Well, wrote this somewhere else. After 5 minutes my hissing noise diappears and becomes an ultra low level high tone(4kc).
The electronic transf. uses a 40kc cycle rectified by schottky diodes.
When I measure on the plug on the amp1b pcb on the + and- supply line i see a 3mc disturbance in the noise at about 200mv.
If I put 2 off 470uf FC Panasonic caps on the supply lines at the plug my amp becomes very silent. Not completely but on high efficiency boxes there is a kind of whistle left. Would never have found this without a scope. When you put the probe on the psu pcb the lines are very clean but the wire from psu pcb to amp1b pcb is an inductance so 3mc is easy to be there. It also shows the caps delivered with the amp are bad ones. Will change them for FC's and test again.
The electronic transf. uses a 40kc cycle rectified by schottky diodes.
When I measure on the plug on the amp1b pcb on the + and- supply line i see a 3mc disturbance in the noise at about 200mv.
If I put 2 off 470uf FC Panasonic caps on the supply lines at the plug my amp becomes very silent. Not completely but on high efficiency boxes there is a kind of whistle left. Would never have found this without a scope. When you put the probe on the psu pcb the lines are very clean but the wire from psu pcb to amp1b pcb is an inductance so 3mc is easy to be there. It also shows the caps delivered with the amp are bad ones. Will change them for FC's and test again.
An externally hosted image should be here but it was not working when we last tested it.
changing the caps for low esr 680uf/35V ones improves the noise but I am left with the 4kc tone, which is very soft on volume but hearable on efficient speakers. Has to do with earthing.
Hi Bgt, this was stolen from the 41.hz forums.......
That would be the 100uf 35v C34 hes speaking of. I wonder if 1000uf would be overkill. I have some Panasonic FC 1000uf 16v caps I would like to try. I know the original is a 35v cap, but I don't see the problem of using a 16v cap instead.
The "tone" from my AMP1-B's isn't half as loud as the hiss. I'm going to try lowering the modulator gain and see if it helps the hiss issue any. I already know its set way to high for my rail voltage, but I'm not sure if thats a real issue for anything but clipping.
That would be the 100uf 35v C34 hes speaking of. I wonder if 1000uf would be overkill. I have some Panasonic FC 1000uf 16v caps I would like to try. I know the original is a 35v cap, but I don't see the problem of using a 16v cap instead.
The "tone" from my AMP1-B's isn't half as loud as the hiss. I'm going to try lowering the modulator gain and see if it helps the hiss issue any. I already know its set way to high for my rail voltage, but I'm not sure if thats a real issue for anything but clipping.
I did, no change. Changed it for a low esr 100uf/35V cap. Will try a higher value. I found out it nearly disappears if you change the earthing of the unit. But than it has more humm.
When I connect my supply ground to earth ground I don't get any change in sound good or bad. I'm using SMPS though so there's no trafo hum that can find its way to my speakers.
theAnonymous1 said:
Ok, cured it. Put a 1000uf/25V FC capicitor there and the whistle is gone. Cured the hiss with a 10uF MKT cap. on the PSU + and 0V where the power lines enter the PCB. It is now very quiet. Earthing remained the same...no humm.
Now for a test I exchanged the Amp1B for a stereo UCD180AD system and switched it on. I think I have to sit in the speaker to hear a tiny bit of hiss. Remarkable.
Tried this all out with a very efficient dual paper cone speaker from the 80's.
I am happy how it is now. Now snubberizing it a bit.
Thanx for the tip😀
Mine is also a kind of switched supply. I have to use schottky's because of the 40kc where the 50Hz sinus is made off. Tried it with normal bridge rectifiers, well forget it. The nice thing of this PSU is the low crest factor, the mains input is rectified and than smoothened(how do you write this?) with some 0,5uF MKT caps. It has hardly any input current.
Wow, I looked for some 10uf MKT caps on the net and their not cheap. I need three of them @ $7 each. Think any other type of cap would work?
Well, I got rid of the "tone" with a 1000uf cap as did you Bgt, but I can't get rid of the hiss. Lowering the modulator gain had no effect. I tried bypassing the the power coming into the board with every kind and size of cap I have available to me and it made no difference.
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