Classic Audio MC Pro Phonostage Review

[Zapper]

This is pretty paranoid IMO. Where would improvements be implemented in an existing design, apart from higher spec capacitors, etc?

I mean audio electronics are not 1960s engines or modern overclock/performance cpus where “factory freaks” exist

There will unit to unit variations based on component tolerances. Some will test better than others, although the differences will be small if low tolerance components are used. If I were the manufacturer and had several units on the shelf, I would be tempted to review their test data and send the best one to the reviewer.

 

[Fontie]

He also makes MM phono preamps, and I'd expect them to be equally good. <https://michaelfidler.com/products/spartan/>

Hopefully the MM version is reviewed by Amir

 

[Thomas_A]

It has nothing to do with rumble, or anything else on the record or from the turntable.

It is entirely to do with the physics.

Seismic transducers are inaccurate up to around 2x their natural frequency by the nature of how they produce an output. This has always been the case. The exact frequency depends on the damping - more damping reduces spurious output at resonance but raises the frequency at which the cartridge body can be reasonably considered a stator. Until this frequency the output of any cartridge is wrong. This is simple transducer engineering.

The 1976 update of the RIAA equalisation did include an improvement in this area but still better to just filter it out in the phono stage and have done with it- like this one does.

This manufacturer understands how record players work, bravo for good engineering.

But this one filters at -6 dB at 20 Hz, unlike e.g. the Cambridge having -0.5 dB at 20 Hz. Choosing a cut-off may be semantic, but at least having linear response down to 30 Hz is something to desire. Here this is not so.

 

[Endibol]

He also makes MM phono preamps, and I'd expect them to be equally good. <https://michaelfidler.com/products/spartan/>

This is the MM Pro sister version:

MM Pro Moving Magnet Phono Stage by Michael Fidler

Precision RIAA MM phono stage by Michael Fidler with linear power supply, balanced outputs, mono switch and low frequency crossfeed

michaelfidler.com

 

[AaronJ]

@amirm the review doesn't say what type of device it is until quite a ways in...

The title of the thread indicates that it is a phono stage. If you’re not sure what it is, https://letmegooglethat.com/?q=what+does+a+phono+stage+do?

 

[DSJR]

But this one filters at -6 dB at 20 Hz, unlike e.g. the Cambridge having -0.5 dB at 20 Hz. Choosing a cut-off may be semantic, but at least having linear response down to 30 Hz is something to desire. Here this is not so.

Oh PLEASE... That filter is deliberately designed and put there!

Can you hear half a dB at 30Hz? Bearing in mind the diabolical setups I've seen with 'record players' taking pride of place in forum system pictures, believe me, that bloody format needs all the help it can get!!!

The other thing is the tiny boxes used by so called 'audiophiles' these days as speakers, ALL of which for physics reasons, will distort at any volume below 60Hz or so and this messes with the midrange!

We'rte not talking digital here, but a highly flawed and dated medium that 'audiophiles' still rate highly, even if many of them haven't an effin' clue what they have and how to use it properly.

Apologies for the grumpiness, but I've been round the block a few times with vinyl reproduction

 

[Michael Fidler]

We'rte not talking digital here, but a highly flawed and dated medium that 'audiophiles' still rate highly, even if many of them haven't an effin' clue what they have and how to use it properly.

I would tend to agree with this statement - I've yet to see any non-noise content below 30Hz on all the transfer spectrograms that I've made. A better goal would be something like no more than 0.1dB response variation at 40Hz which we can see being the limit of the vinyl medium.

As grooves will be 'constant velocity' below 50Hz (where the RIAA curve goes flat again), low frequency content has to be heavily limited below 50Hz when cutting discs to avoid over-excursion of the grooves.

With a 3rd order filter we can get 0.1dB at 40Hz, 0.7dB at 30Hz (which will be negligeable considering all other factors in the system), -3dB at 24Hz, and then most importantly -23dB at 10Hz and lower where all the trouble is.

I think expecting any response below 35Hz or so is rather wishful thinking.

 

[AudioSceptic]

I would tend to agree with this statement - I've yet to see any non-noise content below 30Hz on all the transfer spectrograms that I've made. A better goal would be something like no more than 0.1dB response variation at 40Hz which we can see being the limit of the vinyl medium.

As grooves will be 'constant velocity' below 50Hz (where the RIAA curve goes flat again), low frequency content has to be heavily limited below 50Hz when cutting discs to avoid over-excursion of the grooves.

With a 3rd order filter we can get 0.1dB at 40Hz, 0.7dB at 30Hz (which will be negligeable considering all other factors in the system), -3dB at 24Hz, and then most importantly -23dB at 10Hz and lower where all the trouble is.

I think expecting any response below 35Hz or so is rather wishful thinking.

It's great to see you here. I see you use a linear PSU. Have you found that to be superior to an SMPS?

 

[Michael Fidler]

@Michael Fidler
The RIAA purists would argue that phase-shift associated with a filter such as this is felt up into actual audio territory, and thus it's not appropriate.
I can see both sides of this, but I think the design decision in your unit is perfectly appropriate.
If somebody doesn't like it, they're free to purchase something else.

Indeed. At some point I need to write an in-depth article on the website discussing all of these factors and most importantly actually demonstrating the effects of infrasonic energy on loudspeakers (either through mathematical simulation based upon excursion nonlinearity and excursion response in ported speakers, or in the real world if I can get my act together and make a good measurement setup).

 

[Michael Fidler]

It's great to see you here. I see you use a linear PSU. Have you found that to be superior to an SMPS?

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.

 

[AudioSceptic]

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.

Thanks for that detailed and most informative reply.

 

[restorer-john]

It has nothing to do with rumble, or anything else on the record or from the turntable.

To be fair Frank, have you forgotten the array of H/LPFs we had on preamplifiers and integrated amplifiers back in the day? We had defeatable low (and high) filters for at least three reasons:

1: the filters were not just for the sole use of the phono stage- often open reel, tuners, cassette decks all needed the use of them.
2: the placement of the filters was mostly always after the phono stage.
3: ganging up several different analogue filters results in additional gain stages to keep levels the same.

So we had the correctly designed RIAA stage itself AND switchable susbsonic/15Hz/30Hz//low/70Hz/defeat etc. Sometimes to get rid of excess woofer movement, preventing feedback, knocking down hum or even idler wheel noises. And in tape we had head 'woodles' to kill, mains hum etc. Filters to target what we wanted to without wrecking the music from various sources.

Example Spec1:

This is just a single use phono MC stage, and so the manufacturer has implemented what looks to be a very sensible infrasonic filter, I agree.

 

[xaxxon]

The title of the thread indicates that it is a phono stage. If you’re not sure what it is, https://letmegooglethat.com/?q=what+does+a+phono+stage+do?

oops, apparently I can't read.

 

[DSJR]

To be fair Frank, have you forgotten the array of LPFs we had on preamplifiers and integrated amplifiers back in the day? We had defeatable low (and high) filters for at least three reasons:

1: the filters were not just for the sole use of the phono stage- often open reel, tuners, cassette decks all needed the use of them.
2: the placement of the filters was mostly always after the phono stage.
3: ganging up several different analogue filters results in additional gain stages to keep levels the same.

So we had the correctly designed RIAA stage itself AND switchable susbsonic/15Hz/30Hz//low/70Hz/defeat etc. Sometimes to get rid of excess woofer movement, preventing feedback, knocking down hum or even idler wheel noises. And in tape we had head 'woodles' to kill, mains hum etc. Filters to target what we wanted to without wrecking the music from various sources.

Example Spec1:
View attachment 305647


This is just a single use phono MC stage, and so the manufacturer has implemented what looks to be a very sensible infrasonic filter, I agree.

I have to put it on record, much to the shame of myself and colleagues at the time in the UK, that we rejected this preamp out of hand BECAUSE of the switch-gear Oh the arrogance and utter bloody ignorance of youth back then. I think Pioneer all but gave up in the UK market for years after these SPEC units were dismissed by dealers such as the one I worked in

 

[restorer-john]

I have to put it on record, much to the shame of myself and colleagues at the time in the UK, that we rejected this preamp out of hand BECAUSE of the switch-gear

It's OK, your loss was our gain. Plenty of Specs ended up here in Australia, but nowhere near as many as were sold in the US.

I was just using it as an example as it has the 15/30Hz defeatable low filter and a properly designed phono stage (for the time).

 

[MC_RME]

I am used to these switchable filters as well, all my units had them. By not making it switchable in the MC Pro the unit misses one important factor - the user can not experience the off/on aka not active/active difference himself. And yes, after that it will be on forever...

 

[Chrispy]

I did like the upside down printing on the back so you can read it bent over from the front Seems rather expensive

 

[formdissolve]

Think I found my new phono stage!

 

[Thomas_A]

Oh PLEASE... That filter is deliberately designed and put there!

Can you hear half a dB at 30Hz? Bearing in mind the diabolical setups I've seen with 'record players' taking pride of place in forum system pictures, believe me, that bloody format needs all the help it can get!!!

The other thing is the tiny boxes used by so called 'audiophiles' these days as speakers, ALL of which for physics reasons, will distort at any volume below 60Hz or so and this messes with the midrange!

We'rte not talking digital here, but a highly flawed and dated medium that 'audiophiles' still rate highly, even if many of them haven't an effin' clue what they have and how to use it properly.

Apologies for the grumpiness, but I've been round the block a few times with vinyl reproduction

You don't have to tell me that the medium is flawed and dated. Yet more vinyl products keep coming and are reviewed and here we are. Whether there are audible or rather tactile differences of the filter that is seen here - yes there is. And 30 Hz content in vinyl and even lower do exist, here is Cowboy Junkies Trinity sessions.

 

[Mnyb]

You don't have to tell me that the medium is flawed and dated. Yet more vinyl products keep coming and are reviewed and here we are. Whether there are audible or or rather tactile differences of the filter that is seen here - yes there is. And 30 Hz content in vinyl and even lower do exist, here is Cowboy Junkies Trinity sessions.

View attachment 305673

Is this spectrum from the vinyl ? Then I suspect everything below 30-40Hz is the kind of problems this filter will suppress and not actual content put there by the band . The 7hz peak looks like a resonance to me ?
I migth be wrong sold my vinyl 20 years ago , but I did remeber the speakers cones flapping around when playing vinyl due to that my equipment missed this feature .