Pro-Ject Tube Box S2 Phono Preamp Review

[AudioSceptic]

I don't know about suspended designs like the old AR turntable, but for an SL1200 clone like my Audio Technica, yes because the rubber feet do little to filter out low frequency energy from the environment: You can clearly see it on a real time analyzer even when the record is stationary.

I thought "rumble" meant noise produced by the platter bearing and drive system, not LF noise from the environment (which is where design/construction of the whole TT system comes into it), and I'm pretty sure that is what is meant when figures are quoted.

 

[Labjr]

What the point of making a tube preamp if you're not going to use a conventional power supply etc.? Traditional tube people aren't gonna want a box full of silicon with two tubes added for looks. Doesn't accomplish anything.

 

[Robin L]

I don't know about suspended designs like the old AR turntable, but for an SL1200 clone like my Audio Technica, yes because the rubber feet do little to filter out low frequency energy from the environment: You can clearly see it on a real time analyzer even when the record is stationary.

Even with the AR XA there were LP s with the rumble pressed into the groove. I've owned a lot of suspended subchassis turntables. It's easy to find a turntable that has less rumble than the discs themselves. The greatest problem with the format happens to be the discs and there's nothing to be done to fix it.

 

[Robin L]

Clapton, Knopfler, Hendrix, once you know "their sound" you can't mix'em up. And you probably couldn't get them to switch amps either ...

It's analogous with pianos and players, the choice of a Bosendorfer or a Baldwin has a lot more to do with a pianist's "tone" than the artist's sense of touch or hand position.

 

[anmpr1]

I don't know about suspended designs like the old AR turntable, but for an SL1200 clone like my Audio Technica, yes because the rubber feet do little to filter out low frequency energy from the environment: You can clearly see it on a real time analyzer even when the record is stationary.

Is this the same thing as turntable rumble? Or is it a different effect--acoustic feedback? I was under the impression that rumble is due to the motor/bearing/record/tonearm/cartridge interface and is a static, non-variant measurement. Acoustic feedback is dependent upon SPL levels.

With certain loudspeakers it is easy to determine the need for the subsonic filter. In one of my systems I have a set of JBL L100 (circa 1976). Without the high pass filter woofers pump in and out--you can really see this on the lead in groove. With the filter in this woofer motion is markedly suppressed.

 

[Hiilari]

Nice looking little unit as you said. I agree that tubes do not shine in all circuits but this one does pretty well given the price point and I am pretty impressed that the rumble filter is pretty tight at the low end and does not bother the overall FR very much, that's good to see. A little boost on the low end is not too bad in normal either, and few records go that low anyway. Tubes shine when they play with transformer loads and are making power, other than that the "tube" sound is not really audible in a circuit designed for fidelity. I appreciate your work as always. Cheers!

I fully agree. Sometimes tubes shine even if they have a bit of a sound signature of their own. No snake oil but just magic sauce. Your view on the topic is sort of given away by having Glass Audio magazine cover as user image... and mine sorta given away by showing inside of a Dynaco. I used to subscribe to Glass Audio back in the day. It was somewhat expensive here in good 'old Finland.

 

[JeffS7444]

I thought "rumble" meant noise produced by the platter bearing and drive system, not LF noise from the environment

True, but I meant to point out the value in having such a filter even where the turntable itself isn't generating objectionable levels of low-frequency crud.

 

[milosz]

Subsonic filters are useful to get rid of the 0.1~2 Hz signal that gets generated by the slight vertical variation in an LPs height. And if there is ANY warp to the vinyl, such low frequency garbage can destroy expensive speakers.

Remember what a phono pickup's job is: to transduce minute motions of the stylus to an electrical signal to be amplified many many times and played through speakers. Some of the movement of the stylus for treble detail is around the wavelength of light in size - REALLY REALLY REALLY tiny motions are converted to electrical signals. So imagine what the cartridge will produce if one part of the LP is 0.01 mm thicker than the other, which variation in thickness it will "ride" every revolution of the record.... The phono pickup will convert this unintended motion into a signal just as faithfully as it does the nuance of Norah Jones' voice captured in the groove.... you don't want this 0.5 Hz "signal" being passed through to your speakers.

YEARS AGO many turntables had rumble issues. The precision of bearings, belts, pulleys, idlers, etc used to create consumer record playback gear was not all that great - these things were built to a price point - and so amp manufacturers often included a "Rumble Filter" in their deluxe units. In those days, gear was based on tubes and the amp circuit and output transformers acted as an unintentional infrasonic filter- transformers are not very good at passing these very low frequencies- so generally a 0.5 Hz "warp" signal didn't make it to the speaker.

Once we entered the solid state era and then after a time more advanced solid state designs came along, it was possible to design amplifiers that worked all the way down to 0 Hz (DC) so now the ultra-low frequency signals from the phono cartridge COULD make it all the way to the speaker and it became desirable to include a high-pass filter in phono circuits. By this time, manufacturing had improved so that even mid-fi turntables had very low levels of actual mechanical "rumble" so the filter was not intended to clean up noisy turntables but to filter out the useless ultra-low frequency junk that gets picked up when playing vinyl.

Vinyl is not a very transparent medium; but people are used to the sound and their brains identify it as "natural" or "musical" sounding. For older audiophiles- who tend to be the ones with money to spend on gear- vinyl sounds like music did in their youth. And for young people, playing vinyl offers a ritual and object-fetish cult that they enjoy. Some day Amirm will measure vinyl playback like he measures a DAC, and you'll see some TRULY awful SINAD.

 

[AudioSceptic]

True, but I meant to point out the value in having such a filter even where the turntable itself isn't generating objectionable levels of low-frequency crud.

Yes, but a "rumble" filter typically blocks signal below 20-30 Hz, and most feedback and environmental noise is above that. Of course, as mentioned by Robin L, there's often some LF garbage on the record itself, and that can be far worse than what the TT itself produces. In any case, a well designed high pass filter can only be a good thing.

 

[JeffS7444]

Yes, but a "rumble" filter typically blocks signal below 20-30 Hz, and most feedback and environmental noise is above that.

That doesn't appear to be the case with my setup: Drop needle onto stationary record, observe RTA display, and I see very little higher frequency activity. I experimented with hand-clap noises near the pickup head, even tapping on the thin aluminum platter directly and was surprised how little effect this had, and how effectively even the stock felt slip mat dampened these.

For my purposes, it seemed that airborne pickup of noise wasn't a big deal (at least not below lease-breaking SPLs), but if I wanted to be perfectionist about it, a record weight or clamp would suffice, and wouldn't have to bear down particularly hard on the record to be effective.

By far the biggest problem I observed was in the region 30 Hz and below, and so far as I can see, that's energy being generated by the building and it's occupants and passing right through the turntable's rubber feet to reach the pickup.

 

[Wombat]

That doesn't appear to be the case with my setup: Drop needle onto stationary record, observe RTA display, and I see very little higher frequency activity. I experimented with hand-clap noises near the pickup head, even tapping on the thin aluminum platter directly and was surprised how little effect this had, and how effectively even the stock felt slip mat dampened these.

For my purposes, it seemed that airborne pickup of noise wasn't a big deal (at least not below lease-breaking SPLs), but if I wanted to be perfectionist about it, a record weight or clamp would suffice, and wouldn't have to bear down particularly hard on the record to be effective.

By far the biggest problem I observed was in the region 30 Hz and below, and so far as I can see, that's energy being generated by the building and it's occupants and passing right through the turntable's rubber feet to reach the pickup.

If the stylus is resting on a stationary disc that is likely. What you say in your last paragraph also applies to cutting lathe environments or even the recording studio.
Many recordings were made/cut in the wee-hours to avoid extraneous LF vibrations from trains, heavy vehicles, elevators, etc. Unfortunately many were not and those records may have extraneous LF noises captured in their grooves.

 

[AudioSceptic]

That doesn't appear to be the case with my setup: Drop needle onto stationary record, observe RTA display, and I see very little higher frequency activity. I experimented with hand-clap noises near the pickup head, even tapping on the thin aluminum platter directly and was surprised how little effect this had, and how effectively even the stock felt slip mat dampened these.

For my purposes, it seemed that airborne pickup of noise wasn't a big deal (at least not below lease-breaking SPLs), but if I wanted to be perfectionist about it, a record weight or clamp would suffice, and wouldn't have to bear down particularly hard on the record to be effective.

By far the biggest problem I observed was in the region 30 Hz and below, and so far as I can see, that's energy being generated by the building and it's occupants and passing right through the turntable's rubber feet to reach the pickup.

Gotcha. That seems to be a situation where a subchassis TT would make a big difference. I've used AR XA and Linn LP12 so I haven't experienced the difference a "solid" TT makes. Would accessory feet be worth a try? Even if you use a filter to stop the subsonic noise getting amplified, it's still driving the cartridge and reducing its performance.

Some think that an LP12 sounds better with the lid removed. Presumably it's a trade-off between the lid acting as a sound board and feeding vibration into the plinth versus preventing sound reaching the arm/cartridge directly. Not hearing a night-and-day difference I keep mine on out of convenience and keeping dust out, but some time I ought to do a proper comparison. What did you use for RTA?

 

[Frank Dernie]

REALLY REALLY REALLY tiny motions are converted to electrical signals. So imagine what the cartridge will produce if one part of the LP is 0.01 mm thicker than the other, which variation in thickness it will "ride" every revolution of the record.... The phono pickup will convert this unintended motion into a signal just as faithfully as it does the nuance of Norah Jones' voice captured in the groove.... you don't want this 0.5 Hz "signal" being passed through to your speakers.

This is commonly seen but static explanation for a dynamic system and therefore completely wrong.
At the high frequencies the cartridge mass looks infinite to the stylus so it will be transcribed properly. At low frequency the cartridge mass looks tiny so it doesn't stay still (and the cartridge follows the spiral, thankfully).
I explained how seismic transducers work up thread. Physics has not changed at this level in the 50 years since I started designing them. Pseudo-static explanations never explain dynamic systems properly, and can not, unless well away from resonance.
One of my biggest exasperations is seeing and hearing this sort of misinformation being repeated it has happened for decades.

 

[SIY]

This is commonly seen but static explanation for a dynamic system and therefore completely wrong.
At the high frequencies the cartridge mass looks infinite to the stylus so it will be transcribed properly. At low frequency the cartridge mass looks tiny so it doesn't stay still (and the cartridge follows the spiral, thankfully).
I explained how seismic transducers work up thread. Physics has not changed at this level in the 50 years since I started designing them. Pseudo-static explanations never explain dynamic systems properly, and can not, unless well away from resonance.
One of my biggest exasperations is seeing and hearing this sort of misinformation being repeated it has happened for decades.

The other end of this is, of course, the velocity response. So not only do we reduce the unwanted signal because it's below resonance, it's also reduced because of the low velocity (at least for the 99.9% of cartridges that are velocity transducers).

 

[AudioSceptic]

This is commonly seen but static explanation for a dynamic system and therefore completely wrong.
At the high frequencies the cartridge mass looks infinite to the stylus so it will be transcribed properly. At low frequency the cartridge mass looks tiny so it doesn't stay still (and the cartridge follows the spiral, thankfully).
I explained how seismic transducers work up thread. Physics has not changed at this level in the 50 years since I started designing them. Pseudo-static explanations never explain dynamic systems properly, and can not, unless well away from resonance.
One of my biggest exasperations is seeing and hearing this sort of misinformation being repeated it has happened for decades.

I was about to say something similar. At VLF, unless there's high friction in the arm bearings or a huge mismatch between cartridge compliance and cartridge+arm effective mass, the stylus will simply follow the groove with minimal relative movement of the cartridge (and therefore minimal output). By "VLF", I mean variations in record thickness, warps, and subsonic ripples. I like to compare this with how a car's (or motorcycle's) suspension works, with the wheels being the stylus and the body (frame) being the cartridge body. You expect the suspension to absorb variations in the road surface within a certain range of frequencies and amplitudes, but not to absorb large VLF variations like hills and valleys!

 

[Frank Dernie]

The other end of this is, of course, the velocity response. So not only do we reduce the unwanted signal because it's below resonance, it's also reduced because of the low velocity (at least for the 99.9% of cartridges that are velocity transducers).

Yes but then it is exaggerated again by the RIAA weighting which is at least partly there to cancel this effect. It doesn't change the fact that everything coming out of the cartridge is wrong in both phase and amplitude at frequencies below ~2x resonance so the sensible solution isa to remove it.

 

[SIY]

...everything coming out of the cartridge is wrong in both phase and amplitude at frequencies below ~2x resonance so the sensible solution isa to remove it.

100% agree. And that's why my phono stages have coupling caps.

 

[JeffS7444]

Would accessory feet be worth a try? Even if you use a filter to stop the subsonic noise getting amplified, it's still driving the cartridge and reducing its performance.

I suspect this is really a job for a proper sprung suspension, but I sold off my Linn turntable years ago and don't have any handy way to verify this. But even without changing the turntable, replacing my phono preamp with one which incorporates a high-pass filter has made a substantial difference.

What did you use for RTA?

Behringer DEQ2496.

 

[tomelex]

I fully agree. Sometimes tubes shine even if they have a bit of a sound signature of their own. No snake oil but just magic sauce. Your view on the topic is sort of given away by having Glass Audio magazine cover as user image... and mine sorta given away by showing inside of a Dynaco. I used to subscribe to Glass Audio back in the day. It was somewhat expensive here in good 'old Finland.

Thanks. Dynaco has a definite voice but a nice voice. Yes I do actually like the SET sound quite a bit. That particular edition of the magazine reveals an economical project of mine.

 

[Hiilari]

Thanks. Dynaco has a definite voice but a nice voice. Yes I do actually like the SET sound quite a bit. That particular edition of the magazine reveals an economical project of mine.

Sounds cool. Please share photos, given your project has materialized already.