able to parallel the secondaries. If that's the case, then did my 800VA transformers just become 400VA? If I do parallel, do bad things happen or is it just not "kosher?" I suppose worst case scenario I can do exactly as you say and add another set of rectifiers. Just makes it more complicated than I was hoping for.

[6L6]

Your transformers are Antek AN-8420, yes?

I think you can just parallel 2 pair of the secondaries to make 20v+20v at 800VA

[oneplustwo]

Yes, I have two of the 8420's. After doing a little google searching, my understanding is that the VA ratings are based on making sure you don't have so much power as to saturate the core and also making sure the wires are heavy enough to handle the current. I suppose resulting temperature rise is another factor to consider.

So I think I'll just go ahead and use two of the secondary pairs and leave the other two alone. Just cover up the ends with some shrink and tuck them away somewhere.

[oneplustwo]

Ok... I'm almost to the point of first power on. So far, I've just checked both of the PSU. They output +/- 27VDC without any load as expected. (They are CRC with CL-60 thermistors on each primary winding and 5 1R resistors paralleled for the 'R'.)

I've double checked the wiring and triple checked the polarity of the PSU connections. Now, just need to check once more. Or maybe sleep on it and then check again. Then... I'll use my new Variac to dial up some juice. I figure I'll get to +/- 10V PSU rails and make sure nothing smokes.

QUESTION: Any reco on input caps? I had forgotten to get these so I'm looking for a range of what's acceptable so I can raid my parts bin for something that can get me by for the short term at least.

EDIT: Looks like I have exactly (4) 4.7uF Dayton Audio caps left over from an old crossover. We're in business...

[oneplustwo]

I couldn't wait... took the plunge and powered up! Both amps were turned up to 10VDC first with the Variac to see how things were shaking out. No smoke. No smells. No sounds. Whew! Checked source resistors and got a very consistent 0.5V throughout.

Time to go to 110VAC!!!

Checked the following:
- Rechecked source resistors and got the same result, dropped off slightly as things warmed up. Whew!
- Absolute DC offset was about 10.7V. In the normal range. Whew!
- Relative DC offset was zero but no inputs connected so I didn't expect anything here. Whew!

At this point, I powered down as I didn't want to push my luck. Also, I wanted to try the other channel to replicate what I had just done. Basically the same result.

However... on the first one, I noticed the rectifier heat sinks (MUR1520) were getting really really hot. And on the second one, I noticed a tiny bit of smoke from them. Not sure if that's just my greasy finger residue burning off or not. In any case, I'm wondering if I need to rethink the rectifiers. I thought the 15A rating for these would be good enough. And maybe I just need to go back and apply thermal grease to them. The heat sinks they're mounted to aren't much but perhaps the thermal grease will make a big enough difference to cool them down.

Would welcome any thoughts!

[AudioSan]

rethink your rectifiers get som 30A or higher and mount tham on the big bottom plate, if it's alu.