Classic Audio MC Pro Phonostage Review

[Angsty]

Yep I'll be sure to post impressions and comparisons relative to my current SUT setup.

I purchased a SUT last year to get gain ahead of my integrated amp’s phono input. The combo works better than my prior phono, but there are times I still get hum.

For the price of the MC Pro, I could have gotten a whole new phono and covered a large fraction of the cost with what I paid for the SUT. This is an area where the hobbyist in me conflicts with the pragmatist. You really have to have an expansive knowledge of the market to know the best deals for everything.

 

[fireanimal]

I just want to add my 3rd party measurements to this thread, as there was talk of possibly cherry picked units sent etc. I ordered last week after reading the review, and never made any indication that I would be measuring the MC Pro upon arrival. My results mirror the review sample. Input voltage was 500uV using balanced output.

 

[Angsty]

My Hana SL has an impedance of 30 ohms, not 10. Thoughts about matching this cartridge to the MC Pro with a fixed loading of 120 ohms?

 

[morillon]

My Hana SL has an impedance of 30 ohms, not 10. Thoughts about matching this cartridge to the MC Pro with a fixed loading of 120 ohms?

you need more... not less of 300-330 etc probably 470 -680

 

[Angsty]

you need more... not less of 300-330 etc probably 470 -680

The 10x rule generally applies, but I’m still trying to figure out why @Michael Fidler believes in a fixed impedance for all carts.

That being said, my Bryston phono has an internal SUT without means to adjust load, as well.

 

[Michael Fidler]

The 10x rule generally applies, but I’m still trying to figure out why @Michael Fidler believes in a fixed impedance for all carts.

That being said, my Bryston phono has an internal SUT without means to adjust load, as well.

Because once a suitably low noise input amplifier with a noise figure of less than 6dB against 10 ohms is selected, the coils' thermal noise dominates as it increases past 20 ohms, so insertion loss doesn't degrade SNR as much as you would think (effective degradation would be 3dB by 120 ohms of coil impedance). The penalty is negligible for coil impedances in the 30 ohm range although I believe such cartridges are sub-optimal for noise performance, pushing the effective SNR below 80dB (220Hz to 22kHz). Generally the 10 times rule assumes that impedance bridging is desirable because if the input amplifier has a very poor noise figure it will be the main source of noise in the system.

Additionally the loading network has an important function in preventing RF peaking and also shunting away as much RF interference to ground. Increasing the resistance without reducing the load capacitance peaks the frequency response around 3MHz. Reducing the capacitance increases the RF cutoff point which is undesirable.

In all honesty moving coil cartridge loading is an extremely dull subject and I get more e-mails about it than I care to have about this subject, particularly the 'zero-impedance'/'current input' marketing scam that's currently doing the rounds. I'm writing all of this up for a new article for the website so I can just reference it in future.

 

[Angsty]

Because once a suitably low noise input amplifier with a noise figure of less than 6dB against 10 ohms is selected, the coils' thermal noise dominates as it increases past 20 ohms, so insertion loss doesn't degrade SNR as much as you would think (effective degradation would be 3dB by 120 ohms of coil impedance). The penalty is negligible for coil impedances in the 30 ohm range although I believe such cartridges are sub-optimal for noise performance, pushing the effective SNR below 80dB (220Hz to 22kHz). Generally the 10 times rule assumes that impedance bridging is desirable because if the input amplifier has a very poor noise figure it will be the main source of noise in the system.

Additionally the loading network has an important function in preventing RF peaking and also shunting away as much RF interference to ground. Increasing the resistance without reducing the load capacitance peaks the frequency response around 3MHz. Reducing the capacitance increases the RF cutoff point which is undesirable.

In all honesty moving coil cartridge loading is an extremely dull subject and I get more e-mails about it than I care to have about this subject, particularly the 'zero-impedance'/'current input' marketing scam that's currently doing the rounds. I'm writing all of this up for a new article for the website so I can just reference it in future.

Thanks @Michael Fidler. It may be extremely dull to you, but the phonostage sub-industry has largely adopted a position that matching load to a MC cartridge impedance is normal (it wasn’t always). So, it’s bound to generate a ton of questions. Your article is sure to draw lots of interest.

It’s particularly interesting to me that you panned the “current input” purveyors as a “scam”; I had been considering the case of the Sutherland Little Loco for a good while now.

 

[Michael Fidler]

Thanks @Michael Fidler. It may be extremely dull to you, but the phonostage sub-industry has largely adopted a position that matching load to a MC cartridge impedance is normal (it wasn’t always). So, it’s bound to generate a ton of questions. Your article is sure to draw lots of interest.

It’s particularly interesting to me that you panned the “current input” purveyors as a “scam”; I had been considering the case of the Sutherland Little Loco for a good while now.

Most of them are marketed as being able to 'damp' the movement of the cantilever electrically. If you work out the mass of the moving parts, and therefore the energy in the system at 5cm/s, you can calculate that the total energy pulled out of the system is only a fraction of a percent every second or so. It's just an example of companies either not doing their homework or exploiting the lay intuition of their customers. I would hardly consider a Q factor of 500 at 20Hz to be 'electrically damped'.

Additionally the shorting of the coil inductance pulls the response down by about 0.5dB at 20kHz which isn't great for RIAA accuracy.

EDIT - and it's awful for RF rejection. How can you RF shunt a current input circuit without causing severe issues with stability?

 

[ban25]

I received my MC PRO this morning and was able to put it through its paces. Thanks to Michael for a prompt response and shipping right after a holiday weekend!

Out of the box, the MC PRO is handsome and well-built. The included transformer is substantial. Overall, it's a bit larger than I imagined, particularly compared to something like a Schiit Mani, though I have no complaints with the size.

This unit replaced a step-up transformer that I previously ran into the phono stage of my Integra DRX-8.4 AVR. Ground-noise has been an issue with this setup, though I've mostly mitigated the issue with some high quality ground wires (and fork connectors). However, cable routing remained an annoyance with this solution. With the MC PRO installed, I am now running balanced cables from the pre-amp to the AVR and unbalanced RCA + ground from the turntable to the pre-amp. I'm happy with an overall cleaner installation.

I conducted some unscientific tests to compare ground hum and noise floor using an SPL meter measured 6" from the mid/tweeter in my right tower. The turntable, pre-amp, and AVR were all powered on and the AVR was set to a relative level of -8 dB. I used the low-gain setting of 63 dB on the MC PRO. The Sumiko Songbird low-output MC cartridge was mounted. Here are the results:

	DRX-8.4 Phono + SUT (RCA-in)	MC PRO (XLR-in, Low Gain)
Ambient Background (OFF)	36.5 dB	36.5 dB
No Ground Wire Attached	40.5 dB	N/A
Audible Noise Floor (ON)	39.0 dB	37.5 dB

I ran each test 3 times and it would appear that the MC PRO is up to 1.5 dB quieter than the receiver's phono stage + SUT, and of course, has no audible ground hum. This is a pleasant surprise because I honestly expected no difference aside from easier cable routing! Now, could I tell the difference when listening to actual music? Absolutely not. But with no content playing, the difference is audible.

In terms of content, I gave it a try with some of my best mastered albums, including the UHQR release of Kind of Blue on 200gr 45 RPM vinyl. I also auditioned Yuja Wang's recording of Prokofiev's Sonata No. 8 (180gr 33 1/3) and Diana Krall's Turn Up The Quiet (180gr 33 1/3). I refuse to engage in any audiophile fever dreams, so I'll just note that each album sounded excellent, as they always do.

Some photos -- an optimized installation will have to wait for the weekend:

 

[Angsty]

I refuse to engage in any audiophile fever dreams, so I'll just note that each album sounded excellent, as they always do.

Excellence in the absence of fever dreams - that’s what I look for. Seems like a great phono at a competitive price for the feature set.

 

[Angsty]

I had been considering the case of the Sutherland Little Loco for a good while now.

I had to go back to Stereophile to look at the Little Loco stats for comparison…

“The Little Loco's unweighted, wideband S/N ratio, measured with the input shunted with a 10 ohm resistor as recommended by Ron Sutherland in his email, was 47.8dB, ref. 1kHz at 500µV. Restricting the measurement bandwidth to 22Hz–22kHz increased the ratio to a respectable 64.8dB, while switching an A-weighting filter into circuit increased it further, to 72.85dB.” -https://www.stereophile.com/content...g-little-loco-phono-preamplifier-measurements

I think Michael has made his case.

 

[Michael Fidler]

I had to go back to Stereophile to look at the Little Loco stats for comparison…

“The Little Loco's unweighted, wideband S/N ratio, measured with the input shunted with a 10 ohm resistor as recommended by Ron Sutherland in his email, was 47.8dB, ref. 1kHz at 500µV. Restricting the measurement bandwidth to 22Hz–22kHz increased the ratio to a respectable 64.8dB, while switching an A-weighting filter into circuit increased it further, to 72.85dB.” -https://www.stereophile.com/content...g-little-loco-phono-preamplifier-measurements

I think Michael has made his case.

It just goes to show the state of the market when an (A-weighted I might add) noise figure of 16dB (6.3x noise going out as comes in from the coil resistance thermal noise) is considered respectable. Let alone for a product that costs $3,800.

We could improve this by 7dB to a noise figure of 9dB by using a single BC327 ($0.07) transistor and a 15 ohm resistor ($0.01) in a voltage-feedback input amplifier on the front end...

I'd better crack on with that article and make a table of SNRs and noise figures of various devices with all the weightings imaginable on each row.

 

[Mnyb]

In all honesty moving coil cartridge loading is an extremely dull subject and I get more e-mails about it than I care to have about this subject, particularly the 'zero-impedance'/'current input' marketing scam that's currently doing the rounds. I'm writing all of this up for a new article for the website so I can just reference it in future.

What about MM cartridge loading , capacitance adjustment ? this is OT 8as this the review of your MC amp ) but will you have an article on that too for reference

 

[DSJR]

I received my MC PRO this morning and was able to put it through its paces. Thanks to Michael for a prompt response and shipping right after a holiday weekend!


View attachment 309062

Apologies as I'm genuinely trying not to be antagonistic and I remain programmed to a degree by my decades 'doing' Linns and Regas, but WHAT is that 'thing' you're playing records with? W@nky headshell which looks to be incredibly rigidity compromised? Fancy feet 'cos you don't appear to have an isolation platform and a RECORD WEIGHT on that bearing - should be ok but the entire 'using a weight' thing can be cured with a Notts Analogue Spacemat placed on top of the Techie one (and VTA adjusted accordingly).

There shouldn't be anything wrong with the stock Technics headshell you know, apart from the wiring which can *look* posher with Sumiko or similar wires. A dense foam type Spacemat used to be around twenty odd quid (its benefits away from a Spacedeck aren't fully realised by modern dealers for that brand) and I use one to this day, as a full-on Notts deck is beyond me now (and a terrible dust trap). Absoloutely NO subsequent need to load the bearing up with extra mass.

I'll crawl back under my stone now, but honestly, less can be more you know

P.S. Glad you like the phono stage (trying to bring my rant back to topic...)

 

[Angsty]

It just goes to show the state of the market when an (A-weighted I might add) noise figure of 16dB (6.3x noise going out as comes in from the coil resistance thermal noise) is considered respectable. Let alone for a product that costs $3,800.

We could improve this by 7dB to a noise figure of 9dB by using a single BC327 ($0.07) transistor and a 15 ohm resistor ($0.01) in a voltage-feedback input amplifier on the front end...

I'd better crack on with that article and make a table of SNRs and noise figures of various devices with all the weightings imaginable on each row.

In Ron’s defense, much of the price difference is due to the dealer vs. direct-sales model. However, the consumer still pays a lot more…

Ron’s a well-respected engineer, so I’m sure he has reasons for his design choices, but the bench test numbers don’t lie. The MC Pro produces wonderful results at a price some deluded fellows pay for power cords.

 

[Michael Fidler]

What about MM cartridge loading , capacitance adjustment ? this is OT 8as this the review of your MC amp ) but will you have an article on that too for reference

I'll write up 'Practical MM input design' after I finish 'Practical MC input design'. Generally I believe that 48-50k with 120pF is best for 99% of circumstances. The vast majority of cartridge manufacturers specify 200-300pF load cap which is possible when adding in tonearm and cable capacitances.

 

[VQR]

It just goes to show the state of the market when an (A-weighted I might add) noise figure of 16dB (6.3x noise going out as comes in from the coil resistance thermal noise) is considered respectable. Let alone for a product that costs $3,800.

We could improve this by 7dB to a noise figure of 9dB by using a single BC327 ($0.07) transistor and a 15 ohm resistor ($0.01) in a voltage-feedback input amplifier on the front end...

I'd better crack on with that article and make a table of SNRs and noise figures of various devices with all the weightings imaginable on each row.

It's great seeing someone in the phonograph side of audio not pandering to BS and lay intuition. We gotta protect you at all costs!

 

[ban25]

Apologies as I'm genuinely trying not to be antagonistic and I remain programmed to a degree by my decades 'doing' Linns and Regas, but WHAT is that 'thing' you're playing records with? W@nky headshell which looks to be incredibly rigidity compromised? Fancy feet 'cos you don't appear to have an isolation platform and a RECORD WEIGHT on that bearing - should be ok but the entire 'using a weight' thing can be cured with a Notts Analogue Spacemat placed on top of the Techie one (and VTA adjusted accordingly).

There shouldn't be anything wrong with the stock Technics headshell you know, apart from the wiring which can *look* posher with Sumiko or similar wires. A dense foam type Spacemat used to be around twenty odd quid (its benefits away from a Spacedeck aren't fully realised by modern dealers for that brand) and I use one to this day, as a full-on Notts deck is beyond me now (and a terrible dust trap). Absoloutely NO subsequent need to load the bearing up with extra mass.

I'll crawl back under my stone now, but honestly, less can be more you know

P.S. Glad you like the phono stage (trying to bring my rant back to topic...)

LOL

The Nasotec works quite well and I prefer it to the stock headshell even if it is a bit fiddly when dropping the needle!

The Isonoe feet do a great job of isolating the table without having to resort to unseemly isolation platforms. This table is out in the open, so it needs to blend in. I have another table in a dedicated 2-channel zone with a much more "traditional" configuration. Same for the weight. It's quite small and is just there for looks.

 

[DSJR]

I wonder how much better or worse standard sorbothane feet would be, but point taken Tapping the shelf/cabinet top it's on will tell over the stock feet, which I imagined had improved over the deck generations...

The previous headshell 'replacement' for the stock shell is/was the Sumiko solid shell, but that was 'Art of Sound' from some years back I admit. Anyway, going off topic so apologies. Do bare in mind that the phono stage will only 'sound' as good as the player system feeding it

 

[Michael Fidler]

It's great seeing someone in the phonograph side of audio not pandering to BS and lay intuition. We gotta protect you at all costs!

Thanks for your kind comments. I look forward to writing everything that I've learned during 'UK Stage 1' of my business plan down for everyone to read for free on my website. Hopefully I'll be taking on new challenges for other products and assuming that I'm able to attain the competitive performance that I can get from phonostages I'll very much look forward to describing the design process for those too.

As far as protection goes I might have to take you up on that as quite a few people have tried to get me in trouble and cause issues for the company due to my technical transparency and competitive approach but so far haven't succeeded as I like to be very thorough and make everything air-tight. A disadvantage of this approach is that you have to tell the truth 100% of the time which is inconvenient in the short term and from a traditional 'audiophile marketing' perspective but is really starting to pay dividends.

One day I'll publish my collection of 'cease and desist' threat letters, along with a run-through of my first 2 years once I conclude the current phase of the business. Now and here is neither the time or place... Sadly they never seem to follow through on their promises of legal obliteration but I'm putting aside some of my revenue for a 'truth insurance' fund for when I start writing about good design practice with various examples of contemporary quackery to contrast.