I will try 56k. That's a non standard value for me so might have to go "all ghetto" as you say and solder two in series get that. Could this also be due to unmatched input JFETs?
*****PSU PCB issue
Tea-bag, thanks for another awesome GB, I'm taking some time during the holidays to start on the M2.
I wanted to post a problem I ran into with the PSU PCB in case others run into a similar issue. In testing the fully populated PSU board, the negative rail was shorted, luckily identified with a variac. I was able to isolate it to the last pair of paralleled capacitors on the negative rail of the PSU board. After testing and removing component by component, I identified that the top layer copper pours by the output header must have been shorted during production. The issue was non-obvious because of the silkscreen layer on top.
After scoring between the pours (see picture), the issue was resolved. Easy fix, minus the desoldering, but you may want to test the PSU boards for shorts between the +/G and -/G pins before starting assembly.
Tea-bag, thanks for another awesome GB, I'm taking some time during the holidays to start on the M2.
I wanted to post a problem I ran into with the PSU PCB in case others run into a similar issue. In testing the fully populated PSU board, the negative rail was shorted, luckily identified with a variac. I was able to isolate it to the last pair of paralleled capacitors on the negative rail of the PSU board. After testing and removing component by component, I identified that the top layer copper pours by the output header must have been shorted during production. The issue was non-obvious because of the silkscreen layer on top.
After scoring between the pours (see picture), the issue was resolved. Easy fix, minus the desoldering, but you may want to test the PSU boards for shorts between the +/G and -/G pins before starting assembly.
Attachments
M2 project, grounding
Finally my M2 project is ready, well almost. I’m very pleased with the result. A few things is still on the todo list.
M2Clone and PSU boards from Tea-Bag (http://www.diyaudio.com/forums/blogs/tea-bag/923-dual-rail-power-supply-power-amplifier.html, http://www.diyaudio.com/forums/blogs/tea-bag/203-m2clone-boards-120mm-ums-spacing.html ).
Caps: 8 x 15000uF
Enclosures from HIFI2000.it Dissipante 4U 300mm (little tight but should dissipate the heat. I let You know).
Components mostly from Tea-Bag’s BOM (resistors from Vishay RN60D-serie and two pairs of exotic Fukushimas)
300VA transformer from Toroidy.pl, dual 18V secondaries.
Schematics from firstwatt.com and tea-bags blog.
Bypass or no bypass capacitors(?), I went for the bypass alternative.
I went for Harris instead of IRFP9240 described by Tea-bag(http://www.diyaudio.com/forums/blogs/tea-bag/203-m2clone-boards-120mm-ums-spacing.html).
Inrush: thermistor CL-60
Filter on main: X2 0.47uF parallell(!) on power lines (230V)
It seams like color by numbers but it was not, but fun. After a lot of reading and couple months looking at the parts I tossed them in the case and whisked around with a solder iron. The M2 clone became ready for smoke test. No smoke
, puh.
Observations:
After a couple of hours the heat sinks settled to 45-50°C, 20-25°C above ambient. The 300VA transformer working 200VA at nominal, perhaps little to high. The Fukushimas bias ing at 0.648V-0.662V with offset 2mV. The difference is probably because the Harris. The transformer buzzing a bit, ground-loops? Small speakers reveals a small 50/100/150Hz hum.
Sound:
After smoke test and soundest I decided to hook it up to the bigger speakers. I let it warm up with low volume for half an hour. I took a seat in the sofa and raised the volume to comfortable 60-70dB. Happyface!! The sound is amazing, detailed, clear but still the dash of softness I like. Amazing detailed base, mid and top and with natural attack. My ears agree with the distortion free clarity. My tube amp have a bigger voices at mid range so compared to M2clone it appears the voices is higher. I am convinced the tube amp is not the accurate reference but the one I can compare with.
In silent room the transformer is buzzing. To get rid of the hum and buzz I plan for a hole new set of cables with hopefully rigorous routing. The power cables now is in complete chaos and ground loop friendly. Is the transformer to small? Sensitive capacitors in PSU? The new power cables are going to be tined solid copper tightly twined firmly against chassi. If someone have recommendations for a remedy I receive them thankfully.
I miss the sound of my M2. It’s very addictive.
*DC-bocking, always(!) but no effect.
*Ground-star in chassi near main inlet, check.
*Thermistor between PSU-G and chassi, no effect.
*R10 5W in parallell with X2 0.1uF between PSU-G and chassi, no effect.
*Disconnect transformer ground, no effect
Finally my M2 project is ready, well almost. I’m very pleased with the result. A few things is still on the todo list.
M2Clone and PSU boards from Tea-Bag (http://www.diyaudio.com/forums/blogs/tea-bag/923-dual-rail-power-supply-power-amplifier.html, http://www.diyaudio.com/forums/blogs/tea-bag/203-m2clone-boards-120mm-ums-spacing.html ).
Caps: 8 x 15000uF
Enclosures from HIFI2000.it Dissipante 4U 300mm (little tight but should dissipate the heat. I let You know).
Components mostly from Tea-Bag’s BOM (resistors from Vishay RN60D-serie and two pairs of exotic Fukushimas)
300VA transformer from Toroidy.pl, dual 18V secondaries.
Schematics from firstwatt.com and tea-bags blog.
Bypass or no bypass capacitors(?), I went for the bypass alternative.
I went for Harris instead of IRFP9240 described by Tea-bag(http://www.diyaudio.com/forums/blogs/tea-bag/203-m2clone-boards-120mm-ums-spacing.html).
Inrush: thermistor CL-60
Filter on main: X2 0.47uF parallell(!) on power lines (230V)
It seams like color by numbers but it was not, but fun. After a lot of reading and couple months looking at the parts I tossed them in the case and whisked around with a solder iron. The M2 clone became ready for smoke test. No smoke
, puh.Observations:
After a couple of hours the heat sinks settled to 45-50°C, 20-25°C above ambient. The 300VA transformer working 200VA at nominal, perhaps little to high. The Fukushimas bias ing at 0.648V-0.662V with offset 2mV. The difference is probably because the Harris. The transformer buzzing a bit, ground-loops? Small speakers reveals a small 50/100/150Hz hum.
Sound:
After smoke test and soundest I decided to hook it up to the bigger speakers. I let it warm up with low volume for half an hour. I took a seat in the sofa and raised the volume to comfortable 60-70dB. Happyface!! The sound is amazing, detailed, clear but still the dash of softness I like. Amazing detailed base, mid and top and with natural attack. My ears agree with the distortion free clarity. My tube amp have a bigger voices at mid range so compared to M2clone it appears the voices is higher. I am convinced the tube amp is not the accurate reference but the one I can compare with.
In silent room the transformer is buzzing. To get rid of the hum and buzz I plan for a hole new set of cables with hopefully rigorous routing. The power cables now is in complete chaos and ground loop friendly. Is the transformer to small? Sensitive capacitors in PSU? The new power cables are going to be tined solid copper tightly twined firmly against chassi. If someone have recommendations for a remedy I receive them thankfully.
I miss the sound of my M2. It’s very addictive.
*DC-bocking, always(!) but no effect.
*Ground-star in chassi near main inlet, check.
*Thermistor between PSU-G and chassi, no effect.
*R10 5W in parallell with X2 0.1uF between PSU-G and chassi, no effect.
*Disconnect transformer ground, no effect
great service
Thanks Mike,
M2 package arrived, ordered 16 Juli 2017, received 26 Juli 2017 in Germany (NRW), strait into the mailbox, without custom interference ;-)
It will be a while before this M2 build will be finished, I have an F6 waiting to be completed first. Some here will tell me forget about the F6, but I want to hear the difference with my own ears.
Kind regards
Bert
Thanks Mike,
M2 package arrived, ordered 16 Juli 2017, received 26 Juli 2017 in Germany (NRW), strait into the mailbox, without custom interference ;-)
It will be a while before this M2 build will be finished, I have an F6 waiting to be completed first. Some here will tell me forget about the F6, but I want to hear the difference with my own ears.
Kind regards
Bert
My 400VA Antek buzzes too, and the EMI reaches the signal trafos, inducing hum. I bought some mu-metal shielding for the trafos but have not had time to install.
This would seem to be a common problem for all Pass amps of late that use signal transformers. When I switched to a SMPS for the +/-24v rails, absolutely no hum/buzz. Same grounding scheme - so it is not a ground loop. Also confirmed by moving power trafo outside of case and hum went away. Proximity to main power trafo is a real issue (even at max distance of signal trafo on one end and power trafo on other end of case). I am also using 4U Dissipante case with UMS sinks.
Hi Tea-Bag! Do You still have some M2 pcb? PSU?
A friend vistited for a listening session and was so happy about the sound that he would like to do the same project.
Changes I made after #257 is a new 300VA trafo(!), dead silent. Solid cables, twisted near ground. The onle buzz now is a not noticeable buzz from the 15" elements.
/SOV
A friend vistited for a listening session and was so happy about the sound that he would like to do the same project.
Changes I made after #257 is a new 300VA trafo(!), dead silent. Solid cables, twisted near ground. The onle buzz now is a not noticeable buzz from the 15" elements.
/SOV
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