Classic Audio MC Pro Phonostage Review

[Angsty]

Hoping that Amir gets one of the first run to review!

 

[Michael Fidler]

Hoping that Amir gets one of the first run to review!

That would make things a bit too hectic! I'm secretly dragging my heels just enjoying the peace and quiet.

 

[Angsty]

That would make things a bit too hectic! I'm secretly dragging my heels just enjoying the peace and quiet.

Understood. Demand pouring in before you are ready may not be the best business decision.

Yet still, we are audio enthusiasts who are enthusiastic about your next product!

Ready when you are!

 

[EJ3]

That would make things a bit too hectic! I'm secretly dragging my heels just enjoying the peace and quiet.

I an unusual (and unexpectedly early [by 3 months] occurrence), finally, I am ready, also.
Holding in place, as my new plan does not actually start until Jan. 2, 2026.

 

[stefanovesa]

That would make things a bit too hectic! I'm secretly dragging my heels just enjoying the peace and quiet.

I see 100 pF for the input of the new LO PRO, have you also the value for the MC PRO? I cannot see in the manual or website. Thanks!

 

[Michael Fidler]

I see 100 pF for the input of the new LO PRO, have you also the value for the MC PRO? I cannot see in the manual or website. Thanks!

From the LO PRO manual:

The input loading seen by the cartridge is fixed at 150Ω // 100pF. This combination is designed to over-damp inductive resonances in the 1-10 MHz region of all LOMCs currently on the market, without introducing any significant response variations in the audio band.

The equivalent input noise voltage of the LO PRO is not significantly greater than the thermal noise generated by a 15Ω resistance. As a result, the common 1:10 cartridge-to-input resistance matching rule (intended to reduce the effect of insertion loss on signal-to-noise ratio) no longer applies once cartridge coil resistance exceeds 15Ω, since the cartridge’s own thermal noise dominates. The LO PRO can therefore be used without penalty with LOMCs having coil resistances up to 50Ω.

From the MC PRO manual:

The MC input loading is fixed at 120Ω//800pF, which provides the best trade-off between insertion loss and the absorption of radio frequency interference. After a brief period of research, it was found to be unnecessary to make this variable. It can be reduced below this value using loading cables, but there isn’t any benefit to be had other than pulling the level at the sensitive input down and degrading signal to noise ratio. Speculatively, it’s only popular because it can be implemented with almost no electronics knowledge...

 

[stefanovesa]

From the LO PRO manual:

The input loading seen by the cartridge is fixed at 150Ω // 100pF. This combination is designed to over-damp inductive resonances in the 1-10 MHz region of all LOMCs currently on the market, without introducing any significant response variations in the audio band.

The equivalent input noise voltage of the LO PRO is not significantly greater than the thermal noise generated by a 15Ω resistance. As a result, the common 1:10 cartridge-to-input resistance matching rule (intended to reduce the effect of insertion loss on signal-to-noise ratio) no longer applies once cartridge coil resistance exceeds 15Ω, since the cartridge’s own thermal noise dominates. The LO PRO can therefore be used without penalty with LOMCs having coil resistances up to 50Ω.

From the MC PRO manual:

The MC input loading is fixed at 120Ω//800pF, which provides the best trade-off between insertion loss and the absorption of radio frequency interference. After a brief period of research, it was found to be unnecessary to make this variable. It can be reduced below this value using loading cables, but there isn’t any benefit to be had other than pulling the level at the sensitive input down and degrading signal to noise ratio. Speculatively, it’s only popular because it can be implemented with almost no electronics knowledge...

Thanks, oops it was in the last page of the manual. Which is the idea behind the lowering of the capacitance figure?

 

[Michael Fidler]

Thanks, oops it was in the last page of the manual. Which is the idea behind the lowering of the capacitance figure?

The idea with this one is that the input RF filtering is accomplished by a proper multi-pole network with impedance equalisation on the entry point, rather than relying on the cartridge inductance and just a shunt capacitance. The input capacitance is just 100pF of shunt, to pull out the worst UHF stuff and make sure the cartridge inductance isn't just left open.

 

[Michael Fidler]

Initial web page for the LO PRO with final spec created here: https://michaelfidler.com/products/pro/lo-pro-moving-coil-phono-stage/

 

[NoClipping1337]

Initial web page for the LO PRO with final spec created here: https://michaelfidler.com/products/pro/lo-pro-moving-coil-phono-stage/

Can't wait until these'll ship to the US!

 

[Endibol]

Initial web page for the LO PRO with final spec created here: https://michaelfidler.com/products/pro/lo-pro-moving-coil-phono-stage/

Good to see you managed to start production with SMD-technology, another milestone for you company! Congratulations Michael!

 

[Michael Fidler]

Good to see you managed to start production with SMD-technology, another milestone for you company! Congratulations Michael!

These are starting to come in thick and fast now!

 

[Endibol]

These are starting to come in thick and fast now!

Ah, the Spartans too!

 

[morillon]

It's sometimes useful for potential maintenance to have checkpoints present on this...right?
(with voltage readings, etc.) ;-)

 

[Michael Fidler]

It's sometimes useful for potential maintenance to have checkpoints present on this...right?
(with voltage readings, etc.) ;-)

A few points on the power supply have labels, but generally with this kind of op-amp circuitry where you have two supply rails, everything is referenced to zero, so there's not much point.