MINIDSP Adept ADC & Phono Preamp Review

[lini]

Let me do some more testing when I get a chance with and without reverse RIAA.....

Ok.

Btw, I forgot to ask another question, which would also seem pretty important for correct result interpretation: Is your inverse-RIAA an active one, which applies unity gain at 1kHz, so that the generator levels in the diagram for the 1 kHz graph equal the actual input levels into the DUT and the actual input levels into the DUT for the other test frequency graphs can be correctly calculated/converted according to the RIAA cutting curve?

Greetings from Munich!

Manfred / lini

 

[markstein]

I was waiting for this review - great to finally see it!

The RIAA clipping behavior is concerning, and I think this should be further evaluated. MiniDSP specify much higher overload margins in their official data sheet than measured in the review (220mV @ MM low gain) which does not align at all with the measurements in this review and is much worse.

RIAA EQ means 20kHz is 20dB lower than 1kHz - Amirs clipping measurement shows a factor of only 3,5 (70mV at 1kHz, 20mV at 20kHz), i.e. approx. 11dB. That does not look good.

 

[markstein]

Conpare the headroom of the miniDSP Adept with that of the ProJect DS3B (also reviewed here). The insufficient headroom was the reason for me selling the DS3B - pronounced crackling and ticks are simply not enjoyable, at least to me.

 

[nothingman]

Just so we’re all on the same page, here’s what miniDSP say about the headroom issue:

***

Digital stage​

Here is where it gets tricky. The peaks in the raw audio signal coming from the cartridge tend to contain a lot of high-frequency energy. Non-audio clicks similarly have a lot of high-frequency energy. However, after analog-to-digital conversion, the RIAA EQ reduces the high frequencies:

As a result, we don't need to preserve the full amount of headroom at all frequencies. For example, at 8 kHz, where stylus velocities are the highest, the RIAA curve reduces the output by almost 12 dB. In practice, this means we can reduce the headroom available at lower frequencies without causing clipping in the output waveform of typical musical audio signals.

Therefore, we have added 10 dB of digital gain (at 1 kHz) to the signal flow. This is a compromise between signal level/dynamic range and avoiding clipping. It is still possible that some very "hot" records will clip the digital output even though the ADC doesn't clip. If this occurs, simply reduce the digital volume. (For the full procedure, see the Fine-tuning gain structure page.)

***

 

[Davey]

I was waiting for this review - great to finally see it!

The RIAA clipping behavior is concerning, and I think this should be further evaluated. MiniDSP specify much higher overload margins in their official data sheet than measured in the review (220mV @ MM low gain) which does not align at all with the measurements in this review and is much worse.

RIAA EQ means 20kHz is 20dB lower than 1kHz - Amirs clipping measurement shows a factor of only 3,5 (70mV at 1kHz, 20mV at 20kHz), i.e. approx. 11dB. That does not look good.

The 220mV specification being sans "digital gain and RIAA EQ."
20 * log(220/70) equals 9.94db. Since they apply 10db digital gain, Amir's test result seems right on the money/specification.

 

[nothingman]

Just so we’re all on the same page, here’s what miniDSP say about the headroom issue:

***

In practice, this means we can reduce the headroom available at lower frequencies without causing clipping in the output waveform of typical musical audio signals.​

***

Does this read like a typo to people, or am I not understanding the concept? Seems like it should read “we can reduce the headroom available at higher frequencies” since it appears there’s commonly plenty of headroom at lower frequencies in phono stages including this one, and we’re most concerned about headroom at higher frequencies where it’s almost always a tighter margin.

 

[Jimi Floyd]

Use a digital RIAA preamp, they said. It will be fun, they said...

 

[LtMandella]

This is a review and detailed measurements of the MINIDSP Adept analog to digital converter and phono equalization/capture. It was sent to me by the company and costs US $299.
View attachment 472297
The device is rather attractive for its class. User interface though, is unusual. You push the rotary encoder in and then it selects the first option. You keep rotating it and it will then cycle through all the elements you see in the interface. So to change something, you have to cycle through all until you get to option you want to select. It works but did take some effort to figure out how to use it. Strangely, the rotary encoder does not change the input gain. The included remote control does!

As you see, you can use the device just an ADC to capture analog audio or optionally apply RIAA (phono) equalization, and input loading. Latter is limited to using RCA input:

View attachment 472298

Power is provided externally through a small adapter. I tested using USB but you also have S/PDIF coax and digital output. To set the sample rate of the latter two however, you need to use the USB interface.

I expected an app/control panel to simply interfacing with the unit but found none. I really wish the device had a UI showing digital levels and the rotary control managing it. Without my analyzer, this would be hard although you have some help in the form of clipping indicator. Don't let it come on you risk severe distortion.

Minidsp Adept Measurements
I started the testing by treating the device as an audio interface (sans DAC), using XLR input with medium gain (low gain is not available):

View attachment 472299
This is excellent result with distortion well below audibility and hence, limited by noise which is also very low. Ranking as a result near the best:
View attachment 472300
Noise performance impressively remains almost the same even with RCA input:

View attachment 472301

Frequency response is what you expect (depending on sample rate):

View attachment 472302

You can see the low level of noise and distortion in our IMD test:
View attachment 472303
It clips earlier than professional interfaces but up to that point, it produces class leading results.

Testing phono equalization with three different gain settings was challenging so I went for a representative sample.
EDIT: forgot the dashboard:
View attachment 472415

Here is the frequency response:
View attachment 472304

I have not seen any analog RIAA equalization to be this good! Yes, a high pass filter would be nice but otherwise, this is textbook perfect. I should have noted that the above is with 96 kHz sampling as otherwise, it will stop earlier. EDIT: there is a high pass filter.

There is not much headroom available at higher frequencies:
View attachment 472305
Company has an explanation for why you don't need more at higher frequencies due to RIAA equalization. But in above tests, I have the generator go through inverse RIAA equalization.

Note that the above is achieved with low gain. At higher gains you may clip earlier digitally.

Conclusions
If you just need a digitizer and already have a DAC, Adept provides an excellent solution with very low noise and distortion. For RIAA equalization and LP ripping, you have perfect equalization but headroom is not great. So be sure to clean your LPs before capturing.

I am happy to recommend the Minidsp Adept phono preamp and capture "card." It is excellently engineered while having a reasonably low cost.

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Any time I see the need for a proprietary windoz driver for a USB audio device I cringe. Had some bad experiences with more than one such driver...

 

[markstein]

H

The 220mV specification being sans "digital gain and RIAA EQ."
20 * log(220/70) equals 9.94db. Since they apply 10db digital gain, Amir's test result seems right on the money/specification.

H iDavey, where do I find detailed infos about Adept internal gain structure? Unfortunately this info is not specified in the datasheet.

 

[markstein]

Just so we’re all on the same page, here’s what miniDSP say about the headroom issue:

***

Digital stage​

Here is where it gets tricky. The peaks in the raw audio signal coming from the cartridge tend to contain a lot of high-frequency energy. Non-audio clicks similarly have a lot of high-frequency energy. However, after analog-to-digital conversion, the RIAA EQ reduces the high frequencies:

View attachment 472864

As a result, we don't need to preserve the full amount of headroom at all frequencies. For example, at 8 kHz, where stylus velocities are the highest, the RIAA curve reduces the output by almost 12 dB. In practice, this means we can reduce the headroom available at lower frequencies without causing clipping in the output waveform of typical musical audio signals.

Therefore, we have added 10 dB of digital gain (at 1 kHz) to the signal flow. This is a compromise between signal level/dynamic range and avoiding clipping. It is still possible that some very "hot" records will clip the digital output even though the ADC doesn't clip. If this occurs, simply reduce the digital volume. (For the full procedure, see the Fine-tuning gain structure page.)

***

There is a headroom in A/D conversion, a headroom in internal DSP and a headroom in digital output. I would like to know each of these headrooms.

Which of these headroom is measured in Amir's review?

 

[Jimi Floyd]

There is a headroom in A/D conversion, a headroom in internal DSP and a headroom in digital output. I would like to know each of these headrooms.

Which of these headroom is measured in Amir's review?

YES, exactly this.

 

[amirm]

There is a headroom in A/D conversion, a headroom in internal DSP and a headroom in digital output. I would like to know each of these headrooms.

Which of these headroom is measured in Amir's review?

All of them in a package. Note that there are interdependence in the various parameters which I tried to optimize.

 

[Davey]

H iDavey, where do I find detailed infos about Adept internal gain structure? Unfortunately this info is not specified in the datasheet.

It's in Post #104. With a link to their documentation.
C'mon.

 

[markstein]

It's in Post #104. With a link to their documentation.
C'mon.

Reread this post and also the link provided. Thank you for highlighting this post.

Good:
- There are separate clipping indicators for A/D clipping and digital clipping. Did not know that. Helps you sort out where an issue occurs.
- You only have some discrete A/D gain settings (H/ M/ L) but can fine adjust the digital volume. Did not know that.

Still: I do not understand why the overload margin gets smaller with high frequencies. Must it not be the other way round? Can anybody explain this for "dummies" like me?

 

[markstein]

Okay, this might be the explanation. Amir writes in his review:
"But in above tests, I have the generator go through inverse RIAA equalization."

This test signal does not reflect the spectrum that can be expected from a record. Spectrum on a record prior to RIAA EQ is relatively flat, not at all like the inverse RIAA of a flat line. So the test methodolgy might be flawed?

 

[morillon]

This is a review and detailed measurements of the MINIDSP Adept analog to digital converter and phono equalization/capture. It was sent to me by the company and costs US $299.
View attachment 472297
The device is rather attractive for its class. User interface though, is unusual. You push the rotary encoder in and then it selects the first option. You keep rotating it and it will then cycle through all the elements you see in the interface. So to change something, you have to cycle through all until you get to option you want to select. It works but did take some effort to figure out how to use it. Strangely, the rotary encoder does not change the input gain. The included remote control does!

As you see, you can use the device just an ADC to capture analog audio or optionally apply RIAA (phono) equalization, and input loading. Latter is limited to using RCA input:

View attachment 472298

Power is provided externally through a small adapter. I tested using USB but you also have S/PDIF coax and digital output. To set the sample rate of the latter two however, you need to use the USB interface.

I expected an app/control panel to simply interfacing with the unit but found none. I really wish the device had a UI showing digital levels and the rotary control managing it. Without my analyzer, this would be hard although you have some help in the form of clipping indicator. Don't let it come on you risk severe distortion.

Minidsp Adept Measurements
I started the testing by treating the device as an audio interface (sans DAC), using XLR input with medium gain (low gain is not available):

View attachment 472299
This is excellent result with distortion well below audibility and hence, limited by noise which is also very low. Ranking as a result near the best:
View attachment 472300
Noise performance impressively remains almost the same even with RCA input:

View attachment 472301

Frequency response is what you expect (depending on sample rate):

View attachment 472302

You can see the low level of noise and distortion in our IMD test:
View attachment 472303
It clips earlier than professional interfaces but up to that point, it produces class leading results.

Testing phono equalization with three different gain settings was challenging so I went for a representative sample.
EDIT: forgot the dashboard:
View attachment 472415

Here is the frequency response:
View attachment 472304

I have not seen any analog RIAA equalization to be this good! Yes, a high pass filter would be nice but otherwise, this is textbook perfect. I should have noted that the above is with 96 kHz sampling as otherwise, it will stop earlier. EDIT: there is a high pass filter.

There is not much headroom available at higher frequencies:
View attachment 472305
Company has an explanation for why you don't need more at higher frequencies due to RIAA equalization. But in above tests, I have the generator go through inverse RIAA equalization.

Note that the above is achieved with low gain. At higher gains you may clip earlier digitally.

Conclusions
If you just need a digitizer and already have a DAC, Adept provides an excellent solution with very low noise and distortion. For RIAA equalization and LP ripping, you have perfect equalization but headroom is not great. So be sure to clean your LPs before capturing.

I am happy to recommend the Minidsp Adept phono preamp and capture "card." It is excellently engineered while having a reasonably low cost.

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

It would be worth measuring THD+N/THD vs. the frequency present on the hilo2 test...
An important measurement... (more so in my opinion than just at 1 kHz)
and thd+n vs level too...
;-)
the sweeps are fundamentally more important and informative...

and the small pocketadc ?

 

[lini]

Still: I do not understand why the overload margin gets smaller with high frequencies. Must it not be the other way round? Can anybody explain this for "dummies" like me?

See my questions in post #77 and post #101 - with the one in post #101 still being unanswered. Hence so far it's not really clear, which input levels into the DUT (= device under test) the generator levels for the different test frequencies would actually convert to.

Greetings from Munich!

Manfred / lini

 

[Davey]

See my questions in post #77 and post #101 - with the one in post #101 still being unanswered. Hence so far it's not really clear, which input levels into the DUT (= device under test) the generator levels for the different test frequencies would actually convert to.

Greetings from Munich!

Manfred / lini

In this case, there is not an interim (passive or active) filter inserted between the excitation and the DUT.
As I understand it, Amir's AP unit can generate an inverse RIAA equalized signal directly, with the reference level shown being that at 1khz.

In any case, the option to measure some aspects of phono preamps with/without an inverse RIAA equalization is available.

 

[lini]

As I understand it, Amir's AP unit can generate an inverse RIAA equalized signal directly, with the reference level shown being that at 1khz.

Alright - so then it should be as already assumed in post #77. I.e., if the inverse-RIAA of the AP is activated, for test frequencies other than 1 kHz conversion factors according to the RIAA cutting curve would need to be applied, in order to calculate the actual input levels into the DUT.

Greetings from Munich!

Manfred / lini

 

[markstein]

@amirm: From my point of view and understanding, inverse RIAA should only be used to measure frequency response of a phono preamp.

All other measurements should be done with linear generator signal.

Your thoughts?