A Tale of Two Phono Preamps, Part 1: Pro-Ject Phono Box DS+

[restorer-john]

I know Technics had a fairly extensive range of cartridges.

Here's the 1983/4 range...

6 Boron piped cantilevers, a titantium cantilever etc.

And here's their Crosley killer from the same year

 

[restorer-john]

I wish I had the cartridges, not just the brochures...

 

[anmpr1]

Interesting the P-mount system on a high end deck, and an EPA-100ish-like tonearm. At least here in the US, P-mount was marketed as a low to mid range plug-'n-play solution. I never saw (or heard) Technics cartridges; they were not advertised much, if at all. On the other hand, you never ran into SP-10 Mk III turntables at your local Crazy Eddie's, either.

Mainstream brands such as Stanton/Pickering, Shure, Ortofon, AT, and even Grado marketed P-mounts. Many came with a little plug adapter allowing them to mate with standard mount headshells. I checked Needle Doctor and you can still get a top of the line Prestige Grado P-mount.

In earlier days, Shure, Pickering and a few long forgotten others marketed integrated cartridge/tonearms with plug-in cartridges. B&O was probably the best non-Japanese champion of the idea. I also recall SME with their Series III wand mated to an Ortofon OM cartridge.

Today, low mass for the sake of low mass, or even low tracking forces, are something few people talk about, or are really interested in. Back in the '60s and '70s it was a big thing. I remember how folks were incredulous when Mr. Ikeda said you needed his heavy FR-64 arm and cartridges. Other Japanese 'high enders' were also touting the benefits of old gear like the Grace/Gray oil damped arm and DL-102. Mr. Sakuma of Direct Heating taped coins to the arm in order to give it enough 'weight' for his mono records. LOL

Some of my records from the late '50s and early '60s suggest (in the liner sleeve) that best results require a cartridge that tracks at less than 5g.

 

[Soniclife]

Not a double review yet, but I'll have the second part up this weekend.

Did I miss this, or did schiit happen?

 

[SIY]

Did I miss this, or did schiit happen?

My fault. New job and I got busy. Measurements were done, I just have to assemble the post. And a Puffin just descended, courtesy of @JPJ .

 

[JP]

My fault. New job and I got busy. Measurements were done, I just have to assemble the post. And a Puffin just descended, courtesy of @JPJ .

Any progress?

 

[SIY]

Any progress?

Yes, if only work and paid reviews didn't keep getting in the way! I have a bunch of data, need a little more, then time to write it up. Preview: RIAA channel to channel is excellent, EQ conformance through the midrange is likewise excellent, half a dB drop in the top octave common to both channels. 71dB SINAD, distortion in the 0.003-0.005% range across the band with 5mV in. Overload margins will be remeasured, since I was surprised by the numbers I got the first time around. I have a bunch of noise data, where it's not a champion, but good enough- well below cartridge noise in the areas of highest aural acuity.

 

[Thermionics]

Today, low mass for the sake of low mass, or even low tracking forces, are something few people talk about, or are really interested in. Back in the '60s and '70s it was a big thing. I remember how folks were incredulous when Mr. Ikeda said you needed his heavy FR-64 arm and cartridges. Other Japanese 'high enders' were also touting the benefits of old gear like the Grace/Gray oil damped arm and DL-102. Mr. Sakuma of Direct Heating taped coins to the arm in order to give it enough 'weight' for his mono records. LOL

I can't speak for the FR-64, but the FR-24 Mk2 is a hell of an arm and plays well with a wide array of carts.

 

[Dogsled21]

Regarding the Project phono box DS, where exactly should one ground the outputs once disconnected from the inputs? I do have a hum issue that will not leave..Unfortunately no schematic.

 

[cgallery]

Member @BDWoody was kind enough to send two phono preamps my way for testing. One was the Pro-Ject Phono Box DS+, the other was an almost-antique (vintage 1983) Straight Wire Audio (SWA) Phono Preamp. The results and comparison were interesting...

I do have a couple of concerns here: first, I don't like seeing the wires from the power supply connector (the red and black twisted pair) running across the length of the board near sensitive circuitry. Second, the RCA connectors are rather cheep'n'cheesy, with input and output grounds connected directly together.

In the spirit of there being no such thing as a stupid question, what is the alternative to the grounds being connected? The phono preamps I've examined all seem to have the RCA grounds tied to the same ground plane/bus/whatever on the circuit board?

 

[Dogsled21]

In the spirit of there being no such thing as a stupid question, what is the alternative to the grounds being connected? The phono preamps I've examined all seem to have the RCA grounds tied to the same ground plane/bus/whatever on the circuit board?

Ditto on schematics I have analyzed. Also, the wall wart is not grounded, and provides 18VAC, where the incoming supply does provide gnd on board which (I think) is tied to the input and output grounds.

 

[SIY]

In the spirit of there being no such thing as a stupid question, what is the alternative to the grounds being connected? The phono preamps I've examined all seem to have the RCA grounds tied to the same ground plane/bus/whatever on the circuit board?

There's a few different ways of doing grounding. Inputs can float, for example or be balanced. For a common ground, the order of connection can run from input to output, with chassis ground being connected at the input, sometimes through a resistor (see, e.g., Morgan Jones's "Valve Amplifiers" for a discussion of this). The latter is how single-ended phono preamps ideally should be constructed.

 

[cgallery]

There's a few different ways of doing grounding. Inputs can float, for example or be balanced. For a common ground, the order of connection can run from input to output, with chassis ground being connected at the input, sometimes through a resistor (see, e.g., Morgan Jones's "Valve Amplifiers" for a discussion of this). The latter is how single-ended phono preamps ideally should be constructed.

Thank you, the various approaches and how similar they seem in theory and yet how much they differ in real-world performance has been surprising to me.

OTOH, my lack of understanding may explain what I perceive as similarity, those that understand better may not agree that these are very similar.

 

[SIY]

Thank you, the various approaches and how similar they seem in theory and yet how much they differ in real-world performance has been surprising to me.

OTOH, my lack of understanding may explain what I perceive as similarity, those that understand better may not agree that these are very similar.

The problem is that just looking at a schematic, all ground points are equipotential, all ground runs have zero resistance. So it shouldn't matter. In the real world, they're not, so layout and the order of grounds becomes important at these low signal levels.

 

[mash]

One think on the Puffin. I own one (with digital out) and enjoy it quite a bit. I found that it is very sensitive to physical placement. Basically, it can’t sit within 6” of my topping D90 without emitting an auditable hum. I originally thought it was a ground loop issue and spent quite a bit of time trying to isolate it until I moved it while playing one day only to find out that lessened/killed the hum. Not sure if that means it was an RF issue or still is a ground loop….either way the hum is gone.

 

[Ifrit]

I guess there was no time to post the results for the Straight Wire?