re post47 & attached sch
The LOOP AREA of that input circuit must be kept small. That's why I asked you to check for close coupling of the traces.
The amplifier is a differential amplifier (not balanced impedance).
It reads the (differential) voltage between the two input wires and processes that signal. That becomes the output.
Your amplifier requires the input voltage to be pure audio signal. You don't want any interference. You minimise the interference by close coupling the TWO wires all the way from Source (including it's terminals) to the TWO inputs to the power amplifier.
The TWO inputs are the Bases of the LTP. The LOOP AREA of the input circuit all the way into those TWO bases must be small.
The TWO wires from RCA are BOTH signal wires. They both must go to the amplifier. One connects to the DC blocking capacitor the other one goes to the bottom of the 200pF and that ties into the NFB loop and the other LTP base lead.
The LOOP AREA of that input circuit must be kept small. That's why I asked you to check for close coupling of the traces.
The amplifier is a differential amplifier (not balanced impedance).
It reads the (differential) voltage between the two input wires and processes that signal. That becomes the output.
Your amplifier requires the input voltage to be pure audio signal. You don't want any interference. You minimise the interference by close coupling the TWO wires all the way from Source (including it's terminals) to the TWO inputs to the power amplifier.
The TWO inputs are the Bases of the LTP. The LOOP AREA of the input circuit all the way into those TWO bases must be small.
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Would it be best to put the HBR (if needed) between the screen and the PCB track since all the "S" he labelled are connected on the board?
read D.Joffe, he shows why a multi-channel amplifier needs help in reducing interference current and where to fit HBRR/HBRL.
Adding resistance into the signal current route increases the interference in the loop!!!!!!
And your suggested relocation is the same mistake that Bonsai made in his various schematics. It took him over two years to finally remove/move the offending resistors, despite being alerted to the problem.
Adding resistance into the signal current route increases the interference in the loop!!!!!!
And your suggested relocation is the same mistake that Bonsai made in his various schematics. It took him over two years to finally remove/move the offending resistors, despite being alerted to the problem.
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OK, will do, before I get even more confused, haha....
Thanks, I get it now, Joffe's explanation and the reason are very clear
Thanks, I get it now, Joffe's explanation and the reason are very clear
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I tried all the different grounding configurations we talked about. All made the buzz slightly worse, so, I went back to the original configuration. I did some resoldering on the left FEB where I thought the traces on the top and bottom may not be connected. I checked all the resistors (now, all of the components on the left FEB board test good when the amp is cold) and rerouted the ground wires away from supply wires.
-I thought I had it beat, when I first turned on the amp, it was much quieter when plugged into the preamp. Then the amp stared to warm up and the buzz came back. I could change the buzz by moving the speaker or RCA cable or by placing my finger on the speaker output posts.
-I decided to keep it in the system for about 4 hours using it. As the amp got hotter, the buzz died down again. No more change in buzz when the speaker or RCA wires are moved and buzz did not change when I touched the speaker output posts.
-This was late at night, there were no other electrical items turning on or off in the area that could have altered EMFs (other than the LED lights in the room that increased the buzz a little when on). I ran the same test this AM with the same results.
-I'm thinking I have a defective component that is reacting differently as the amp heats up. Does this make sense?
-I'm assuming a ground issue would be there all the time and would not change as the amp heats or cools.
Any thought?
Thanks again for help, this one is tricky.
Eric M.
-I thought I had it beat, when I first turned on the amp, it was much quieter when plugged into the preamp. Then the amp stared to warm up and the buzz came back. I could change the buzz by moving the speaker or RCA cable or by placing my finger on the speaker output posts.
-I decided to keep it in the system for about 4 hours using it. As the amp got hotter, the buzz died down again. No more change in buzz when the speaker or RCA wires are moved and buzz did not change when I touched the speaker output posts.
-This was late at night, there were no other electrical items turning on or off in the area that could have altered EMFs (other than the LED lights in the room that increased the buzz a little when on). I ran the same test this AM with the same results.
-I'm thinking I have a defective component that is reacting differently as the amp heats up. Does this make sense?
-I'm assuming a ground issue would be there all the time and would not change as the amp heats or cools.
Any thought?
Thanks again for help, this one is tricky.
Eric M.
Here is something new that might shed some light.
-Amp on, both RCAs to preamp plugged in. Remove left channel RCA and the buzz goes through both channels at full power (200 watts). I was able to make this happen twice, but now it won't do it. No fuses blow, amp still plays through both channels.
Could I maybe have a faulty ground in the right channel that is causing a loop through both channels? I never went through the right channel, I just assumed if I was testing it by itself and had no issues that it was not the problem.
-Amp on, both RCAs to preamp plugged in. Remove left channel RCA and the buzz goes through both channels at full power (200 watts). I was able to make this happen twice, but now it won't do it. No fuses blow, amp still plays through both channels.
Could I maybe have a faulty ground in the right channel that is causing a loop through both channels? I never went through the right channel, I just assumed if I was testing it by itself and had no issues that it was not the problem.
This could be a bias stability issue. I'm not familiar with this amp's set up. Hopefully someone more knowledgeable will chime in.
With nothing plugged in the input can become an aerial and amplify anything it picks up without attenuation
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