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Gyrodec plus QC is going to fast.

monty

monty

pfm Member
Hi

I've noticed my Gyro is spinning too quickly. When I compare with the same track ripped from a CD, the vinyl track (about 4 mins long) finishes a second or two before the CD rip
I've noticed this since I fitted a new belt and changed the oil. Could this be the issue?

I've always used 2 belts but heard that one belt was better so bought just the one.

I don't think the QC can be adjusted so does anyone have any experience with this? It's starting to annoy me with recordings I know well as he pitch is slightly higher than it should be

Thanks as always
 
monty said:
Hi

I've noticed my Gyro is spinning too quickly. When I compare with the same track ripped from a CD, the vinyl track (about 4 mins long) finishes a second or two before the CD rip
I've noticed this since I fitted a new belt and changed the oil. Could this be the issue?

I've always used 2 belts but heard that one belt was better so bought just the one.

I don't think the QC can be adjusted so does anyone have any experiment with this. It's starting to annoy me with recordings I know well as he pitch is slightly higher than it should be

Thanks as always
Click to expand...

I don't know for sure but the VC power supply has a trim screw inside it. You have to take the cover off to get to it though. Maybe something similar inside?
 
Thanks. Just had a look inside the QC and indeed there are some pots to adjust. What's the best way of checking the speed is accurate. I remember strobe discs back in the day. There must be an electronic checker these days?
 
PS. There are 4 pots to adjust. Only one seems to adjust the speed.

Any ideas what the other 3 do?
 
Just done a google search and a voltage meter seems like best solution

Can anyone recommend one that offers best accuracy for this purpose?
 
There is an electronic speed checker. It's called a stopwatch. Time 100 revolutions at 33.33 rpm, it should take 3 minutes. Too simple?
 
A strobe disk and old fashioned lightbulb are the easiest way. Were do you live as I am sure someone could lend you a strobe disk if needed, I have one if London based. Even you have a friendly dealer they may even have one.
 
If you have an iPhone, you can download iRPM for free. I put mine on an old 45 adapter with some blu-tack and put it on the spindle of my Amadeus. Maybe not the last word in ultimate accuracy, but it gets you pretty close. I find it easier than using a strobe disc.
 
I'd be careful about those trimmers if I were you. I'm not familiar with the circuit of this power supply but the adjustments could be for things like output stage bias and it is possible you could cause damage by twiddling....
 
monty said:
PS. There are 4 pots to adjust. Only one seems to adjust the speed.
Click to expand...

NONE adjusts speed. The QC/AC motor combo speed is frequency-dependent. The four pots set the gain of the QC's two times two output amplifiers (one phase each for 33.3 and 45). Set them too low and it won't start, too high and the motor gets overloaded. Just wrong and the phases get unbalanced, and the motor might vibrate.

I think each phase needs about 19V, but I may misremember.


monty said:
Not so simple if checking minute adjustments
Click to expand...

Very simple, in fact. And you don't have to rely on any external (and potentially erroneous) factors such as strobe discs, mains frequency, suspect apps, ...
 
1 second in 4 minutes is about 0.4%. This is about half the allowable variation of the mains frequency, to which many decks are locked. It also implies that if you want to get a proper measurement a strobe sync'd to the mains won't do unless you are also monitoring mains frequency (http://www.dynamicdemand.co.uk/grid.htm for example, I don't know whether Europe is in sync).

A thinner belt will slow things down a bit. Perhaps the new belt is thicker than standard that's the root cause?

Paul
 
No. The QC was the upgrade Lingo-like supply for the original Papst AC motor.

image.php
 
Hi

FYI - I found the answer after a google search and some reading (cut and pasted below)

I borrowed a volt meter and managed to adjust after a bit of steady handed adjusting :)

"In case anyone has the same issue. I rang the factory in the UK and they were incredibly helpful. I removed the QC cover, identified the 3 output solder points at the bottom right of the board in the photo above and with a voltmeter, measured the AC across the green (right solder spot) output wire and the centre solder spot (blue wire), I adjusted the top trim pot for 19 Vrms with 33rpm. I then measured the AC across the green ( right solder spot) output wire and the left solder spot ( red wire) and adjusted the next trim pot down for 19 Vrms with 33 rpm.

To do 45 rpm, it was the same again ( depress the switch at top left and the LED goes from green to red) but the bottom two trim pots and measuring for 21 Vrms and adjusting as required.

My Gyrodec has an outboard Papst AC motor as I had John make it for 2 arms and it also has 2 belts. However, I think piano flutters a little with 2 belts and have removed the top belt.

I called Steve back to thank him at the factory for their guidance and mentioned the 2 belt back to 1 belt move and he surprised me by suggesting I try the belt in the other direction! Apparently, when they are polished, it can be that the belt has fine scales, in one direction the scales are running with the pulley, in the other, they are flaring up against the pulley and can alter the note stability!

More on that later this week!

Anyway, I am happy to be able to listen to piano again without the wow I was hearing and the motor starts without needing to spin the platter.

Take care"
 
Ideally you need a scope to look at the waveforms (voltage). I adjusted mine a few years back. Yeah frequency is set but I had an issue with one phase it was clipping and screwing up the sound...should be nice sine-waves. Other issue was wear on the pulley - the belts are quite abrasive. The adjustment of the pots inside got rid of the clipping and a new pulley fixed the speed variation. Yeah Michell are very friendly and helpful too.
 
Thanks for the info guys, I reckon I need a new pulley (1998 Orbe AC/QC) as the speed is fine on the lower 45 notch, are they easy to fit?
 
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