My new mini Aleph

Hello all,

My little Aleph is up and running, and humming from the left channel. This only occurs when the rca signal cable is hooked to the amp and source, otherwise it is dead silent. The hum is independent of volume setting. The amp is single ended only and is showing very low dc offset. I have searched and read lots of posts. I’ve tried all that I can think of right now, including…

1 switch rca input cable left to right, right to left.
Result- hum stays in left channel

2 connect to a different source component
Result- hum still there

3 rotate the toroid
Result- hum still there

4 re-route ground lines in chassis (every variation I could think of) including jumper across input rca grounds w/ one wire return to star ground
Result- hum still there

5 lift earth ground (then reconnected it after test)
Result- hum still there

6 other stuff I can’t think of right now. Yup, hum still there.

Oh yeah, a little more background info. I have 3ohm resistors for R0. The pcb’s are from BrianGT. Power supply is LT1083 regulated and star grounded. The amp will live in a biamp system powering compression drivers (where any hum is really annoying).

Perhaps try a serial ground instead of the star ground?

Any other suggestions or obvious things I missed?

Thanks in advance,
PSz.
:)
 

PSz.

Member
2003-07-18 4:17 am
California
20 and 30 millivolts.

the shielded wire I just put in for the inputs helped, but the left channel is still humming. I have been reading up on toroid shielding, but my hum is low frequency (120Hz ?) and the shields I am reading about don't block those too well...

perhaps I am just being too picky about all this... every other amp I have built is run on batteries, and after all my hum (through horns) requires a silent room or an ear on the horn mouth to hear it.

am I being unreasonable?

I just have the impression that because the amp is silent when not connected to a source, that I should be able to get it to that level when a source is connected...

regards,
PSz.
 

PSz.

Member
2003-07-18 4:17 am
California
I haven't tried that yet. I'll have to try in the morning because my wife is watching TV right now with that amp in the system. I just don't understand how a bad ground could have eluded me all day today. I've tried everything I can think of including the series ground. Nothing has helped except the shielded wire.

Could it be the transformer coupling such a low frequency into the circuit?

regards,
PSz.
 

Netlist

Ex-Moderator
2003-01-18 9:50 am
I don't think it's the transformer because you said the amp is quiet with no input.
The idea of shorting the input is to make sure your input ground is well connected. If the amp still hums with shorted input the problem could be the female RCA connector or it's ground and grounding wire.

/Hugo
 

PSz.

Member
2003-07-18 4:17 am
California
I just realized that I have neglected to give any impressions of how this little wonder sounds.

It's running on 13.8 volt regulated rails. Two IRFP044 output devices per channel. Caddock MK132 resistors. Cerafine 220uF caps except the Black Gate nonpolar feedback cap. It is built inside a Hafler DH120 chassis.

Back to the sound...
This little amp is INCREDIBLE. :cool:
I have heard detailed amps, and warm smooth amps. But somehow I have never experienced both together like this before. Tube or solid state.

During full range testing I was not disappointed by the bass as I had begun to expect.

I found that my heart would match time with the music being played! That is involvement! (or a serious medical problem);)

more later,
PSz.
 
Ummmm....:xeye:

Now my humming mini aleph doesn't hum when the inputs are shorted!

However, it still hums whenever ANY source or combination thereof is connected to it. But it is dead silent with no source connected. So I've been reading everything I can get my hands on, thinking, meditating...

Then I came across this www.raleighaudio.com/chapter_3.htm page and it got really interesting starting with

"The cause of the buzz was harder to find. At first I thought that I had a ground problem, "

Now I have to ask (sheepishly) if having my gate stopper resistors too far from the mosfets could cause LOW frequency hum/oscillation only when connected to a source. The leads are currently 2 inches long on the left channel and 4 inches on the right.

I haven't smoked my compression drivers yet. And they are connected directly to the amp in an actively crossed system so I don't know if it is oscillation.

Oh , I don't have a scope. So if any one in the SF Bay area has a scope and is interested I would be forever grateful for help troubleshooting.

any thoughts on the gate stoppers?

much thanks,
PSz.
 
Update:

I went ahead and relocated the gate resistors at the same time that I changed over to to-3 output devices. The amp takes much longer to warm up now, so I assume it was oscillating before.

However, there is still some humming. I think I'm getting very picky now because the hum is below the noise floor of most recordings. I pulled a Bryston amp out of my mothball fleet and it is much noisier than the lil' Aleph. But I will continue searching for ways to make it quieter. All suggestions are welcome.

regards,
PSz.
 
Here is a quick picture. Hope it's not too big to attach...
 

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BillWW

Member
2005-01-29 5:52 am
aleph hum problem

I am also using 110 plus Db/w compression drivers and found using a single transformer causes hum.

High efficiency speakers pick up the slightest hums or noises very easy. A conventional speaker would not notice these minor hums.

I ended up going dual mono power toroids and that seemed to isolate the ground loop that you have.

I also isolated the common rail ground with a bridge rectifier. I ran channel 1 toroid to the 1 ac side and the other channel 2 to the other ac leg and grounded the plus and minus to the chassis and ac outlet ground. So far that seems to keep the ground loop isolated. I do not know if you could isolate your grounds with only one toroid, so that was why I ended up using a second one to get rid of that annoying hum.

I was still getting some noises, which I believe were from my star ground being tapped too close to the capacitor bank, so I am experimenting with moving my star ground away from the capacitor bank.

Good luck!
 
Try this tip from Leach's site:

If you are sure that the hum is due to an internal ground loop, the procedure for breaking this loop is as follows:

Turn the amplifier off and wait for the power supply to discharge. Do not perform this procedure with the amplifier on.
Cut the wire to the central ground on the input side of one circuit board.
Solder a short circuit jumper wire between the ground lugs on the two input jacks.
The circuit board with the cut ground wire is now grounded back through its input ground lead to the ground of the other circuit board. Use an ohmmeter to verify the new ground connection before turning the amp back on.

Worked for me.

Blessings, Terry