A few Aleph 5 questions...

[PolishedSteel]

Hello, after assembling the major part of my Aleph5 on BrianGT's boards, I still have some (newbie as usual) questions on my mind:

First of all, for the PSU I'm considering to buy one of the top transformers from Schuro.de with an output rating of 800VA - unfortunately, the lowest output voltage they have to offer for this VA class is 2x35V AC. Will I run into problems with this high voltage (original schematics ask for 34V DC, which may equal 28V AC), or is it just a thing of a few more watts of heat output (which I'm not too scared of, since this baby is gonna be watercooled using a car radiator plus the dual 25cm fans that came with it, sitting in the next room/garage), or will this push any components to their limits?

Also, I would originally have been considering some 40V rated electrolytics for the PSU filtering, since they are rather inexpensive at Schuro.de as well (47mF BC/Philips caps for €11 a piece), but with such a high secondary voltage, I would very much be asking for disaster, wouldn't I? How tolerant of voltages around and slightly above their rated voltage are electrolytics in general?

Then I have a question regarding the mosfets. I've already matched those IRF9610/SFP9610s to 10mV, and I soldered them in. Now I have a bad feeling concerning the actual soldering process, as I fear I might have run them too hot. Is there any simple way to test their functionality while they are installed to the circuit? Excuse me, this is probably a very simple and wellknown thing, I just couldn't find the answer anywhere.

And another one regarding the 1-Ohm Resistors sitting next to the output Mosfets' - I got some 2W rated Metalfilms left, but I think this power rating might be a bit conservative - what is your experience one the power requirements of those?


Best regards and thanks a lot!

Christian

[PolishedSteel]

Oh, and another question I have had on my mind for a long time:

How much sense does it make to add smaller bypass capacitors to the large smoothing capacitors in the PSU? I mean, it would probably be an improvement to use only expensive Slitfoils or T-Net capacitors, but would it make sense to add only one of those $$$-devices to a less expensive array of decent quality electrolytics?

Thanks again,

Christian

[Nelson Pass]

The transistors will work, or they won't. Don't worry about
it until they don't work. It's easy enough to add more
capacitance of various sorts in parallel, and at worst it is not
likely to degrade the sound.

[jh6you]

Originally posted by PolishedSteel

And another one regarding the 1-Ohm Resistors sitting next to the output Mosfets' - I got some 2W rated Metalfilms left . . .

Originally posted by PolishedSteel

How much sense does it make to add smaller bypass capacitors to the large smoothing capacitors in the PSU?

I have never built this amp.
Nevertheless, the original circuit seems to apply the Q bias of 0.5A per MOSFET so that the minimum power rating of the source resistor is to be of 0.5A*0.5A*1ohm = 0.25W. Even if the bias is doubled, the minimum power rating would not go up more than 1*1*1 = 1W. The 2W rating is considered useful. If it burns off, just replace them with higher rating. It is not too late.

I think that there are too many mis-leading information about the effect of the bypass caps. Yeah . . . the bypass caps would be not harmful, at least . . .

[Gooch]

Hi Christian

Please post some pictures when you’re done with your amp. I just received my PCB's from Brian last week I am putting to together a parts list. It seem the hardest part is going to be getting the right heat sinks.

Regards

Dave

[PolishedSteel]

Well, I can of course take some pictures... But it's going to take me a while until I'm done, my monthly budget for the amp is about €100, so I hope I'll have it finished before my new attempt at university starts (October). I'll attach a picture of what I've got so far (god it's hard to take close-up photos with that camera - even at makro setting it's blurry and the flash draws huge shadows).
Now unfortunately I may not be able to help with heatsink selections, as I'm going for water cooling. The "heatsinks" I've ordered are just plain aluminium blocks (220x80x30mm body and 220x80x6mm lid for each heatsink, two in total), and I will simply (I hope that's what you call it in english) carve some cooling channels into them for the water to flow through.



Christian

[Gooch]

Nice start Christian I think I am going to order heat-sinks from Conrad and get 4 of the biggest ones they make and mount 3 devices to each heat-sink. Water cooled sounds neat can't wait to see the results of how that going to work.

Good luck keep us posted

Regards'

Dave

[traw]

Looks like a good place to ask my question about the aleph 5, within the scope of the thread...

Is using a 300VA dual 24VAC secondaries per channel enough to handle aleph5?... Have three of them, imagine could just parallel all of them up, but would be easier to dual mono it.

[Nelson Pass]

300 VA is just enough to do one channel.

[wuffwaff]

Hi Christian,

please ask Schuro if nowadays their transformers are also suited for class A amps. I´ve bought two of their 600VA´s for my Aleph 5 wich had very bad mechanical hum.

William