Turntable not spinning fast enough on 45 Options

[powerstone05]

I have (now) a GemSound BJL-1150. The problem I'm having is that the 45 rotation is quite slow and is noticeable in playing. The 33 seems to be fine though. I checked the belt and it's still in working order. Any ideas?

[DVDdoug]

How's the torque? Does it seem like the belt is slipping?

Is the speed-change done with pulleys, or electronically? If the different speeds use different pulleys, you can try cleaning the 45RPM pulley or try changing the belt. If the same pulley is used for both speeds, I'd assume the belt is good.

If there's no mechanical difference with the two speeds, or if you don't think the belt is slipping, then you've got a problem in the electronics. If it's in the electronics, it's probably not worth the cost of getting it repaired. You could buy a used one and steal the PC board out of it... But, if you buy a working-used one, you could just use that one.

[powerstone05]

Well looking at it, the turntable appears to use just the one pulley & belt for both speeds. I'll try to see if I can figure out of the belt is slipping out.

[Glenn Gundlach]

I have (now) a GemSound BJL-1150. The problem I'm having is that the 45 rotation is quite slow and is noticeable in playing. The 33 seems to be fine though. I checked the belt and it's still in working order. Any ideas?

So you get a strobe disc and measure it. It's not at all difficult or costly. You print this sheet and put it on the turntable and use an OLD STYLE fluorescent light. Rapid start or really old with a starter. This will NOT work with electronic ballast lights. Alternatively one of those neon tester lights would work fine. If the pattern appears to be standing still, it's dead on. These folks also have a 50Hz version if you're not in North America.

http://extremephono.com/ftp/60Hz.PDF

G²

[powerstone05]

I have (now) a GemSound BJL-1150. The problem I'm having is that the 45 rotation is quite slow and is noticeable in playing. The 33 seems to be fine though. I checked the belt and it's still in working order. Any ideas?

So you get a strobe disc and measure it. It's not at all difficult or costly. You print this sheet and put it on the turntable and use an OLD STYLE fluorescent light. Rapid start or really old with a starter. This will NOT work with electronic ballast lights. Alternatively one of those neon tester lights would work fine. If the pattern appears to be standing still, it's dead on. These folks also have a 50Hz version if you're not in North America.

http://extremephono.com/ftp/60Hz.PDF

G²

Funny you mention this, I tried this exact disc (along with the strobe system built into the platter itself) and it proves my point again, it's too slow. Even with the pitch adjustment all the way to max (+10%), its still not enough.

[mzil]

Short of getting it fixed or buying a new turntable, what about recording the music to your computer and correcting the speed (and therefore pitch) in software? Just a thought. If the optical disc shows the speed error is constant and non-wavering I'd think this would work well.

This post has been edited by mzil: Jan 5 2013, 07:00

[powerstone05]

Probably a stupid question but I know that playing a 33 LP at 45 and then slowing it down compromises the quality, but wouldn't the same thing happen if I play a 45 at 33 and then speed it up? (Yes I do plan to record some records off of it)

[Glenn Gundlach]

Probably a stupid question but I know that playing a 33 LP at 45 and then slowing it down compromises the quality, but wouldn't the same thing happen if I play a 45 at 33 and then speed it up? (Yes I do plan to record some records off of it)

If the speed is only off a few percent 'tweaking' it in digital is OK. I don't know how big a problem it is but the RIAA curves crossover points should really track the speed difference but it's probably more of an OCD thing.
Question: You say the speed control is still slow when at +10%, is the speed _range_ about right? Does it seem to go to -20% less ? A 20% span would be a little more than 3 semitones.

G²

[powerstone05]

Probably a stupid question but I know that playing a 33 LP at 45 and then slowing it down compromises the quality, but wouldn't the same thing happen if I play a 45 at 33 and then speed it up? (Yes I do plan to record some records off of it)

If the speed is only off a few percent 'tweaking' it in digital is OK. I don't know how big a problem it is but the RIAA curves crossover points should really track the speed difference but it's probably more of an OCD thing.
Question: You say the speed control is still slow when at +10%, is the speed _range_ about right? Does it seem to go to -20% less ? A 20% span would be a little more than 3 semitones.

G²

Well I just posted a similar question over at the Audacity forums, and used the formula to determine the actual RPM. I did a test with a 12" single I have and put it on 45 with pitch adjustment at max (10%). The result was approximately 44.826 RPM, which bugged me, so close but not there. But its enough that I can notice.

[mzil]

You can increase the speed slightly by applying a twist to the belt before it loops around the pulley. [One high-end TT maker a decade or two ago, Well-Tempered, used to do this as a normal course of action, claiming it reduced flutter.] Depending on if you flip it around one way or the other [top edge flipped away from the main platter vs toward the platter] the belt may have a tendency to ride around the pulley rather high or rather low. Try both ways and see what gets you to the speed you want.

[mzil]

^Here's a pic:
http://t0.gstatic.com/images?q=tbn:ANd9GcR...NfcBMKeAKYMWBsV

Ideally, the belt used should be precisely manufactured to have a smooth, uniform surface on both sides, not just the inner one, and I'm not sure how common this practice is, however I know some manufacturers specifically point out that they do exactly this. [Early AR, for example] I guess this was to ensure that consumers couldn't put the belt on the "wrong" way, inside out. Both ways were the same.

This post has been edited by mzil: Jan 6 2013, 16:09

[DonP]

You can increase the speed slightly by applying a twist to the belt before it loops around the pulley

Unless the problem is slipping, I don't see how this would increase the speed. The ratio between capstan and platter pulleys will be the same.

[mzil]

The turntable designer Bill Firebaugh described the belt linkage of turntables as such, in this Stereophile interview:

"...if you try and calculate the platter speed from the pulley speed and the two circumferences, it doesn't work out right. The platter doesn't run at the predicted speed; it will always be slow. I'll tell you, this drove me nuts until I found out what was going on. I wasn't the first person to discover this by any means. I was explaining my speed problems to my belt manufacturer, and he knew all about it. He confirmed that this is a known phenomenon in belt-drive systems, especially ones with relatively compliant belts. The pulley goes faster than the belt." [emphasis mine]

The belt twist(s) slightly reduces the effective length of the belt and therefore changes it's "stretch" and compliance.

Powerstone5 will hopefully try this quick, simple and free test and then share with us his measurements. [Also, more than one twist might be in order, to tighten the belt even further.]

This post has been edited by mzil: Jan 6 2013, 18:03