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Simple DC motor control

Can anyone make a suggestion for a better voltage reference, using 2 transistors and resistors rather than the single transistor that's been tweaked to behave like a zenor diode. I'm still not sure why anyone would do that.
 
Because it will be cheap and therefore efficient; reverse-biased base-emitter junctions breakdown will be a reasonable zener of around 6volts. not the 'quietest' but that's not really a problem if feeding a motor-drive circuit.

What voltage does this 'reference' give? You'll need to achieve something close as a two-terminal device to keep within reasonable range of adjustment without further mods. An LM329 will likely be close as a drop-in (a very good 6.9v reference, works fine over the span of 1-15mA reverse current) and a very good choice; stable against drive current, temperature, and excellent PSRR, for about £1.

(If you want even cheaper, try three LEDs in series instead (3 x cheap red LEDs will give about 5.5- 5.6v, 3 x cheap green, about 5.9-6.0v). very low noise, but drift with temperature a few mV per degC.)
 
The voltage across both the resistor and the transistor wanders around between 8.1 and 8.15 volts, measured over 20 minutes this morning

Across the transistor it's a stable 2.49V
 
TPA said:
Dan, i've done some experimenting with DC motors etc on an LP12. I originally used the diy motor controller which I got from someone here and used it with several different pulley arrangements and speeds.

Essentially the controller could not compensate for stylus drag and so ultimately was no use. Also subjectively it was dramatically inferior to the Linn Radikal. I also learned that they inject ridiculous amounts of mechanical noise in to the top plate. However I recently installed a new DC set up which works on a similar (ish) principle to the Radikal from Edmond (of Hercules fame) - this was an early prototype unit and uses 4 markers per revolution to track speed as opposed to Linn's single one.

Again the mounting system for the motor was a weak area being directly connected. I changed the motor and also mounted it in a foam pot to reduce resonance. It is not as sophisticated as the Radikal in terms of getting up to speed and stabilising, however once there it now measures very similarly to the Radikal and subjectively sounds very similar. At 45rpm it is almost identical and hard to tell apart.

I have limited electronic expertise (non existent) so my work has mainly been focused on how the motor is mounted physically and this has had considerable influence on the outcomes. I have not gone back to re try the diy dc controller with this new mounting system so must get round to trying it. I'm not familiar with how the PT Too arrangement works but would certainly suggest investigating ways to isolate the motor.
Click to expand...

Hi TPA, is there any chance that you could PM me contact info for Edmund? I'm not on Vinyl engine

thanks

Dan
 
Dan K said:
The voltage across both the resistor and the transistor wanders around between 8.1 and 8.15 volts, measured over 20 minutes this morning

Across the transistor it's a stable 2.49V
Click to expand...

Little point swapping the transistor for a reference IMO.
 
My original controller that I obtained used is slowly dying from too many component changes, so I thought that I would have a go of making a new one. Here is a preview of the layout.

image.php


The board is sized to fit within the inexpensive case used by both Origin Live and Funk Firm. As there is a lot of extra space on this board, I added some of the enhancements recommended earlier in this thread, and have a few questions. I may still want to adjust the layout a bit going forward.

1. R48, C32 are the commutation filter. I wanted to double check that I had this oriented correctly, including the polarity of cap?

2. I added R49 on the positive rail between the reg and bypass cap, based on a recommendation earlier in this thread. I hope this is correct?

3. PR3 is an optional trimpot in series with R45 to help adjust compensation.

4. I'm using a DPDT rotary switch on the front of the case to switch between 33 and 45. Connected to that will be a single dual color LED to indicate speed. I'm wiring the switch to be center NC. It was unclear to me how to connect the switch to flip the LED from + to - supplies as in the original description, so I've set it to run both speeds from +12V, and added an extra filter cap C31. Not the most elegant.

5. Are there any other tweaks/suggestions?
 
Hi,

I've built a GSC controller and it's working well but after all the component changes the board looks very abused. I'd like to have more PCB's made locally in Cape Town to do a rebuild since I'm still getting some speed drift on my current controller and I suspect it's due to the condition of the PCB.

The gerber files are the files the local PCB manufacturer is asking for in order to start production.

Long shot but worth a try.

Thank you.
 
I have one of these PCBs from way back when...

Is the consensus that it is worth building one up, using the DC100 motor kit from Origin Live?

I've read through the thread and is the commutation filter still required? I notice that there was some confusion as to its use and a problem that was eventually tracked down to a worn bearing.

I assume that the BoM on post one is still the BoM to build to?

Ta.
 
It is.
Do use a big cap across the motor terminals, 100-1000uF, as the commutation filter.

Yes, the positive feedback component does make this 'experimental', as made clear from the outset; and for some, perhaps a wide band of combinations of inertial masses, motors and damping (mechanical, cumulative) it cannot be made usefully-stable. *
In which case - as advised above - short-out the R used to 'match' the DC motor resistance, and the circuit behaves exactly as a simple, quiet, discrete & adjustable voltage regulator - which may be all you wanted, for a simple DC motor.


* there was a small effort offline to analyse this - it became very,very messy maths, quite quickly, and none of the quantifiable dimensions would really help the DIYer who just wants 'something better to make at home'. For that it would be better to come up with a more-universal PID DC motor controller...with a servo loop.
 
Allegro make current sensor ICs, which would very simply measure the motor current without adding series resistance. This makes the possibility of making an Arduino based motor controller with software setting of the time constants
 
DC motors are affected by temperature. The no load speed goes up, but the maximum torque goes down. This makes it a bit hit or miss which way turntable motors go as the weather gets warmer or the motor gets hot in use.
Does anybody here know how their motors speed up or slow down with temperature?
 
David, I do know that the speed changes slightly after ten to fifteen minutes or so from cold but I can’t remember which way. To set the speed I let the deck play for a while and then reset the speed. I only have to do this the once and the speed is stable thereafter. It’s just a matter of letting the deck warm up for ten minutes or so at the beginning of a session. No different to when I had a 401 really.
I’m on holiday atm but when I get back I can check both my dc turntables and let you know which way the speed changes during warm up.
 
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