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Old 23rd June 2004, 05:59 PM   #21
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I would really recommend this I/v stage: Less simple I/V for TDA1543

I've built it and it sounds very good. You might experiment with PS for best results.

He also came with a simpler version, which I didn't try: Single rail, active I/V for TDA1543, TDA1545A
“Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC
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Old 23rd June 2004, 06:05 PM   #22
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Originally posted by IpsilonSound

Setmenu, with all due respect, this is gross overgeneralization. Why being so dependent on others' mishaps with active i/v stage experiments? You can find dozens of different implementations of the i/v active stages, ranging from simple to complex. For some it did result with inferior sound, but that shouldn't preclude one from trying it out for himself and rushing to decisions only after all the possibilities have been explored.
I never said the passive i/v is bad, to me it sounds great, but I cannot implement it with the same power supply feeding both my PPA and DAC. That's Reason #1. Reason #2 - attempt to reduce the distortions and spikes visible on the spectrum, and they are clearly dependent on the load/impedeance put on the TDA1543. Therefore, properly implemented 3 channel, virtual ground, class-a, precision, extremly low noise/distortion wideband active i/v stage may be the only remedy for this? Did you check the datasheet specs for LM6171 amp? I also read what others think about i/v active opamp conversion, after conductive some interesting opamp experiences. They are not that negative, indeed. Unfortunately, it's in another language forum, otherwise, i could send the link to prove it. Well worth reading...
Hi IpsilonSound
My comment was meant to reflect my own lack of knowledge..

Regarding my 'birdies' perhaps this is the result of a incorrectly optimized IV ?
I don't know as yet.
would that result in the my extra/missing tones?

I raise my hand in guilt here because I simply used Peters
values [2.7k and 1.5k] on the assumption they would work with my setup[8v dac supply].
Perhaps I ought to do some surgery and insert a pot in place of
the 1.5k and do some twiddling eh?

It would be interesting to hear my dac with a decent test tone
performance, may well transform it!

If the IV is not the problem then I am at a bit of a loss as what to do next
with things such as regulators my choice is limited, I need ldo types, as I am using a 9.6v batt pack.

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Old 23rd June 2004, 06:20 PM   #23
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Setmenu, just occurred to me... remember this earlier discussion about omitting the DAC ground when connecting the output to the amp? I tried it and the sound wasn't too good then, some distortion was heard alright. That's probably what causes your 'extra' sounds when running high frequency test tones thru DAC. Unless you connected them normally and feeding both from separate batteries already, of course, that would be the primary reason for high-freq. garbage sounds, i guess.

Try to feed your DAC from a separate supply and connect 3 output wires to the amp, see what happens?
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Old 23rd June 2004, 06:37 PM   #24
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[QUOTE][ Unless you connected them normally and feeding both from separate batteries already, of course.


I am doing the above, I agree single supply does not sound too nice.

The fact that you are getting clean test tones is going to bug me,
until I find out why mine are not clean

I had begun to put it down [in part] to the nature of the nos beast..

I suppose I should draw up a list of areas of suspicion.
Afterall , the design is not my own ,except the detail of layout and reg choice.

Makes me wonder whether it,s a single area that is causing the problems or a combination of many

So , what can cause such polluted test tones from around 16K upward?
Lots and lots of things I should imagine

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Old 23rd June 2004, 09:43 PM   #25
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I just fed the output of my Sony2000 portable into my soundcard and got this at 1K.
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File Type: jpg sony-at-1k-73k.jpg (73.5 KB, 146 views)
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Old 23rd June 2004, 09:44 PM   #26
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And this with my Sony feeding the Nos dac at 1k

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File Type: jpg nos-at-1k-76k.jpg (76.5 KB, 127 views)
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Old 23rd June 2004, 09:58 PM   #27
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I had no time last night to post the 20kHz graphs taken yesteday.

Here's the graph:
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Old 23rd June 2004, 11:22 PM   #28
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Default test graphs taken from Panasonic dvd player

The output directly from Panasonic dvd player lineout connected to the Audigy soundcard revealed the same spikes which I thought were caused by the DAC:
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File Type: jpg 1khz.jpg (68.1 KB, 103 views)
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Old 23rd June 2004, 11:59 PM   #29
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Default first test

Denon DCD3300 with PCM56K

1kHz -60dB test tone.

This is a player that measures very bad, best adjustment gives harmonics that are up to -39dB, the worst one.

This is clearly audible.
Turning the adjustment pot can not make the tone pur.
It is getting better until this high sizzling sound fades to very low level and then it gets stronger again.

But the player sounds not so bad.

I wonder if I can hear -50dB harmonics...

Another thing:

This Denon got 4 HP optocouplers just in front of the PCM56s and a bad noise floor with -60dB signal.
Today I bypassed the optos and another 74HC04 and the noise is gone.
It did not affect distortion !

This machine is so nice mechanical but a cheap Kenwood with same chip measures much better.
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