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classalpha 5th May 2006 10:23 AM

power supply issue
hi, everyone.
i'm going to build two aleph 5. my problem is i already have a 500VA and two 300VA transformer. all of them are having 36 - 0 -36 secondary voltage. after the bridge, the DCV will be ~ 46 - 0 - 46.

quite high for the amp. So, what part of the circuit on the amp do i need to modify?


Nelson Pass 5th May 2006 06:52 PM

If you need to take the voltage down, I suggest coils in series
with the primaries on the transformers.

classalpha 1st June 2006 10:00 AM

Thanks for the advice.
Is a great honor, having your replie. Mr Nelson.

i had found a solution to my problem. The aleph 4 uses the same DC value that i have from my PS. So build a aleph 4 but with less output devices, as the trans of mine is only rated at 500VA.

Jennice 1st June 2006 10:33 AM


Originally posted by Nelson Pass
If you need to take the voltage down, I suggest coils in series
with the primaries on the transformers.

Won't that alter the impedance of the transformer (on the secondary side) considerably, compared to a number of diodes, if the voltage doesn't need to be lowered that much (general consideration)?


Nelson Pass 1st June 2006 09:05 PM

It works for the Alephs since they have a net constant draw
from the wall, so a given impedance coil will reliably lower the
voltage. This is not true of Class AB (and D) type amplifiers.

Jennice 2nd June 2006 06:56 AM

:bulb: Ahh... THAT's the catch! Class A operation.

Thanks for the feedback, Mr. Pass.

Maybe you have a good idea for my little problem (and reason for reading this thread).
I have plans about a Class D, design, where the currrent draw will obviously vary immensly.
I'd like to lower the idle (no-load) output voltage of my supply a few volts. It's rated voltage is fine for my planned class D modules,, but it's idle voltage is on the high side.
Could a simple constant current source make this controlled load (I know it's not in the line of power saving class D design, but it's not about conserving power), or do you have a better idea to avoid the "no load" condition?


jacco vermeulen 3rd June 2006 12:54 PM

What advantage is there in using a coil on the primary side, compared to a secondaries CRC arrangement ?

Kirchhoff's 1st and 2d laws, wattage in is wattage out.
In Mr Dury's words: Hit Me. (textbook slaps only)

The Scot worm remark was pretty funny,Jennice.

Jennice 3rd June 2006 03:32 PM

To Jacco:

My "Scot worm" remark?

Uhmmm-... thanks, but where, what thread **Puzzled**

jacco vermeulen 3rd June 2006 04:03 PM


Originally posted by Jennice
Really ? :clown:
Of course i believe you, here goes:

Jennice 3rd June 2006 05:56 PM


Thanks. I was confused since I didn't recall any worms in this thread, or your participation in the other thread. Thus my confusion.

I felt that AndrewT was making a lot of noise before thinking it through, and that I was verbally attacked by him without him being able to prove me wrong. He went after the player, not the ball (the subject), and I didn't feel an urge to be very polite to him. :devilr:

He also made me wonder what he was really after. He gave an example with an unknown resistor, and a "reference" of which he even described the materials and the design of the trimming method. Knowing all that, I would assume he also had data on the inductance value of this reference, which is much more obvious than finding a describtion of it's value trimming method. -- So his contribution seemed more like the result of having a bad day, than a serious contribution tio the original question: "Is it possible to find out if a resistor is non-inductive?"

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