[Genoa1893]

Greetings all!
I know it's almost a zombie thread, I'm about 10 years late but I happened to start playing with my old SB3 and so far I bypassed the standard input and output elco caps with some wima 0.1uF/100V MKS I had in my drawer and the same for the 3300/16 and the smaller elco-cap behind the connection panel. Power is supplied by a 5V/2.1A battery charger for mobile, and sound is nice, although less deep and refined than those out of my dac.

I read the option to get completely rid of the input caps, bypass and remove the op-amp and use just a pair of 4.4uF for coupling the output, but I'd like to try using the spdif coax-out to my dac. As a first step it's not clear to me if I have to bypass (replace with a wire) or just remove the L8/L9 inductor pair. Can anybody share some light/advice?

Thanks and best wishes for 2022!

Stefano

[Genoa1893]

Probably writing to myself, anyway just for sharing...

I found the sound with bypass caps very fatiguing.

So, I decided to remove both input and output smd caps, together with U1 and U4 and original RCAs, lto et wire go out from the SB3 and add/swap caps outside. Plans are to put in series a 0.56 MKP cap and in parallel another one (like 30-40nF), to filter the high frequency noise certainly generated by PCM1748KE.

Happy new year!

[Genoa1893]

Done,
and the thing hisses as hell. I thought that the 20K input impedance would do the trick to remove HF noise with the 30nF parallel capacitance. I was wrong.

Strange that I couldn't see anybody mentioning similar issues by removing the sallen-key output LPF...

Stefano

[Genoa1893]

Success, at last.

To reduce the chance to get noise from wi-fi I moved the analog filtering offside. For each channel lhe LPF is the 0.56uF MKP I mentioned previously and value has been calculated to hopefully match my 20KOhm input impedance.

Across the DAC output signal, I put a bunch of caps totalling about 40nF in series with a 240 Ohm, to have a HPF of around 19500Hz.

Before inserting the 240Ohm resistor, there was a lot of digital noise which followed someway the music, now it's lovely silent.

I'm listening to music out of this ugly thing (it's hidden behind my tv), and it sounds very very ok... Thanks for the advices on the thread. Next thing is to add a trafo to the digital output and listen how it sounds through my existing dac...





Stefano

[mgalusha]

Glad you got it working, I have not touched one in many years. I had added a tube output stage to mine maybe 10-12 years ago and gave it to a friend maybe 5 years ago.

[Genoa1893]

Thanks for your feedback!!! 

Yes, I know it's nothing special nowadays, but I wanted to diy and experiment the removal of the op-amp stage I also have on my "official" dac (a monarchy 22B, based on pcm63K). AFAIK the digital noise out of the pcm63 should be even easier to deal with.

In any case, actual sound out of this thing is amazing...