Power rating Aleph 2 and a few other questions

[mrchecker]

Hello everyone,

I'm currently planning on building the Aleph 2.

1. The 'problem' is, that I found different values for the output wattage of the amplifier. 100W continuous RMS @ 8 Ohms seems to be clear, but for 4 Ohms the service manual says 160W RMS, the user manual says 200W RMS aswell as a 400W peaks. So what is the real value?

2. Since I'm using the B1-pre, I will need more than the 26dB gain using the unbalanced input and shortened GND and minus-pin of the XLR-jack. So I thought about changing R2, R3 and R5 to 4,7k. If I'm not mistaken, that would push the gain up to ~32dB, if I'm not mistaken Might there occur any problems when doing this? And will the input impedance be affected?

3. The B1 version I'm using is the one with symmetric power supply and no coupling caps. Will I have to use coupling caps, or does C5 act as a coupling cap? (I guess so)

4. Will two 0,31K/W heat sinks be enough for the gain and the contant current stage? How much power do they exactly dissipate. The second option would be two 0,2K/W heat sinks, they would definitly be good enough, right? I just ask because I'm quite stingy and could save a few bucks there


Thanks a lot in advance,

Thomas

PS: The component identifiers are from the original Pass service manual

[Bill Fuss]

Hi Thomas,

I'll answer a couple of your questions as best I can.

Two .2K/W sinks per ch would barely be enough, depending on the actual rating and how it was determined. There are big differences depending on what ambient temp was used. There's a good tutorial on the Conrad website.

Each channel will dissipate 300 watts or so.

4 ohm power will depend on the actual AC current gain and bias current, and both can be adjusted somewhat.

Do you really need that much power? If you do the B1 is not a good choice.

You might want to change the front end to the A60 front end.

Aleph 2s are monsters, don't be stingy with anything.

[mrchecker]

Hi Bill,
thanks a lot for your reply. I'll use the 0.2K/W heat sinks then. Un fortunately I won't be able to find out how exactly this value was measured, but 30°C above ambient should be ok..
So we've got point 4 crossed out
Concerning point 1: Do you know on which resistor values the bias current depends? I've downloaded the BrianGT layout v3 and was planning on using that.
I'd be very glad if I could stick to my B1, 'cause I really love it So if changing those resistor values I mentioned would do the trick, I'd be happy..

Best regards,
Thomas

[Bill Fuss]

It would be best for you to read the ZEN articles at PassDIY. Everything you need is there.

If you're going to copy the Aleph 2, copy it exactly, unless you know what you're doing.

I would still recommend going to the Conrad website to get a better handle on ratings.

Best, Bill

[Russellc]

Originally Posted by Bill Fuss

It would be best for you to read the ZEN articles at PassDIY. Everything you need is there.

If you're going to copy the Aleph 2, copy it exactly, unless you know what you're doing.

I would still recommend going to the Conrad website to get a better handle on ratings.

Best, Bill

That's what I'm doing, and in fact, I'm going to build a bunch of them. I have the Zen amp boards, Bride of Zen boards, BOSOZ boards, etc, so I will be building a few as well. Hopefully, I will finish with some answers for many of my questions.

Russellc