• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Does such a beast exist: ADC Digital Preamplifier

OP
G

garbz

Active Member
Joined
Sep 17, 2021
Messages
111
Likes
172
ESS ADCs have integrated Riaa digital filter which can be engaged via register setting so you get (in theory) perfect riaa response. I also put low noise linear amplifier at the phono input. These "old" ess adcs had a bug (riaa worked only @48khz) and they stopped the production but @IVX recently presented small top-notch ADC but unfortunatly not audiophile oriented (no high impedance input buffer, no riaa option and no spdif out). Maybe one day...
Oh fascinating. Not heard of that before. In my brief sketch I was considering adding a DSP in the path between the ADC and the SRC4392 I currently have noted down as a potential digital input switcher. Maybe I need to look around to see if any other ADCs have this functionality.
 

radix

Senior Member
Joined
Aug 1, 2021
Messages
497
Likes
381
That looks interesting. If it had a phono stage it would be a full featured solution.

Curious as to how you did the RIAA. I'm just coming off the back of building a Preamp with integrated DAC so I fully support building something myself. Playing with digital DSP is the only thing I've not done hobby wise before. But I've built my fair share of ADCs, preamps and DACs before.

If you search for something like "RIAA BIQUAD FILTER" you will find the correct digital filter parameters for RIAA equalization. I have heard that some people with MM cartridges can go direct from TT to minidsp and use the RIAA biquad, so no phono stage. If you need it, you can get a +22dB step-up transformer (e.g. from Rothwell). I've never done this, so please consult those riaa biquad threads.

I have MC @ 0.4mV, so I decided to get a true phono stage (SUT + preamp).
 
OP
G

garbz

Active Member
Joined
Sep 17, 2021
Messages
111
Likes
172
If you need it, you can get a +22dB step-up transformer
Can't help but think the insanely high distortion and loading caused by the use of audio transformers completely negates the benefit of doing RIAA eq digitally in the first place. The pre-amp problem remains.
 

holbob

Active Member
Joined
Nov 1, 2020
Messages
202
Likes
261
Location
Lincoln, UK
One thing I don't get is whenever somebody asks about a quality ADC, people usually recommend an audio interface like a Motu. But I have no idea how to connect to one with either input or output in a "normal" system.
 

Jimbob54

Master Contributor
Forum Donor
Joined
Oct 25, 2019
Messages
9,084
Likes
11,587
One thing I don't get is whenever somebody asks about a quality ADC, people usually recommend an audio interface like a Motu. But I have no idea how to connect to one with either input or output in a "normal" system.
RCA to TRS cable isnt it? Looks like they have RCA out on the back.
 

levimax

Major Contributor
Joined
Dec 28, 2018
Messages
1,498
Likes
2,134
Location
San Diego
Curious as to how you did the RIAA. I'm just coming off the back of building a Preamp with integrated DAC so I fully support building something myself. Playing with digital DSP is the only thing I've not done hobby wise before. But I've built my fair share of ADCs, preamps and DACs before.
RIAA works well using an ADC and DSP. Just make sure you load the cart properly as the input impedance of an ADC is not correct for a cart. I made a simple "balanced transmitter" with 47 K input impedance https://sound-au.com/project87.htm which then connects to a balanced input on the ADC. The ADC microphone input has plenty of gain for MM for MC I put a SUT in front of the "balanced transmitter". For RIAA I use FIR filters created in Rephase which is easy, go to the "Filters Linearization" tab and create 3 filters. Normal- Low Pass- 1st order- 2122 Hz, Compensate- High Pass - 1st order - 500 Hz, Normal- High Pass- 1st order - 50 Hz . I also add a subsonic filter.
 

kokoon

Member
Forum Donor
Joined
Mar 13, 2021
Messages
86
Likes
45
Location
Slovenia
MiniDSP SHD, think it only has 1 analogue input, but it does the rest.
MiniDSP SHD actually has 2 pairs of analog inputs: 2x balanced and 2x single-ended, as far as analog goes. That's in addition to all digital inputs - usb, AES, toslink and spdif.
Four channels of output, simultaneously as balanced analog, single-ended analog, dual spdif rca digital.
 
OP
G

garbz

Active Member
Joined
Sep 17, 2021
Messages
111
Likes
172
One thing I don't get is whenever somebody asks about a quality ADC, people usually recommend an audio interface like a Motu.
In defense of the people, it's vanishingly rare that in a hifi you actually want to convert something to digital for the purposes of replaying. I'd wager 99.99% of ADC in the world is done with a PC as the intended destination for the signal.

The ADC microphone input has plenty of gain for MM for MC
I've been sloshing around schematics in my head, I'm thinkin a Phono gain stage to bring the high end of the record up to line level and then switch that with any other line level input into a fully-differential-amplifier like an OPA1632 and then balanced into an ADC. I can then either find an ADC that has a filter in it like the ESS parts mentioned or add a DSP chip via i2s.

Either way I think I have found my 2022 project. :)
 

rwortman

Addicted to Fun and Learning
Joined
Jan 29, 2019
Messages
506
Likes
411
That looks like a bog standard DAC/Preamp to me, doesn't even have digital outputs.
My mistake. I didn’t see that the OP wanted a digital output. Not a bog standard DAC/Pre though because it performs ADC on all inputs.
 

Mnyb

Major Contributor
Forum Donor
Joined
Aug 14, 2019
Messages
1,478
Likes
1,934
Location
Sweden, Västerås
My Meridian G68J predates the MQA debacle ( so does most of the 800 series ) . As used products maybe ?

Caveats .

Don’t know how versatile the digital outs are for non Meridian speakers ? Suppose end to end 24/96 5.1 from DVDA is out of the question due to needing the MHR link ( for the copy protection schemes).

Performance is not SOTA and the gear is expensive, well it may be SOTA for digital pass trough, but the analog parts are just ok .

Company has “ jumped the shark “ of lately and just remakes their 20 year old designs these days . Not competitive.

You be locked in with the brands own digital speakers for maximum system flexibility and user experience, the user experience is very good in my experience no complaints there. The execution of the digital xover and plate amps in the speakers are probably good .
The actual acoustic engineering of their speakers are simply not up to modern standards and has not changed much.

I’m probably back to passive speakers next upgrade. But with a mini DSP
 
Top Bottom