Hi Brian,
I did check it a while back, but probably should again.... one thing that is odd is that if I disconect the preamp from the power amp and test it, it has very good distortion performance, but when it is connected to the amp it goes up dramatically....
Clem_o I tried 560 Ohms first as it was closest I had to 680, distortion increased slightly... so I tried 1K increased a little bit more 🙁 I think I better disconnect the pre and test it again stand alone in case I've disturbed something else again.
Tony.
I did check it a while back, but probably should again.... one thing that is odd is that if I disconect the preamp from the power amp and test it, it has very good distortion performance, but when it is connected to the amp it goes up dramatically....
Clem_o I tried 560 Ohms first as it was closest I had to 680, distortion increased slightly... so I tried 1K increased a little bit more 🙁 I think I better disconnect the pre and test it again stand alone in case I've disturbed something else again.
Tony.
hmmm! I'm certainly out of ideas (for now at least!)... I think you better get an oscilloscope!!
Cheers
Cheers
clem_o said:
hehehe 🙂 I always seem to get the doozies 😉.... I've been monitoring ebay, and a scope went last night for about $20 AUS, but it was an AS IS, and from the pictures it had a damaged bnc input, a dent, and wasn't showing any trace, so I suspect it was dead. I checked the bank balance last night and was pleasantly surprised, I guess I haven't had a chance to spend any money lately 😉 the bitscope is starting to look attractive again 😉
I just did a couple of runs with just preamp and just power amp to make sure something else hadn't gone wrong.... both still performing ok. But one thing!!! I have always been testing the amp with sound card direct, without using the 1uf polyester coupling caps..... Time to try it with them in place I think!!!!
I had tested the preamp both sides of the coupling caps with no difference, but maybe the right one appears ok with no load, but misbehaves once there is a load.....
http://home.people.net.au/~tonywww/preamp_only_1k.htm
note that the freq response variations in the right channel have disapeared, when it isn't coupled to the amp......
http://home.people.net.au/~tonywww/power_amp_direct.htm
the other weird thing with the power amp, is that when testing using the DVD player as input (with the rmaa tones on a cd) the stereo cross talk is much better, up around 70db... bit strange, but I don't think that is part of my problem.... distortion when running through the DVD player is pretty much the same.
Tony.
edit: ok putting the coupling cap in caused a very slight increase in distortion 0.044 to 0.047.... so not the culprit....
OK, so I decided to drive the amp into clipping and look at what happened. I decided to do it with a 20Hz sine wave....
in the past the clipping performance of the amp has been fine, just get a flat on the crests and dips of the sine wave no nasties...
today it is a very different result to what I have seen before. I'm wondering if this might shed some light on what is going on.
the top trace is the power supply ripple... it is being modulated by the 20Hz sine wave and is peaking at 600mV not so good. Might be time to hook up that second transformer 😉
The bottom trace is what is happening to the sine wave when it clips... yuck.... any ideas as to what is causing that?? the supply rails droop severly when it starts to clip. no load they are about 62V, heavy load no clipping about 59V, as soon as clipping occurs about 58V.
voltage on the 8 Ohm dummy load is only about 21V before clipping. I don't think I'm getting max power here
in the past the clipping performance of the amp has been fine, just get a flat on the crests and dips of the sine wave no nasties...
today it is a very different result to what I have seen before. I'm wondering if this might shed some light on what is going on.
the top trace is the power supply ripple... it is being modulated by the 20Hz sine wave and is peaking at 600mV not so good. Might be time to hook up that second transformer 😉
The bottom trace is what is happening to the sine wave when it clips... yuck.... any ideas as to what is causing that?? the supply rails droop severly when it starts to clip. no load they are about 62V, heavy load no clipping about 59V, as soon as clipping occurs about 58V.
voltage on the 8 Ohm dummy load is only about 21V before clipping. I don't think I'm getting max power here
Attachments
Looks like you've been doing some work hey!
1. What's the sound card baseline performance like? You may find that its got a lot of crosstalk to begin with, which would explain why running a DVD player as the source "cleans up" the crosstalk perfrmance a lot.
2. Your supply voltage drops, IMHO are pretty normal (well, at least as far as power transformers where I live go, its much worse!) You can always expect a few volts of drop when load is heavy.
3. Sinewave at 20Hz with a funny clip - is that happening on both channels? With the 8-ohm dummy-load connected, place something like a 47ohm resistor and drive a loudspeaker. Listen to the speaker and verify that the signal you see on the computer is really what is coming out of the amp...
Power levels do look way too low. Try probing around the VAS stage and see what the voltage swing is like...
Cheers!
1. What's the sound card baseline performance like? You may find that its got a lot of crosstalk to begin with, which would explain why running a DVD player as the source "cleans up" the crosstalk perfrmance a lot.
2. Your supply voltage drops, IMHO are pretty normal (well, at least as far as power transformers where I live go, its much worse!) You can always expect a few volts of drop when load is heavy.
3. Sinewave at 20Hz with a funny clip - is that happening on both channels? With the 8-ohm dummy-load connected, place something like a 47ohm resistor and drive a loudspeaker. Listen to the speaker and verify that the signal you see on the computer is really what is coming out of the amp...
Power levels do look way too low. Try probing around the VAS stage and see what the voltage swing is like...
Cheers!
Oh Yeah I have been doing WAY to much on this amp 😉
I've sussed out the crosstalk it appears to be some sort of earth loop (or at least earth sharing) between the PC and the amp. Since the computer is connected to the amp via the output and then again via the sound card preamp, there is an earth loop going down the output and back up the input to the computer.... I put some 6.8 Ohm resistors on the earth connection between the dummy load and the sound card preamp and the crosstalk improved to 71db which is roughly what it is when using the DVD player.
I also replaced the CCS in the left channel, and surprisingly it made little to no difference.... the left channels distortion performance is still worse than the right when driven directly, but vastly superior when driven through the preamp
Yeah both channels were exhibiting that weird clipping behaviour, and it was at the dummy load, also it seemed to make little difference if it was one or both channels being driven. I decided to resolder the power supply connections, as I have had weird distortion problems that went away after resoldering the PS before.
Right channel performance improved slightly (.05% to .04% distortion, could be just measurement errors). Left channel got worse.... 0.08% to 0.1%..... I'm starting to think that this amp is so sensitive that just moving it might be causing problems 😉
here is a link to some tests I did on my soundcard, and the soundcard preamp ages ago... I did check them both again before starting these tests to make sure they weren't contributing to my problems. http://home.swiftdsl.com.au/~tonywww/rmaa/preamp_compare_MKII.htm
I'm pretty sure that my poor IM distortion performance is power supply related.... I've wanted to replace/upgrade the PS for a long time but getting decent caps without paying a fortune is an issue... (I'm probably going to get some nichicons from percy audio, or some UCC's from mouser.... The ps is really crude. It is a singe metal can bridge rectifier, with 4 X 8000uf Caps (16,000uF per rail) That is it! I tried putting some 100nf bypass caps across the rails, and also accross the ac side of the rectifier but it didn't seem to make much difference noise wise.... Though maybe I should take them out and check the clipping behaviour again....
OK will get the probe out and check the waveform at each stage in the power amp 🙂 should have thought of that last night, but my brain probably wasn't working so well at midnight 😉
edit: that'll teach me to do testing late at night, that weird clipping behaviour goes away if I change the sc preamp to X 0.01 instead of X 0.1.... it was either the sc preamp or the sound card exhibiting that behaviour.... I think I need to recalibrate the clipping indicators on the sc preamp!!
Tony.
I've sussed out the crosstalk it appears to be some sort of earth loop (or at least earth sharing) between the PC and the amp. Since the computer is connected to the amp via the output and then again via the sound card preamp, there is an earth loop going down the output and back up the input to the computer.... I put some 6.8 Ohm resistors on the earth connection between the dummy load and the sound card preamp and the crosstalk improved to 71db which is roughly what it is when using the DVD player.
I also replaced the CCS in the left channel, and surprisingly it made little to no difference.... the left channels distortion performance is still worse than the right when driven directly, but vastly superior when driven through the preamp
Yeah both channels were exhibiting that weird clipping behaviour, and it was at the dummy load, also it seemed to make little difference if it was one or both channels being driven. I decided to resolder the power supply connections, as I have had weird distortion problems that went away after resoldering the PS before.
Right channel performance improved slightly (.05% to .04% distortion, could be just measurement errors). Left channel got worse.... 0.08% to 0.1%..... I'm starting to think that this amp is so sensitive that just moving it might be causing problems 😉
here is a link to some tests I did on my soundcard, and the soundcard preamp ages ago... I did check them both again before starting these tests to make sure they weren't contributing to my problems. http://home.swiftdsl.com.au/~tonywww/rmaa/preamp_compare_MKII.htm
I'm pretty sure that my poor IM distortion performance is power supply related.... I've wanted to replace/upgrade the PS for a long time but getting decent caps without paying a fortune is an issue... (I'm probably going to get some nichicons from percy audio, or some UCC's from mouser.... The ps is really crude. It is a singe metal can bridge rectifier, with 4 X 8000uf Caps (16,000uF per rail) That is it! I tried putting some 100nf bypass caps across the rails, and also accross the ac side of the rectifier but it didn't seem to make much difference noise wise.... Though maybe I should take them out and check the clipping behaviour again....
OK will get the probe out and check the waveform at each stage in the power amp 🙂 should have thought of that last night, but my brain probably wasn't working so well at midnight 😉
edit: that'll teach me to do testing late at night, that weird clipping behaviour goes away if I change the sc preamp to X 0.01 instead of X 0.1.... it was either the sc preamp or the sound card exhibiting that behaviour.... I think I need to recalibrate the clipping indicators on the sc preamp!!
Tony.
OK here is what the "real" clipping looks like. This is different to when I tested this amp a year or so ago, in that back then the clipping was completely flat across the top and bottom of the sine wave, now it is sloping.....
just before clipping the voltage was about 31V so that should equate to pretty much full power. the ps sagged to 53V (its sitting at 63.5 at idle today)....
the blue trace is taken with the probe connected between the collector of Q6 and the trimpot... the red trace is at the dummy load. I'm guessing that one rail is collapsing a little earlier than the other giving the slight slope in the clipping...
Anyway I'll stop looking at that, but might try resoldering the PS wiring yet again It is one area where a bigger soldering iron would be nice 🙂
edit: just realised I hadn't checked the clipping at 20Hz before, was 1Khz... just checked with 1Khz and the tops and bottoms of the sine waves are completely flat 🙂
Tony.
just before clipping the voltage was about 31V so that should equate to pretty much full power. the ps sagged to 53V (its sitting at 63.5 at idle today)....
the blue trace is taken with the probe connected between the collector of Q6 and the trimpot... the red trace is at the dummy load. I'm guessing that one rail is collapsing a little earlier than the other giving the slight slope in the clipping...
Anyway I'll stop looking at that, but might try resoldering the PS wiring yet again
It is one area where a bigger soldering iron would be nice 🙂edit: just realised I hadn't checked the clipping at 20Hz before, was 1Khz... just checked with 1Khz and the tops and bottoms of the sine waves are completely flat 🙂
Tony.
Attachments
Tony, that looks like it could be more caused by small coupling capacitors on your sound card. Here's a simple test - switch over to a slightly higher frequency - say 80Hz. Have a look at the output waveform - I think it'll be a much less slanted. It would also explain why 1KHz clip looks flat - there isn't enough time for the coupling capacitors to discharge at that frequency to make it visible as a slope...
I think this is all getting to one thing - there are some pretty severe limitations testing with a sound card!
BTW regarding the ground loops - I just remembered why I don't seem to have too much of a problem with that - where I live, earth ground isn't mandatory - in fact practically 99% of the power outlets don't have a ground hole!
Cheers
I think this is all getting to one thing - there are some pretty severe limitations testing with a sound card!
BTW regarding the ground loops - I just remembered why I don't seem to have too much of a problem with that - where I live, earth ground isn't mandatory - in fact practically 99% of the power outlets don't have a ground hole!
Cheers
Hi Clem_o,
well I'm just about at the end of my deadline and no luck 🙁
I spent yesterday trying to track down the source of higher distortion in the left channel. It is currently sitting at about .11% THD compared to 0.03% on the right channel. (ironically it is the right channel which plays up when run through the preamp)....
Both chanels before I did anything to the amp used to run at about .05% distortion. I thought putting the ccs back in would fix it but it didn't... maybe I'm worrying about this for no reason, but It is bugging me... I thought it was due to the non-optimal choice of ccs replacement but it doesn't look like changing the ccs makes much difference regardless. I haven't tried to work out what is going on between the pre and power amp, I've just been concentrating on the power amp driven directly off the sound card.
anyway attached is a zoomed in look at the thd measurements.. I changed the test freq to 1020 Hz so that I could see what was PS related and what was harmonics. One thing that seems strange to me is that the second harmonic is almost identical between the two channels but the third and higher harmonics there is a big difference. The other thing that I find very strange is that there is a huge difference between what appears to be PS related noise between left and right, at 100Hz and then each harmonic above this. I thought I was onto something there and resoldered the local filter caps (100uF and 22uF) on the pcb, but no change.
I think I'm going to have to accept that the amp worked better before I touched it, and maybe one day I can work out what I stuffed up. I went back through all of the RMAA tests I have done, and at one point everything was actually pretty good performance wise, but I was still seeing big differences between chanels voltage wise, and still had more noise in the right channel, so I continued on, then it all went bad... the point it went bad was when I changed the 27K ccs replacement resistors to 30K. I think if I ever do this again, I need to write a diary!!!! so I know EXACTLY what changed at each step. I don't think I did anything but replace those resistors, but maybe I did....
anyway thanks for all the help, hopefully one day I'll get it sorted.
cheers
Tony.
edit.... changed the left and right above, it is actually the left channel that has the higher distortion... I guess one positive is that the right now has lower distortion than when I started 😉 I might just do my speaker testing with the right channel and the pc direct connected... it was because of problems with my speaker testing I decided to have a break from that and "improve" the amp.... big mistake 😉
well I'm just about at the end of my deadline and no luck 🙁
I spent yesterday trying to track down the source of higher distortion in the left channel. It is currently sitting at about .11% THD compared to 0.03% on the right channel. (ironically it is the right channel which plays up when run through the preamp)....
Both chanels before I did anything to the amp used to run at about .05% distortion. I thought putting the ccs back in would fix it but it didn't... maybe I'm worrying about this for no reason, but It is bugging me... I thought it was due to the non-optimal choice of ccs replacement but it doesn't look like changing the ccs makes much difference regardless. I haven't tried to work out what is going on between the pre and power amp, I've just been concentrating on the power amp driven directly off the sound card.
anyway attached is a zoomed in look at the thd measurements.. I changed the test freq to 1020 Hz so that I could see what was PS related and what was harmonics. One thing that seems strange to me is that the second harmonic is almost identical between the two channels but the third and higher harmonics there is a big difference. The other thing that I find very strange is that there is a huge difference between what appears to be PS related noise between left and right, at 100Hz and then each harmonic above this. I thought I was onto something there and resoldered the local filter caps (100uF and 22uF) on the pcb, but no change.
I think I'm going to have to accept that the amp worked better before I touched it, and maybe one day I can work out what I stuffed up. I went back through all of the RMAA tests I have done, and at one point everything was actually pretty good performance wise, but I was still seeing big differences between chanels voltage wise, and still had more noise in the right channel, so I continued on, then it all went bad... the point it went bad was when I changed the 27K ccs replacement resistors to 30K. I think if I ever do this again, I need to write a diary!!!! so I know EXACTLY what changed at each step. I don't think I did anything but replace those resistors, but maybe I did....
anyway thanks for all the help, hopefully one day I'll get it sorted.
cheers
Tony.
edit.... changed the left and right above, it is actually the left channel that has the higher distortion... I guess one positive is that the right now has lower distortion than when I started 😉 I might just do my speaker testing with the right channel and the pc direct connected... it was because of problems with my speaker testing I decided to have a break from that and "improve" the amp.... big mistake 😉
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Hey, you'll still have the weekends to work on it! 🙂
- check the bias - the optimal bias point for each channel is not necessarily the same. Could explain the odd harmonics difference.
- Try to find out why there is PS-noise getting in, stronger on the left. Easy to parallel some electrolytics, particularly at the CCS, just for a quick try!
Cheers
- check the bias - the optimal bias point for each channel is not necessarily the same. Could explain the odd harmonics difference.
- Try to find out why there is PS-noise getting in, stronger on the left. Easy to parallel some electrolytics, particularly at the CCS, just for a quick try!
Cheers
Thanks Clem_o, I suspect that the higher noise and THD are related... would seem to make sense, I thought maybe the NFB wasn't working properly so resoldered around all those components yesterday with no change.
I just tried paralleling 2 X 680uf caps across the 100uf caps... (680uf was then only cap I had that was high enough voltage rating)...
no change whatsoever.... weird.
I'm really thinking that something isn't working correctly in the nfb, either that or I have some damaged transistors or mosfets, due to the short I had when I first finished the resolder... (I replaced Q6 a short while ago, because it got really hot when I had the short, but alas it made no difference) If I do a really low level rmaa test both channels have quite low distortion (.008 and .009%) this is at less than 1W though (about 1.5V on the dummy load).
I'm just feeling a bit frustrated at the moment, as I have made changes to the amp before and not had so many problems!! Also I want to make a new amp, I was considering a P3A or an AKSA 100, I'm leaning towards the AKSA 100 (even more so now, because it is an almost complete kit), but I'm losing confidence that I'll be able to get it working properly!! At least with that I guess I will be starting with new components and a new pcb, I will look at every solder joint with a 10X magnifiying glass after soldering too!
This was all supposed to have been a 1 day job, and it's been nearly 3 weeks 🙁
Tony.
I just tried paralleling 2 X 680uf caps across the 100uf caps... (680uf was then only cap I had that was high enough voltage rating)...
no change whatsoever.... weird.
I'm really thinking that something isn't working correctly in the nfb, either that or I have some damaged transistors or mosfets, due to the short I had when I first finished the resolder... (I replaced Q6 a short while ago, because it got really hot when I had the short, but alas it made no difference) If I do a really low level rmaa test both channels have quite low distortion (.008 and .009%) this is at less than 1W though (about 1.5V on the dummy load).
I'm just feeling a bit frustrated at the moment, as I have made changes to the amp before and not had so many problems!! Also I want to make a new amp, I was considering a P3A or an AKSA 100, I'm leaning towards the AKSA 100 (even more so now, because it is an almost complete kit), but I'm losing confidence that I'll be able to get it working properly!! At least with that I guess I will be starting with new components and a new pcb, I will look at every solder joint with a 10X magnifiying glass after soldering too!
This was all supposed to have been a 1 day job, and it's been nearly 3 weeks 🙁
Tony.
ok, how about ground-side modulation from the PS then? Does changing the location where you take your ground do anything? Could also be a ground loop making wierd readings since your signal gen and 'scope would practically put a large ground loop on the amp. You could try unhooking one side of the ground (i.e. only 'hot' signal from amp output).
As for the DIY amp - sure, why not? The AKSA and the P3A are pretty uncluttered, many seem to think that the AKSA is great-sounding... (and I'm sure you have more than enough skills to do this stuff - think of this simply as a string of bad luck... !! )
Cheers!
As for the DIY amp - sure, why not? The AKSA and the P3A are pretty uncluttered, many seem to think that the AKSA is great-sounding... (and I'm sure you have more than enough skills to do this stuff - think of this simply as a string of bad luck... !! )
Cheers!
Tony,
You may be skirting around a design problem in your amp. It is possible.
If you build a kit amp you can usually get assistance from the designer until it is working to spec. This is certainly true with my products; this is all part of the service.
Cheers,
Hugh
You may be skirting around a design problem in your amp. It is possible.
If you build a kit amp you can usually get assistance from the designer until it is working to spec. This is certainly true with my products; this is all part of the service.
Cheers,
Hugh
One down one to go
Well, I just pulled out the two bc556's in the first diff pair.... when I put them in they were matched for hfe (beta) at 215 each, after pulling them out they measured 186 for the input side and 197 for the nfb side. I thought bingo 🙂 must have been damaged when I had the short!
I replaced them with a couple with hfe of 192. and I decided to put the emitter degen resistors in at the same time (yeah I know I shouldn't change more than one thing at once, but I was pretty sure it was the trannies!) I haven't adjusted the queisient current yet but the distortion went from .11% to .044% and the big humps at 100Hz and subsequent harmonics are gone!!! yay!!!!
I'm now thinking that the problem with the right channel when running through the preamp may be due to the hfe being too high on the 1st diff pair (I think it was you Clem_o who said that I should be carefull if I change the bc556's for something else that their hfe isn't too high).... well I'm going to have a shot at finding another matched pair with lower hfe (I had 30 to start with) that I can put in the right channel and see how I go 🙂
But right now I am much happier 🙂
Tony.
Well, I just pulled out the two bc556's in the first diff pair.... when I put them in they were matched for hfe (beta) at 215 each, after pulling them out they measured 186 for the input side and 197 for the nfb side. I thought bingo 🙂 must have been damaged when I had the short!
I replaced them with a couple with hfe of 192. and I decided to put the emitter degen resistors in at the same time (yeah I know I shouldn't change more than one thing at once, but I was pretty sure it was the trannies!) I haven't adjusted the queisient current yet but the distortion went from .11% to .044% and the big humps at 100Hz and subsequent harmonics are gone!!! yay!!!!
I'm now thinking that the problem with the right channel when running through the preamp may be due to the hfe being too high on the 1st diff pair (I think it was you Clem_o who said that I should be carefull if I change the bc556's for something else that their hfe isn't too high).... well I'm going to have a shot at finding another matched pair with lower hfe (I had 30 to start with) that I can put in the right channel and see how I go 🙂
But right now I am much happier 🙂
Tony.
AKSA said:
Hi Hugh 🙂 it is certainly possible!! but I do have before and after measurements, so I know what it should be able to do 🙂 I'm feeling a lot happier and more confident again now, I have solved one problem 🙂 Whether I can solve the pre/power amp interaction problem I'm not sure, but that one is not so bad, as I plan to use this as the amp for my subs and not use the preamp anyway!! One step closer to getting that AKSA now 🙂 It's been a struggle but at least I'm getting somewhere now 🙂
Tony.
Well.... this is a little hard to believe but, I decided to check the amp through the preamp before I did anything else.
the distortion on the right channel has gone from 1.3% when through the preamp, to 0.055%!! go figure.... I haven't touched anything on the right channel at all!
It's still slightly higher than the left but only marginally... One would probably conclude from this that there is a switch happening between channels when I'm testing between the pre and power amps, but this is definitely not the case.
how on earth highish (though not rediculously so) distortion on the left channel, was interacting with the right channel of the preamp to induce even higher distortion in the right channel I don't know, but at least I have a properly working amp again!!!! I think my GF should have given me the deadline 2 weeks ago!! 🙂 (I guess I should really do a listening test with the DVD player to be sure)....
The amp now has the transistor based ccs in the left channel, resistor based in the right channel, and 47 Ohm emiiter degen resistors on each bc556 in the 1st differential stage. Because I have had so many problems, and the differences in performance are now very small, I'm thinking I should leave it alone for now 🙂 though I do still want to do the power supply.
The other thing I have noticed with the noise, is that most of it is 50Hz or harmonics thereof, the torioidal isn't centrally positioned, it is much closer to the right channel, I suspect that the noise difference between the two channels is actually noise being radiated from the torroid. I might try moving it 🙂
but once again, thanks to all (especially Clem_o) for all the help, suggestions and encouragement 🙂 I think I would have given up a while ago without it!!
Now if I can just get my speaker acoustic measurements working properly!! time to buy the resistors for my second attempt at the walin preamp 2, this time with Vikash's pcb, rather than with an IC experimenter board like I used last time 😉
Tony.
the distortion on the right channel has gone from 1.3% when through the preamp, to 0.055%!! go figure.... I haven't touched anything on the right channel at all!
It's still slightly higher than the left but only marginally... One would probably conclude from this that there is a switch happening between channels when I'm testing between the pre and power amps, but this is definitely not the case.
how on earth highish (though not rediculously so) distortion on the left channel, was interacting with the right channel of the preamp to induce even higher distortion in the right channel I don't know, but at least I have a properly working amp again!!!! I think my GF should have given me the deadline 2 weeks ago!! 🙂 (I guess I should really do a listening test with the DVD player to be sure)....
The amp now has the transistor based ccs in the left channel, resistor based in the right channel, and 47 Ohm emiiter degen resistors on each bc556 in the 1st differential stage. Because I have had so many problems, and the differences in performance are now very small, I'm thinking I should leave it alone for now 🙂 though I do still want to do the power supply.
The other thing I have noticed with the noise, is that most of it is 50Hz or harmonics thereof, the torioidal isn't centrally positioned, it is much closer to the right channel, I suspect that the noise difference between the two channels is actually noise being radiated from the torroid. I might try moving it 🙂
but once again, thanks to all (especially Clem_o) for all the help, suggestions and encouragement 🙂 I think I would have given up a while ago without it!!
Now if I can just get my speaker acoustic measurements working properly!! time to buy the resistors for my second attempt at the walin preamp 2, this time with Vikash's pcb, rather than with an IC experimenter board like I used last time 😉
Tony.
Great to read its finally getting 'good'! Congratulations!
Regarding the 50Hz stuff - you need to have a strong magnetic field and a wire passing through the field to get any induced voltage. The stray field of a toroid isn't supposed to be that big/strong (though this is really at the fringe of my knowledge), so its not very (I think!) likely to be the cause (well, unless of course its getting in at the most sensitive part of the amp - the front-end). More likely its capacitor charging currents on a bad PCB layout. I can't remember if you have your diodes / capacitors on the PCB or not, maybe you can move them away i.e. a bridge bolted onto the chassis instead, run wires to the capacitors, then run wires from the capacitors to the integrated amplifier's PCB. You can run a separate set of wires to each channel of the amplifier, in case its ohmic losses through the PCB foil that's causing the problem...
But - that's a lot more tinkering to do.. Ah well, save it for next weekend!!
Cheers!!
Regarding the 50Hz stuff - you need to have a strong magnetic field and a wire passing through the field to get any induced voltage. The stray field of a toroid isn't supposed to be that big/strong (though this is really at the fringe of my knowledge), so its not very (I think!) likely to be the cause (well, unless of course its getting in at the most sensitive part of the amp - the front-end). More likely its capacitor charging currents on a bad PCB layout. I can't remember if you have your diodes / capacitors on the PCB or not, maybe you can move them away i.e. a bridge bolted onto the chassis instead, run wires to the capacitors, then run wires from the capacitors to the integrated amplifier's PCB. You can run a separate set of wires to each channel of the amplifier, in case its ohmic losses through the PCB foil that's causing the problem...
But - that's a lot more tinkering to do.. Ah well, save it for next weekend!!
Cheers!!
Hi Clem_o,
The PS is separate from the pcb, rectifier is mounted on the bottom of the chassis and so are the caps, with wires running up to the pcb. I actually have a lead sheild over the transformer as it does emit a certain amount of emf (and the lead cuts it down somewhat). I too was under the impression that a torroidal shouldn't do this but it seems with this amp, I have been unlucky on a number of counts 😉
When I first got the amp, transformer had the wrong colour coding on the secondary windings (this is 17 years ago) when I turned on it was wired with the two secondaries shorted!!! it sort of made a crackling noise and the lights dimmed 😉.... I took the transformer back to where I got the kit and they replaced it with a different (same spec different brand) transformer.
My friend made the exact same kit and had no noise problems at all, I did however 🙁 (note that this is noise where you have to have your ear close to the speakers to hear it). After a few years I bought a new torroidal same brand as the one that originally came in the kit. It was a little quieter but not by much.... later again I put the lead sheild on it. and it improved quite a bit.
I think next for this amp is definitely a PS upgrade... I'll get some caps (as it still has the no-name 17YO caps in the PS) and think about putting in the other toroid, as it only has a single 300VA which is really inadequate for a 100W / Channel amp! two X 300VA should be ok though 🙂
I'll move the torroidals centrally within the chassis and see how I go 🙂
actually re-reading your post might just have given me the clue 🙂 the wire which runs between the right channel, and the speaker protection circuit relays (which are on the left channel side of the pcb) passes very close to the torroid.... could be that it is picking up noise!! might be making it's way back through the nfb and actually correcting for something that wasn't actually amplified in the first place!!! might have to try a sheilded wire there... 🙂
though it's time to start looking at a preamp, second amp, and active crossover so I can get on with my speaker project 🙂 I think I have enough to keep me busy for a couple of years 😉
Tony.
The PS is separate from the pcb, rectifier is mounted on the bottom of the chassis and so are the caps, with wires running up to the pcb. I actually have a lead sheild over the transformer as it does emit a certain amount of emf (and the lead cuts it down somewhat). I too was under the impression that a torroidal shouldn't do this but it seems with this amp, I have been unlucky on a number of counts 😉
When I first got the amp, transformer had the wrong colour coding on the secondary windings (this is 17 years ago) when I turned on it was wired with the two secondaries shorted!!! it sort of made a crackling noise and the lights dimmed 😉.... I took the transformer back to where I got the kit and they replaced it with a different (same spec different brand) transformer.
My friend made the exact same kit and had no noise problems at all, I did however 🙁 (note that this is noise where you have to have your ear close to the speakers to hear it). After a few years I bought a new torroidal same brand as the one that originally came in the kit. It was a little quieter but not by much.... later again I put the lead sheild on it. and it improved quite a bit.
I think next for this amp is definitely a PS upgrade... I'll get some caps (as it still has the no-name 17YO caps in the PS) and think about putting in the other toroid, as it only has a single 300VA which is really inadequate for a 100W / Channel amp! two X 300VA should be ok though 🙂
I'll move the torroidals centrally within the chassis and see how I go 🙂
actually re-reading your post might just have given me the clue 🙂 the wire which runs between the right channel, and the speaker protection circuit relays (which are on the left channel side of the pcb) passes very close to the torroid.... could be that it is picking up noise!! might be making it's way back through the nfb and actually correcting for something that wasn't actually amplified in the first place!!! might have to try a sheilded wire there... 🙂
though it's time to start looking at a preamp, second amp, and active crossover so I can get on with my speaker project 🙂 I think I have enough to keep me busy for a couple of years 😉
Tony.
Hi Tony,
Haha good for you. I think there's going to be little free time in your future, juggling work, GF and audio! Maybe you can change chassis and make a pure power amplifier, with a new power supply and essentially the components of the power amplifier section. A new PCB with better layout will probably pull all the potential performance of the amplifier topology...
Cheers!!
Clem
Haha good for you. I think there's going to be little free time in your future, juggling work, GF and audio! Maybe you can change chassis and make a pure power amplifier, with a new power supply and essentially the components of the power amplifier section. A new PCB with better layout will probably pull all the potential performance of the amplifier topology...
Cheers!!
Clem
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