Simple I/V for TDA1541

[Peter Daniel]

I would also suggest you use non oversampling. It can be easily tried and if not satisfied you can always return to regular setup (oversampling). Heres the link: http://members.xoom.virgilio.it/hi_fi/com.htm
http://members.xoom.virgilio.it/hi_fi/cd960.htm

I actually didn't cut any traces, just the three of the I2S carrying wires and soldered them directly to decoder's corresponding pins. But your lay out may be different.

[apassgear]

Even though I will try non oversampling when the time comes I'ts my gut feeling that is better a digital filter than an analog low pass filter.

I'll do the non oversampling after I get the analog portion working and then figure out how to do the analog low pass.

What's your feeling regarding this two (different) filter approach?

[Peter Daniel]

I will simply remove low pass analog filter. I don't think it's needed

[apassgear]

Interesting, so no attempt to reduce the hall of mirrors, wide open, no digital or analog filtering.

[tschrama]

Hi Apassgear,

Thanks for your info and pics. I am not a real-pro-experienced-diy-freak like Peter but I would like to share my experience with you:

I have wonderfull results with a CS8412 / TDA1541A / single BTJ I/V /capacitor / to amplifier or direct (4mApp) into headphone. There's only 1 cap in the signal path, no low-pass filter, no oversampling. There's a snap, rythm and ambiance to the bass I've never heard before in my other DACs. The CS8412 has it's own regulator, like the TDA1541A, but the I/V stage (the single BJT) shares its +/-15V power supply with the TDA1541A, decoupled with 100hm/1000uF, running 13mA Iq each channel.

This setup has a assymetrical slewrate but I don't know wheter that actually mattters. Anayways, the discrete single BJT I/V stage can be made small enough to fit a 8 pin DIP package, just to give you another option.

Goodluck, regards,

Thijs

[apassgear]

Thijs,

Well that's a very minimalist TDA1541 and very atractive proposal for me and specially if it sounds as you say, this is what I'm looking at the end.

Did you make a dedicated PCB or is it a P2P setup?

Just to get an idea, is the BTJ connected similarly to Rbroer shema without the opamp? Grounded gate?

Why did you select a CS8412?

Thanks for your input hope to hear more from you.

[apassgear]

Coming back to my LM6181 I/V "stage".

I removed the ceramic bypass caps and connected the DAC directly to the inverting input of the opamp still with the 1K FB resistor. I did not remove the 0.01u cap across both rails though.

To my surprize I got some AC noise through the speakers which was not present before and this is without any signal going through the CDP!!!

Feeding signal I got same noise as before.

Beats me!

Any suggestion?

[Jocko Homo]

Peter.....you really didn't say this did you:

I will simply remove low pass analog filter. I don't think it's needed

You either need to borrow a spectrum analyzer.....or drive down to Texas to borrow mine.

Guido........Phred.......this one is yours......

Jocko

[Peter Daniel]

I think it was Phred who liked the sound of Scott Nixon's DAC. As far as I know, it doesn't use low pass filter.

And I remember when you said that both TDA1541/43 are ancient chips and non-oversampling can't be any good. It happens that I just tried both of them without digital filter and they are not any worse than my PCM1704 DACs. I can only blame myself for not trying it earlier

But, I also don't measure anything and rely only on my (and some friend's) ears. Maybe it's good, maybe not.

[Fred Dieckmann]

I have a low pass filter on mine. I had a talk with Scott and think you might get away without one in some cases. The high output impedance of the DAC's I to V stage (a resistor in this case) acts as a filter with the cable impedance to provide some filtering. Many amps and preamps also contain low pass filters at the inputs. In light of this you actually do have a low pass filter but at a pretty high frequency. I put low pass filters on the inputs of most analog circuits to suppress RFI noise at the input. I do it because it sounds better (and I know the engineering reasons why) So much for the objective versus subjetive debate on this one.

"But, I also don't measure anything and rely only on my (and some friend's) ears. Maybe it's good, maybe not."

Jocko and I listen to everything we design as well as circuits designed by others. That's how you make correlations between good sonics and good engineering pratices. Often, one hears sonic differences and then goes back to measure things to see what the technical reason might be. You can then pay attention to this part of the design on the next go around. It's kind of like the joke about the guys who goes to the doctor and says" It hurts when I do this." The doctor tells him "Then don't do that!"