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.
zdr, you are presumably powering up the front end as per post 640? I further presume that the output stage driver transistors are not installed? This latter aspect was not spelled out in post 640 but is the condition under which I was able to get the front end working.
Keith
Keith
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.
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
They should definitely not be connected to anything. I don't know why not use one resistor, missing specific value maybe?
This is because of dissipation limitation of a single 18K2 1/4W resistor!
The dissipation might be as high as approx. 300mW, it is actually lower, but exceeds 250mW, so one resistor can't be used here.
The dissipation might be as high as approx. 300mW, it is actually lower, but exceeds 250mW, so one resistor can't be used here.
But they are not 1/4W, they are 0.6W resistors in the BOM... Moreover LTSpice simulation is showing 121mW dissipation at DC operating point.
I don't think so. I re-calced it, and it is 256.3mW. LTSpice and my calculation show the same result zdr.
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.
3.63mA x 3.63mA = 13.1769 x 10^-6
(13.1769 x 10^-6) x 18,200 = 240mW
But, I think the voltage is 68.3V not 66V
If you finished your FE stage, measure it,
it's better to measure it zdr.
Green LED is 2.1V and red LED is 1.7V, this
is what I found on the internet.
(13.1769 x 10^-6) x 18,200 = 240mW
But, I think the voltage is 68.3V not 66V
If you finished your FE stage, measure it,
it's better to measure it zdr.
Green LED is 2.1V and red LED is 1.7V, this
is what I found on the internet.
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Ok, you were talking about dissipation on single 18K2 resistor, that makes sense. I still think 240mW is ok for 0.6W resistor, no?
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.
Music is on!
Channel one up and runnin', and I mean without the bulb
Dead silence, no turn-on transients on speakers, simply amazing so far.
How should I bias NJL diode array? I searched the thread, read it twice, and I think I saw a post somewhere before, but cannot find it anymore. 😕
Channel one up and runnin', and I mean without the bulb
Dead silence, no turn-on transients on speakers, simply amazing so far.
How should I bias NJL diode array? I searched the thread, read it twice, and I think I saw a post somewhere before, but cannot find it anymore. 😕
