Audio Research SP-3 preamplifier Page 2
We mentioned the creeping distortion menace, though, and the question that a lot of prospective SP-3 buyers are going to raise is "If tube-decay distortion comes on so gradually, how will I know when it's time to replace the tubes?" Well, there are two ways of deciding. You can elect to be conservative, assume that five years is the life of the tubes, and replace all of them routinely on that basis. Or, you can check them all periodically on one of those dinky tube testers that you see in supermarkets, drug stores, etc. If you're in doubt about the veracity of the readings, try the tester on a new 12AX7 out of its own stock bin. (Our warning about the use of tube testers, many issues ago, referred to the complex high-conductance multigrid types used mainly in tuners and TV receivers.)
Inevitably there are some things to criticize. Here they are:
There are two pushbutton-operated Tape Monitor switches for selecting either of two recorders, but it is not possible to switch one recorder's output into the other's input (for copying) without modification of the preamp. This will be done free by ARC on special order, but some other preamps have that provision as a standard feature.
There are two unswitched AC outlets at the rear and four switched ones. The only things in a typical installation that should b switched on and off with the preamp are the power amps, so why not two switched and four unswitched outlets?
There are separate AC power switches for the preamp and for the switched outlets, presumably to prevent switch-on thumps from other components from getting through to the speakers. But only solid-state components have switch-on thumps, and if these are ahead of the preamp in the circuit, the preamp's slow tube warmup would prevent them from getting through anyway. If the power amp thumps, it will do it regardless of when it is switched on, so the extra switch serves no purpose there either, So why the separate switches?
Oh well, it's still a hell of a good preamp. In fact, after having lived with one for several months, it has occurred to us that we just can't do without it. We can't afford it, but we can less afford to be without it.
J. Gordon Holt wrote about the SP-3A in Winter 1973/1974 (Vol.3 No.7):
This has none of the SP-3's subtle softness, and is clearly superior to it in bass detail and tautness, but it appears that there are some sonic differences from sample to sample of this. Some (including ours) have a hair better inner definition than the SP-3, and a sweeter yet crispier high end—very nearly a straight wire with gain. Other samples have been described as slightly hard and almost steely at the top.
We have not had the opportunity as yet to dig into the cause of these differences, in the hope of ascertaining how a buyer can pick one of the better ones, but we hope to have word on that in our next issue.
And there is still no instruction manual.
Incidentally, the new version costs $795 and is still called the SP-3; you can identify it by the "A" following the serial number.