built a Gilmore headphone amp and it puts ~1.47v dc at output, w/o an input signal. some resistors were hard to find. here's a schematic of how i built it 
An externally hosted image should be here but it was not working when we last tested it.
the matching isn't very exact in the output stage, any help is greatly appreciated, let me know if you want voltage readings or anything else thanks 
here's the schematic i tried to build it from
and one more thing , the 4 2sc1815's on the output stage get hot, and their adjacent 25ohm resistors get really hot. everything else is room temp.
An externally hosted image should be here but it was not working when we last tested it.
and one more thing
, the 4 2sc1815's on the output stage get hot, and their adjacent 25ohm resistors get really hot. everything else is room temp.Hi!
Getting hot seems O.K. to me unless the temerature of the output transistors does not rise above 80°C or so.
This amp is very sensitive to unbalanced tail currents from the dual FETs. Try to measure the voltage at the 500R resisors near the LED's. They should be exactly the same. Different voltages will be amplfied with a factor of 16.
Thermal coupling of the LEDs and the 2SA1015/2SC1815 is required. Mount the LED and the Transistors together as close al possible. Match the LED's and Transistors and use 1% metal film resistors. BTW, is the -I input of your amp tied to ground?
Getting hot seems O.K. to me unless the temerature of the output transistors does not rise above 80°C or so.
This amp is very sensitive to unbalanced tail currents from the dual FETs. Try to measure the voltage at the 500R resisors near the LED's. They should be exactly the same. Different voltages will be amplfied with a factor of 16.
Thermal coupling of the LEDs and the 2SA1015/2SC1815 is required. Mount the LED and the Transistors together as close al possible. Match the LED's and Transistors and use 1% metal film resistors. BTW, is the -I input of your amp tied to ground?
Yes the servo loop is correct.
Hundreds of these have been built.
For sale too at www.headamp.com (not me)
check out all archived threads at
www.headwise.com and
www.head-fi.com
look too for sijosae's miniature versions.
Hundreds of these have been built.
For sale too at www.headamp.com (not me)
check out all archived threads at
www.headwise.com and
www.head-fi.com
look too for sijosae's miniature versions.
Hi kevin,
I didn't meant that the circuit with the servo loop will not work ( it does, a simple integrator...) but if you have a output voltage of about 1.47V this might me caused by a not properly working servo loop, maybe incorrect grounded or maybe two different LEDs used or ???. I would check the output voltage of the integrator first, if it's in the range of +/- 10V this is OK. If it's out of this range the servoloop cannot work.
I didn't meant that the circuit with the servo loop will not work ( it does, a simple integrator...) but if you have a output voltage of about 1.47V this might me caused by a not properly working servo loop, maybe incorrect grounded or maybe two different LEDs used or ???. I would check the output voltage of the integrator first, if it's in the range of +/- 10V this is OK. If it's out of this range the servoloop cannot work.
you guys won't believe this. the first datasheet i read on the 2sa1015's said flat part facing you left to right ebc. the second one i read (today) said ecb. so i checked and mine were ecb. thank you both so much for all the help. (btw, i followed your advice, matched the 500r's, diodes, and bypassed opamp supply rails and got 1.32v, transistors in wrong!) thanks again
thank you both so much for all the help. (btw, i followed your advice, matched the 500r's, diodes, and bypassed opamp supply rails and got 1.32v, transistors in wrong!) thanks againpdf's for the semiconductors for all of my designs
(not including uberamp)
http://gilmore.chem.northwestern.edu/2sa1015.pdf
http://gilmore.chem.northwestern.edu/2sa1156.pdf
http://gilmore.chem.northwestern.edu/2sa1968.pdf
http://gilmore.chem.northwestern.edu/2sa970.pdf
http://gilmore.chem.northwestern.edu/2sc1815.pdf
http://gilmore.chem.northwestern.edu/2sc2240.pdf
http://gilmore.chem.northwestern.edu/2sc2705.pdf
http://gilmore.chem.northwestern.edu/2sc3675.pdf
http://gilmore.chem.northwestern.edu/2sj109.pdf
http://gilmore.chem.northwestern.edu/2sj79.pdf
http://gilmore.chem.northwestern.edu/2sk216.pdf
http://gilmore.chem.northwestern.edu/2k389.pdf
http://gilmore.chem.northwestern.edu/irfbc30.pdf
hopefully without spelling errors this time.
(not including uberamp)
http://gilmore.chem.northwestern.edu/2sa1015.pdf
http://gilmore.chem.northwestern.edu/2sa1156.pdf
http://gilmore.chem.northwestern.edu/2sa1968.pdf
http://gilmore.chem.northwestern.edu/2sa970.pdf
http://gilmore.chem.northwestern.edu/2sc1815.pdf
http://gilmore.chem.northwestern.edu/2sc2240.pdf
http://gilmore.chem.northwestern.edu/2sc2705.pdf
http://gilmore.chem.northwestern.edu/2sc3675.pdf
http://gilmore.chem.northwestern.edu/2sj109.pdf
http://gilmore.chem.northwestern.edu/2sj79.pdf
http://gilmore.chem.northwestern.edu/2sk216.pdf
http://gilmore.chem.northwestern.edu/2k389.pdf
http://gilmore.chem.northwestern.edu/irfbc30.pdf
hopefully without spelling errors this time.
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