Project Debut Carbon DC - Playing Too Fast

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matty007
England
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Joined: 26 Sep 2019 22:17

Project Debut Carbon DC - Playing Too Fast

Post by matty007 » 26 Sep 2019 22:27

Hi,

So I recently acquired this table used, but in very good condition, and mostly I am very very happy with it.

However, it appears to be playing too fast. I have used RPM apps on my phone (not the most accurate method I know) and it is giving me readings of 33.50-33.55rpm. Before it was giving me 33.60rpm but I changed the belt in the hope it would get it close to 33.33, only to get .5-0.10rpm improvement.

Now I know that this isn’t the most high end table but it is certainly rather good and has a DC motor. I would have expected it to be very close to 33.33, if not bang on it. Sometimes I can hear the added pitch in records, sometimes not. However, I know it’s playing fast and that’s what’s annoying.

Even my crappy LP60 I got to a speed of 33.34 with minor adjustments. Obviously this has no speed adjustment, but given the DC motor, there must be something causing it to play fast?!

I have noticed that on the motor pulley, the belt does not stay in the top spot. When spinning, the belt slips down to the bottom of the 33rpm ring. It’s hard to explain, but there is two indentations for the pulley on 33rpm. One is for 50hz, the other for 60hz. As I’m in the UK, it should be 50hz, which is the topmost indentation. However, it’s like the belt is too thick to stay in here, and slips down to the bottom indentation upon spinning. Could this be affecting the speed?

I would really like some advice on what causes this and a possible fix. I know it’s not a massive speed error, but it’s certainly significant and enough to make my perfectionist brain weep. I would even be happy to get it under 33.40

Thanks everyone

ravelax
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Re: Project Debut Carbon DC - Playing Too Fast

Post by ravelax » 28 Sep 2019 15:39

I wouldn't worry about it. I used to have the same turntable and never noticed it ran a tiny bit fast until I measured it. Still couldn't actually hear it, though. I compared some albums I have on both CD and LP, and any minute difference I may or may not have noted (when you're really trying to hear a difference, your brain can often fool you into hearing one regardless of whether it's there or not) was insignificant. More important, I find, is speed stability. 33.5 should be fine, as long as it's steady. My Pro-Ject was always rock solid speedwise, if apparently a little fast. That wasn't the reason I sold it (mostly it was due to me getting fed up with having to take off the platter to change speed! Hehe).

That said, many belt drive turntables are apparently known for running a tiny bit fast, not only the dirt cheap ones. Rega is one brand I know I've heard this complaint about, although I can't remember if it also applies to their very top-end models. If you really can't stand the thought of your turntable doing this, I suggest replacing the Pro-Ject, nice table as it is, with something quartz locked (there are such belt drives, not only direct drives), or at least something with a pitch control or speed adjustment of some sort.

Coffee Phil
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Re: Project Debut Carbon DC - Playing Too Fast

Post by Coffee Phil » 28 Sep 2019 18:00

Hi matty007,

Welcome to the forum.

It is hard to get clear information on Project turntables but I'm pretty sure yours has an AC motor. If it were DC you would not have different spots on the capstan for 50 and 60 Hz.

I'm guessing that you have a flat belt. If so it should run on the centered on the crowned portion of the respective spot on the capstan. If it does not check the suspension of the motor to insure that the motor shaft is vertical. After that check the speed with a strobe. There are discs which you can print on this site.

In addition to the above, platter speed is effected by the belt. The capstan effective radius includes ~1/2 the belt thickness so a thick belt will cause the platter to turn fast. If you can't secure a belt which will get the platter on speed you may be able to grind the belt thinner. Remove the top platter and run the machine while holding a Dremel tool with an abrasive cylinder against the belt. Stop and check the speed periodically as you can't add thickness. When done you will have a rubber dust mess to clean. I had to do this to my Rek-O-Kut Rondine 2 as the correct belt was not available at the time.

Good luck and let us know how it goes.

Phil
matty007 wrote:
26 Sep 2019 22:27
Hi,

So I recently acquired this table used, but in very good condition, and mostly I am very very happy with it.

However, it appears to be playing too fast. I have used RPM apps on my phone (not the most accurate method I know) and it is giving me readings of 33.50-33.55rpm. Before it was giving me 33.60rpm but I changed the belt in the hope it would get it close to 33.33, only to get .5-0.10rpm improvement.

Now I know that this isn’t the most high end table but it is certainly rather good and has a DC motor. I would have expected it to be very close to 33.33, if not bang on it. Sometimes I can hear the added pitch in records, sometimes not. However, I know it’s playing fast and that’s what’s annoying.

Even my crappy LP60 I got to a speed of 33.34 with minor adjustments. Obviously this has no speed adjustment, but given the DC motor, there must be something causing it to play fast?!

I have noticed that on the motor pulley, the belt does not stay in the top spot. When spinning, the belt slips down to the bottom of the 33rpm ring. It’s hard to explain, but there is two indentations for the pulley on 33rpm. One is for 50hz, the other for 60hz. As I’m in the UK, it should be 50hz, which is the topmost indentation. However, it’s like the belt is too thick to stay in here, and slips down to the bottom indentation upon spinning. Could this be affecting the speed?

I would really like some advice on what causes this and a possible fix. I know it’s not a massive speed error, but it’s certainly significant and enough to make my perfectionist brain weep. I would even be happy to get it under 33.40

Thanks everyone

old_spinner
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Re: Project Debut Carbon DC - Playing Too Fast

Post by old_spinner » 28 Sep 2019 18:08

It maybe confusing, as the name of the unit suggests a DC motor indeed, but its (still) an AC type, driven by a freqency generator which is powered by DC.

That means, the AC coming from the mains is first rectified and then a generator creates the neccessary AC-frequency.

This method is more precise then using the AC-freqency directly, as this maybe a bit unstable for several reasons.

Look here:

https://www.henleyaudio.co.uk/products/ ... BrandIds=2

If you can't live live with 33,5 rpm, simply put one or two layers of thin adhesive tape around the subplatter, this will shorten the gear-ratio and make the platter spin slower.


regards

kalaur
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Re: Project Debut Carbon DC - Playing Too Fast

Post by kalaur » 29 Sep 2019 01:51

Keep in mind the table may run slightly slower when an actual album is playing.

If the belt is not riding in the center of the correct groove on the pulley, this may be contributing to the issue. Try scooting the belt lower on the subplatter as well, if its too high or low it may not want to center on the motor side. If this doesn't help, I'd seek out a replacement belt of proper size.

Coffee Phil
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Re: Project Debut Carbon DC - Playing Too Fast

Post by Coffee Phil » 29 Sep 2019 06:45

Wow!

I was a bit hasty in this. As old_spinner pointed out apparently while this machine has an AC motor it is powered by DC. The DC powers an AC power supply which in turn makes AC to drive the motor.

While I’ll still stand by my comments on checking the angle of the motor shaft, before grinding the belt I’d look at dripping the frequency of the AC power supply. Most likely the clock is a Pierce crystal oscillator. They can be pulled up to ~ 5% max by capacitive loading. Look for the crystal. At each terminal you should find a capacitor to ground. They should be tens of pF. Try increasing them by a factor of two and the frequency and hence the speed will drop.

Phil

old_spinner
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Re: Project Debut Carbon DC - Playing Too Fast

Post by old_spinner » 29 Sep 2019 08:59

There seems to be a little bit of confusion about the role of the pulley.

The two diameters of that pulley are for "switching" between 33,33 and 45 rpm platter speed.
The upper, smaller diameter is for 33, the lower, bigger one for 45, whilst the motor running at the same speed, it's just a change of the gear ratio. To "switch" to the other speed, the belt must be moved to the other diameter, after removing the platter.

This all has nothing to do with 50 or 60 Hz, as the table uses DC and an oscillator to create the neccessary frequency, independent of the mains frequency.

The "SB"-Version of this turntable allows changing the speed by the push of a button. This changes the frequency and forces the motor to run faster or slower, the bigger pulley size is for playing shellacs (78rpm) then in combination with the speed selector set to 45.

If the belt, hopefully an original one, does not stay in the middlemost position of the pulley, the motor mount maybe a bit misaligned, what results in a slightly wrong position of the motor shaft, as CoffePhil stated.

Look at the picture:

https://www.henleyaudio.co.uk/shop/prod ... ductId=576

Are the two screws numbered with "1" in place or are they removed?

In earlier versions of that turntable those screws were for transportation security and had to be removed for playing.

In the actual version, they stay where they are, as they provide the neccessary tension for the rubber grommets (are they present?) between the wooden chassis and that tin parts.

After adjusting those thwo screws in a way that the belt stays in the middlemost position of the pulley, fix them with a drop of laquer and forget them.

And, if the table really runs at 33,5, this is within the 0,2 % tolerance. Nothing to really worry about.

Please note that the rpm calculator only shows correct results, if the phone's sensors are correctly calibrated.

My old debut III turned at 33,45, just for information.

Hope this helps.

regards

Coffee Phil
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Re: Project Debut Carbon DC - Playing Too Fast

Post by Coffee Phil » 29 Sep 2019 21:17

Here is a tutorial on Pierce oscillators:





The amplifier is likely part of the IC which divides the oscillator frequency down to the motor frequency.

Phil
Coffee Phil wrote:
29 Sep 2019 06:45
Wow!

I was a bit hasty in this. As old_spinner pointed out apparently while this machine has an AC motor it is powered by DC. The DC powers an AC power supply which in turn makes AC to drive the motor.

While I’ll still stand by my comments on checking the angle of the motor shaft, before grinding the belt I’d look at dripping the frequency of the AC power supply. Most likely the clock is a Pierce crystal oscillator. They can be pulled up to ~ 5% max by capacitive loading. Look for the crystal. At each terminal you should find a capacitor to ground. They should be tens of pF. Try increasing them by a factor of two and the frequency and hence the speed will drop.

Phil

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