Pro-Ject Phono Box DC MM/MC Phono Preamp Review

[JeremyFife]

Although 'headamp' makes me think of guitar pre-amps ... different use

 

[welwynnick]

Although 'headamp' makes me think of guitar pre-amps ... different use

Yeah - or it could mean microphone head amps. It's a bit ambiguous, it depends on the context - live, recording or replay.

 

[somebodyelse]

Is the term "headamp" synonymous with phono pre amp?

Possibly. It depends who you're talking to, possibly based on country, age or areas of experience, so you'll probably have to work it out from context. I've heard it used as a generic term for the first amp stage in the signal chain of an instrumentation system, possibly responsible for signal conditioning for the transducer. That fits the audio usage for a stand-alone phono stage, an active MC to MM step-up stage, or a mic preamp. I've not encountered separate amps for tape heads, but it would fit that too. The other main audio usage is for a headphone amp. I don't know if the guitar amp head comes from the same root.

 

[ryanmh1]

This looks okay for the price, but when it comes down to it, if you look just at noise, this is barely competent. It does not do as well as multiple other offerings for the same or similar price, many of which have loading options and filters. One would think Pro-Ject, which is a turntable company, could and would do a little better than what amounts to a ($175) phono dongle from Emotiva. Aiyima posted measurements of their $99 T3 Pro which (if they hold up) were much quieter that the Pro-Ject, plus it offers a lot more flexibility for $100. Really curious how the MC is in that Aiyima. Even the built-in stage in the Marantz pre/pro is quieter, and there's some reason to think that might be in every Denon/Marantz AVR since they spec the phono stage identically in every AVR at least from the X3500H on up, and have no particular discussion of any special phono stage in AV10 despite it being a premium product...

 

[Kimbrough Xu]

I was totally impressed by the implementation of RIAA equalization:
View attachment 387285
It is rare that we see such flat response regardless of price! Would have been nice to have a high pass filter though to deal with LP rumble and other low frequency noise but that would have increased the cost.

Hi, Amir, thank you for your great review, but with my knowledge, I can not understand why do you say a HPF is nice feature for this phono stage? Do you mean you dont want the signals under 20Hz?

 

[nathan]

Hi, Amir, thank you for your great review, but with my knowledge, I can not understand why do you say a HPF is nice feature for this phono stage? Do you mean you dont want the signals under 20Hz?

LPs don’t have much if any real content there other than the mechanical noise of the gear and the groove Think of it as a rumble filter.

 

[AudioSceptic]

Hi, Amir, thank you for your great review, but with my knowledge, I can not understand why do you say a HPF is nice feature for this phono stage? Do you mean you dont want the signals under 20Hz?

You might find the conversation starting here <https://www.audiosciencereview.com/...o-mc-pro-phonostage-review.47139/post-1685555> of great interest.

 

[NTTY]

20mV input at 15kHz causes clip, that is ridiculously low!
A cartridge output is mainly at higher frequencies, and that's where the headamp needs the headroom.
Michael Fidler Spartan 5 (£150) quote 420mV @ 10kHz as opposed to about 27mV that this device can take.
Headroom is vital is headamps.

Hi, it might be because the view includes noise in the calculation (?), but it does not clip at 20mV input at 15kHz. A friend of mine asked me to review his Phono Box and I found that noise floor is elevated relative to the low voltage input at high frequencies, and that causes the THD+N to go above -60dB.
Fact is because of the RIAA curve, if non compensated by the Software performing the measurement, it will compute high level of noise at low level input. The Box is noisier at 15kHz compared to 1kHz. Let me try to show that. The below is 20mV input into the box at 15kHz:

That descending noise view is the RIAA curve that compensate for the one of the vinyl. And if we compensate it in the software, as it happens IRL, then we get:

It is the same measurement, but and you can see that the former one had a THD+N of -52dB and the later shows -62dB of THD+N. The second view is the realistic one because it would be the reproduction of a 15kHz as it was recorded on the vinyl.

So, I did a THD vs level sweep and only included THD (5 harmonics) in the below view:

You can see at what levels the Box truly clips. At 15kHz, it is around 155mV input.

That said, it does not explain the -20dB THD+N that Amir measured for 50mV input at 15kHz. On my side I see -66dB, entirely dominated by the distortion:

Cheers

 

[NorthernSoul73]

I have this box although not sure if there are any benefits upgrading to the CA Duo.

For my turntable I have a Clearaudio Concept paired with an AT33PTG/II ...

If I go for the duo will I see any difference in sq?

 

[JeremyFife]

I have this box although not sure if there are any benefits upgrading to the CA Duo.

For my turntable I have a Clearaudio Concept paired with an AT33PTG/II ...

If I go for the duo will I see any difference in sq?

Highly unlikely that you will get better sound. Any slight improvement will be swamped by record-to-record variation.

If you have a problem with the noise floor then you might get some benefit, but you are looking in the wrong places if your goal is sound improvement.

I understand the drive to upgrade (it's a demon we all wrestle with!) but resist

Take a critical look at your speakers, speaker position and your room. Start a new thread if you want to discuss that.

Otherwise, just enjoy your music

 

[Carl-Fosi Audio]

Thanks

The lack of HPF is indeed too bad.
Those guys are producing a lot of those Phono preamps. We have quite a few measured here already.
This one is pretty good, especially for the money.

Why do you need HPF?

 

[nathan]

Why do you need HPF?

Prevent rumble.

 

[welwynnick]

Prevent rumble.

And subsonic speaker excitation due to record warps and tone arm oscillation.

 

[AudioSceptic]

Prevent rumble

There is no real signal down there anyway <https://www.audiosciencereview.com/...-vinyl-playback-discussion.34143/post-2336940>.

 

[somebodyelse]

Why do you need HPF?

There are different arguments here. One side is specific to phono amps, but the other applies to any source.

The phono specific part is down to a few things. First the physics of the transducer, as @AudioSceptic points to, referencing a post by someone who used to work on such things at Garrard. The compliance of the cartridge and the combined mass of cartridge and effective mass of arm form a resonant system, usually around 10Hz if a suitable combination of arm and cartridge have been chosen, but could be higher or lower if they are less well matched - 15Hz is probably a practical upper limit. The resonance can be excited by warps or ripples in the record, among other things. Below ~2x the resonant frequency the cartridge output is inaccurate because of the resonance. Second, during the mastering process there is usually a high pass filter applied - they understand the physical limitations of the medium. Third, on a poorly engineered turntable there may be motor and/or bearing noise, predominantly at low frequency. Given all of these, there is no real signal below 20-30Hz - anything below that is noise not signal, so should be removed. Preferably this should be at source so it doesn't cause problems downstream. Summing left and right at low frequencies can help here too - warps excite the vertical resonance which will appear out of phase on left and right, so summing at low frequencies cancels this.

The more general argument is about frequencies below those that the system can reproduce causing problems (cone flap, excessive power, saturation of transformers etc.) It doesn't really matter whether the source is subsonic noise from phono, LFE from movies or music with a lot of very low content. The solution there is to high pass at a frequency suitable for the limiting part of the system, such as speaker or transformer. This is an argument for a filter in the preamp for all sources rather than just for phono.

From a system perspective you probably want only one filter to do this, rather than phono, preamp and power amp all doing it. That suggests each one should be switchable.

 

[AudioSceptic]

There are different arguments here. One side is specific to phono amps, but the other applies to any source.

The phono specific part is down to a few things. First the physics of the transducer, as @AudioSceptic points to, referencing a post by someone who used to work on such things at Garrard. The compliance of the cartridge and the combined mass of cartridge and effective mass of arm form a resonant system, usually around 10Hz if a suitable combination of arm and cartridge have been chosen, but could be higher or lower if they are less well matched - 15Hz is probably a practical upper limit. The resonance can be excited by warps or ripples in the record, among other things. Below ~2x the resonant frequency the cartridge output is inaccurate because of the resonance. Second, during the mastering process there is usually a high pass filter applied - they understand the physical limitations of the medium. Third, on a poorly engineered turntable there may be motor and/or bearing noise, predominantly at low frequency. Given all of these, there is no real signal below 20-30Hz - anything below that is noise not signal, so should be removed. Preferably this should be at source so it doesn't cause problems downstream. Summing left and right at low frequencies can help here too - warps excite the vertical resonance which will appear out of phase on left and right, so summing at low frequencies cancels this.

The more general argument is about frequencies below those that the system can reproduce causing problems (cone flap, excessive power, saturation of transformers etc.) It doesn't really matter whether the source is subsonic noise from phono, LFE from movies or music with a lot of very low content. The solution there is to high pass at a frequency suitable for the limiting part of the system, such as speaker or transformer. This is an argument for a filter in the preamp for all sources rather than just for phono.

From a system perspective you probably want only one filter to do this, rather than phono, preamp and power amp all doing it. That suggests each one should be switchable.

Just to add that Mr Dernie has also been a highly regarded F1 engineer and designer!

 

[somebodyelse]

Just to add that Mr Dernie has also been a highly regarded F1 engineer and designer!

Correct, but his work at Garrard is more directly relevant for knowledge of transducer physics as it applies to turntables. That said, a lot of the underlying physics for dynamic systems is the same whether it's a turntable, a car, some machine in a factory, or a building vibrating in the wind or earthquake. And the equations parallel each other on the electrical and mechanical side, which is why we can use an electrical model to model the mechanical properties of a speaker, and a transformer to model the electromechanical part of the speaker motor. There are similar analogies in heat transfer, fluid flow etc.

 

[AudioSceptic]

Correct, but his work at Garrard is more directly relevant for knowledge of transducer physics as it applies to turntables. That said, a lot of the underlying physics for dynamic systems is the same whether it's a turntable, a car, some machine in a factory, or a building vibrating in the wind or earthquake. And the equations parallel each other on the electrical and mechanical side, which is why we can use an electrical model to model the mechanical properties of a speaker, and a transformer to model the electromechanical part of the speaker motor. There are similar analogies in heat transfer, fluid flow etc.

Yes, indeed (I did learned some of this stuff in a previous life ;-) ). (Just edited that because it might've given the wrong impression.)

 

[Carl-Fosi Audio]

Thanks

The lack of HPF is indeed too bad.
Those guys are producing a lot of those Phono preamps. We have quite a few measured here already.
This one is pretty good, especially for the money.

Why do you need HPF?

Prevent rumble.

What is the High-pass filter band? 80Hz, 120Hz or any other?

 

[Rja4000]

What is the High-pass filter band? 80Hz, 120Hz or any other?

Usually subsonic: below 20Hz, typically 10Hz