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Old 15th March 2011, 12:18 PM   #31
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Location: Jackson,michigan
Interesting project.

Way back 1980 I had design a high power DAC that was to drive the drive the speaker directly without an analog buffer.

This was before the advent of digital audio which didn't hit the market until 1984.

I never got it off of the ground because of non linearity problems due to changing speaker impedences.

So I ended up scrapping the idea as the technology was still too new for the day.
Also when cd's finaly started to come around I was not happy with the way they sounded.
Although they were (and still are) very impressive the sound was not to my liking.
Even back then I felt that what is now todays 24bit standard should have been implemented.
It wasn't until the 24 bit format came about that I started to like and apperciate digital audio.
Anyway, keep at it. jer
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Old 15th March 2011, 10:15 PM   #32
hbc is offline hbc  United Kingdom
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My original inspiration for this project was the AD768, which is a 16 bit dac which can kick out 20mA, but as I prototyped the output stage I realised I could prove principle more quickly with TDA1543, just using 10 in parallel. In practice, I found I got sufficient performance using just two. The C10 and 13 give me a bit of HF roll off so I don't totally clobber the output tranies, the ECC88 can easily cope! The convinient place is across the volume pot, but would give a variable time constant.
A true multi bit power dac would be an interesting, if one could make it work, but a bit ambitious for me...
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Old 26th June 2011, 06:43 AM   #33
hbc is offline hbc  United Kingdom
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Default a few months later

The amplifier is built and tested (and marked) and my life has slowed down sufficiently to post the full circuit.

I am very happy with the amplifier, and it has bought about a shift in my perspective so much that I am wondering how to “de transistor” my home stereos. I even toyed with the idea of acquiring a “vintage” valve receiver, those guys are a bit pricey now days! So I am thinking of building my own, or a “happy hybrid” which would be an analogue input version of the amplifier, possibly with modest feedback...

My original suspicion that a single device, be it valve, transistor or whatever, providing modest gain and with modest (or less distortion), should be fairly indistinguishable from each other in the same circuit, is gone, I now hear transistors every where (at least I think I do!).

Various caveats about the circuit, If you wish to use /copy the PSU put a resistor in series with the voltage setting pot RV1 to stop shorting the input power supply in to the controller chip when the pot is reduced.
Attached Images
File Type: png spdif inputb90.png (161.4 KB, 76 views)
File Type: png classa final90.png (162.3 KB, 77 views)
File Type: png power90.png (172.0 KB, 72 views)
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