Eminent Technology ET-2 Tonearm Owners

Regarding pumps and pressure:
a) Back in the 80's I found that the WISA 300 "high pressure" model (of which I bought several, directly from the company) was a single membrane pump, not a double one like the original HiBlow. My high pressure WISA model dropped in actual measured pressure level at the arm below the HiBlow, and had a high variation of pressure (mains frequency) - and the needle vibrated. This resulted in a "homeopathic 50Hz drone" that subjectively gave more, but a slihtly tubbier bass - this was *with* a ca. 7.5l tank.
b) I then chained two HiBlow pumps, ie. I hot-glued a piece of silicon tube to the inlet of one pump and to the outlet of the other pump. This resulted in (if I remember correctly) ca. 0.45 Bar (6.5 psi?). Three pumps were around 0.6 Bar, all this sounded very good, and was more silent  than a WISA pump. The HiBlow has a surprisingly steady flow and it's limitation can be surmounted by chaining two or three. On the ET 2's "normal" low pressure bearing the two HiBlows were a remarkable improvement.

^^

"This resulted in a homeopathic 50Hz drone"

’8^0

If one wants to hear if their pump is introducing noise.
Ensure your setup is good before attempting this.
With the air pump ON and system on mute, lower the ET2 onto a "STILL" record.
Now turn OFF the air pump, and unmute the system.
Have your friend now turn ON the air pump, while you listen close to the speaker.
Ensure your setup is good before attempting.

This is indeed the way I tested this. Stylus in groove, platter stationary, pump running, phono gain turned up. In this test the HiBlow was audibly quieter than *my* WISA 300 high pressure.

I use two wisa pumps working out of phase with each other in parallel, two large surge tanks in series with a small surge tank made from a plastic radio control gas tank, sitting a few feet from the ET-2. When I did the above test, it was complete silence with and without the pumps on. -Guess my pumps are different?
-John

Hi John, no, your WISA pumps work the same. But connecting them parallel and out of phase makes them work the same way as a double diaphragm pump, like the original HiBlow: Single ended vs. push-pull... The air pressure is much more constant, "stabilized" pressure being about the same as the pressure peaks of a single WISA.
How high is the pressure? I assume it’s still not much higher than the original pump, and the worse noise/vibration is remaining. Besides I was not able to connect WISAs in series (nor will such a parallel combo), contrary to the HiBlow pumps with their air-sealed housing, which allows operating them above normal atmospheric pressure.