Aleph 5 hum...

[glaieuldeboua]

Hello there,

I just finished to build an Aleph 5 and I need some help…

Everything is fine with the amp. Sound is wonderful: deep bass and nice high. The pre-amp is the balanced Zen. But there is a hum… on both sides. I have tried the amp with a Daniel II from Curcio. Hum is still there. And the hum is still present with no input wire connected…

The difference between my Aleph and the “official” Aleph 5 are these:

First, I used one transfo (toroid, 700 VA), only one diode bridge, two banks of capacitors with the Center Tap of the transformer to the ground. The ground is a star ground, though I did not use the thermistor between the chassis and the ground. By the way, the ground from mains is not connected to the chassis. I did not use thermistor for inrush current management as I did not find the proper one. And last, I did not use the inductors in the power supply.

I guess that is it. Every connection was checked and is OK and as I said, the amp operates very correctly.

Would you have an idea as to where I should look for eliminating the hum?

Many thanks for your help. guys

Gilles

[Zen Mod]

and how big caps you have there?

[glaieuldeboua]

Hi Zenmod,

Caps are 22,000 mfd at 63 volts. I have 8 of them on each of the two cap banks.

This seems to be according to specs from Kristijan.

Thanks.

[cviller]

Do you have a fuse on the mains?

Does the hum go to 50% when you only power one of the channels from the psu?

Do you have a scope?

[glaieuldeboua]

Yes, I have a fuse on the main (5 amp slo blo).

Hum is constant.

Yes, I have a scope.

Ripple on PSU is about 150 mv.

It seems that the ripple is passed on the FET gates.

[Zen Mod]

Originally posted by glaieuldeboua
Yes, I have a fuse on the main (5 amp slo blo).

Hum is constant.

Yes, I have a scope.

Ripple on PSU is about 150 mv.

It seems that the ripple is passed on the FET gates.

are all voltages on pcbs in expected range?

if yes- try different ground wiring scheme

[cviller]

Originally posted by glaieuldeboua
Hum is constant.

If you say the hum is the same when only running one channel, I think you have a ground loop problem. If it was a psu rejection problem, you should be able to hear or measure an improvement with half the load on the psu...

Yes, I have a scope.

What is the frequency and amplitude of the hum?

It seems that the ripple is passed on the FET gates.

Input fets?

Could you take some pictures or make a diagram on your wiring?

[Nelson Pass]

Originally posted by cviller
If you say the hum is the same when only running one channel, I think you have a ground loop problem.

Bingo. It's a grounding layout issue - the power transformer is
inducing current in the external ground connection.

[vitalstates]

Not sure this is relevent but I just picked this up on another forum.

Toroids sometimes induce hum if the exit wires are oriented towards parts of the circuit. Twisting them a few degrees can reduce the hum.

Apologies if this is a bit naive but I've only recently come to this solid state/toroidal malarky.

Regards

Ed

[Nelson Pass]

That will help, but it is equally important to arrange your input
and other grounding so that they experience exactly the same
magnetic field, and towards that end, you want to avoid
surface area (the interior of any conductor loop) in your separate
ground wires. Most often the practical way is to wire your
RCA grounds together at the connectors and use that spot for
a signal star ground, and running a wire from there to the
main supply ground.