Hi, I built a Cmoy powered by 2x9v. Then I tried to add Sijosae's discrete rail splititer to avoid dc offset forcaused for uneven discharge of the batteries (tangentsoft advice). The problem is that 'm not sure if I did well. Can anyone check attached scheme to confirm that everything is OK?
Thanks
Thanks
Attachments
could work - use the same type Q for the diodes (short c-b) for better bias current control
there are several different ideas to keep track of
balancing battery drain
as shown if one battery V drops more than the other, the circuit will drain the other battery to match
the Qs can be very lightly biased so as not to draw much current when the batteries balance - in fact a little "deadband" from underbiasing is desirable as there will be AC signal caused V drop in each battery's internal resistance which you probably don't want to "balance"
active gnd/supply splitter
if you disconnect the battery midpoint then you have a "active gnd" where all of the headphone drive return current flows in the splitter Q - you probably want Class AB bias in this case - and lower emitter R
the batteries aren't "balanced" this way but they see exactly the same current drain - ps anti-reversal diodes would be a good idea though
I'm not really certain any balance circuitry is needed if you use the same manufacturer's batteries from the same production batch - after all there are 6 or more cells inside each "9 V" battery that you can't get at to balance
it would help if you never totally drained them - a low V cutoff circuit would maybe be a better use of componenets
there are several different ideas to keep track of
balancing battery drain
as shown if one battery V drops more than the other, the circuit will drain the other battery to match
the Qs can be very lightly biased so as not to draw much current when the batteries balance - in fact a little "deadband" from underbiasing is desirable as there will be AC signal caused V drop in each battery's internal resistance which you probably don't want to "balance"
active gnd/supply splitter
if you disconnect the battery midpoint then you have a "active gnd" where all of the headphone drive return current flows in the splitter Q - you probably want Class AB bias in this case - and lower emitter R
the batteries aren't "balanced" this way but they see exactly the same current drain - ps anti-reversal diodes would be a good idea though
I'm not really certain any balance circuitry is needed if you use the same manufacturer's batteries from the same production batch - after all there are 6 or more cells inside each "9 V" battery that you can't get at to balance
it would help if you never totally drained them - a low V cutoff circuit would maybe be a better use of componenets
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I appreciate your quick answers. The CMOY works right with both 2x9v batteries charged. I tried then connecting one completely discharged battery and the other fully charged. The circuit went immediately very hot (it even started to smoke). I've not taken any measure of the output for different loads but I'm doing it next weekend. Thanks for your advice
I can't read the language, but sijosae's own post on the matter:
http://www.headphoneamp.co.kr/bbs/zboard.php?id=diy_sijosae&page=1&sn1=&divpage=1&sn=off&ss=on&sc=on&keyword=split&select_arrange=headnum&desc=asc&no=159
http://www.headphoneamp.co.kr/bbs/zboard.php?id=diy_sijosae&page=1&sn1=&divpage=1&sn=off&ss=on&sc=on&keyword=split&select_arrange=headnum&desc=asc&no=159
Hi, I checked the output. Vout was 2-3mV DC when both batteries are charged. Vout is 6 V when there's only one battery (I took out the other one to simulate a uneven discharge). So there's quite high offset DC voltage that could damage the cans. Then I tried this modification:
Vout with both batteries: 2-3mV and I got same result wiht only one battery. No offset at all, so I think that sijosae's rail splitter is not needed with this configuration. What do you think?
An externally hosted image should be here but it was not working when we last tested it.
Vout with both batteries: 2-3mV and I got same result wiht only one battery. No offset at all, so I think that sijosae's rail splitter is not needed with this configuration. What do you think?
I have used the circuit in post #5 successfully for many years in many different configurations (bias currents).
But I find it better using resistors to replace D1 and D2. That way, you have much better control of bias current. If you worry about PSRR, just add something like a220uF cap in parallel.
Patrick
But I find it better using resistors to replace D1 and D2. That way, you have much better control of bias current. If you worry about PSRR, just add something like a220uF cap in parallel.
Patrick
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