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Old 18th April 2011, 09:45 AM   #1
vivanco is offline vivanco  Italy
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Default integrated amplifier with aleph p1.7 and mini aleph

guys i need your help because I'm going crazy;I finished installing a built-in amplifier using the Aleph P1.7 preamplifier and the final mini aleph 10W; I state that the wiring is always the classic, one star point to which converge through a single thread, all the masses of the various circuits;specifically, the conductive wires connected to the star point, are from the following circuits: ground supply for the final ground supply for the preamplifier ground of the power amplifier right ground of the power amplifier left ground of the preamplifier right ground of the preamplifier left ground ALPS potentiometer everything is connected, via another conductive wires, at metal chassis, which is also connected to the earth.the signal is taken from the XLR to the preamp and connected with shielded cable, the 5K ALPS potentiometer on the output of the preamplifier is connected with twisted wires, and is connected to the amplifier through shielded cable, the shield is connected only on the amplifier;the sound is amazing, exceptional, scene, detail, smoothness, everything at the highest level, but with the volume control set more than half, you hear ringing, which increases up to the end of the volume.please help me
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Old 19th April 2011, 07:13 AM   #2
vivanco is offline vivanco  Italy
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no one can help me?
yesterday I did more testing, for example I put in short-circuit the input of the preamplifier, but unfortunately the buzz is always present;
I repeat, the buzz is perfectly correlated to volume, in fact it increases or decreases depending on the adjustment knob;
Another thing I noticed is that the 300VA transformer, emits a low buzzing and sound that I hear this buzzing sound from the speakers is amplified, as if picking up the preamp,,, my inference from the fact that if you exclude the preamplifier The two power amplifiers are noiseless.
Give me a hand please.
forgot
trimmer 2K in the preamplifier, which is necessary to set the gain, is set to 221 ohms, while the input, I have not mounted dipswitch, simulating all to off.

Gianni
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Old 19th April 2011, 07:58 AM   #3
hates ground loops
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Okay, first, as alway, we need pictures.

Then, if you have apprpriate wires and screw terminals (morsetto isolante most likely), remove the transformer from the chassis and wire it up by extednding the leads. If the hum goes away it was really the preamp-section picking up the stray magnetic field. If not, it may be a groundloop, even though it's unlikely when you're using a star ground scheme.
Did you use a thermistor (CL60) to make the connection between the circuit ground to earth ground (like in the Firstwatt amplifiers) or is it made directly?
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Old 19th April 2011, 10:25 AM   #4
vivanco is offline vivanco  Italy
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Originally Posted by Rodeodave View Post
Okay, first, as alway, we need pictures.

Then, if you have apprpriate wires and screw terminals (morsetto isolante most likely), remove the transformer from the chassis and wire it up by extednding the leads. If the hum goes away it was really the preamp-section picking up the stray magnetic field. If not, it may be a groundloop, even though it's unlikely when you're using a star ground scheme.
Did you use a thermistor (CL60) to make the connection between the circuit ground to earth ground (like in the Firstwatt amplifiers) or is it made directly?
Rodeodave thanks!
Indeed it is precisely the evidence he will do tonight when I get home, that is, move the transformer outside of the case, hoping that he is really the cause of the problem.
no, I did not use the thermistor to be connected to earth, but I do not think that could affect the presence of the hum.
At first I thought the buzz was generated by the fact that the 5K potentiometer is used instead of 1K (as required by the project), but then I changed his mind, because after connecting a resistor to 1,3K in parallel to the potentiometer, just get a decrease of noise and not its elimination.
I do not know which way to turn.

Gianni
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Old 19th April 2011, 10:49 AM   #5
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One way to tackle ground loop hums is to make a few cables with aligator clips on both ends, then use those to connect earths together and see which way is the quiet one.
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Old 19th April 2011, 12:19 PM   #6
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There are of course the usual suspects...such as:
Are the RCA/XLR sockets isolated from the chassis?
Are wires running parallel instead of crossing at right angles (especially PSU wiring and singal-carrying wires)?
Do you transport the ground connections from the sockets to the circuit? You say something about twisted pair+shield, does this mean signal+ground+shield? Are you running you mini Aleph balanced?
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Old 19th April 2011, 02:16 PM   #7
vivanco is offline vivanco  Italy
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Quote:
Originally Posted by Rodeodave View Post
There are of course the usual suspects...such as:
Are the RCA/XLR sockets isolated from the chassis?
Are wires running parallel instead of crossing at right angles (especially PSU wiring and singal-carrying wires)?
Do you transport the ground connections from the sockets to the circuit? You say something about twisted pair+shield, does this mean signal+ground+shield? Are you running you mini Aleph balanced?
the XLR jacks are isolated from the frame;
they are interconnected with the circuit of the preamplifier via two cables pole shielded Asthe balanced configuration is used;
the question that I / we ask is,,, but a balanced system should be immune from this kind of problems external interference, because mine does not have this behavior? it may be a problem depending on the preamp circuit?
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Old 19th April 2011, 02:29 PM   #8
vivanco is offline vivanco  Italy
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Originally Posted by digits View Post
One way to tackle ground loop hums is to make a few cables with aligator clips on both ends, then use those to connect earths together and see which way is the quiet one.
I just used this system to perform my tests, that the alligator clips, I repeat do not think I have problems with ground loops, because I made the correct connection, namely:
- a wire connected between the preamp board and the star point
- a wire connected between the ground pin of the potentiometer and the star point
- a wire connected between the mass power supply for the preamp and the star point
- a wire connected between the mass power supply for the two power amplifiers and the star point
- a wire connected between the mass of the power amplifier A and point star
- a wire connected between the mass of the power amplifier B and point star
- a wire connected between the point star and chassis
- a wire connected between the earth and chassis

it seems incredible, but the feeling is that the preamplifier noise captures and sends it to the final power amplifier


Gianni
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Old 19th April 2011, 03:22 PM   #9
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Quote:
Originally Posted by vivanco View Post
I repeat, the buzz is perfectly correlated to volume, in fact it increases or decreases depending on the adjustment knob;

Gianni
Gianni--you mentioned a "key point" in one of your earlier posts (above),since the buzz (hum) varies with the setting of your volume control, you ought to look for causes in the pre-amp (and the circuits between your inputs and the volume pot).

If you have a scope (or can borrow one), it would be good to short your pre-amp inputs, and trace the signal path in the pre-amp with the scope. I'd do the same with your power leads (and grounds) going into your pre-amp. Somewhere along that path, leading to the volume control, you should find the source of your hum.
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Old 19th April 2011, 04:16 PM   #10
vivanco is offline vivanco  Italy
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Originally Posted by CanAm Man View Post
Gianni--you mentioned a "key point" in one of your earlier posts (above),since the buzz (hum) varies with the setting of your volume control, you ought to look for causes in the pre-amp (and the circuits between your inputs and the volume pot).

If you have a scope (or can borrow one), it would be good to short your pre-amp inputs, and trace the signal path in the pre-amp with the scope. I'd do the same with your power leads (and grounds) going into your pre-amp. Somewhere along that path, leading to the volume control, you should find the source of your hum.
with my oscilloscope, I was able to verify that the two power sources, namely for the final section and the preamp are clean, free of ripple, just the first 18V + / 0 / - 18V and the second 0 - 60 V;
I tried also the input of the preamp and I have no problem, while it is on the potentiometer,,,,, now you teach me that I can not test it on the circuit, because it is a balanced circuitry, just insert the probe behavior varies his pleasure.
among other things, being made with the preamplifier KK-PCB using all of Dale 1% resistors, capacitors, Vishay and Vishay MOSFET, I do not think there is any error in the implementation, because the sound is fantastic
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