Time to give you some update...
It works!!!! Yesssss!
But I still have some problems...
So, I re-melt almost everything, I de-soldered the toroids, re-soldered 'em (it looks better even I'm sure it wasn't the cause) and while checking every component on the board I found that IN2B (TP2050 pin32) wasn't soldered correctly. Arggghhh! It was very difficult to see. I had to look at the pins from the side and even like that I wasn't sure.
So, I had to re-solder it. Then, the offset was "tunable" on both channels, a good sign.
I tried the amp and it worked! On both channels! Hourra!
So, I have now some questions:
- I find the trimmers very hard to use. From -10mV to 10mV in offset, I have to turn the trimmers by maybe only one half degre. It is very difficult to tune the offset in these conditions.
- I have some noise in the speakers... The amp in not very silent with no input (on both channels) (much less than my amp6). The amp ground is connected to main ground. Where do you think it can come from? The inputs cables are around 12 cms long and are not shielded.
- When I connect my Ipod to the amp and then turn it on (the mute jumper is connected), I have a "thump" in the speakers but not when there is no input.
Thank you for your help.
It works!!!! Yesssss!
But I still have some problems...
So, I re-melt almost everything, I de-soldered the toroids, re-soldered 'em (it looks better even I'm sure it wasn't the cause) and while checking every component on the board I found that IN2B (TP2050 pin32) wasn't soldered correctly. Arggghhh! It was very difficult to see. I had to look at the pins from the side and even like that I wasn't sure.
So, I had to re-solder it. Then, the offset was "tunable" on both channels, a good sign.
I tried the amp and it worked! On both channels! Hourra!
So, I have now some questions:
- I find the trimmers very hard to use. From -10mV to 10mV in offset, I have to turn the trimmers by maybe only one half degre. It is very difficult to tune the offset in these conditions.
- I have some noise in the speakers... The amp in not very silent with no input (on both channels) (much less than my amp6). The amp ground is connected to main ground. Where do you think it can come from? The inputs cables are around 12 cms long and are not shielded.
- When I connect my Ipod to the amp and then turn it on (the mute jumper is connected), I have a "thump" in the speakers but not when there is no input.
Thank you for your help.
The trimmers are connected between ground and +5V. In order to increase its precission, you would need to add aresistor between trimmer and ground and another resistor between trimmer and +5V. I'm not sure whether there is a space provided for this on the board.
It seems to me that the input cables should be shielded and you may have some problems with ground loops.
Marek
It seems to me that the input cables should be shielded and you may have some problems with ground loops.
Marek
Thank you for the answer.
There is no space to add some resistors. But I could find a way if necessary.
About the ground loop, since there is almost nothing connected on the board, that's to say I have it on the board...
Since the input cables weren't shielded and the experiment was just near a fluorescent light, I'll try to reproduce it with shielded cable and away from a noisy electrical source 🙄
There is no space to add some resistors. But I could find a way if necessary.
About the ground loop, since there is almost nothing connected on the board, that's to say I have it on the board...
Since the input cables weren't shielded and the experiment was just near a fluorescent light, I'll try to reproduce it with shielded cable and away from a noisy electrical source 🙄
I know that there is not space for this but still you e.g. desolder the trimmer and solder small resistors with trimmer of top of them. Of course I advice to do it only after you have solved all other problems. Desoldering of double-sided boards is not that ease as soldering it. So do it carefully. And first calculate resistor values (because this operation cannot be repeated several times).
Marek
Marek
I just completed an AMP5, and had the same problem. I believe the two circuits are similar, and I think the solution isn't really that far away.
There's a resistor that connects the wiper of the trim pot to the feedback ground. Just increase the value.
TriPath's schematic has a 500k resistor there, and I bet what you have is a much lower value resistor.
Rune
There's a resistor that connects the wiper of the trim pot to the feedback ground. Just increase the value.
TriPath's schematic has a 500k resistor there, and I bet what you have is a much lower value resistor.
Rune
Thank you for the help. Jan replied almost the same thing, adding he delivers now his kits with different trimmers (multi turns).
BTW, I finished to put my AMP4 in a (paper) box and tested it tonight. I changed the input wires to shielded one's and the amp is now almost silent. With my ears at 50cms from my loudspeakers, I can't hear anything. If I go closer, then I can hear a light "hiiiiisss". So, it seems reasonably good (much better than my current amp).
But I have another problem (why is there always a problem?!): the turn on thump is loud.
When I turn on the amp, I hear the relay close after a few seconds and the loudspeakers emit a big "thump" exactly at this moment (relay closing). I thought there shouldn't be any thump with the relay. 🙁
Please note that I have exactly the same problem with my AMP6 when I unmute it a few seconds (or even minutes...) after the turn on.
So, does anyone have a suggestion about the origin of this annoying thump?
Thanks.
BTW, I finished to put my AMP4 in a (paper) box and tested it tonight. I changed the input wires to shielded one's and the amp is now almost silent. With my ears at 50cms from my loudspeakers, I can't hear anything. If I go closer, then I can hear a light "hiiiiisss". So, it seems reasonably good (much better than my current amp).
But I have another problem (why is there always a problem?!): the turn on thump is loud.
When I turn on the amp, I hear the relay close after a few seconds and the loudspeakers emit a big "thump" exactly at this moment (relay closing). I thought there shouldn't be any thump with the relay. 🙁
Please note that I have exactly the same problem with my AMP6 when I unmute it a few seconds (or even minutes...) after the turn on.
So, does anyone have a suggestion about the origin of this annoying thump?
Thanks.
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