Classic Audio MC Pro Phonostage Review

[Angsty]

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.

Now that’s a book to write! “Lessons from the Audiophile Battlefield”!

 

[Michael Fidler]

Now that’s a book to write! “Lessons from the Audiophile Battlefield”!

Attack of the Quacks

 

[Risto_H]

For this application the linear approach is certainly a lot less prone to trouble. You can generate internal +17V rails fairly easily and importantly keep them quiet at high frequency where opamp PSRR isn't as good as it is at mains frequency due to falling feedback factor as a result of frequency compensation.

For a standard 24V external SMPS (without any internal conversion in which case a 5V SMPS is best) you can only split the rails down to +-12V with a suitable rail divider and then you have to deal with quite a lot of noise current going into the ground path due to the EMI suppression cap that links the SMPS output to the mains to shunt away switching RF energy. It's a bit messy to say the least and you're limited to about 7V RMS output. If you do switching conversion internally with a 5V to +-15V module then you can get 9V RMS out but they're rather unstable and need a constant load.

That being said, many new products use custom SMPS modules internally that give very good results as is evidenced by measurements on the forum. For me at least with this product, reliabilty, simplicity, the absence of switching noise, isolation from the mains, and ease of repair should anything go wrong made the linear option the clear winner.

Having designed a couple of phonostages myself, I find this very interesting. I like the reasoning behind your choices and the end result is also very impressive.

Still, I took a quite different approach. This is the power supply part of my RH RIAA 3.0. First of all, almost all the components are SMD and in this case the PSU is a switched capacitor up & inverting IC with built in LDO regulators. It also gives clean and steady output (+15 V / -15 V) without injecting any audible or measurable noise to the amplifier stages.

I believe this approach is practically maintenance free with usable service life of at least 20 years. There's no electrolytic capacitors to give you trouble.

Like your product this one is also hand-soldered with lead-free tin that contains silver. It also has an active mute to stop any noises entering the rest of the system (realized by A1 and A3 in the picture).

 

[Risto_H]

I just don't understand why these THT designs are still a thing. SMD parts are so much better. You can get 0805 SMD thin film resistors with 0,01% tolerance for the same price as 1% THT metal film resistor.

And you can get very high quality acrylic and PPS SMD film capacitors with 2% these days.

Well, I prefer full SMD design myself and I also hand solder them on 4-layer boards, no problem at all and don't have to cut those extra wires after soldering. But THT design has its benefits too so it is more a matter of preference than anything else. I can of course say that fighting RF and other types of disturbances is easier with SMD but you can do it with THT as well if you know what you are doing. It is the board layout that is the most important detail.

You are right about the PPS caps. The 2 % series is exactly what I'm using in my RIAA eq part. But 0.01 % thin film SMD resistors are very expensive. I don't think you really meant 0.01 % but rather 0.1 % which I'm using in all the amplifier sections? They are still quite expensive and cost more than typical 1 % metal film THT resistors.

There are two factors that decide how accurate your RIAA eq is:

• Circuit design. Wrongly calculated or inaccurate component values due to price reduction throw the eq accuracy immediately off.
• Parts tolerance. Even with 2 % caps and 0.1 % resistors, the RIAA curve can be off by several tenths of dB.

Obviously @Michael Fidler has succeeded in both design and parts selection. It is simply impressive how well this amplifier performs and RIAA curve is practically flawless even with 1 % resistors (I bet they are hand picked). My own amp that is full SMD construction and has switching PSU reaches very similar performance but if I wanted to make it significanty better than this one it would be really hard, regardless of SMD construction or number of board layers.

I just took a look at Michael's web site and was delighted to notice that his design philosophy matches my own in most cases. There are some differences too but perhaps I should start a thread of my own sometimes when I have time to avoid any more OT.

 

[Michael Fidler]

Obviously @Michael Fidler has succeeded in both design and parts selection. It is simply impressive how well this amplifier performs and RIAA curve is practically flawless even with 1 % resistors (I bet they are hand picked). My own amp that is full SMD construction and has switching PSU reaches very similar performance but if I wanted to make it significanty better than this one it would be really hard, regardless of SMD construction or number of board layers.

Generally I put the caps into matched groups but I've noticed that the accuracy of the '1%' through-hole resistors that I'm using is considerably better. The topology of the RIAA network as well (parallel) also plays a big part in averaging/mitigating component tolerance so the whole thing performs considerably better than you might expect in the worst case (which is a stastically unlikely outcome).

As far as using SMPS goes I don't see the need to introduce it, so it's better to do without it. If we're going to the trouble of using THT then it's better to use more readily-available parts to 'future proof' the design. There is of course the need to dissipate about 1.5W or so inside the enclosure at idle but in this case the internal temperature stays well below 40c so all good.

That is not to say that SMPS is necessarily a bad thing if you have a limited amount of space and thermal headroom, or need to convert what's coming in to your power supply to DC with great efficiency. For through-hole it's difficult to keep the loop sizes low enough to avoid trouble even with a fair amount of PCB space available. In regards to a 15V internal rail it can certainly work well, but you'll be limited to about 9.2V RMS output unless you use rail-to-rail opamps which significantly limit your choices. Although if you structure the gain stages so that the final stage applies the last couple of decibels of gain and uses a rail-to-rail device then you can push past 10V RMS while still using 5532/4s, 2068s or any other suitable op-amp for the front end.

If I had to use an SMPS I would use a 5V input type and bring the rails up to about +-17V with a suitable DC to DC arrangement, hopefully with some isolation...

 

[ObjectiveSubjectivist]

Performance is well out of track in 2023.
Voted POOR.

Are you kidding?

 

[lamda18]

MM Pro By Michael Fidler Phono Stage Reviewed - Audio Appraisal

As far as I can determine, £600 is enough to buy you the finest moving magnet phono stage currently in production. And that phono stage is the MM Pro by Michael Fidler. I will stand by that stateme…

www.audioappraisal.com

 

[AudioSceptic]

MM Pro By Michael Fidler Phono Stage Reviewed - Audio Appraisal

As far as I can determine, £600 is enough to buy you the finest moving magnet phono stage currently in production. And that phono stage is the MM Pro by Michael Fidler. I will stand by that stateme…

www.audioappraisal.com

Has anyone also linked to their review of the MC Pro <https://www.audioappraisal.com/classic-audio-mc-pro-moving-coil-phono-stage-reviewed/>?

 

[AudioSceptic]

J

Has anyone also linked to their review of the MC Pro <https://www.audioappraisal.com/classic-audio-mc-pro-moving-coil-phono-stage-reviewed/>?

I have to quote this snippet from another review at that site.

But there’s a great need for honest, unbiased reviews in this industry. I firmly believe that hi-fi should be accessible to everyone and that you shouldn’t have to wade through marketing hyperbole, disingenuous advertising, BS audiophile pseudoscience and brand snobbery when you’re trying to make a purchasing decision.

Could it be that things really are changing at last and honest, objective reviews, as we see at ASR, Archimago, and Audio Appraisal, are gaining ground against the borderline-dishonest delusional nonsense that's dominated for so long?