Transformer for Aleph 30 Build Peter Daniel's Boards

[eeyore]

Hi, I have search far and wide on this forum, and would like those who have gone before me to comment on whether a 300VA 18Vx2 transformer will be suitable for the Aleph 30 build, using Peter Daniel's boards. From all that I have read, it is suitable, but just barely. It seems people favour 400VA plus for a stereo implementation.

But from my research, each Aleph 30 channels drawings around 1.5A quiescent current, with the devices biased around 0.8A each (with R13 at 47k5???). At +/-25V, the idle dissipation would be around 60W per channel. So the total would be 120W. Allowing for losses in the PSU, etc, the standing requirement is 130W, or 130VA. There should be enough headroom in a 300VA to power both channels right?

Or have I missed something completely?

[Bill Fuss]

You apparently have the service manual and there is some conflicting info in there. You can pretty much count on 200 watts constant load so a 400VA trafo would be wise.

Are you sure you are referring to the A30 and not the A3? The 30 uses 6 fets per channel and biases around 2 amps per channel. The bias can be lowered some by lowering R13.

Best, Bill

[eeyore]

Sounds like it'd be cheaper for me to buy another 300VA and go dual mono... since I have the extra PCB and the caps already...

[Bill Fuss]

That's a good option. Another is building the A30 with only 4 fets per channel like the A3 but that depends on your speaker requirements. If you have reasonably efficient 8 ohm spkrs the A3 would do if you don't need all the watts.

[eeyore]

Sounds like an idea, to reduce the fets to 2 per channel. My speakers are generally 92 db+, which the exception of one which are the Jordans at around 89 dB... 20W might be enough, but then again, for the cost of the extra transformer around AU$60...