Quote:Does anyone know the approximate overload margin for the ZP3? I'm starting to experiment with step up transformers, and that info would be great as a baseline.
Hi, Metal. "Sorry you had to wait."
Decware doesn't give the spec for that, a lot of phono preamps don't. But there are still enough who do, so I poked around a bit. The lowest I saw were an Art Pro w/ 40 mV rms (= 56 mV peak) and an entry level Graham Slee at 41 mV. A soundsmith w/ 53 mV, another unit at 60, an ARC phono at 70, and a number of others at ~80, 90, 100, 120 mV. If not given in rms, I assume peak. (Peak/√2=rms; rms*√2=peak). The lower numbers specified @ 1,000 Hz, the higher numbers did not.
What these numbers mean . . . The CBS test record (most often used) has bands cut at level of 5 cm/sec peak, @1,000 Hz. This is related to the IEC reference cutting level of 5cm/sec RMS = 0 dB. The actual level of recorded sound will of course vary a lot, and can be much higher. The practical limit at 1 kHz is (supposedly) 35cm/sec. For a common 5 mV output from MM carts at this level, that leaves a 35/5 ratio of 7x (~ 17 dB) of headroom.
Look at this page;
http://pspatialaudio.com/max_velo.htm Scroll down to half page, the chart titled 'What Signals Are On Records?' Informative.
So then about SUT situation. A .5mV MC cart through a 20x / 26dB SUT will have 10mV output. But when a record is playing and some big surge or blast pushes the cart to 6x the test figure, it's now putting out 3mV, after a 20x SUT, now 60mV.
A number of phono preamps spec higher than that, but still . . . I think the usual MO is to use a 10x SUT for .4 mV and above, 20x for <.4mV cartridges.
I could have said that at the beginning.