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First One - mosFET amplifier module

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#1,842
First One has voltage gain of +27 dB so no gain from preamp needed if CD (2 Vrms) or adequate DAC is the source. It is allways good to have buffer stage to source an amplifier's input impedance, of course if transparency is preserved followed by low distortion figures. My advice: try and compare with or without named buffers and choose the better option.
 
#1,844
I have a problem at the moment after setting up my stereo set again in my new house. The problem is "pumping" of the woofers, with "plop, plop" sound coming from the speakers... The loudspeaker cables have been changed by longer ones and from different make and AC Power Cords to the amps have been changed. All other things didn't change.

Before making final install, I have tested the set with previous LS cables and old power cords in my new house and I didn't have this problem.

When connecting one power amp to the speakers and the mains, no problems. When connecting the 2nd amp (I have 2 mono FO amps with one Hypex PS for each amp) to the other speaker and mains the problems begin. Similar behavior when connecting one amp to the pre-amp.

Is this ground loop problem? Is it oscillation? How can I solve it???

Thanks for any help.

Mark.
 
#1,847
Tried to find out what is causing the problem. First connected both amps with the loudspeakers and switched the amps on. Absolutely noise free. After that I connected the IC's to both amps and it remained silent. (both of the ic's connected to FO only) The problem occurs when I connect both of the IC's to my pre amp. Even when the pre amp is off or even when the mains cable is not connected to the pre, the problem is still there.

Andrej, you suggested the use of a input filter previously. Do you think this could cure my problem? Previously I had the same problem and at that time I could cure it by changing IC to a different one. Now I am discovering the same problem with the IC which worked fine before... (before moving house and change of LS cable and power cables)
 
#1,848
pinnocchio said:
Hi LC,

Are you still putting some efforts onto your preamp or the project is on hold?

Thanks
Do
Click to expand...

Accu powered preamp was done last October, since then it works fluently in my system, charged only few times in between. It could be released but it uses tweaked accu charger so it couldn't be reproduced in large quantities. Other parts of the circuit, PCBs, pots etc. defined. I don't expect the line level analog only preamp to be popular these days, a lot of competition out there: DACS, streamers, ... other modern stuff on the market, so it'll probably stayed as once time experiment.
 
#1,849
Mark Verhoeven said:
Tried to find out what is causing the problem. First connected both amps with the loudspeakers and switched the amps on. Absolutely noise free. After that I connected the IC's to both amps and it remained silent. (both of the ic's connected to FO only) The problem occurs when I connect both of the IC's to my pre amp. Even when the pre amp is off or even when the mains cable is not connected to the pre, the problem is still there.

Andrej, you suggested the use of a input filter previously. Do you think this could cure my problem? Previously I had the same problem and at that time I could cure it by changing IC to a different one. Now I am discovering the same problem with the IC which worked fine before... (before moving house and change of LS cable and power cables)
Click to expand...
Two options possible here: input ground loop issue or interconnect cable induced oscillations. Try to observe amp's output on the scope, measure DC resistance of interconnect cables, change their directionality (rotate them), try standard coax cable as control.
 
#1,853
hcbonfim said:
Hi LC , Do you still have the FO to sell ?
How much each one ?

cheers

hcbonfim
Click to expand...

First One modules available as explained and planned in post #1 :up:

... and counting 😎
 

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#1,856
Andrej, what is the correct procedure to calibrate DC bias? when amp is already warm/hot or when the amp was just powered on? Is the DC offset calibration should be done first or doesn't really matter?

One of my FO channel had DC offset and DC bias been adjusted a couple of times and I want to calibrate the right way. I observed that when the amp was just powered on, the DC bias start to climb up little by little. So, I'm thinking that DC bias should be done when the amp is already warm. Whats' your opinion?

Fred
 
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