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Advice on setting bias...

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M4trix View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote M4trix Quote  Post ReplyReply Direct Link To This Post Posted: Yesterday at 6:17pm
Before I get attempted, what are the voltages on the power supply ?  +/-50-60VDC ?

Edit: OK, it's +/- 52VDC according to JBL's document.


Edited by M4trix - Yesterday at 6:22pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote monkeypuzzle Quote  Post ReplyReply Direct Link To This Post Posted: Yesterday at 6:32pm
Cheers, I can't remember what the voltage was, I want to fix this before I fire it up again just incase something fries.. Its just really odd that one way it reads half what it should and the other way it reads so incredibly high, almost like the resistor is acting like a diode... This is measuring directly off the solder that surrounds the resistor leads that come through the board so theres no track in the circuit... They are good joints as well. I'll get the glass on it and look over the tracks in details later though and give the T03s another check over as you suggest, cheers.
blah blah blah blah blah......
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M4trix View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote M4trix Quote  Post ReplyReply Direct Link To This Post Posted: Yesterday at 8:04pm
I'm almost there. Some BIAS problems...

Edit: Well, MD8003 (dual transistor) is dead as a Dodo bird and 2N3440 as well. No simulation model for those so I fitted two 'low noise' 2SC2240 instead. Still have problems with the quiescent current which is waaay too high. I'm pushing the BIAS pot wiper all the way down but to no avail. Heck if I knew what is in the output. Tried MJ15003 and 2N3773. Anyways, this is still a simulation which is far from ideal. Ouch



P.S. Well I'm doin' my best ! Tongue

Edit 2: Ok, bypassed R17, changed R30 & R32 to 47R, replaced MJ15003 with 2N3773 and the quiescent
current is now 50mA which is acceptable. Probably MJ15003 has a higher gain. The BIAS wiper is
still in the corner. LOL


Edit 3: I'm done. Changed R30 & R32 to 22R. BIAS trimpot is now useful and the quiescent current
can go down to zero. LOL.


Testing under full load with some slight clipping -->


Any suggestions guys ?

 





Edited by M4trix - 17 hours 6 minutes ago at 4:18am
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jbl_man View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 4 hours 26 minutes ago at 4:58pm
Well done,and a schemematic my eyes can actually see too! Thumbs Up
Be seeing you.
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