Thanks prasi. DC offset is no more than 3mv. At turn on, the bias is around 600mv on the lowest pot setting across an emitter resistor pair but there is a different value across other pairs by 100mv. I can increase the bias and have control and stability for a short period of time, then the bias begins to climb spontaneously until it eventually blows a rail fuse..
Hope this helps..
I have a fully operational AA9 and it has good sound. Looking forward to hearing AA9MD!
Thanks X,
Thanks X.
Yes FH-9 hvx is on my build list too. I have posted both stereo version and mono version on this thread. Some members have built it too and very happy with it.
meanwhile, here is the final compact double sided pcb version of the APEX FX-8 amp. I have a few pairs of original renesas lat fets, might use them here.
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Hi Joel,
may be apex can help point out the issue, if I remember correctly a member had built AA9MD.
wish you all the best with troubleshooting.
Dear respected apex sir can u upload a quasi complementary apex amplifier schematic which uses only npn 2Sc5200 one pair or 2 pair transistors with pre bias adjusted..
Mean just plug and play for home and party use. . Bcoz I mostly like to use baxandal diodes bias amplifiers..
I have also download many circuits from internet and built them but they did not work for me well..
Up to just 100 watt is enough Sir...
Many thanks sir in advance..
Mean just plug and play for home and party use. . Bcoz I mostly like to use baxandal diodes bias amplifiers..
I have also download many circuits from internet and built them but they did not work for me well..
Up to just 100 watt is enough Sir...
Many thanks sir in advance..
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Thank prasi and Apex.. I built up 4 of aa9md boards.. I'm trying the 3rd board and ran it for about an hour idling and at full power. Its stable, but I'm questioning the different bias voltages. Is it normal to have a large difference with the bias voltages across emitter resistor pairs? I have about 1.3A across 2 different pairs and about .6V across the other 3 pairs? If that amount of difference is normal for amps with multiple output devices I can continue and try 4th board and hopefully finish amp completely. If output transistors are matched would all bias voltages be similar?
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Hi Prasi,
I have read that irfp240-irfp9240 mosfets can be used instead of 2sk1058-2sj162 mosfets. 2sj-2sk mosfets are both very expensive, and it is difficult to find the originals. Why don't you adapt this circuit to irfp240-9240.
hi fazildiken, its exactly what xrk did with FX-8 to FH-9 hvx. you already built it I think.
https://www.diyaudio.com/community/threads/100w-ultimate-fidelity-amplifier.164093/post-6972650
https://www.diyaudio.com/community/threads/100w-ultimate-fidelity-amplifier.164093/post-6972650
Hi Joel,
congrats on nice build. how were you able to troubleshoot ?
Also, keep an eye on rectifiers, they might get too hot. if they do, consider using a small aluminium plate as a heat sink.
regards
prasi
Thank you Prasi!
One piece of 20 pieces of BDW93C was not a darlington pair, it was type shown in first attachment that I named type 1, Type 2 is a darlington pair. The 3rd attachment displays the large difference in IC vs Vbe Between Type 1 and type 2. I measured all 20 Pieces and the trend for 19 pieces closely resembled the curves grouped on the right side of the graph, with small variations between the curves.. I then went ahead and matched, as close as possible, 5 per board and found this produced more bias stability and settling at start up. I now believe that close matching from a larger batch would be beneficial.
Also, at initial start up I had far to much bias current with R14 set to minimum and believe this is what shorted one BDW94C
. I changed R20 to 560 ohms and boards are now set at 350ma per emitter pair for total of 1.75A.- Maybe this is a little high and should be lowered to 1.5A as per set up by Apex.btw; The 20 pieces of Onsemi BDW93C were purchased at the same time and have identical markings!
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Hi Prasi,
Did you release revised AA9MD gerbers that included your proposed power rail decoupling caps and ground lift from post#9462?
