DIY Turntable Motor Drive

analog music reproduction discussion

DIY Turntable Motor Drive

Postby Shannon Parks » Fri Dec 14, 2007 7:37 am

I started a new thread for R&D rambling purposes based on an Altmann design. Please - kool-aid drinkers only. ;)

I've spent the last two months fiddlin' with different motor control circuits based on Altmann's use of a 7.5 deg stepper as a pseudo AC sync motor. He then drives it with an Ipod device (two 90 degree apart sine waves around 60Hz) and a stereo (as the power driver). I started to implement this with two of the Hitachi IC amp boards (the 18W mono amps you see for $12) and a Wein Bridge Oscillator.

[EDIT will continue]
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby Shannon Parks » Sat Dec 15, 2007 2:16 pm

The Wein Bridge Oscillator is a fun circuit but the feedback values are critical to get the thing working. I rigged up some divider network on the output to get a 90 degree offset, but then making all this adjustable ended up screwing up the phase offset (as the divider was calculated for one frequency). At that time, I ditched it for another direction.

Still wanting to do like Altmann did, but not using an MP3 player as the source, I tried an Atmel microcontroller using a PWM scheme with RC filter. This was pretty straight-forward (I used a demo board with an ATMega16), and a 90 degree offset would be easy. After writing the demo code and playing with it for awhile, I was disappointed in the complexity I was headed into. Why not just use a discrete stepper driver <gasp> instead? It is work looking at.

I ordered Kit 179 from Alltronics (I think). It has a schmidt trigger oscillator drive the a logic circuit that controls a bipolar motor. I think it was $16. Nifty thing is that there is a spare inverter on the board I will use for a 60Hz blue LED strobe for speed tweaking. Initial tests thusfar look great. With a heavy platter- currently a pile of ten laserdiscs though I may go to twenty with some lead shot - the inertia will totally erase any perceived motor jerkiness.

More to come...
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby wiredbecker » Fri Dec 28, 2007 7:16 pm

Shannon,

Fascinating project. Gotta love the thread drive! I have a small assortment of actual platters harvested from dumpstered turntables that you're welcome to. I'll post pics of my "stock" when I get home in a week or so.
User avatar
wiredbecker
KT88
 
Posts: 301
Joined: Mon Mar 26, 2007 3:48 pm
Location: Albany Landfill, CA

Postby Shannon Parks » Sat Dec 29, 2007 9:31 am

Stuck on a home DIY project the last couple weeks, making a listening/family room. But I've got most of the parts together. I'll use these awesome little blue Pomona boxes for the motor and the tonearm mounts. They are dumpster dive booty from a government agency I can't identify. :) Also just bought +50lbs of cast lead bullets from a kid that pulled them from a dumpster behind our business - looks like a hunter got rid of all his black powder rifle gear.

And lastly, I got a carbon fiber arrow from a local Hunter's Haven that fits the gimble from the Pioneer PL-10. Thinking 12" or better. :) The arrow was used, and covered in grime, but it was the only one that fit the gimble and I knew I could get it cheap. He asked for $2 cash. He also exclaimed, "wow, that arrow is still covered in deer blood!". Cool - I can now say I have a 'killer tonearm'. Yellow_Light_Colorz_PDT_04

Hmmm - government dumpsters, 50lbs of bullets and arrows covered in blood. This turntable sounds dangerous.

Oh yeah - I did get all the Harley parts, but my valve guide and valve intake won't seat. They are from misc manufacturers, so I'll just find a Rowe dealer and ask them to confirm a perfect fit for me. This part of the project is a little bit of a headache. I'll post part numbers when finished. Also, I have no idea what the plinth will take the shape of.
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Postby wiredbecker » Sat Dec 29, 2007 5:25 pm

separks wrote:They are dumpster dive booty from a government agency I can't identify. :)


Rad post.

Over the years I've pulled some great stuff from the local VA hospital dumpster in San Francisco. Hospitals in general though.. man, great shit! No need to worry because all toxic and disease communicable stuff has been sorted into a separate sealed dumpster. Still, always a good idea to wear gloves when digging.
User avatar
wiredbecker
KT88
 
Posts: 301
Joined: Mon Mar 26, 2007 3:48 pm
Location: Albany Landfill, CA

Postby Shannon Parks » Sun Dec 30, 2007 7:58 am

My tube godfather, a gentleman who gave me my first Allied 6BQ5 amp to tinker with, was a maintenance man at a VA hospital for years. He was a lifelong dumpster diver while he worked there. Probably the best thing that I've inherited from his salvaging was all the electronic DIY and ham radio mags he collected from the hospital circulation in the sixties and seventies. Several boxes of good reading material! ;)
User avatar
Shannon Parks
Site Admin
 
Posts: 3764
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington


Return to plastic fantastic lovers

Who is online

Users browsing this forum: No registered users and 3 guests