Vintage DD turntables. Are we living dangerously?

Richard

I believe the timeline shoots four pulses per revolution so it will be every 90 degrees - however if there is any deviation what so ever in speed in between the pulses it will be impossible for the dot to appear at the exact same spot over and over and over again.

The Roadrunner that I install in the DP80/DN308 machines use a magnet thats mounted on the perimeter of the platter, it passes over a sensor thats mounted to the plinth, a very precise oscillator/clock times the time it takes for the magnet to reappear at the sensor then calculates the precise PRM that's displayed.   

The method that the electronic one that Mikey use I believe you replay a record with a 3150Hz tone recorded into it the the reproduced signal is listened to with a microphone and how accurate the 3150Hz tone is reproduced makes for the speed accuracy calculation - this probably is the most accurate method IMO if the 3150hz test tone in the record is a steady 3150Hz tone.

Halcro I'll try to do a video of the DP80 soon - I only have a one tonearm setup.  Once I get another DN308 complete Ill do one of that one too, this possibly I could do with two arms, I still have two donors ready to be assembled - currently I'm sold out :-) these latest two will make a total of 8 units of this fabulous machines rebuilt/retrofitted. 

Good Listening

Peter

Ok Videos uploaded on Facebook on our home page PBN Audio Shows the GrooveMaster Vintage Direct DP80 with a SME 310 carrying a Ortofon MC Anna VTF 2.6 Gm playing an entire album side in this case 17 minutes and 28 seconds.  The Timeline dot is 26 feet away from the turntable center - in the 17minutes and 28 seconds the dot moves about 3 inches forward , progressively , probably indicative of the 33.334 speed indicated by the Roadrunner Tachometer.  Don't know how to calculate this but I'm certainly sure it is well within specs :-)

Once I get a DN308 online again Ill do the same experiment

Good Listening 

Peter   

Peter, I use the Roadrunner/Eagle to control my Lenco.  It is comforting to see the RR display 33.333, every once in a while.  In practice, the speed takes about 5 minutes to stabilize usually around 33.3, then 33.33, then flirting with 33.333, maybe after 10 minutes in.  I think the bearing lubricant may be warming up during this early time.  But I don't understand why you would want to "control" the Denon DP80 or the DN308 motor with the RR feeding back to the Eagle.  Wouldn't you want to leave that in the hands of the built-in feedback mechanism which is making constant readings (not just once per revolution) off the tape that is attached to the inner circumference of the platter? You could certainly use the RR for a numerical readout of speed without having it control the motor; maybe that is what you are doing.  (I don't think anyone would hear a problem with 33.334 vs 33.333.  I don't even hear any significant difference between 33.3XX and 33.333. (Talking with respect to the Lenco.)

Chakster, I am of the belief that a cylindrical plinth that has a diameter minimally greater than that of the platter is optimal, regardless of drive system.  I think our conventional rectangular plinths with a large surface area beyond the platter area add a subtle coloration that is appreciated when one compares the sound to the cylindrical type, which sounds most "open" to me, for want of better words to describe it.  But I do not associate OMA with originating the idea, at all.  Nottingham and Verdier and also Galibier, Teres, Redpoint, etc, beat them to it.

The OMA copy of the Verdier idea, is, like the Verdier, a can of worms.  Center of gravity is way way too high, for one thing.  Springy footers plus rotating mass raised high above = instability.  IMO, of course.

Lewm

The road runner is only for display - it has no control purpose - I opted for the inclusion the Roadrunner in the 308 because it has no strobe, keeping the DP80 in the Pro line I included it in that too, eliminating the strobe.

Good Listening

Peter