Sound Smith Phono Pre Attenuators

Back in the late 70's early 80s, I experimented with variable attenuators between the phono cartridge and the phono pre-amp inputs. But this was in the days before the prevalence of MC cartriges, as an audiophile friend of mine observed that phono pre-amps with high overload margins sounded better. Our tests were done with MM cartidges.

We indeed found a significant sonic improvement with the attenuators. These were designed to provide a constant 47K load to the cartridge so that was not a variable.

What I believe to to be the true effect of the attenuator was to isolate the varying source impedance of the catridge from the input of the phono stage. For many amplifier designs, source impedance has a big impact of performance and stability, especially for bipolar (as opposed to FET) designs. This may indeed still be true today for MM carts.

For MC carts I suspect the effect to be much less significant, due to the very low impedances of these carts.

Jonathan, I inserted the attenuator between the TT and phono pre, and then between the phono pre and the line stage. It didn't matter. In either case the sound quality was degraded. FWIW, I called ARC to ask about the attenuator thingy. They said not necessary. Oh well, I tried a new tweak and it didn't work out. No big deal. Peter, being the gentleman he is, issued me a credit towards the Zephyr re-tip. No worries. Just reporting the news for the benefit of other ARC owners.

Hi Bifwynne: In general I find that such attenuator devices should be inserted between phono stage and line preamp rather than cartridge and phono stage.

Although my experience is that the sonics of low-voltage MC cartridges suffer far more from electrical contacts than MMs or MIs, I don't think that it is a good idea to send the Zephyr's signal through any more electrical contacts than are absolutely required, nor would I attenuate its signal into the phono stage (unless the phono stage clips).

You should experience less sonic degradation if the attenuator is inserted right in front of the line preamp, or right in front of the power amp (if it turns out that the line preamp isn't overloading). Keep the wiring from attenuator to preamp (or power amp) as short as possible.

You can make a fixed attenuator by soldering an RCA female jack to an RCA male plug by way of two resistors configured as an attenuating network (-3dB, -6dB or whatever you need). With a little more work with pliers, nippers and soldering iron, you can build a fixed attenuator right into the interconnect RCA plug (receiving end), which will save an extra electrical contact and sound better. I make frequent use of both devices for bypass testing.

Scott Endler produces ready-made attenuators which may also accomplish what you need. Note that I haven't used his products.

hth, jonathan carr

Received and returned the attenuators. Sorry to report that there was no improvement, if anything I lost dynamics, range and depth.