Hi All!
Attached to this post is a pdf containing screen captures of a parallel opamp headphone amplifier.
it is build as follows:
1 zero impedance fader amplifier + 3 buffers with 150 Ohm output resistors in parallel. (50 ohms output impedance). This way it nearly matches the impedance of 55ohm studio headphones.
I first build this amplifier on a test board with a quad opamp : MC33079. It worked well. No problems.
Then i build a pcb version with two dual opamps and one quad: MC33078/MC33079.
I placed two 220uf35v electrolytics in the supply rails, to act as reservoir caps.
After all checkings i powered the little beast.... only one channel worked... more checks.....layout is ok all tracks checked with the multimeter...etc... new test...still sounds only one channel.... then......booomm the output caps popped!!
Well, ok so i pull out the 220uf 35v output caps....replaced for a piece of wire.... and still only one channel works.....
Today i try to make it work with the output jack gnd connected to circuit gnd to see if this makes a change....noo.....worse...i played an old discman, and only i could hear sound when i switch down power of the headphone amp..... ??? hmm...¿ a time constant...? no clue really....just guessing...
FADER AMPLIFIER FEEDBACK LOOP: 4k7 / 2k2 to ground
fader resistance: 10k linear.
Input capacitor: 2u2 63v. orientation: input +_____-
Output capacitor: 220uf 35v. orientation: output -_____+
BUFFERS: 150 Ohms at their outputs. 3 in parallel.
Any comment is wellcome!!
Thanks a lot!
JAY X.
Attached to this post is a pdf containing screen captures of a parallel opamp headphone amplifier.
it is build as follows:
1 zero impedance fader amplifier + 3 buffers with 150 Ohm output resistors in parallel. (50 ohms output impedance). This way it nearly matches the impedance of 55ohm studio headphones.
I first build this amplifier on a test board with a quad opamp : MC33079. It worked well. No problems.
Then i build a pcb version with two dual opamps and one quad: MC33078/MC33079.
I placed two 220uf35v electrolytics in the supply rails, to act as reservoir caps.
After all checkings i powered the little beast.... only one channel worked... more checks.....layout is ok all tracks checked with the multimeter...etc... new test...still sounds only one channel.... then......booomm the output caps popped!!
Well, ok so i pull out the 220uf 35v output caps....replaced for a piece of wire.... and still only one channel works.....
Today i try to make it work with the output jack gnd connected to circuit gnd to see if this makes a change....noo.....worse...i played an old discman, and only i could hear sound when i switch down power of the headphone amp..... ??? hmm...¿ a time constant...? no clue really....just guessing...
FADER AMPLIFIER FEEDBACK LOOP: 4k7 / 2k2 to ground
fader resistance: 10k linear.
Input capacitor: 2u2 63v. orientation: input +_____-
Output capacitor: 220uf 35v. orientation: output -_____+
BUFFERS: 150 Ohms at their outputs. 3 in parallel.
Any comment is wellcome!!
Thanks a lot!
JAY X.