MINIDSP Adept ADC & Phono Preamp Review

[Soniclife]

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

I can see no logic in using inverse RIAA for this test, but it finally explains to me why we get the pattern we regularly see. Surface noise isn't boosted by RIAA, and that's the biggest output at high frequencies.

I'd also be interested in how clipping behaves when it clips in the digital domain, is recovery instant? Would that be a good thing if they top of a click was reduced?

 

[zenmastering]

One note though: the clocks won't be synchronized. So you cannot do any real-time/live mixing. For offline editing, that doesn't matter.

Easy enough to sync them: DAW is set to use ADC as master clock and DAC set to take it's clock from DAW-stream. Standard in any such setup.

 

[Loz]

Great review, I've been waiting for this for a while, so thanks. I currently have an all digital system, using the minidsp flex digital as a digital preamp, both to switch in other digital sources but also to do Dirac room correction. I recently have got into vinyl and I'm currently using a relatively modest rega mini a2d phono stage, analog outputs into the Flex analog input. I'm wondering what peoples opinions on how much of an upgrade the adept would be, going directly into one of the Flex digital inputs. I suppose there are two questions really, 1) how much better is the Adept adc than the Flex's. 2) how much better is the adept riaa equalisation and any other reduced signal chain over the phono into the Flex? Obviously, the adept also has lots of other options and flexibility over my current setup, but for the time being I'm ignoring those.

 

[Sokel]

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 ?

What should Adept have is a rock-solid ground lift from all sides.
You suspect why, right?

 

[MaxwellsEq]

I'm currently using a relatively modest rega mini a2d phono stage, analog outputs into the Flex analog input. I'm wondering what peoples opinions on how much of an upgrade the adept would be, going directly into one of the Flex digital inputs

I bought a Rega a2d as a cheap temporary measure (previous phono preamplifier failed). It can easily be bettered by most phono preamplifiers measured here. I suspect that the Adept would be a noticeable upgrade.

 

[Loz]

I bought a Rega a2d as a cheap temporary measure (previous phono preamplifier failed). It can easily be bettered by most phono preamplifiers measured here. I suspect that the Adept would be a noticeable upgrade.

Good to know, thanks.

 

[Davey]

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?

That test signal DOES reflect what's recorded on an LP. That's the whole point.
I'm unsure where your understanding comes from on this. Did you read this somewhere? If so, can you point me to it? I'd like to read it.

A couple of myriad references on this topic:

RIAA equalization - Wikipedia

en.wikipedia.org

Cut and Thrust: RIAA LP Equalization | Stereophile.com

Until the Recording Industry Association of America hit the headlines in recent years with its antipiracy campaign, the initials RIAA meant one thing to seasoned audiophiles: the vinyl-disc equalization characteristic introduced in the 1950s to standardize what had previously been an anarchy of...

www.stereophile.com

https://cdn.shopify.com/s/files/1/0433/2441/files/riaa.pdf

 

[markstein]

Well, capture some of your records prior to RIAA EQ and tell me how the spectrum looks like. It will definitely not look like an inverse RIAA.

 

[Davey]

Well, capture some of your records prior to RIAA EQ and tell me how the spectrum looks like. It will definitely not look like an inverse RIAA.

I don't need to capture anything. They'd have not much bass and whole lotta treble. Just like an inverse RIAA curve.

 

[markstein]

I don't need to capture anything. They'd have not much bass and whole lotta treble. Just like an inverse RIAA curve.

Ignorance is bliss

 

[Davey]

Ignorance is bliss

Indeed it is.

 

[amirm]

@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?

How about distortion vs level? The "level" would have been subjected to inverse RIAA equalization at mastering.

 

[markstein]

How about distortion vs level? The "level" would have been subjected to inverse RIAA equalization at mastering.

Yes, this is exactly the data that should be provided IMO.

Your measurement shows clipping at specific levels and specific frequencies, however, it seems to be unclear if the level specified in the diagram is referenced to the specific frequency (e.g. 20mV at 20kHz) or if the level specified in the diagram is referenced to 1kHz of the inverse RIAA generator curve used for this measurement (i.e. +20dB at 20kHz). This obviously makes a significant difference. Could you kindly clarify this matter?

 

[MaxwellsEq]

I think there is confusion about words. The use of "reverse" and where this is applied seems to be an issue.

Personally I think of them as encoding and decoding. A flat FR master tape arrives and is played through a RIAA-encoder on the way to the cutting head. The encoder reduces the bass and boosts the treble. Later, the finished record is played through a phono preamplifier to decode the RIAA-encoded disc, which boosts the bass and reduces the treble.

So if you feed a flat frequency response sweep from a test set into a RIAA phono preamplifier, the output of the preamplifier will be high in the bass and low in the treble. To get a flat response out of the phono preamplifier, you have to encode the frequency response sweep from the testset through a RIAA-encoder (identical to the cutting lab) which will reduce the frequency generator's bass and boost its treble, emulating an LP.

But, which is "reverse"? I think of the encoder at the cutting lab as applying RIAA filtering and I think of the phono preamplifier as applying a reverse RIAA filter. So that means the testset signal generator case is not applying "reverse RIAA" but applying RIAA filtering to to the test signal for the preamplifier to reverse it back to flat.

 

[Sokel]

It's simple:
Any phono pre expects a RIAA conditioned signal, that's a given.
Any test should address that.

So we either feed it with a non-RIAA signal and expect the output to be visually "weird" (like an opposite RIAA curve) or we apply one of the standard RIAA's (IEC 1970, 1954, etc) to the test signal and expect a visually flat outcome.

One would think it's only about visuals but it's not, a normal, non-RIAA test signal can very well overload DUT at randoms ways.
Proper signal is the only way, after all testing it as a black box means a life-like conditions, like if a TT was playing it.

 

[Soniclife]

How about distortion vs level? The "level" would have been subjected to inverse RIAA equalization at mastering.

Do you test distortion at frequencies other than 1khz? As that frequency isn't affected by RIAA.

 

[morillon]

You just have to be sure that the inverse RIAA is at the generator level, and not by cacul processing on the incoming signal... (otherwise there are small passive modules, non-saturable and known negative gain, certainly practical just for these saturation observations *)
;-)

*
to see if this offers an output load that can also achieve a relevant load in mm, quite standard...would "kill two birds with one stone"

 

[Winner]

Quite unfortunate that the price of this jumps from $299 in the US to £399 in the UK. That's hard to justify.

Why don't you order it directly from Adept !!! It's only £220!
add Import Tax that will be £264 + shipping cost it will be still a lot cheaper.

 

[somebodyelse]

Why don't you order it directly from Adept !!! It's only £220!
add Import Tax that will be £264 + shipping cost it will be still a lot cheaper.

So long as you're aware that the warranty may be shorter (statutory 2yrs UK/EU vs. 1yr direct) and you'll be sending it back to HK rather than locally. People often seem to forget about this when opting for cheaper overseas direct sales rather than a local dealer.

 

[SoySalsaPicante]

Can this thing be used as a loopback (reference) device in REW? Simultaneously can this be used as an input to REW for an XLR-based microphone (in place of a USB microphone) and would there be benefits as such of using an XLR-type microphone over using a USB-type microphone? Perhaps for synchronizing speakers to each other and to a subwoofer in REW more accurately or without relying on the use of an acoustic reference tone (since those are typically too high for subs to reproduce)?