![]() When the most significant bit of the counter toggles, the counter is preset (reloaded) with a number, the value of this number is determined by the CAL switch, or if not in CAL then by the note selection switch. The Model ST-11 uses two 74121 dual one-shots to generate a 6.825usec clock pulse for a chain of six 7476 dual J-K flip flops which are configured as a 12-bit binary presettable ripple counter. I looked at the ST-11 schematic and made a few measurements on the circuit. I suppose by now the OP has built a stable master oscillator for his unit, I doubt if my information will help him, but maybe it will help someone else. The Conn users forum that was on the Peterson Electro-Musical Site is defunct. it may be drifiting, but you should be able to empirically get the data you want. I have no idea what RPM the wheel spins on each note. ![]() A moving pattern on the screen works the same way as the image on the spinning disc. Peterson is shifting to LCD screens with a graphic representation of the wheel pattern. Tube driven tunig fork oscillator as the basis. I have several of the old 12-wheel COnn 6T5s here. If you want it as a project fine, then marketing is irrelevant. It may well be, but I don't assume that as a starting point.Īnd while we are at it, all those ICs are in sockets, are they not? And over the decades some of the socket contacts may be getting resistive. I brought up things like mechanicals and motor caps because I don t automatically assume speed instability is caused by the oscillator. Then use the existing divider matrix to get the individual speeds. Unless the existing dividers are also unstable, all you really need is a master oscillator to replace the RC one. Just how much is there really? And is the power supply stable or does it drift? But i think the first step is to accurately quantify the instability in the existing circuit. One could buy a higher freq oscillator and divide it down. Here where to buy an high precision oscillator with the correct frequency: what do you think ? Is it possible to get those data somewhere ? those data will help to improve this circuitry maintaining the old fashion estetic. Then I have even a question: what's the frequency of the oscillator ?Īnd also: what is the ratio of this synchro motor ? I mean: If I drive it with 50 Hz, how many turns per minute I will get ? 500 ? 5 000 ? 600 ? 6 000 ? Not clue. the engine rotates supposing that it's own speed stills constant all the time. so that it was possible since early '70s. At that time, there were photocells and lamps. as a turn counter made by otpical disk for instance. in order to compensate little changes in rotation, it's needed to have some kind of feedback that here in the ST-11 there is not. it means that some kind of precision is reached. but consider that Peterson still producing turning wheel tuners for professional use. it's interesting to change this oscillator with another one more stable.Īll the problematics you told are true. ![]() but just wanting this instrument, for fashion, and just to have fun. There are probably far more talented people than I, so I thought I would suggest the project.Ĭlick to expand.Hi Enzo indeed you're right. There are a lot of ST-11's out there so I think it would be a good update. ![]() Thus retaining the original value of this old classic. Without making permanent modifications to the unit. So a new board could be easily installed. The good thing is that the oscillator circuit is all on one module which is removable. Maybe even with a center detent which locks the oscillator to dead-on 440 HZ concert pitch, since most people want to calibrate it for perfect pitch. I'm hoping someone can help to devise a nifty circuit that retains the adjustability, yet is very stable. It outputs 146.66666 khz when calibrated so it's not an off-the-shelf frequency.Īctually the line frequency is used just as a reference to calibrate the oscillator. The oscillator circuit probably needs to be redesigned. The oscillator circuit is TTL and is unstable no matter how long your warm it up. I've actually worked on quite a few of these units. ![]()
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