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traw 21st November 2006 03:55 AM

p17 power supply
Finally putting togeth aleph p17 pre using veteran's boards from early this year.

Testing the supply (, i'm getting 75 volts out using a 57 vac in. I thought it was supposed to be around 60? What am i not accounting for?

Never can find conclusive answer, how much current is needed? Using a 57vct, 270va right now but could drop down to a 100va or so, 55vct.

zei 21st November 2006 08:21 AM

Maybe it is because there is no load ?

And 100VA will do just fine. that i,m shure of :)

steenoe 21st November 2006 09:21 AM

The psu on the schematic you linked to, should put out 60 volts.
Sounds like your zener-string is not working properly. Did you use 7 pcs of 9.1V Zeners? Are they connected correctly?


traw 22nd November 2006 02:10 AM

think i found problem, will know soon (have few more things soldering now). had a zener in D5 instead of std diode. Had check the zener ladder making sure each volt ~ 9 volt more and it was then saw the error.

ahhh.... hope to hear it tonight

wayne325 23rd November 2006 08:49 PM

that would do it....

wayne325 23rd November 2006 08:52 PM

...and actually 30 VA will work just fine also. That's what I have - 30 VA,
one per channel. The amp only uses 6W per channel if I remember
correctly. I put a truckload of caps in there also... and a film cap or two
right on the rails of the amps. It is nice and quiet.

traw 28th November 2006 06:44 AM

got it up and running... trying to find the right setup , switches on input side on veterans boards, that add/remove 3.32 shunt to ground and add/remove 10k serial resistance. one setting gave me horrible buzz...

Also then trying to tweak the 2k pot, seems best when lowest.

But, then after about 15 minutes, get white noise on one of the channels. wonder if i have a faint solder bridge or cold joint. Or is that a bad fet? found that one of my fets wasn't insulated properly after having already powered on. I used a chunk of aluminum bar stock as a sink for the 4 610's and 2 9610's - that is one thing making this iteration of veterans board tricky.

So.... any ideas on the whitenoise after a few minutes ? Gotta sit down and unmount to check underside of board then if nothing there, guess i'll swap out the 2 fets (1 610 and 1 9610) that were commoned to the heat sink.

Planning on using 10k pot on the input side... zero out the 10k series input resistance then?

zei 28th November 2006 07:24 AM

I,m using a 10k Alps pot on the input, Works just fine.

Also for me it do not matter if i turn the 2k trimpots fully clockwis or anticlockwise, the "only" thing changing is the Gain (of course)
Sound is good any way.

The dipswitches i have,nt even tried yet.. :)

So, you might be right that you have a faulty Fet ..

Best of luck!!


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