A difficult LP reproduction question

Johnnantais...Thanks for the good writeup about idler wheel turntable technology. The ones that I had, including the ubiquitous Garrards, never worked that well, and were easily surpassed by early belt drive tables like the Empire 598 that I used. Perhaps the belt drive is just harder to screw up, and doesn't require the precision engineering and construction needed to make the idler wheel effective.

The speed changes that you cite as a result of groove modulation is something that I have never actually seen (with LPs) using a strobe on either my belt drive or direct drive tables. Probably it happens more with 78s, and perhaps the phono pickup and downforce play a role. I have long used Shure V15 at about 1 gram.

Johnnatais has answered the variable speed questions about the Lenco.

As for why this is necessary, here is a section from a page on 78 RPM disc playback.

      By no means all 78s were actually recorded at 78 RPM. Even in the late 1920s English Columbia was still using 80 RPM, and prior to about 1921 speeds were widely variable. Some of the audio tracks included in the Music hall section of this site were transferred at speeds as low as 74 RPM, and I have come across records where the speed was as low as 68 or as high as 84 RPM.

As to a turntable capable of coping with these speeds, that is yet another problem. Few turntables have more than a tiny variation (usually 2 or 3 per cent, which is nowhere near enough); but electronically controlled turntables may be modifiable. You need a speed range of 72 to 82 to cover most records. I'm using a Goldring-Lenco turntable which has a mechanical system for continuously varying the speed from about 32 to about 84 RPM, but it's not available any more - indeed I have had mine since 1963

Exactly why I think it's a valid choice for 78 RPM playback and still deliver good performance on modern LP.

Eldartford, the speed variations caused by belt reaction falls beneath the radar, so to speak, happening too fast to be captured by a strobe. This is why certain 'tables measure superbly averaged over a minute, yet don't hold up sonically (audibly) under pressure. But it is audible as confusion, loss of focus, orchestra melding into a single monstrous violin, loss of attack, and so on. And yes, it is far more difficult to design and properly set up an idler wheel drive than a belt drive, which is why belt drives won the war: a matter of price and profit margins. Fortunately there are the Lencos, whose simplicity in execution and design (a closed system of silent high-torque motor, perfect idler wheel and high-mass flywheel/balanced platter in which groove modulations have no effect) makes optimization much easier. The models I recommend were built from the late '60s to the mid-'70s, when many of the problems you cited were identified, understood and eliminated. I had never actually thought about the effect of stylus pressure, and you're right, lower tracking force would go some way towards mitigating this effect in belt drives, but with the Shure stylus profile (which digs deeply) the problem is increased, probably balancing out in the end. Yet one more thing I will have to experiment with!

Another deck, unfortunately more rare (particularly outside UK) that would be excellent for 78rpm replay is the Strathclyde Transcription Developments Ltd STD305D. This, sadly no longer available, deck is belt drive (using a DC motor) and has an electronic speed control unit complete with digital readout which can be varied electronically over quite a wide range. Check it out on my STD site:

http://members.lycos.co.uk/willbewill/

regards
willbewill

Johnnantais...A massive turntable will prevent high frequency speed variations. If you know the stylus drag force variation, and the angular inertia of the platter you can calculate speed variation, even neglecting any tendency of the motor to smooth things out.

I think that the stylus drag probably correlates with "Trackability", a parameter where Shure pickups excel. What do you use nowadays for stylus downforce for 78's? In the old days, when 78's were new, downforce of 5 to 10 grams was used, and this would certainly cause a lot more drag.