Using an audio interface for phono RIAA/preamplification

[Digby]

Hello,

This is my first post, so if this is the wrong subforum please feel free to move somewhere more appropriate.

I am in need of a new phono preamplifier, my old one in a 1980s integrated amplifier is giving up the ghost (and probably isn't particularly accurate). I stumbled across this forum while looking for reviews and given the excellent measured performance of the Cambridge Duo, was about to purchase that. However, I have seen users mention that a potentially even more accurate way to amplify a phono signal may be to bypass analogue amplification and do everything (RIAA curve + amplification) once the signal has been digitized.

I have an RME UC interface, which is among the best interfaces in ADC capabilities. How would I go about taking a signal from the turntable, applying an RIAA curve/preamplification and digitizing it with the RME and would this be expected to provide better results than RIAA/preamplification using a Cambridge Duo and then digitizing with the RME?

Also, would it be possible to listen to records live, as I do now (monitoring input through recording software) when using digital software to apply RIAA+ preamplification or would all equalization and amplification have to happen post recording?

 

[dfuller]

Hmm... Well, the main thing to consider here is the standard load for a MM phono pre is 47k ohms. The Fireface UC's line inputs are only 10k. That may affect frequency response and will certainly affect level. If you can get a good phono pre without RIAA correction enabled, you could feed that into the line inputs and do all your RIAA curves in software.

 

[somebodyelse]

https://linearaudio.net/article-detail/2240 has detailed coverage including schematics for headamps to match the cartridge to a phantom powered mic input (mentioned as it's not in the article summary). Live playback should be possible if you put together a suitable signal processing chain, similar to what you'd need for software room EQ. Scott Wurcer also posts here and might answer if you have further questions.
The Parks Audio Puffin review might also be of interest - it's a reasonable though not outstanding analog front end and ADC, but the EQ is done by DSP.

 

[Digby]

Thanks for the replies. I'm really just trying to ascertain whether there is any tangible benefit to sound quality by doing the processing inside the computer as opposed to using a phono stage.

 

[levimax]

Thanks for the replies. I'm really just trying to ascertain whether there is any tangible benefit to sound quality by doing the processing inside the computer as opposed to using a phono stage.

I went through the exercise of hooking up my TT directly though an ADC and doing RIAA in the digital domain. It works perfectly but I can't say that it sounds "better" that the phono stage I was using before. For me the main reason I did it was because I had a lot of hum and "Wi-Fi/ computer noise" I was picking up which I could not solve. I connected the TT to a "balanced transmitter" with a 47 K ohm input impedance and then took the balanced output and connected it to the balanced input on the ADC (which has enough gain for a MM cart). The result was no more noise so I was happy.

 

[Lambda]

Of cause a digital filter can be better and more flexible then an analog filter
And ADCs have become good enough.
but if you digitize the record why not record it at the same time.
If it's already digitized and recorded why play it again...
For me personally this would destroy the Mojo

 

[Digby]

Levimax, it is interesting you mention wi-fi/computer noise. I am getting some of that, but the level seems relatively low, perhaps within normal range (about -68db, when recorded peaks set to around -1.5db). If I turn the volume right up, I can hear some intermittent radio type noises. I don't know whether this a function of the phono stage starting to clap out or would be the same whatever phono stage was used.

Lambda, as for recording, sometimes I am too lazy to set up the recording function and just want to listen to a record. I am uncertain as to whether the record playback sounds a little better than the digital recording - sometimes I think I hear a difference, sometimes I'm not sure. I think this speaks to the quality of RME equipment, as the recordings made with a previous Focusrite Scarlett 8 left me in no doubt that direct vinyl playback sounded better.

 

[Wombat]

FWIW:

http://waynestegall.com/audio/riaaiir.htm

 

[levimax]

FWIW:

http://waynestegall.com/audio/riaaiir.htm

Wow that is complicated... I just used Rephase to create a minimum phase FIR RIAA filter based on 3 entries that I saw on the Rephase forum. My understanding is that minimum phase filters act like analog filters but the article is way over my head. I tested my filter with a test record sweep and it seems to work the same as my phono pre amp and sounds the same to me but I am sure there could be some small differences.

 

[Digby]

It's starting to sound as though this may be more trouble than it is worth. I will try the Cambridge Duo and see how I get on with that.

 

[abdo123]

If you can come up with the ~60 dB gain necessary, then it's quite alright.

Check this out:

https://www.diyaudio.com/forums/pc-based/353387-phono-preamp-riaa-eq-using-iir-digital-filters.html

and this:

https://www.minidsp.com/forum/hometheater-av-applications/12510-2x4-hd-as-phono-preamp

 

[levimax]

If you can come up with the ~60 dB gain necessary, then it's quite alright.

Check this out:

https://www.diyaudio.com/forums/pc-based/353387-phono-preamp-riaa-eq-using-iir-digital-filters.html

and this:

https://www.minidsp.com/forum/hometheater-av-applications/12510-2x4-hd-as-phono-preamp

;
I am using a Steinberg UR22MK2 ADC and there is enough gain for MM... Need a SUT for MC. It is a fun project and has some advantages but you won't go wrong with the Cambridge phono pre either.