Audio Projects Blog & AC Motor Controller

[SoundBound]

I have enjoyed reading the threads and seeing member's contributions to this forum. Picked up some good information too. Thanks to all who posted, maybe now I can add something.

I am fairly active in the audio hobby, not only listening but also refurbishing, modifying and building equipment. I have a few projects currently on the active list. Right now I am designing / building an AC synchronous motor controller. Wanted a very flexible, precise design and did not want to pay the price for the higher end units. Also wanted to have some fun.

Friends and family encouraged me to start a blog and I thought kicking it off about my audio hobby would be the logical place to start. It currently covers this project and in future I may also add comments on some of my past projects too. If anyone is interested in following my adventures I am including a link to my blog.

So, if you decide to look in or to follow my blog, welcome aboard.

By the way, if anyone is interested in this project, when it is completed, let me know.

SoundBound

Link:

Audio This 'n Audio That

[vdi_nenna]

Looks very interesting. The block diagram makes it look easy, but in practice, it's a lot of work. Nice job.

I'm in the process of building a TT with a stepping motor as describes by Charles Altmann on his web page, but a setup like this is self-contained.

Do you have any plans on making boards when complete?

Thanks,

Vince

[SoundBound]

Thanks Vince;
I think most of the hard work is behind me, except for the final enclosure, I think now it will just be testing, maybe some tweeking. The software is complete as a first version, I may want to add the odd feature otherwise it does what I want it to do.

I will for sure have more boards than I can use, and if I get inquires for them, maybe I can run a batch for those interested. I want to test it with steppers too, for low voltage steppers, the output transformers will not be needed (for steppers up to 24V or so, maybe more a different op-amp and increased power supply components).

If you want you can send me an email address, or follow the blog, and when things progress to a decent point, hopefully soon, I can let you know how the boards are.

[SoundBound]

Just a correction to my previous comment:

(for steppers up to 24V or so, maybe more a different op-amp and increased power supply components).

what I meant to say is that the board should work for motors up to 24V as is, for motors requiring higher voltage, a different power op-amp can be used but may also need some components upgraded for higher values and voltage ratings. I have already sourced an alternative op-amp if the unit has to drive more than +&- 18V.

[vdi_nenna]

I have 4 stepper motors, 7.5 degree type, 4.6 a/c.

I'll join the blog. Looking forward to hearing more.

Regards

Vince

[rcthweatt]

Currently using a free program, Cognaxon 2 channel frequency generator, on a Windows laptop, output via headphone jack to a T-amp, from there to two 20:1 transformers via 4 1 ohm resistors(to keep the amp from overheating). L is at 0 degrees, R at 90.08; so 1.5 degrees phase shift steps may prove limiting.
Motor is permanent magnet synchronous, Berger Lahr,out of VPI Mk III(600 rpm).

[SoundBound]

Originally Posted by rcthweatt

Currently using a free program, Cognaxon 2 channel frequency generator, on a Windows laptop, output via headphone jack to a T-amp, from there to two 20:1 transformers via 4 1 ohm resistors(to keep the amp from overheating). L is at 0 degrees, R at 90.08; so 1.5 degrees phase shift steps may prove limiting.
Motor is permanent magnet synchronous, Berger Lahr,out of VPI Mk III(600 rpm).

The Cognaxon software looks pretty good and your approach works great if you're ok with running a laptop. Nice that their software is free. When I was experimenting with the phase shift on the second sine wave it was quite hard to detect strong changes on the motor with even greater phase differences than 1.4 degrees, so I decided to leave it alone at that stepping range. I have already thought about the software changes I could make to decrease the phase step size, but unless I see a strong need for it will not implement it. It would require some code changes.

So I will keep an eye on it, and if it proves worthwhile maybe add that change in a future firmware.

[SoundBound]

Originally Posted by rcthweatt

Currently using a free program, Cognaxon 2 channel frequency generator, on a Windows laptop, output via headphone jack to a T-amp, from there to two 20:1 transformers via 4 1 ohm resistors(to keep the amp from overheating). L is at 0 degrees, R at 90.08; so 1.5 degrees phase shift steps may prove limiting.
Motor is permanent magnet synchronous, Berger Lahr,out of VPI Mk III(600 rpm).

By the way, what was your method to determine that 90.08 degrees was the correct setting? Was there a way you could measure the performance or was it by some other method? .08 degrees is quite small.

[rcthweatt]

By felt vibration, not at the motor itself, but at the tip of an idler/tensioner on the belt. The tensioner is set up to be sensitive-a compliant extension spring, anchored close to the idler arm pivot, resulting in increased arm movement for spring displacement. The spring is damped-it rests in a trough filled with(currently) 2000 cSt silicone fluid. There is a lot of swing on start up, no visible motion after, typically. The felt vibration is quite low, but differences in small changes can be felt(I think-fooling oneself is always possible! gonna have to come up with a good vibrometer eventually). I had similar experience with Audacity, where you have to clickn'drag at very high magnification. With Cognaxon, you enter a number and "Enter"(this will 'bong' out to your motor if you're connected). No way to save that I've seen, but see it as provisional-have two Ampex hysteresis motors I intend to try, but I have to build a new TT to fit them. if they work out, will look for something permanent.
The idea was to combine the virtues of belt and idler drive. By being very careful with spring tension adjustment, I can achieve high frequency 'bloom' with greater drive and 'punch' than the belt alone. The idea came from idler/tensioners on the fan belts on large diesel engines! There is one production TT with an idler(magnetic tape, DC motor), Artemis Labs SA-1, which I ran across after.
The motor, platter, and belt are all from VPI Mk III.

[rcthweatt]

Postscript-the differences in sound, I have recently found, are quite marked-more than the vibration differences. I once ran across a description of the effects of a VTA adjustment as producing a markedly 'taller' image. This is, in my experience, quite accurate, and can be consistently heard-the individual images get bigger,and the increase in their perceived height is the most striking effect. This actually makes sense if 'correct' VTA produces the highest output. At any rate, I found that varying phase between 90.07, 90.08,and 90.09, had a very marked effect on the height of the images- that is, they were very noticeably'smaller' at 90.07 and 90.09 than at 90.08, as if a VTA change had been made. I do know how this sounds....