Hi,
I've completed my first GainClone! Yee-hah! It is based on Peter Daniel's LM3875 kit found on audiosector.com, but despite what I hoped it doesn't really work well yet.
I used a conventional aluminium U-profile, mounting everything on a wooden board, much like the excellent tutorial that came with the kit (although not nearly as neat as the tutorial, but this is just the demo -does it work- version). A picture says more than thousand words, so here it is:
One transformer, one PSU board, powering two amplifier boards.
At first inspection it seems to work. The sound produced sounds reasonably well, although there tends to be some hard-edged-ness to it.
However, what is really bugging me now, is that there seems to be some sound pressure/problem beyond the range of human hearing which results in a feeling of pressure on the ears, it even starts to get a little painful after a while.
After taking measurements with a scope this afternoon, I can at least conclude the following:
- There is no noticable DC-offset at the output
- The chips stay wonderfully cool
- The power supply looks fine, only when turning up the volume really loud it starts to show
- There is no oscillation
Does anyone care to share their ideas as to what might be causing the ear pressure problem? I don't really know how better to describe it, besides there seeming to be a unheard sound that irritates the ears.
The extra puzzling thing is that it almost sounds ok, and it is hard to pinpoint what is wrong with the sound. I'm not an expert at this. It just sounds hard edged somehow.
Something I did notice, using a test CD with a freq. sweep track, is that low frequencies (50 Hz and below) are amplified more than the rest. So my next step would be to add high pass filter capacitor.
My guess is it is related to wrong grounding of some sort. I wired it similar to the kit instructions with one twist:
- I connected PG- and PG+ on the PSU board to each other with a solid piece of wire
- To this wire I connected wires to CHG on each amp board
- And a wire to the chassis (which is grounded)
- Input ground comes together from the input RCA and potmeter on the amp boards.
I assume this is enough, although I am a bit worried I also should have explicitly connected PG+ and PG- from the amp board to the rectifier board.
Any helpful comment is highly appreciated.
Regards,
Simon
I've completed my first GainClone! Yee-hah! It is based on Peter Daniel's LM3875 kit found on audiosector.com, but despite what I hoped it doesn't really work well yet.
I used a conventional aluminium U-profile, mounting everything on a wooden board, much like the excellent tutorial that came with the kit (although not nearly as neat as the tutorial, but this is just the demo -does it work- version). A picture says more than thousand words, so here it is:
One transformer, one PSU board, powering two amplifier boards.
At first inspection it seems to work. The sound produced sounds reasonably well, although there tends to be some hard-edged-ness to it.
However, what is really bugging me now, is that there seems to be some sound pressure/problem beyond the range of human hearing which results in a feeling of pressure on the ears, it even starts to get a little painful after a while.
After taking measurements with a scope this afternoon, I can at least conclude the following:
- There is no noticable DC-offset at the output
- The chips stay wonderfully cool
- The power supply looks fine, only when turning up the volume really loud it starts to show
- There is no oscillation
Does anyone care to share their ideas as to what might be causing the ear pressure problem? I don't really know how better to describe it, besides there seeming to be a unheard sound that irritates the ears.
The extra puzzling thing is that it almost sounds ok, and it is hard to pinpoint what is wrong with the sound. I'm not an expert at this. It just sounds hard edged somehow.
Something I did notice, using a test CD with a freq. sweep track, is that low frequencies (50 Hz and below) are amplified more than the rest. So my next step would be to add high pass filter capacitor.
My guess is it is related to wrong grounding of some sort. I wired it similar to the kit instructions with one twist:
- I connected PG- and PG+ on the PSU board to each other with a solid piece of wire
- To this wire I connected wires to CHG on each amp board
- And a wire to the chassis (which is grounded)
- Input ground comes together from the input RCA and potmeter on the amp boards.
I assume this is enough, although I am a bit worried I also should have explicitly connected PG+ and PG- from the amp board to the rectifier board.
Any helpful comment is highly appreciated.
Regards,
Simon
i might be wrong, but if you have hi speed rectifiers, and the filtering caps are on the amp boards, the hi frequency from the switching would go through the 10 cm of wire and ground between the boards. I hope you haven't ignored the decoupling capacitors.
and now that i looked up the kit, i can see that you have to use two wires, pg+ and pg-, so you don't have a ground loop like you do right now.
and now that i looked up the kit, i can see that you have to use two wires, pg+ and pg-, so you don't have a ground loop like you do right now.
Simon -
The crucial earthing information for using one rectifier board with two amps is on p.29 of the user guide. I don't think you have followed these instructions, but whether that is causing your problem I couldn't say.
Why not ask in the Audiosector section of the Forum? - the man himself will very likely reply.
The crucial earthing information for using one rectifier board with two amps is on p.29 of the user guide. I don't think you have followed these instructions, but whether that is causing your problem I couldn't say.
Why not ask in the Audiosector section of the Forum? - the man himself will very likely reply.
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How high actually is the voltage that is not noticable? All amps have a DC offset and DC-coupled amps usually have a higher offset than AC-coupled amps.
Very unlikely. The increased output below 50 Hz must come from the speakers or their interaction with the room.
A high-pass filter is a good idea nevertheless, but not with a corner frequency of 50 Hz. Start with the one in the feedback loop. If the DC offset was not as unnoticable as you thought, you may get rid of the harshness by that.
You have already bridged them with a solid piece of wire on the PSU board, so there is no need to bridge them again through the amp PCB's ground plane.
Ground loop buzz is at 100 Hz (2 x 50). You would hear that quite clearly, not as inaudible pressure on the ears.
What speakers do you use that are able to produce subsonic content at sound pressure levels which bother your ears?
I having the same 'ear pressure' like you said.
but it is from my pc sound card, tested with headphone.
with shielded pc sound card, I can't feel the pressure.
once take the shield off, I can feel the pressure and kinda headache.
cannot listen to any longer than 10seconds.
I feel like going to deaf after remove headphone.
but it is from my pc sound card, tested with headphone.
with shielded pc sound card, I can't feel the pressure.
once take the shield off, I can feel the pressure and kinda headache.
cannot listen to any longer than 10seconds.
I feel like going to deaf after remove headphone.
Hi Simon are both chipamps mounted in that small aluminium chassis.Hi,
I've completed my first GainClone! Yee-hah! It is based on Peter Daniel's LM3875 kit found on audiosector.com, but despite what I hoped it doesn't really work well yet.
I used a conventional aluminium U-profile, mounting everything on a wooden board, much like the excellent tutorial that came with the kit (although not nearly as neat as the tutorial, but this is just the demo -does it work- version). A picture says more than thousand words, so here it is:
One transformer, one PSU board, powering two amplifier boards.
At first inspection it seems to work. The sound produced sounds reasonably well, although there tends to be some hard-edged-ness to it.
However, what is really bugging me now, is that there seems to be some sound pressure/problem beyond the range of human hearing which results in a feeling of pressure on the ears, it even starts to get a little painful after a while.
After taking measurements with a scope this afternoon, I can at least conclude the following:
- There is no noticable DC-offset at the output
- The chips stay wonderfully cool
- The power supply looks fine, only when turning up the volume really loud it starts to show
- There is no oscillation
Does anyone care to share their ideas as to what might be causing the ear pressure problem? I don't really know how better to describe it, besides there seeming to be a unheard sound that irritates the ears.
The extra puzzling thing is that it almost sounds ok, and it is hard to pinpoint what is wrong with the sound. I'm not an expert at this. It just sounds hard edged somehow.
Something I did notice, using a test CD with a freq. sweep track, is that low frequencies (50 Hz and below) are amplified more than the rest. So my next step would be to add high pass filter capacitor.
My guess is it is related to wrong grounding of some sort. I wired it similar to the kit instructions with one twist:
- I connected PG- and PG+ on the PSU board to each other with a solid piece of wire
- To this wire I connected wires to CHG on each amp board
- And a wire to the chassis (which is grounded)
- Input ground comes together from the input RCA and potmeter on the amp boards.
I assume this is enough, although I am a bit worried I also should have explicitly connected PG+ and PG- from the amp board to the rectifier board.
Any helpful comment is highly appreciated.
Regards,
Simon
Mad Mark
I've listened to Simon's Gainclone and have helped him with taking some measurements.
As I see it, there are two separate problems:
1) A 'pressure' sensation that feels as if there is a very high frequency noise present. I can't hear it, but there is definately something there. Weird thing is that the feeling persists, even after the Gainclone is turned off. Measuring the output did not show any oscillation, however.
2) We measured an increasing amplitude below 50 Hz. A frequency sweep clearly showed the output to rise significantly below 50 Hz and even more below 30 Hz. These frequencies are approximate, as they are measured on an oscilloscope and not verified by a counter. Even so, output is almost doubled below 30 Hz compared to, say, 1 kHz.
This 'bass-boost' has been observed both with speakers attached as well as with a dummyload. The effect of the speaker can therefore be ruled out.
Apart from these two issues, the GC actually sounds allright, there is no obvious flaw in the soundscape.
Anyway, just thought I'd add some more detail and clarification.
Eric
As I see it, there are two separate problems:
1) A 'pressure' sensation that feels as if there is a very high frequency noise present. I can't hear it, but there is definately something there. Weird thing is that the feeling persists, even after the Gainclone is turned off. Measuring the output did not show any oscillation, however.
2) We measured an increasing amplitude below 50 Hz. A frequency sweep clearly showed the output to rise significantly below 50 Hz and even more below 30 Hz. These frequencies are approximate, as they are measured on an oscilloscope and not verified by a counter. Even so, output is almost doubled below 30 Hz compared to, say, 1 kHz.
This 'bass-boost' has been observed both with speakers attached as well as with a dummyload. The effect of the speaker can therefore be ruled out.
Apart from these two issues, the GC actually sounds allright, there is no obvious flaw in the soundscape.
Anyway, just thought I'd add some more detail and clarification.
Eric
Thanks all for your thoughts on this matter, it is highly appreciated.
Based on some remarks I decided to redo my grounding, following the kit guide more closely by using a solid copper wire attached to OG instead of CHG. On top of that I noticed that I got LM3875TF's, which should be insulated from a grounded heatsink. Since both the chips are attached to the chassis, which is grounded, I should have insulated them but I didn't. Wrong assumption on my part, I somehow figured the kit would come with the easier type
After changing that, I believe the ear pressuring is gone and it sounds more like an amplifier should, meaning it is no longer tiresome to listen to.
Final verdicts will have to wait though, I currently have a cold which is affecting my ears, besides giving me a stuffed head
Based on some remarks I decided to redo my grounding, following the kit guide more closely by using a solid copper wire attached to OG instead of CHG. On top of that I noticed that I got LM3875TF's, which should be insulated from a grounded heatsink. Since both the chips are attached to the chassis, which is grounded, I should have insulated them but I didn't. Wrong assumption on my part, I somehow figured the kit would come with the easier type
After changing that, I believe the ear pressuring is gone and it sounds more like an amplifier should, meaning it is no longer tiresome to listen to.
Final verdicts will have to wait though, I currently have a cold which is affecting my ears, besides giving me a stuffed head
Insulation
Hi
The lm3875tf are an insulated package. if you had fixed then to the chassis and they where the non insulated version at least you would of blown a fuse in the -v rail and if no fuse a flash and a bang maybe.
Mad mark
Ps let your amplifier burn in for a while and will/ should sound much smoother.
Thanks all for your thoughts on this matter, it is highly appreciated.
Based on some remarks I decided to redo my grounding, following the kit guide more closely by using a solid copper wire attached to OG instead of CHG. On top of that I noticed that I got LM3875TF's, which should be insulated from a grounded heatsink. Since both the chips are attached to the chassis, which is grounded, I should have insulated them but I didn't. Wrong assumption on my part, I somehow figured the kit would come with the easier type
After changing that, I believe the ear pressuring is gone and it sounds more like an amplifier should, meaning it is no longer tiresome to listen to.
Final verdicts will have to wait though, I currently have a cold which is affecting my ears, besides giving me a stuffed head
Hi
The lm3875tf are an insulated package. if you had fixed then to the chassis and they where the non insulated version at least you would of blown a fuse in the -v rail and if no fuse a flash and a bang maybe.
Mad mark
Ps let your amplifier burn in for a while and will/ should sound much smoother.
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hello waki has you neck retracted yet
Then again it could be that i quoted his post, i have tried to delete the unwanted imformation when quoting but it never seems to work.
Im sorry i offended you and i will make a note " i must improve my quoting"
Friendly with Regards Mad mark. please let me know wich it is . pm me if you must
My question had a very valid reason . i guess you have been snooping around my posts and got a lttle sore with a comment i made to someone not being at all helpfull and in fact being totaly unhelpfull.
Then again it could be that i quoted his post, i have tried to delete the unwanted imformation when quoting but it never seems to work.
Im sorry i offended you and i will make a note " i must improve my quoting"
Friendly with Regards Mad mark. please let me know wich it is . pm me if you must
Finally an update about my problem...
Yesterday 'That Guy Eric' was here, and we did listening tests using his fresly built LM3886 kit, and mine. His sounded much better, as expected. Upon inspection of mine, he exclaimed in triumph: "Duh, you didn't connect the ground pads, small wonder
". I thought: "How st*pid , can it really be...".
I believe I wired everything as described in the kit manual though, which only seems to connect a solid copper wire from OG's to a star ground, and it does not do so for PG- and PG+. So I didn't connect PG- and PG+ to the star ground. This left the impression on casual inspection I didn't connect the ground.
Because I thought I had tried everything else anyway, we invoked Murphy's law, and went ahead and did it, connected PG+ and PG- to the star ground.
And what a difference! The difference is so remarkably big and huge and gargantuan, I would almost say it works as it should now. Great stuff
(Eric said it still sounded horrible, but that is due to a different taste in music)
Yesterday 'That Guy Eric' was here, and we did listening tests using his fresly built LM3886 kit, and mine. His sounded much better, as expected. Upon inspection of mine, he exclaimed in triumph: "Duh, you didn't connect the ground pads, small wonder
". I thought: "How st*pid , can it really be...". I believe I wired everything as described in the kit manual though, which only seems to connect a solid copper wire from OG's to a star ground, and it does not do so for PG- and PG+. So I didn't connect PG- and PG+ to the star ground. This left the impression on casual inspection I didn't connect the ground
.Because I thought I had tried everything else anyway, we invoked Murphy's law, and went ahead and did it, connected PG+ and PG- to the star ground.
And what a difference! The difference is so remarkably big and huge and gargantuan, I would almost say it works as it should now. Great stuff
(Eric said it still sounded horrible, but that is due to a different taste in music
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