DIY Turntable Control Calculator
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 Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 24th October 2010, 03:48 PM #1 flyinglemur   diyAudio Member   Join Date: Jul 2005 DIY Turntable Control Calculator Hi Guys, I just thought I'd knock up a quick calculator for a turntable motor control system. You can go as deep as you want into topologies (From simple LM317-style regulators up to full-blown Buck/Boost/Flyback circuits) and if you need assistance on that, please email me at : liam(at)liammartin.com. This would be a closed loop (ie. with feedback) system, so it'll try to keep the speed as constant as possible with respect to load. The overall accuracy will depend primarily on the % of allowed variation around the reference voltage...although most switching regulators are accurate to within a few percent these days. However, this is simply a calculator for the 'handy-to-know' ratios - contained herein are : Platter vs Drive wheel RPM Motor RPM + Drive wheel vs Platter RPM DC-DC Controller Feedback Resistances based on the above. http://liammartin.com/Misc/TTCalc/Turntable_Driver_Calc.xls If you spot a hole in the calculations, please let me know! I hope this is of help. Liam Last edited by flyinglemur; 24th October 2010 at 03:54 PM.
 24th October 2010, 07:31 PM #2 Mark Kelly   diyAudio Member   Join Date: Feb 2006 Location: Willy, VIC Your platter speed to pulley speed ratio is wrong. The correct ratio for rubber belts is (platter diameter + belt thickness) / (pulley diameter + belt thickness). For non rubber belts the belt thickness term on top and bottom must be multiplied by twice the Poisson's ratio of the material. For rubber and other incommpressible materials the Poisson's ratio is 0.5, hence the short version above.
 24th October 2010, 07:34 PM #3 flyinglemur   diyAudio Member   Join Date: Jul 2005 Cheers for that! I will make amends ASAP. It's a couple of MM, if that...so can it be declared negligible? Last edited by flyinglemur; 24th October 2010 at 07:44 PM.
 24th October 2010, 10:25 PM #4 flyinglemur   diyAudio Member   Join Date: Jul 2005 Updated to reflect Mark Kelly's suggestions, however I will assume a non-compressible material - if you want to go into compressible belt media, so be it - and I will pop it in the calculator if enough people ask for it! Hope it's OK! L
 30th October 2010, 03:16 AM #5 flyinglemur   diyAudio Member   Join Date: Jul 2005 Something simple to calculate weights required/exerted on the tonearm. VERY simple, though! No circular torque is taken into account. L http://liammartin.com/Misc/TTCalc/Arm_Calculator.xls
cbdb
diyAudio Member

Join Date: Oct 2008
Location: Vancouver
Quote:
 The correct ratio for rubber belts is (platter diameter + belt thickness) / (pulley diameter + belt thickness).
Maybe I am missing something, but this dosnt make sense to me. Draw a picture with 2 pulleys and a very thick belt. The only thing that matters is the inside surface of the belt (the surface touching the pulleys). The thickness dosnt matter.

flyinglemur
diyAudio Member

Join Date: Jul 2005
Quote:
 Originally Posted by cbdb Maybe I am missing something, but this dosnt make sense to me. Draw a picture with 2 pulleys and a very thick belt. The only thing that matters is the inside surface of the belt (the surface touching the pulleys). The thickness dosnt matter.
I thought this too.

Jacques Merde
diyAudio Member

Join Date: Oct 2009
Quote:
 Originally Posted by Psychobiker I thought this too.
The effective radius of each pulley or platter actually occurs at somewhere near the belt centerline.
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dnewma04
diyAudio Member

Join Date: Mar 2005
Location: MI
Quote:
 Originally Posted by cbdb Maybe I am missing something, but this dosnt make sense to me. Draw a picture with 2 pulleys and a very thick belt. The only thing that matters is the inside surface of the belt (the surface touching the pulleys). The thickness dosnt matter.
You are missing something, Mr. Kelly is dead on with his explanation.

 31st October 2010, 08:19 PM #10 Nanook   diyAudio Member     Join Date: Feb 2004 Location: Chinook Country.Alberta well, belt drive is not the only drive system out there.... after doing some thinking (which is not always my way...), I've given up on belt drives when designing a drive system, I'm sticking with either idler drive or rim drive. I've looked at various systems and ran my choice and basic design past a mechanical engineer whose opinion I trust. As Mark Kelly points out, the modulus of elasticity is quite high for rubber (regardless of thickness but at smaller thicknesses the forces required to deform it is smaller) if using a rubber belt at room temperature. This implies that in small enough diameters to allow use in belt drive systems the modulus of elasticity does need to be considered. I think this is one of the reasons why many have reported the benefits of changing belt materials--- belts do vibrate and can introduce "smearing" of the sound. Even some rather expensive tables have benefitted from a change in belt materials or in motor or drive type upgrades (like the Teres Verus upgrade) Perhaps a different belt material could be used. I have used high strength nylon upholstery thread to very good effect. Difficult to get the correct length and tension required to drive a platter, but stable once done. I assume a good quality silk thread would also provide the same, and perhaps unwaxed dental floss. Something that may be considered is what some have used. 1/4" cassette tape, or 1/2" video tape or mylar (as per the Redpoint and Teres designs) with suitable pulleys. Take care all... __________________ stew ☮ -"A sane man in an insane world appears insane."

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