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In Reply to: RE: Just purchase a Little Bear T10 Pro phono-stage ...... posted by drummerwill on April 29, 2016 at 09:12:59
Hi Drummerwill,
Here is a thread which will get you to sleep on a night when you have insomnia.
The LB is from a circuit standpoint a knock-off of an Ear phono stage which is north of $1K.
Have fun,
Phil
Follow Ups:
Phil, this reminded me of the tubes I had promised. Sorry but it slipped my mind, been pretty preoccupied lately. I have the tubes boxed up, too late to get out today, but should ship tomorrow. When they get a chance to break in, would appreciate a post of your opinion of them. I'm interested in this pre as a stop gap, until I can afford to build the LCR phonostage of my dreams.BTW, more info coming soon on VFD. For some reason, with my quick initial testing, I didn't see a need to up the voltage with frequency. Making a few changes, and will test more in the next couple of days. Will post soon.
twystd
Edits: 04/29/16
Hi Twystd,
Thanks! No rush as my LB is not together at the moment. Currently it has a bogus 34 db RIAA feedback network installed. I had reasonably working 40 dB network installed. The final values were tweaked from what I had calculated. I dismissed that to lack of open loop gain. If that were so the calculated 34 dB values should have worked with minimum tweaking. I then started reading Lipschits' paper and saw the error of my ways. Humbling experience! After more study of Mr. Lipschits' work I'll decide on a new network and fire it up again. Then I'll compare the Chinese 6N2s to the Russian ones. I can also compare some 12AX7s.
On of the "shiny objects" distracting me from the LB is the R-O-K, in particular the Papst motor. I lost the link to the three phase function generator which you are using. Please refresh me on that. I found a two channel DDS function generator which can control the offset of two phases. As you know it is my belief that if you get two phases to the delta connected motor right, Mr. Kirchoff will take care of the third. Even so having all three phases at my disposal has to be a good thing.
Looking forward to your updates to the three phase drive.
Thanks Much,
Phil
you can use that thing to drive a 3-phase tt motor directly?
I am thinking about buying it for use on my workbench; it does much more and takes up less space than my present old technology HP audio signal generator, which does only sine waves, for one thing.
Hi Lew,
The function generator won't drive the motor directly. It will need to be followed by a stereo amp and some transformers to get to ~115 VAC. The one which I found is just two channels but they apparently can be slaved together and the phase difference can be adjusted form ~0 to 360 degrees. It is my belief that If two correct phases can be applied to the Delta connected Pabst motor, Mr. Kirchoff will take care of the third. The generator may displace my Old HP 3311 function generator which is not synthesized. Also since it goes up beyond the AM broadcast band it will be useful to calibrate my '40s vintage RF signal generator and my old AM radios.
Phil
They're cheap enough that one might consider using two of them to derive all 3 phases, with one channel of one unit left to idle. Thanks for your response.
Hi Lew,
That may be possible if the second generator can be synced to the first.
If you are thinking of doing that see if they will email an owners manual first and be sure you can get the three phases 120 degrees apart.
I believe the generator which Twysted is using is an uncased circuit board as opposed to a packaged instrument, but it does all three phases.
Phil
The Lenco has an induction type motor. My other turntables are DDs, each with its own equivalent of a motor controller. Possibly some of those could be improved upon with modern technology, but the electronics are over my head. I would like to work through it just for the learning experience, however.
Hi Lew,
An induction motor can be poly-phase as well as a synchronous motor. With the Lenco there is little incentive to use variable frequency drive as variable speed is pretty much covered. If it is a two or three phase motor there is incentive to get the phases matched as that will give the quietest running. If it is a shaded pole motor it is pretty much what it is. Some shaded pole motors for turntables have fairly sophisticated stators with complicated shading ring arrangements (I'm thinking B&O) which produce a pretty good rotating field and are quiet.
Phil
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