I've finally taken some time to work a bit on some of my audio projects, it has been some years since I worked on anything audio related. I finally have my fall/winter M2 project to the point that I could fire up the right channel for some testing (a little a head of schedule). The left channel is 99% done, but I need to give it one last check to make sure I don't have any solder bridges around the input JFETs as the solder pads are pretty close together. I'm using grimberg's boards by the way, which are fantastic!
The left side seems to be working fine, it bias up to about 1.3A. However, I've only been able to get the offset to about -0.126v before I reach the limit of my 5k pot. I just wanted to confirm with the experts before I changed anything; to adjust that last bit of offset out I need to lower the value of R6 correct? I just want to maker sure I'm interpreting what ZM suggested way back in post #17 correctly. Thanks in advance!
The left side seems to be working fine, it bias up to about 1.3A. However, I've only been able to get the offset to about -0.126v before I reach the limit of my 5k pot. I just wanted to confirm with the experts before I changed anything; to adjust that last bit of offset out I need to lower the value of R6 correct? I just want to maker sure I'm interpreting what ZM suggested way back in post #17 correctly. Thanks in advance!
I am glad the boards worked out well for you. Regarding the stubborn offset, you have the option of adjusting the values of either R6 or R7. In my case it got stuck around -50 mv. I resolved it by replacing R7 with a 49.9K resistor.
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Thanks Grimberg
I give them warm for 1 hour.
Always measure offset with RCA input hot shorted to the ground or not necessary?
Non need connect dummy load power resistor to speaker outputs for the 0 V offset adjustments ?
My DMM probes polarity and speakers are ok the sames + with +
Nice Grimberg !
Heat sink is at his full warm temperature.
Offset values is close to perfection so i don't touch it.
I wait for the toroids so i do it the same regulations again with finished psu.
It's easy with precision in mouvements and pattience.
Thanks
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IRF from Tea-Bag kit.
9240 are Harris brand, 240 are Vishay's.
I enjoy a lot music session I play now my diy M2 at night.
Can't resist was ready hot hahaha.
One more perfect example of Papa design amazing amplifier made with ordinary ~ 1 $ mosfets and affordable cost Edcors.
Sure vfets are interesting to play with in this audiophile hobby, but I can keep M2 forever.
I can't say it is powered on or off because is the total silence noise floor with my modified gain chain structure.
Yummy
Soundhappy thought he would have to make changes to his M2. He was not sure what to do, that's why I asked him for the polarity of the DC offset. It would be useful in determining what resistor value to use.
If yours has <1 mV, to me that's perfect. No need to do any thing, just enjoy the music.
If yours has <1 mV, to me that's perfect. No need to do any thing, just enjoy the music.
OK F6 pcbs sleep in the drawer for some time, but I try with pleasure.
BA-3 are interesting, especially this one pre without n feedback.
First,I get finish vfet's and Schade Feedback 50 on the bench
Back to M2 I do final bias value with new psu Tea-Bag version as well.
They are great! I used a HiFi2000 case that was sitting around and the pcb hole spacing was perfect for the heat-sinks. I was able to drill through holes for everything and just drop socket head screws between the fins, can't see them at all. Significantly easier than drilling and tapping blind holes in the heat-sinks. Thank you for making them available!
Thanks for the info everyone about the offset, I'll play with some resistor values and see what I can do. I'm using IRFP240/9240 FETs from Vishay by the way.
I have the other channel hooked up and another issue has arisen. Upon full power-up the bias takes off and rises steadily to a tad over 1.166v across the source resistors (about 2.5A), almost exactly double the bias of the right channel. Parts values seem to check out OK, but I'll give the board a better look when I'm less tired. I switched out the 4N35 and no change. Only thing I think of is wrong resistor values(?).
I don't know if you saw it, but in January of 2016 I posted pictures of standoffs installed using through holes, as you described. I am providing a link to the post for the benefit of members who have not read this thread since the beginning.
http://www.diyaudio.com/forums/pass-labs/281520-official-m2-schematic-21.html#post4581816
http://www.diyaudio.com/forums/pass-labs/281520-official-m2-schematic-21.html#post4581816
