No HUM but a "twiiiiiiiiiiiiiiiiiiiiiit" in my Aleph3 - diyAudio
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Old 23rd April 2004, 12:08 PM   #1
JEKYLL is offline JEKYLL  France
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Default No HUM but a "twiiiiiiiiiiiiiiiiiiiiiit" in my Aleph3

I have a very big problem with my just finished Aleph 3.
In my speakers I hear a noise who is doing something like: twiiiIIIIIiiIIIiiiiiiiiiIIiiiit. It seems to be a high frequency parasite noise.
And what is curious is that when I move some wires, particulary the inputs wires and the power wires, the noise increase or decrease.
I forgot to say that it is the same when i disconnect the CD player and that the noise is loud.

I am sad, because the sound seems to be very good.

Am i the first who have this problem, do you have an idea of the origin of my problem?
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Old 23rd April 2004, 01:19 PM   #2
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JEKYLL,

Its oscillation... warning can do damage to final and speakers...

1)- Try to add about 100 microF at all positive and negative power supply
inputs right on the PCb at the +-25Volts arrivals.

2)- Add some 0.1 microF right on the big capacitors of the powersupply.

Regards.

Alain.
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Old 23rd April 2004, 01:40 PM   #3
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I'm posting here beaucse I'm working on email with Jekyll.
I hope he will manage to correct his problem.

So, i've got a little question. On the enter of Aleph 3 what is the voltage level needed.
Because I'm using a kit preamp giving 40dB controled gain. So i've got a signal about 100mV --> 1,5V. This is not too much?
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Old 23rd April 2004, 02:08 PM   #4
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Miles Teg,

>>On the enter of Aleph 3 what is the voltage level needed.
>>Because I'm using a kit preamp giving 40dB controled gain.
>> So i've got a signal about 100mV --> 1,5V. This is not too much?

Your preamp output is correct , less than 2 volts is perfect ;
and the Aleph gain is 20 Db.
You just have to check for the output impedance to match with the input impedance of the Aleph 3 which is 23 Kohms.

Regards.

Alain.
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Old 23rd April 2004, 02:14 PM   #5
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I've tried before your answer. It works !!!

My 1 voice aleph have emit his first sounds !

But my preamp is too much. The sound is a little bit loud for the minimum setting of the preamp.
And the sound quality is really poor. I guess a lot of cut in the signal. I need an oscilloscope...!

This is my first prototype of Aleph, mounted spread on the bench. Now i know I can create my chassis and start a better one with all the improvements I know.
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Old 24th April 2004, 01:03 PM   #6
nar is offline nar
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Miles , essaye de réduire le gain de ton préamp ( momentanément mets un pot de volume à l'entrée pour ne pas le saturer , ni saturer l'Aleph

Le voltage d'entrée est 2V pour obtenir 20V en sortie , et dans ce cas le son risque d'etre TROP FORT !

@+

Anael
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Old 24th April 2004, 01:57 PM   #7
JEKYLL is offline JEKYLL  France
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Mr Dupont, I added the capacitors like you said yesterday, but it doesn't work.
What is also curious is that when I move the wires, the frequency of the parasite sound changes.

Nobody knows what could be the origin of this phenomenon???
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Old 24th April 2004, 02:36 PM   #8
MBK is offline MBK  Singapore
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A lot of things could be the reason, starting with grounding routing (usually that leads to just hum though), interference pickup, missing/dropped ground reference of some component etc.

So... you could try to re-rout your grounding, and before that at least make sure that everything that is supposed to be connected to ground actually IS on ground (slder joints, forgotten connections). Also, both the signal ground/PCB ground , and the power ground (return from speaker), should come together only at the PSU, and not directy between the PSU caps but at some distance from the filter caps. A few mm can make a big difference in noise here, as I found out with my own Mini-Aleph.
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Old 27th April 2004, 12:06 PM   #9
JEKYLL is offline JEKYLL  France
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MBK, I controlled with an ohmmeter, and all seems ok.

All the grounds are connected on one screw isolated from the chassis, and there is only one wire who go to the ground of the power supply.

What I don't understand is that both level and frequency of that noise change when I move some wires inside the amp.

It is like if there was a transmitter and a receiver, and the wires were working like an antenna. And when I move the wires, I only change the orientation of "THE" antenna.

IS IT POSSIBLE???
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Old 27th April 2004, 12:18 PM   #10
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"All the grounds are connected on one screw isolated from the chassis"

Make sure the chassis is grounded.
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