Pioneer PL-400X turntable

[ppppenguin]

I've been sorting out stuff in the loft and found a Pioneer PL-400X turntable. Not sure what cartridge. Despite being sat around for many years I plugged it in and it just worked. Typical Pioneer. I'll probably hang on to it as a spare turntable.

https://www.vinylengine.com/library/pion...-400.shtml

Question: Has anyone tried to make one of these work at 78 and/or varispeed? As a direct drive turntable it should be possible by tinkering with the electronics. This isn't an urgent requirement but could be useful one day.

[joebog1]

I have never even had much success repairing direct drive turntables, let alone hot rodding one.
They are fine if they dont plug ( and ALL of them did to some degree ) when they break, skip em.

Just my take on the subject.

Joe

[ppppenguin]

I've downloaded the service manual. This block diagram is the nearest thing to a schematic. If we ignore the strobe then the output of the PD1003 needs to be replaced by a variable frequency signal. Not sure what the switched resistor on pin 11 of the PA2004 is doing. Possibly some kind of range control for the F/V converter or, less likely, setting a loop time constant.

I'm making the assumption that the motor and its 3 phase driver have enough oomph to spin the platter at 78rpm without getting hot and bothered.

[radioman]

I got hold of a Sony direct-drive turntable and as an experiment wired in a pot. to the speed control circuit - had it going at 90rpm for a while !
It seemed to work OK but in the end I didn't permanently modify it.

Andy

[ppppenguin]

I found a full schematic though the quality is poor. Looks like the switched resistors for 33/45 are really preset pots to set speed. So it may be as simple as changing the resistor values.

[Mark Hennessy]

No, can't be right.

If that were the case, why on earth did they bother to fit the XTAL?

Indeed, the PD1003 also has provision for an RC oscillator, which is not used in this deck.

I'm pretty sure the presets are to set the loop conditions for each speed. Sadly, the adjustment of these are not explained in the service manual. It references another document (ART-467), which I haven't turned up yet.

However, this gives a lot of extra detail about the chipset. Jump to page 13.

http://www.cieri.net/Documenti/Altri%20m...~1980).pdf

On page 30 they give some general information about adjusting the pre-sets when in using the chipset in an XTAL setup.

I've also included a copy of the service manual from Elekrotanya which gives a better quality copy of the schematic.

To make it run at 78 RPM, I think you'd need to use the RC oscillator in PD1003, and ground pin 11 (probably). At the same time, you'd probably need to switch in another resistor in place of the two pre-sets. And that's assuming the power IC is happy working at the higher speeds. Or, assuming you want to digitise the record rather than just play it for fun, speed correction software. Audacity lets you do it:

https://manual.audacityteam.org/man/reco...cords.html

[Murphyv310]

Used to do these back in the day. I'm sure the pots are for speed set up and I do believe they will run fine on 78. Remember the increase in load is not great unless you decide you want a big horn and with an old fashioned soundbox.

[ppppenguin]

On p8 of the service manual kindly shown by Mark it clearly says: " VR1 Speed adj 33rpm, VR2 Speed adj 45rpm" These are the switched resistors connected to pin 11 of the PA2004. I don't think that leaves too much doubt. Might need to change the oscillator frequency too, but for a first attempt I think I'd just play with those resistors.

My unit is a PL-400X. Can anyone spot any differences between that and the PL-400?

[Mark Hennessy]

You've forgotten how PLLs work then?

The manual refers you to ART-467 for instructions to about adjusting those presets. In lieu of ART-467, refer to page 30 of the first link I provided, where they discuss adjusting those controls to ensure that the PLL is in the centre of its lock range.

Note pin 13: is grounded when in 33 RPM and open when in 45 RPM - this changes the divider ratio in the PLL.

Of course, if you adjust the pre-sets such that the PLL is no longer locked, then that'll change the speed!

[Murphyv310]

I've not forgotten how a PLL operates. All I can remember is that the pots were designated 33 & 45 speed. So if these are to lock the PLL adjustment would put it out of lock so no speed accuracy and hence drift, something I never came across once set up!