Pheonix Engineering Road Runner

 It’s kind of a moot point, because as we both know, the Phoenix engineering stuff is no longer available. However if you really wanted to acquire same you could probably find it. However, the improvements that I notice are an increase in the definition of individual musical instruments and voices within a complex presentation. In addition there was an improvement in the sense of pace and timing. I would not be without. This was with a Notts Hyperspace at first and now with a highly modified Lenco idler.

Goofy, Your reasoning eludes me.  I assure you that your Thorens is not so speed stable as you would like to think it is now and that you would benefit, or rather your listening experience would benefit, if you were to install a Roadrunner in combination with a Falcon (which ought to have enough power to drive your Thorens motor).  The company did not go away because of financial difficulties.   The products were taken off the market because they represented a small fraction of what Phoenix Engineering does business-wise, and I think the owner just got fed up with solving problems for audiophiles.  The devices themselves are not toys for the anal. 

cleeds, What in your opinion are the "very best" belt drives? For me, the very best belt drive turntables cost at least $25,000, new.  Once you get up to that price point and above, you can buy some nice BD machines.  I have less than that tied up in four DD turntables, total.

Did you mean to imply by your response as regards the Phoenix Engineering products vs other outboard devices for BD turntables (which probably should not be called "controllers", since only the Phoenix and maybe also the new SOTA devices, actually do control speed when it varies over the course of playing an LP), that the PE stuff sounds inferior to a VPI SDS (for one example you chose to mention)?  Those without an external feedback mechanism like the RR still do employ a sort of feedback; you set the speed under a load or no load condition, and the controller relies upon the constancy of the AC frequency to keep the motor operating at a certain speed, always based on the pre-set condition. There's feedback going on, but it's referenced to AC frequency (or I suppose some other internal reference), and it is inflexible for responding to the variation in load due to stylus drag, etc.  Most listeners of my acquaintance do not love the VPI SDS, but I cannot say I have any opinion, since I never heard it.  I own a Walker Audio Motor Controller; it doesn't hold a candle to the PE stuff, which I also own and use to drive my Lenco.  Most reviewers said the WAMC was superior to the SDS.

 I apologize to anyone if I sound vitriolic. But one more thing about belt drive aficionados does irk me. That is, they have no problem claiming they can hear the servomechanism of a direct drive turntable hunting, yet most are eager to acquire a speed controller for their a belt drive turntables, a device that  itself relies upon a feedback mechanism to maintain constant speed. It seems to me you can’t have it both ways. And indeed I have found that such add on devices almost invariably make belt and idler drive turntables sound a lot better.

Nor can I (imagine a return to BD).
Nor do I hear any “veil” coloration or “hunting”, once the plinth is made proper for the device. This is with serviced and calibrated DD tables at quality level DP80 and up. (SP10 Mk3, Kenwood L07D, Victor TT101.)

If you pick up a DD at a garage sale or from your uncle’s closet in unknown condition don’t assume that because it “works” you are getting its best performance. And then don’t think you know how they “all” sound, please.

DP80 also allows speed adjustment but I think it disengages the servo.

 Peter, your comments lead me to believe that you have probably installed your tachometer on a few Denon turntables that you have restored. I am wondering whether you find that your tachometer is in agreement with the built in strobe device on Denon dd turntables. Which is to say, when the strobe image is stable, indicating 33.33 RPM, is the tachometer reading the expected value?
thanks.

The RR is half the battle.  The real benefit is realized when the RR is used in concert with either the Eagle or the Falcon to power the motor.  In that case, the RR feeds back to the power supply and holds speed steady as a rock (once equilibrium is achieved).  The RR alone only monitors platter speed; it does not autocorrect the speed.  If SOTA is going to market the duo, I don't see why you could not use the SOTA product(s) with any 3-phase AC synchronous tt motor.