ADC input Nadja for Vinyl.

What people are working on at the moment
Post Reply
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#1 ADC input Nadja for Vinyl.

Post by vinylnvalves »

I have kicking this around for a few months in my head. The weak link with the Nadja DSP is it’s ADC, as I am playing more vinyl these days I thought I would upgrade the input. The best sounding digital input it has is via I2s, so I thought that would be the most appropriate, I have 3 spare inputs too. Both of my phono amps have the capability for balanced input and output, so I thought that would be a nice feature to use... if it effects the noise floor is questionable.

As I don’t do proper electronics I need a plug and play solution, so I have been considering using evaluation boards, I have really only found the following to be suitable the PCM4222 EV https://uk.farnell.com/texas-instrument ... dp/3125792 getting hold of it is another matter. :( I already have a 5v and 15v linear powers supply’s feeding the Nadja, with plenty of spare capacity. Anyone got any suggestions for another well respected ADC. Ideally I want to fit it inside the DSP/Preamp so I can keep the leads for I2s input as short as possible.
My budget doesn’t stretch as far as the AK5574 before anyone suggests it. :)
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#2 Re: ADC input Nadja for Vinyl.

Post by Nick »

Which part of your existing ADC is worst than the vinyl front end that feeds it?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#3 Re: ADC input Nadja for Vinyl.

Post by vinylnvalves »

Not sure really - I played with an M-Tec Joplin phonostage a few years back which was feed in via Spdif. It sounded better than my vinyl one phonostage.

The ADC in the DSP is integral https://www.mouser.com/datasheet/2/76/C ... -33496.pdf.

I know there is a school of thought that anything better than 96k is wasted on vinyl..
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#4 Re: ADC input Nadja for Vinyl.

Post by Nick »

I cant help thinking you should try some more phono stages into your existing ADC. Just to be sure where to point the finger.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#5 Re: ADC input Nadja for Vinyl.

Post by vinylnvalves »

I may see if I have another analogue source which works that I can try - that then takes the RIAA out of the equation too.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#6 Re: ADC input Nadja for Vinyl.

Post by vinylnvalves »

No quality analogue source - but a Walkman doesn’t sound too bad :) . Looking at the impedance, it’s 10k input into the Preamp/DSP. The project RS phono has an output impedance of 50 ohms, so shouldn’t be an issue there. The vinyl one with its cathode follower output stage will be a lot higher, which probably explains why it doesn’t sound as good.
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#7 Re: ADC input Nadja for Vinyl.

Post by Nick »

A cathode follower should be fine into 10k. What's the output valve?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Nick
Site Admin
Posts: 15707
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#8 Re: ADC input Nadja for Vinyl.

Post by Nick »

Looked it up, as ecc83. Not the worlds best valve for a cathode follower, so maybe 1-2k output impedance, not ideal. But TBH there are a lot of other things a ecc83 phono stage can get wrong. Want to borrow a inverse RIAA then you can listen to your walkman through and compare directly?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#9 Re: ADC input Nadja for Vinyl.

Post by vinylnvalves »

After some playing around, I think I may have found the culprit- gain. The Nadja analogue input is limited to 1V RMS, so have been using the lowest gain on the Project RS phono stage. Putting some in line attenuators on the input to the preamp and increasingly the gain on the phono stage has made a massive difference. Why is another question, I suppose it all depends where and how the gain is controlled in the phonostage. It is using OP amps- which work best at high gains I believe, so that could be the reason.

Now how to sort this out properly, as haven’t room to have the attenuators in line behind the preamp.
1) Add couple of resistors in the RCA plug.
2)Add resistors to the phono inputs on the amp- so it’s a 2v RMS input.
3 Add the XLR input with a THAT 1206 chip so I can use the balanced topology of the RS phonostage - is it worth it??

As the analogue input claims to be 10k - do I match this with attenuator, ie 2 10k resistors?

For info my valve preamp doesn’t sound as good, it’s 30 odd years old and probably needs re-capping. I know it’s heresy but will be sticking with the jfets and opamps for know.
Post Reply