[jrebman]

Hey Jim,

A little late, but nice running into you again at RMAF .

I have an interesting problem that I've been brainstorming about and I came across the UFO and thought that it might be part of the solution.

I'm looking for a way to set my TT speed without being able to see a strobe -- i.e. some sort of audible cue that I'm on speed.  I am having a bit of difficulty understanding how the UFO works from the description so I don't know if some sort of mod for an audible cue is possible or not.

I'd be using this with either my VPI HW-19 with PLC or possibly an SL-1200 down the road.

Looking at picking up a Ripper half kit too.

-- Jim

[hagtech]

Well, if you connect the UFO output to a small speaker, it would output a constant 75Hz buzz (square wave with lots of harmonics).  However, it has no relation to platter speed.  What is needed is a differential between a reference tone and one generated by the platter.  Hence you get interference beat patterns.  Basically the audible version of a visual strobe.

So I can't think of a way to make the UFO useful for you.  What might work is if you run the system backwards.  Rather than illuminate the strobe, have the strobe optically illuminate a sensor.  This optical encoder can then spit out a tone that is proportional to platter speed.  It can also be compared to a reference (multiplied) to create an interference tone.  I suppose you could make it operate like a metal detector.  Lowest tone, or perhaps a null tone, means proper speed.

A cheaper method would be to get a calibrated tuning fork and an LP with a reference tone.  Pain in the butt, but it would be very accurate.

So let me ask, I am going to assume your sense of pitch is highly refined.  Do you find a slight error in TT pitch really annoying?  I'm curious if you think it bothers you more than average.  Do you feel you have to adjust for each LP?  I'm wondering if the standard visual strobe is inadequate.  You have me thinking here, that maybe there is a need for a platter speed sensor that is 100x more sensitive than what is available.  Maybe something that can even detect the slight cogging from a dc motor.

jh

[jrebman]

Jim,

Thanks for the suggestions.  Yes, there are a lot of possibilities for dealing with this and I was just curious if the UFO might be able to be used for this with some modification.

As for my sensitivity to deviations from absolute pitch, the answer is that I don't really know yet.  Once the table is working and properly setup and I can play some albums that I'm extremely familiar with, then I'll be able to see to what degree this is actually a problem.  One issue with the PLC is that it allows for a pretty wide range of speed adjustment, and if it's really off -- as it may be if playing a 78, then it would be nice to be able to get back to 33-1/3 fairly quickly.  I suppose I could also just establish some reference points and count clicks on the thumbwheel switches, but I'll also have to see how stable the 60 Hz is in my area -- the PLC is not a true regenerator like the SDS.

Thanks,

Jim