Rega P5 running too fast

[asmneto]

Hi Frank, the fact that counting revolutions by eye may not be accurate doesn't matter if you do several testings for an average. I'm not trying to determine if the speed is running 2.25% or 2.15% faster, 2.2% is more than sufficient to see that it is actually running fast.

By the way, "measuring" speed by ear is always the best option and measuring it by eye just corroborate to my ear findings.

[mr.datsun]

Is there a possibility that the belts are somehow loose and riding on the outer part of the pulley grooves, thus appearing to be of wider diameter?

Regards,

That occurred to me. My stock Planar 3 with 24v motor and the black belt (2yr old) was +0.44% fast. When I added the white belt it then ran slightly slow (-0.2%). But the next day it then ran fast (but only by 0.07%).

The black belt felt loose. The white felt much stiffer and of course tighter. So, yes – it occurred to me that the stiffness of the belt changed the contact it had with the interior surfaces of the pulley. I favoured this idea more than that the belts were different in thickness as its use over a number of hours, in theory, led to the belt 'giving' slightly.

[asmneto]

Hi mr.datsum. I'll try to re-adjust the pulley position a bit far from the subplatter, by setting one of the motor screws further on the slotted mounting hole (LHS), thus tightening the belts. If the deck runs a bit slower it would back up this theory.

Is there a possibility that the belts are somehow loose and riding on the outer part of the pulley grooves, thus appearing to be of wider diameter?

Regards,

That occurred to me. My stock Planar 3 with 24v motor and the black belt (2yr old) was +0.44% fast. When I added the white belt it then ran slightly slow (-0.2%). But the next day it then ran fast (but only by 0.07%).

The black belt felt loose. The white felt much stiffer and of course tighter. So, yes – it occurred to me that the stiffness of the belt changed the contact it had with the interior surfaces of the pulley. I favoured this idea more than that the belts were different in thickness as its use over a number of hours, in theory, led to the belt 'giving' slightly.

[Lelolee]

Hello, I have done some testings for speed, I counted 100 revolutions (should be exactly 3 min at 33 1/3 rpm) several times and came up to this average:

02:56.1

This means my P5 is running 2.2% faster. This is acceptable?

It has the PPSU, dual pulley and 2x Rega "white' belts.

It's the dual pulley.

[Lelolee]

Put the stock pulley back on, and one white belt. Then check the speed, you will see that its the dual pulley.

[asmneto]

Do I need to glue the stock pulley back?

Put the stock pulley back on, and one white belt. Then check the speed, you will see that its the dual pulley.

[Lelolee]

No, just push it back on.

[asmneto]

OK, done several speed tests with the pulley farther from the subplatter and belts a bit more stretched. The outcome was 1.8% faster than 33 1/3 rpm. So yes, I can conclude that the belts are loose and that this have to do with running fast -- loose belts tend to sit on the outer part of the "V" shaped pulley grooves.

Anyway, the fact is that it is still running a bit fast. Well, better fast than slow.

I'll give the old stock pulley a try later.

[mr.datsun]

Mr. Datsun, what formula are you using to calculate the pulley diameter, and what belt diameter are you using in that calc?
Sorry I'm too lazy to back-calculate myself. I'm also not sure of what the belt diameter should be, assuming there is a standard diameter.

To restate Frank's formula:

Gearing ratio = motor speed / platter speed (33.33rpm)

Pulley D = Subplatter D/Gearing ratio

UK speed at 50Hz = 250rpm
US speed at 60Hz = 300rpm

I think subplatter should be 100mm diameter but I reckon Frank has a better idea about that. But subplatter diameter of 100mm gives a nice 13.33333mm diameter for the UK pulley .

As an extension of Frank's drawing from a few weeks ago, I drew this for my own understanding last week. It is based on measurements taken with digital callipers using my old motor. The callipers will not get into the V groove and the thickness of the calliper's tip had to be used to estimate the inner diameter. The belt diameter was supplied by Jack on this forum. The drawing's measurements therefore are not 100% exact but it is all to scale. I don't use technical drawing s/w at home so used Illustrator. I think it gives a pretty good idea.

[mr.datsun]

OK, done several speed tests with the pulley farther from the subplatter and belts a bit more stretched. The outcome was 1.8% faster than 33 1/3 rpm. So yes, I can conclude that the belts are loose and that this have to do with running fast -- loose belts tend to sit on the outer part of the "V" shaped pulley grooves.

Anyway, the fact is that it is still running a bit fast. Well, better fast than slow.

I'll give the old stock pulley a try later.

asmneto,
Seems like the pulleys may not have been the problem. Is the motor seating a bit off? Anyway glad to hear you're getting to the bottom of it.
D.

[asmneto]

Hi mr.datsum, what do you mean by the motor seating a bit off?

OK, done several speed tests with the pulley farther from the subplatter and belts a bit more stretched. The outcome was 1.8% faster than 33 1/3 rpm. So yes, I can conclude that the belts are loose and that this have to do with running fast -- loose belts tend to sit on the outer part of the "V" shaped pulley grooves.

Anyway, the fact is that it is still running a bit fast. Well, better fast than slow.

I'll give the old stock pulley a try later.

asmneto,
Seems like the pulleys may not have been the problem. Is the motor seating a bit off? Anyway glad to hear you're getting to the bottom of it.
D.

[mawari]

I believe you need to include the thickness of the belt ( approximately it's radius ) into the pulley diameter ( plus "gap" if the pulley profile does not match the belt profile ) when calculating theoretical drive ratios. The rotation is not transmitted from the belt/pulley contact point, but from ( approximately ) the centre of the belt. So in Mr Datsun's excellent drawing above, if drawn to scale, the effective diameter would be closer to 14.62mm than 13.33mm. Similar adjustment is necessary for the subplatter effective diameter. Theoretically, a replacement pulley designed using the "contact point" radius, would, other things beng equal, be too large and cause fast running.

The belt is compressed on one side a little in use, and so the cross section is not a pure circle, hence "approximately". Varying this compression by moving the motor back and forth, or the belt stretching with age, will affect speed.

2% fast is almost a 9Hz increase on an orchestra tuned to A=440Hz. Pitch inflation will sound exciting, and louder, but in some circles, it would be an abomination too far.

.... A = 440 Hz is the only official standard and is widely used around the world. Many orchestras in the United Kingdom adhere to this standard as concert pitch. In the United States some orchestras use A = 440 Hz, while others, such as New York Philharmonic and the Boston Symphony Orchestra, use A = 442 Hz. Nearly all modern symphony orchestras in Germany and Austria and many in other countries in continental Europe play with tune to A = 443 Hz

Paul

[mr.datsun]

Hi mr.datsum, what do you mean by the motor seating a bit off?

As you were talking about adjusting the position of the pulley to make the belt tauter , I wondered whether the motor was in the exact right spot. Now I realise that as I have no experience of the P5, I may talking out of my arse. With the Planar 3 the pulley has to be inserted and centred in the hole in the plinth through which it protrudes. When mounting the motor it is important for us Planar 3 owners to get the mounting position right first time as the motor is mounted with high-tack adhesive pads. I imagined that the P5 also has a hole through which the pulley is inserted BUT I have no idea how the motor is mounted. I assume that there is an optimum motor position to get the correct belt tautness, though and wondered whether your motor is in that spot.

[mr.datsun]

The rotation is not transmitted from the belt/pulley contact point, but from ( approximately ) the centre of the belt. So in Mr Datsun's excellent drawing above, if drawn to scale, the effective diameter would be closer to 14.62mm than 13.33mm. Similar adjustment is necessary for the subplatter effective diameter. Theoretically, a replacement pulley designed using the "contact point" radius, would, other things beng equal, be too large and cause fast running.

Paul, I assumed that the belt contact point would be the radius of the pulley. If it is the centre of the belt that gives the effective radius of the pulley (and this is something that I wasn't aware of, as I've been working from a kind of naive mechanistic logic), then my diagram is probably wrong. Certainly, the effective diameter could not be 14.62 as that would make the deck too fast – unless the additional half belt thickness at the subplatter end corrects the gearing ratio back to 7.5.