Pro-Ject Phono Box DS3 B Review

[Michael Fidler]

Which is unfortunately rather common with certain entry-level (a.k.a. "cheapo") turntables. For example, the original AT-LP120-USB phono cartridge signal path has a non-bypassable L-C filter circuit always in place when set to "Phono" mode (e.g. when supposed to bypass the internal preamp). Additionally, there appears to be a SMD component jumpering all of the cartridge's negative lines as they come out from the tonearm and into the circuitboard inside the chassis. Audio-Technica was so "kind" as to include this pre-soldered ground loop path which is permanently installed for the user.

Another example would be this Udreamer 009 turntable which is currently popular on Amazon. Testing this one revealed multiple issues, including a built-in ground loop when in bypass mode. Another hilariously bad issue with this one: The "Line" / "Phono" switch was actually labeled in reverse! So, when switched to "Phono", actually a Line-level signal was output on the RCA jacks, except without any bass, and with very harsh high frequency range. It seemed like they forgot to apply the RIAA curve when in internal preamp (Line-level) mode (even if it was labeled backwards). There was no continuity between RCA pin and shield with the headshell pins when the switch was set to "Phono" mode and the level of the signal was at Line-level instead. When switched to "Line" mode, as labeled, then the headshell pins were connected to the RCA jacks (as it would be for Phono / "bypass" mode). However, both negative (L-, R-) lines were shorted to each other AND the chassis ground lug. So yet another built-in ground loop path when chassis lug & an external preamp ground lug are connected.

A final example, is even mentioned on the Pro-ject site regarding the use of certain MM cartridges:


This issue may not affect all moving magnet type cartridges, and some include a removable ground clip (usually on the R- line, but sometimes L-). Shure has this page describing how to remove the jumper clip for their cartridges.

So, as with most things of sufficient complexity... "The devil's in the details"... and there's a lot of details to get wrong! (Also, the "great" thing about standards is there are so many to choose from ) It seems Pro-ject is recommending to use MC cartridges as a guaranteed way to achieve a truly floating & balanced signal path from the headshell. Presumably this is because the moving coil design is less likely to allow for manufacturers of the cartridge to short one of the - signal pins.

There's quite a lot to be said here. I think there's no mileage in balancing phono inputs, but really it's a topic for another thread, along with further discussion of overload and overload behaviour...

 

[Martin]

Nice to see the Pro-Ject Phono Box DS3 B measure reasonably well; I bought a used Phono Box RS several years ago. I went through three other phono preamps before I settled on the RS. I had a Cambridge Audio Alva Duo that was good but did not have enough gain in my system. I also tried a PS Audio GCPH (also very adjustable) and a Lounge Audio LCR MKIII. One was absolute junk with prominently audible 2nd, 3rd, 4th and 5th order harmonics and the other not much better.

I bought a Pro-Ject Connect-it 5P/XLR phono cable and am running fully balanced from cartridge (Grado Sonata 3) to phono preamp to preamp (Benchmark HPA4) to amplifiers (ICEpower monoblocks) and I could not be happier. I think I'll sit down and listen to a few LPs this weekend.

Martin

 

[manisandher]

As you see, the effective gain is 6 dB...

Wouldn't be much use as a phono preamp then!

But I suppose you meant 46dB .

Mani.

 

[trinitronx]

There's quite a lot to be said here. I think there's no mileage in balancing phono inputs, but really it's a topic for another thread, along with further discussion of overload and overload behaviour...

Yes, it's a surprisingly complex topic... especially given the "overloaded" term, "balanced" (differential symmetric signaling vs. impedance-balanced) and the deceptively simple concept of "grounding", with it's own often overlooked hidden complexity.

Definitely worth it's own topic, as many presentations [1, 2, 3], papers [4, 5, 6], books [7, 8], and forum threads [a, b, c] can and have been written about it.

With regard to balanced phono preamp inputs... The discussion would first have to center on what the goal and design requirements for the particular application are. There could be good rationale for using impedance-balanced interconnects and/or symmetric differential signaling instead of the simple "unbalanced" 2-wire with or without ground lug, or maybe there would not be depending on what the goal is (e.g. what are we trying to accomplish by using them?).

Given that phono cartridge output is in the milliVolt range, noise and ground loop hum can easily end up on the signal lines (as common-mode noise) which a preamp will happily apply gain and the RIAA curve to magnify (or attenuate) the noise spectrum along with the transducer signal. If the goal is to avoid noise and ground loops on a signal interconnect... then multiple solutions exist, and they usually involve impedance-"balanced" wheatstone bridge circuits, whether or not the signal on the "hot" (+) & "cold" (-) lines is a symmetric & differential signal.

Spoiler: References

[1]	Audio Engineering Society. "AES Tutorial: Audio System Grounding & Interfacing by Bill Whitlock", YouTube, Feb. 2, 2010 [Video file]. Available: https://www.youtube.com/watch?v=g9M45U87ybg . [Accessed: Feb. 2, 2024].
[2]	AES - Detroit. "Bill Whitlock - Signal Interfaces Debunked - 4/27/2021", YouTube, May. 7, 2021 [Video file]. Available: https://www.youtube.com/watch?v=qYRhwnxHuYo . [Accessed: Feb. 2, 2024].
[3]	Audio Science Review. "Understanding Grounding in Audio", YouTube, Mar. 15, 2021 [Video file]. Available: https://www.youtube.com/watch?v=f2soKg9JAUA . [Accessed: Feb. 2, 2024].
[4]	Bill Whitlock & Rod Elliott, “Design of High-Performance Balanced Audio Interfaces”, Elliot Sound Products, 2010. [Online]. Available: https://sound-au.com/articles/balanced-2.htm . [Accessed: Feb. 2, 2024].
[5]	J. Brown and B. Whitlock, ‘Common-Mode to Differential-Mode Conversion in Shielded Twisted-pair Cables (Shield-Current-Induced Noise)’, in Audio Engineering Society Convention 114, 2003. [Online]. Available: http://www.aes.org/e-lib/browse.cfm?elib=12594 . [Accessed: Feb. 2, 2024].
[6]	B. Whitlock, ‘Balanced Lines in Audio Systems-Fact, Fiction, and Transformers’, in Audio Engineering Society Convention 97, 1994. [Online]. Available: http://www.aes.org/e-lib/browse.cfm?elib=6315 . [Accessed: Feb. 2, 2024].
[7]	C. Motchenbacher, E Fitchen, "Low-Noise Electronic Design", John Wiley & Sons, 1973
[8]	C. Motchenbacher, J. Connely, "Low-Noise Electronic System Design", John Wiley & Sons, 1993. [Online]. Available: https://pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Motchenbacher_Connelly/Low-noise_Electronic_Design.pdf . [Accessed: Feb 2, 2024].

 

[zonk]

Nice to see the Pro-Ject Phono Box DS3 B measure reasonably well; I bought a used Phono Box RS several years ago. I went through three other phono preamps before I settled on the RS. I had a Cambridge Audio Alva Duo that was good but did not have enough gain in my system. I also tried a PS Audio GCPH (also very adjustable) and a Lounge Audio LCR MKIII. One was absolute junk with prominently audible 2nd, 3rd, 4th and 5th order harmonics and the other not much better.

I bought a Pro-Ject Connect-it 5P/XLR phono cable and am running fully balanced from cartridge (Grado Sonata 3) to phono preamp to preamp (Benchmark HPA4) to amplifiers (ICEpower monoblocks) and I could not be happier. I think I'll sit down and listen to a few LPs this weekend.

Martin

I still wished someone could send a "Pro-Ject Phono Box RS" to Amir for testing

https://www.project-audio.com/en/product/phono-box-rs/

 

[Snoopy]

I don’t get it, $800 for a phono stage! Is it really that much better? The reason I gravitated to this site is because they call this stuff out.

530 euro in Germany, including 19% tax. So 575 USD.

I wonder if someone made a direct comparison with the shiit skoll that is 559 Euro over here or 606 USD.

 

[restorer-john]

There's quite a lot to be said here. I think there's no mileage in balancing phono inputs, but really it's a topic for another thread, along with further discussion of overload and overload behaviour...

Did you start another thread- I can't find it?

 

[Michael Fidler]

Did you start another thread- I can't find it?

Not yet. I need to do one about current input MC too. I'm just wondering whether I should start it off with a long post containing everything I have to offer up, or a short one with a basic premise/objection and then let everything else I'm considering flow as an organic product of the dialogue that will hopefully follow...

 

[Daviede]

Not a fan of the 18 volt external switching power supply though at this price level. The low voltage is also liable to limit the headroom of DS3B.


What is the impact of the power supply voltage between 5V/12V/18V or 24V on the playback? Which one is better? Isn't the higher the power supply voltage, the better the parameters of the product? What are the benefits of a low-voltage power supply?

 

[Stephen Bayley]

Not a fan of the 18 volt external switching power supply though at this price level. The low voltage is also liable to limit the headroom of DS3B.


What is the impact of the power supply voltage between 5V/12V/18V or 24V on the playback? Which one is better? Isn't the higher the power supply voltage, the better the parameters of the product? What are the benefits of a low-voltage power supply?

The DS3B has internal power supply circuits to generate positive and negative 16volt rails for the analog sections, and other power curcuits to generate the logic and relay control voltage supplies. The external 18vDC supply just provides the raw power input.

 

[Daviede]

The DS3B has internal power supply circuits to generate positive and negative 16volt rails for the analog sections, and other power curcuits to generate the logic and relay control voltage supplies. The external 18vDC supply just provides the raw power input.

As for the internal power circuit, if it is set to supply 18V to internal components, the upper limit of the headroom of DS3B should be higher than that of 16V. In that case, why don't these manufacturers set the internal voltage higher?

 

[audio_tony]

As for the internal power circuit, if it is set to supply 18V to internal components, the upper limit of the headroom of DS3B should be higher than that of 16V. In that case, why don't these manufacturers set the internal voltage higher?

The internal voltage will likely be 15-0-15 (+15v gnd -15v) (this is typical for opamps) but it could be 18 gnd -18 - which means 30v or 36v in total.

This will be derived from an internal step up as @Stephen Bayley has said, and will have ample voltage swing.

 

[Stephen Bayley]

The internal voltage will likely be 15-0-15 (+15v gnd -15v) (this is typical for opamps) but it could be 18 gnd -18 - which means 30v or 36v in total.

This will be derived from an internal step up as @Stephen Bayley has said, and will have ample voltage swing.

I have the DS3B and off course have had the covers off. The circuit board, near the center in the analog phono amp location, has three test points labeled: Grn, +16 and -16; indicating that a split supplies of 16 volts are in use (a total of 32 volts rail to rail). While these test points are visible in promotional images on the Pro-Ject website the actual text is not clear in those images.

 

[Stephen Bayley]

For those that are interested this is what the spectrum of the stock DS3B 18v switching power supply looks like on my simple measurement system.

The switching frequency of 24khz is prominent along with the harmonics up to the 96khz limit of the sample. The measurement system is basic but useable for this type of analysis, consisting of a Cro probe, 10uf polypropylene DC blocking cap and an ASUS Xonar MkII USB interface shielded from local EMI in a metal enclosure.

I have used a long REW FFT Length and 32 samples to discount random noise and reveal the persistent noise elements.

I thought this switching noise may impact the DS3B SNR and output noise artifacts. So, I assembled a simple two stage LC filter network to clean up the 18V DC supply before entry to the DS3B. This filter reduced the incoming 18V DC noise elements (using the same REW measurement configuration) by 40db at 100Hz and 20db at 10kHz with the switching noise nowhere to be seen.

The result: a miserly 1db improvement in the DS3B noise floor. So, it seems the DS3B has a well-engineered power supply arrangement within the box.

 

[Stephen Bayley]

This is the output of the DS3B on my measurement system using the standard switching power supply, and no external LC filter network to clear the 24khz switching noise. Again, I have used a long REW FFT Length and a very large number of samples to discount random noise and reveal the persistent noise elements.

Note that I have shielded the DS3B from external EMI the best I could to reduce unwanted noise components in the measurement. Without the shielding there is an extra 10db of mains 50Hz component and harmonics from the local environment.

DS3B configuration is: RCA in (not shorted), 10ohm input load via variable setting and 40db gain, measurement is via the RCA outputs for convenience with my measurement system.

There is no sign of the 24khz switching frequency or harmonics even with these very revealing measurement conditions. There is a very low level 36khz element that may be USB noise within the Xonar itself.

 

[MbphotoX]

I've used the Phonobox S3B for a while now.
Beautiful design, same balanced circuitry (without XLR inputs, though, but it does have that 5-pin stereo XLR input for the pro-ject tables)

Used it with a dedicated Pro-Ject RCA to 5-pin mini-XLR cable on my Perspective Anniversary (the tonearm is wired in a balanced configuration when used with an MC cart, so you can actually use the balanced phono preamp with any pro-ject turntable, if you have the correct cable)

All that said, the phono stage works great. I love the design.

Currently, I'm feeding XLR cables into my Yamaha integrated amp, but am using the non-balanced RCA inputs, because my Yamaha Turntable has a fixed cable soldered on. (GT-2000)

Since I have it set to the absolute standard settings, I'm considering just ditching the Pro-Ject and using the built-in phono stage of my amplifier. It shouldn't be any worse when looking at these measurements.

How come the manufacturer releases 100+ dB of SINAD and Amir measures some 65?!

Cheers