Question.
Is it normal to have the p3a running hot with no signal? I have set the bias to the recomended value by putting my voltage meter across the two .47 ohm resisters and set it to 94mv. That is what I believe Elliot recomended. I have a decent heat sink and have used thermal grease. I can replace the heat sink with a bigger one I just find it funny that it would get so hot with no signal.
Thanks a lot.
Ted Polzin
Is it normal to have the p3a running hot with no signal? I have set the bias to the recomended value by putting my voltage meter across the two .47 ohm resisters and set it to 94mv. That is what I believe Elliot recomended. I have a decent heat sink and have used thermal grease. I can replace the heat sink with a bigger one I just find it funny that it would get so hot with no signal.
Thanks a lot.
Ted Polzin
i've just finish building 2 sets of P3A last month on my test boards. even being pushed to 120 to 150mV, this amps won't go anywhere near hot with LOUD music.
but this will depends on how much voltage you are feeding to the amp and the size of your heatsink. any picture? or how about more info on you amp?
but this will depends on how much voltage you are feeding to the amp and the size of your heatsink. any picture? or how about more info on you amp?
Mine stays cold, and gets only warm after hours of continious play. Whats the size of the heatsinks ?
Any chance you have 0.940 volts instead of 0.094 across the collector resistors? This would certainly account for the heat. My p3a barely puts off any heat at idle. I don't think the size of the heatsink is much of an issue at idle.
- Rory
- Rory
After going over the amps the only problem I can find that is consistant is, due to a math error, c+ c- and c7 are all 10Nf instead of 100nf. Would that make a big diffrence? I am also seeing quite a bit in instability.
Thanks
Ted
Thanks
Ted
Ted,
What do you mean by "signs of instability"? Have you tried putting a signal through the amp yet? Aside from the excessive heat, does it seem to be working otherwise?
I don't think that 10nF C+ and C- would cause a problem, but C7 might be a different story. The easiest way to find out would be to replace them with the specfified value and see if that fixes the problem. Maybe someone more knowledgeable than myself can comment on the effect of C7.
- Rory
What do you mean by "signs of instability"? Have you tried putting a signal through the amp yet? Aside from the excessive heat, does it seem to be working otherwise?
I don't think that 10nF C+ and C- would cause a problem, but C7 might be a different story. The easiest way to find out would be to replace them with the specfified value and see if that fixes the problem. Maybe someone more knowledgeable than myself can comment on the effect of C7.
- Rory
Actually I had two extra boards for another set of amps I want to build at a later date. I built them now paying very close attention to all the values. It works perfectly now. I now am having more problems with ground loops than anything else. I'm waiting for a few more days for my project 33 boards to come in before I hook up my good speakers. I have some old crap speakers to test with for now.
As far as my ground loop. I can hook up my front left and center from my amp no problem. As long as they are to separate amp boards (each board has two amps) then the ground loop is very small. When I hook up an extra channel (example front right) to the second channel of a amp board I get a ground loop that is quite loud. Any ideas? I can post a picture of my amp later today when I get home. I am using stock ESP boards. I have seperated the power to each amp by cuting the +- power traces. I did not cut the ground trace on the boards.
It is all but silent when I have no signal coming to it or just a signal to each separate amp board.
Thanks a lot for all your help.
Ted
P.S signs of instability means, on my oscilloscope, when I drive the amp hardish (not really hard just a single tone coming though) I get distortion on the signal. When not driven hardish I get a perfect signal. I plan on going back to the original boards and playing with them later after I get this amp working well.
As far as my ground loop. I can hook up my front left and center from my amp no problem. As long as they are to separate amp boards (each board has two amps) then the ground loop is very small. When I hook up an extra channel (example front right) to the second channel of a amp board I get a ground loop that is quite loud. Any ideas? I can post a picture of my amp later today when I get home. I am using stock ESP boards. I have seperated the power to each amp by cuting the +- power traces. I did not cut the ground trace on the boards.
It is all but silent when I have no signal coming to it or just a signal to each separate amp board.
Thanks a lot for all your help.
Ted
P.S signs of instability means, on my oscilloscope, when I drive the amp hardish (not really hard just a single tone coming though) I get distortion on the signal. When not driven hardish I get a perfect signal. I plan on going back to the original boards and playing with them later after I get this amp working well.
C+ and C- really shouldn't cause problems at 10nF, but C7 is part of the output zobel and should be replaced. Since it should be easy it wouldn't hurt to replace C+ and C-. With no load though none of this c
Sounds like the bias adjustment or bias servo is messed up, or you are oscillating. More info?
Looks like i am out of date!
Sounds like the bias adjustment or bias servo is messed up, or you are oscillating. More info?
Looks like i am out of date!
Well one of the two original boards seems very close to working right. It would allow me to adjust the pot and seems to work at lower volumes. It would oscillate at higher volumes (as high as my signal generator would allow which is really not that loud at all).
The other board I will probably play with but it does not allow me to adjust the pot (bias) and one half seems to not work at all. (q7 side) I have replace many components on this board and will not use it even if I seem to get it working since I do not trust it. If I can the board 1 working, though, I would use it.
If you want I can post pictures of the boards later today. Maybe you can see something I missed.
Of a higher concern to me right now is the ground loop problem on my newly made boards. As I said before I can connect a signal to each board and get next to no loop. When I connect a signal to both sides of a single board it gets quite loud. Even if I connect the same signals that worked fine before. Any ideas?
Thanks for all your help
Ted
The other board I will probably play with but it does not allow me to adjust the pot (bias) and one half seems to not work at all. (q7 side) I have replace many components on this board and will not use it even if I seem to get it working since I do not trust it. If I can the board 1 working, though, I would use it.
If you want I can post pictures of the boards later today. Maybe you can see something I missed.
Of a higher concern to me right now is the ground loop problem on my newly made boards. As I said before I can connect a signal to each board and get next to no loop. When I connect a signal to both sides of a single board it gets quite loud. Even if I connect the same signals that worked fine before. Any ideas?
Thanks for all your help
Ted
Q7 side? What does this mean? All active components are on both boards...I would go back and recheck every resistor, capacitor value, and check the orientation of all active devices. Once you have double-checked every component and looked for missing components check for heating of any component--you may have fried one or more active devices previously.
Does it oscillate into a load, or into no-load? Is the load resistive, or a loudspeaker?
Not sure about the ground loop issue but the easiest thing to try is cut the shared ground trace and return both board's ground to star ground.
Does it oscillate into a load, or into no-load? Is the load resistive, or a loudspeaker?
Not sure about the ground loop issue but the easiest thing to try is cut the shared ground trace and return both board's ground to star ground.
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