I was too sleepy, 2AM
Anyway, from PSU schematics, it seems to me R3=33R limits the load to 40mA for front end psu, so I guess I am pulling it to the limit.
I measured all the voltage drops across resistors and it seems I get too much reverse current into Q14/Q16 bases (200mV drop across 22R is way off), so I am checking now what went wrong in there. 2SA1360Y pair seems to be still ok.
Anyway, from PSU schematics, it seems to me R3=33R limits the load to 40mA for front end psu, so I guess I am pulling it to the limit.
I measured all the voltage drops across resistors and it seems I get too much reverse current into Q14/Q16 bases (200mV drop across 22R is way off), so I am checking now what went wrong in there. 2SA1360Y pair seems to be still ok.
Thanks! I am actually powering frontend up with output transistors mounted, but without power resistors as described here:
It looks to me that DC bias should be fine like this, but it's not. Weird thing is, I am getting 17mA base current through Q14 (R14=22ohm produces drop at 380mV), and I cannot explain how. Q14 was taken out and still reports good Hfe and Vbe/Vbc with DMM . All other BJTs have proper Vbe except Q14, which is at 8V. Replaced Q14 and still the same. All this excess current must be coming through D2/D7 since they shine like xmas, and R15/R18 report expected drops.
Total current drain hits the limit of 40mA and drops the rail voltages to +-10V.
It looks to me that DC bias should be fine like this, but it's not. Weird thing is, I am getting 17mA base current through Q14 (R14=22ohm produces drop at 380mV), and I cannot explain how. Q14 was taken out and still reports good Hfe and Vbe/Vbc with DMM
. All other BJTs have proper Vbe except Q14, which is at 8V. Replaced Q14 and still the same. All this excess current must be coming through D2/D7 since they shine like xmas, and R15/R18 report expected drops.Total current drain hits the limit of 40mA and drops the rail voltages to +-10V.
Group Buy for boards for dual brige supply
Is there anyone out there with Eagle experience that can help me modify the original boards for a group buy that provides for dual bridges, physically larger resistors, removal of the speaker R/C components from the board, and flexible groundings schemes?
The design would stay as close to Mihai's original design as possible in accommodating the changes, and also provide the flexibility to use his exact layout, except for possibly the R/C components on board, the removal of which allows for greater layout flexibility.
The design changes would basically be in line with post 263 of the original thread:
http://www.diyaudio.com/forums/solid-state/111756-rmi-fc100-single-stage-audio-power-amplifier-7.html#post1418746
If so, please PM me to see about starting a new group buy thread.
Thanks.
Is there anyone out there with Eagle experience that can help me modify the original boards for a group buy that provides for dual bridges, physically larger resistors, removal of the speaker R/C components from the board, and flexible groundings schemes?
The design would stay as close to Mihai's original design as possible in accommodating the changes, and also provide the flexibility to use his exact layout, except for possibly the R/C components on board, the removal of which allows for greater layout flexibility.
The design changes would basically be in line with post 263 of the original thread:
http://www.diyaudio.com/forums/solid-state/111756-rmi-fc100-single-stage-audio-power-amplifier-7.html#post1418746
If so, please PM me to see about starting a new group buy thread.
Thanks.
It looks to me that DC bias should be fine like this, but it's not. Weird thing is, I am getting 17mA base current through Q14 (R14=22ohm produces drop at 380mV), and I cannot explain how. Q14 was taken out and still reports good Hfe and Vbe/Vbc with DMM
Total current drain hits the limit of 40mA and drops the rail voltages to +-10V.
Error 1: some moron reversed Q15 while soldering my board
Error 2: one short on the PCB
Error 3: both fets reversed
Error 4: Q9: BC560 soldered instead of BC550 --> bingo!
I am up and runnin' on FE with +-38V on rails
Huh, not really working all the way, just front end bias. I tried to power it up fully assembled, but my protection light bulb glows.
Potential issues:
1) my input jfets are not closely matched. Idss is close, but Vgs is off a bit more. Vgj1=0mV, Vgj2=17mV
2) My FE trafo is 2X30V, output section one is 2X25V. This gives +-38V DC on frontend and +-35V DC on output. Is 3V difference enough? Mihai said it should be 5V, but zener in FE PSU is 36V, so I am not sure I would get more than 38V even with higher Vac.
3) All voltages on FE are very close to what they should be. Currents through R15 and R18 are a bit higher, 8.44mA as opposed to 8.25mA.
Potential issues:
1) my input jfets are not closely matched. Idss is close, but Vgs is off a bit more. Vgj1=0mV, Vgj2=17mV
2) My FE trafo is 2X30V, output section one is 2X25V. This gives +-38V DC on frontend and +-35V DC on output. Is 3V difference enough? Mihai said it should be 5V, but zener in FE PSU is 36V, so I am not sure I would get more than 38V even with higher Vac.
3) All voltages on FE are very close to what they should be. Currents through R15 and R18 are a bit higher, 8.44mA as opposed to 8.25mA.
Mihai,
You have R21 and R28 in the input stage connected to each other, but their junction is not connected to anything else. Should they be connected to the base of the transistors? Otherwise, why not use one resistor?
Still trying to trace the circuit boards for an answer, but my eyes are going buggy. Hoping you'd answer first.
http://www.diyaudio.com/forums/solid-state/111756-rmi-fc100-single-stage-audio-power-amplifier.html#post1349109
You have R21 and R28 in the input stage connected to each other, but their junction is not connected to anything else. Should they be connected to the base of the transistors? Otherwise, why not use one resistor?
Still trying to trace the circuit boards for an answer, but my eyes are going buggy. Hoping you'd answer first.
http://www.diyaudio.com/forums/solid-state/111756-rmi-fc100-single-stage-audio-power-amplifier.html#post1349109
Ok, lets see what is going on there:
I used +-38V on rails, minus loss on the folded cascode gives total voltage: 38V-4V+38V=72V.
There are three leds in series, that gives 72V-3*2V=66V across both resistors.
I=66V/18K2= 3.63mA
Pd=R*I^2=120mW.
Am I missing something? LTSpice file posted by Mihai in this thread gives 121mW.
I used +-38V on rails, minus loss on the folded cascode gives total voltage: 38V-4V+38V=72V.
There are three leds in series, that gives 72V-3*2V=66V across both resistors.
I=66V/18K2= 3.63mA
Pd=R*I^2=120mW.
Am I missing something? LTSpice file posted by Mihai in this thread gives 121mW.
Frankly, I did not know/believe there were 0.6W resistors that have size B, or what is called 0207 
I was looking at this datasheet http://www.vishay.com/docs/28766/28766.pdf, and the short-term is 0.6W, while the long-term is 0.4W.
I was looking at this datasheet http://www.vishay.com/docs/28766/28766.pdf, and the short-term is 0.6W, while the long-term is 0.4W.
