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Chip Amps Amplifiers based on integrated circuits

bridged LM1875 >>ASYMMETRY<< issue
bridged LM1875 >>ASYMMETRY<< issue
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Old 10th October 2019, 07:52 AM   #11
ubergeeknz is offline ubergeeknz  New Zealand
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Not quite sure why you want to drive power transistors off the transformers still. What do you want to achieve?
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Old 10th October 2019, 07:54 AM   #12
ubergeeknz is offline ubergeeknz  New Zealand
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Also worth noting, transformers "reflect" impedance. So with nothing on the secondaries of those transformers, you may get strange results. Try putting the expected load on the secondaries so that the impedance is reflected on the primaries.
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Old 10th October 2019, 10:23 AM   #13
johnnyhou is offline johnnyhou  United States
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Honestly, I have not had any luck building a discrete power amplifier as of yet, at least I learned enough to check hfe for matching transistors for LTP but no actual working circuit as of yet. I suppose I got lucky with the first transformer coupled attempt getting a pretty darn good sounding 100 watt amp from 30-0-30 supply. I am hoping to quadruple that number but my transformers have to be right on the money to get those power transistors to deliver. Stumbled on issues with impedence reflection through transformers so that is why I am using 2 seperate, identical transformers tying their primaries together in series and using lm1875 drivers in BTL mode to get the voltage swing as high as possible. A 5:1 ratio on the transformers brings the voltage and current into range to drive the power transistors in common emitter mode class AB arrangement for what I hope to be somewhere in the range of 300 - 500 watts.
I have breadboarded the digi125 and aksa-55 but did not work. I am learning though. No problem setting up working simulations in LTSpice, shouldn't be long before I start having some success with the discrete amps. Anyway, thanks again for sharing.
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Old 10th October 2019, 10:28 AM   #14
ubergeeknz is offline ubergeeknz  New Zealand
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A very interesting approach... Will be pretty cool to see what you come up with. Have fun with your project.
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Old 12th October 2019, 10:35 PM   #15
Mark Tillotson is offline Mark Tillotson
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C2 and C7 are an order of magnitude too small, so at LF there will be asymmetry due to mismatched electrolytics and the LF roll off starts too soon.


R4 and R6 seem suspiciously small. 100nF / 10 ohms are by far the commonest Zobel network used and for good reason.
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