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tda1387 dac pcb "front end"
tda1387 dac pcb "front end"
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Old 5th November 2018, 03:53 PM   #331
Hugh Jazz is offline Hugh Jazz  Taiwan
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And it's done! 220pF Wima bypass on the 3K I/V resistors sounds fine. Actually sounds better than the es9018k2m... pretty impressive given an almost 30 year gap in tech between them. Here are the scope pics from earlier. I expect they would be better now but whatever. The 44KHz noise:
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2.8MHz noise
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Old 5th November 2018, 04:07 PM   #332
PJN is offline PJN  United States
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Great work Hugh, now I'm going to be forced to try some of your mods on my copy. The problem is that I'm sure my hacking skills are not at your level. But if I screw up I won't be out much.
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Old 5th November 2018, 05:01 PM   #333
Alexandre is offline Alexandre
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Good stuff Hugh, but I cant see any of your measurements (Id like to). Indeed this is a good option for low power consumers such as the tda1387 and tda1545.

My friend Jocko Homo would probably use green leds for the reference, with a CCS made of one DNMOS or NJFET. He seems to be concerned with noise at very low frequencies, always. I should do some experiments and try to hear the differences. Measuring sub-Hz stuff is hard and very time consuming.

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Old 5th November 2018, 05:18 PM   #334
Alexandre is offline Alexandre
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Oh, and he would NOT use an oscon for that position; leakage = noise!

-Alex
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Old 5th November 2018, 11:43 PM   #335
Hugh Jazz is offline Hugh Jazz  Taiwan
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Yeah sorry, no measurements, I don't have the gear to do them, and I guess that this wouldn't measure that well anyway given the numbers in the datasheet aren't impressive by modern standards.

Yes, that filter needs a low leakage cap but the Oscon is the only small 47u I had so I didn't even think about it ;-) I'm not sure I'd actually hear a difference though - I cannot hear any background noise at all. Maybe just squeeze out a little more resolution. Anyway, it should be quite easy to replace so thanks for pointing that out. I have yet to finish the buffer op amp resistors so I'll replace the Oscon when I do them.
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Last edited by Hugh Jazz; 5th November 2018 at 11:50 PM.
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Old 6th November 2018, 03:43 AM   #336
Alexandre is offline Alexandre
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Hugh, some of your attachments cant be seen, at least by me. If I copy and paste the URL I get this:
Quote:
This site is marked private by its owner. If you would like to view it, youll need two things:

A WordPress.com account. Dont have an account? All you need is an email address and password register here!
Permission from the site owner. Once you've created an account, log in and revisit this screen to request an invite.
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Alex
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Old 6th November 2018, 06:04 AM   #337
Hugh Jazz is offline Hugh Jazz  Taiwan
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Yes - that's Wordpress' security. Sorry. Here they are as attachments. Not great and arguably would still create audible IMD, but much cleaner after fitting the THS4031. The MHz noise coming out of the IC went from a constant 400mV to an output modulated and decaying/ringing 40mV peak to peak
Attached Images
File Type: jpg p_20181105_203113.jpg (72.8 KB, 16 views)
File Type: jpg p_20181105_202948.jpg (52.6 KB, 18 views)
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Last edited by Hugh Jazz; 6th November 2018 at 06:06 AM.
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