Sander's Speed Controller

[Southeast]

If you would be so kind as to add me to the PCB list too? I need two boards (because I am Ham Fisted and I don't want to take any chances here!).
Thanks to everyone concerned in this project. It looks like my Lenco build will come out of the starting gate (assuming I can get the controller built) up there among the finest turntables in the world.

[YHF]

Hello from Berlin -
Nigel, what a great work! Can you please put me down for 2 PCB's?
Thank you!
Jens

[ropie]

Hi Nigel,

A couple of questions about implementation of the speed controller.  I have had a look back through some of the thread but I couldn't find the answers I need:

What's the physical size of the PCB?

Is it possible to have the transformers and PCB in separate cases?

Sorry if you've already been asked those questions.

[nigel]

Hi Piero  

What's the physical size of the PCB?

As supplied : 120 x 120mm

When split -

Amplifier/PSU: 120 x 85mm
Oscillator     : 120 x 35mm

Is it possible to have the transformers and PCB in separate cases?

Hmm .. depends what you mean, exactly. I think we have discussed the possibility of putting the oscillator PCB (which also carries all the controls) in a separate case from the rest of it, since it is all low voltage/low current, safe and doesn't generate any heat. It could also be made very small, to tuck underneath a plinth, or incorporated into a plinth. This would also have the advantage of completely separating the oscillator from all the heat-generating components (chip amps, transformers), which will improve stability and settling time. Then, the transformers, amplifier PCB and heatsink could be in a seperate, larger box, out of sight and away from the cartridge, phono stage, etc.

The only thing you would have to be careful of, is that the interconnecting cable could not become disconnected in use, as the sudden loss of signal to the amplifiers can destroy them, in certain circumstances (as Gene often says - "don't ask me how I know"    )

So, if you're thinking of a two-box solution, I think that's the way to go and actually, it gives you a number of advantages.

However, if you literally mean just the transformers in a separate box, then I'm not so sure that's a good idea, as then you have some quite high-current wiring between the two boxes. Whilst not dangerous (it would still be low voltage^*), it may have some effect on stability of the amplifiers which again could cause (unwanted) oscillation and possible failure. I don't in any way know that it's a problem, but I wouldn't want to say it's OK without trying it.

Does that help? What did you have in mind?  

(^*Note: I should just qualify that statement - depending on your choice of supply transformer, the voltage on the secondary side might be just high enough to be regarded as "hazardous", at least under EU law)

[ropie]

Hi Nigel,

Thanks for the detailed reply!  Yes, it helps.

I was thinking of incorporating the speed controller PCB(s) in the box with my new phono pre amp, which I'm currently putting together.  You mention that the oscillator PCB can be in a separate box, and this may be good enough, so I may leave space in the preamp box for this.  Your safety concerns have been noted so I'll keep the transformers boxed with the PSU PCB

[Chris65]

Hi Piero,

Interesting idea. In addition to what Nigel mentions, the PSU pcb means a heatsink for the chip-amps, so creating something that may become too large & difficult.
Having the oscillator pcb in a case with a phono pre-amp would take less space, especially if it's only 33/45 - one selector (toggle) switch & two speed control pots (voltage selection can be on the pcb). Only possible issue is then 2 power supplies - one for the controller (supply/return) & one for the pre-amp. Would that be a cause of noise?

I've already been thinking ahead since the test build & am contemplating something along these lines - I like the look of Neutrik Powercon connectors & they may be suitable for the connection between the PSU & Oscillator, with a good locking feature.
But are they too much? Maybe a locking XLR type would be suitable.

[audioblazer]

Audioblazer put me for 2 instead of 1 .
thanks

[ropie]

Having the oscillator pcb in a case with a phono pre-amp would take less space, especially if it's only 33/45 - one selector (toggle) switch & two speed control pots (voltage selection can be on the pcb)

Thanks Chris - this is how I'll do it.  My preamp case will actually be the same size and overall shape as my Lenco, not only to match aesthetically but also to allow for future expansion, so there will be plenty of room in there

Only possible issue is then 2 power supplies - one for the controller (supply/return) & one for the pre-amp. Would that be a cause of noise?

I'm not sure but I'll have mine in separate boxes (the preamp PSU is already made and housed in an alloy case).

I've already been thinking ahead since the test build & am contemplating something along these lines - I like the look of Neutrik Powercon connectors & they may be suitable for the connection between the PSU & Oscillator, with a good locking feature.
But are they too much? Maybe a locking XLR type would be suitable.

I always use locking Neutrik Speakon plugs for my low voltage power connections.  For higher voltage I use captive leads when possible.

[ecosprog]

I always use locking Neutrik Speakon plugs for my low voltage power connections.  For higher voltage I use captive leads when possible.

Neutrik also do power connectors. The ones I have are rated for 240V/16A. They are similar to the speakon connectors just a bit beefier. I am thinking of using them instead of IEC connector because they lock in place, and look a bit sexier (if that´s possible for a connector).

[carolus]

..... List updated please check your entry and location.....

Done, OK .

[nigel]

I always use locking Neutrik Speakon plugs for my low voltage power connections

Those would be fine for connection between the oscillator and amplifier PCBs, or a locking XLR would be fine also. Just about anything, really, as long as it can't accidentally disconnect. You need just three connections - Ground, signal and power, the latter being 13.8V at about 20mA.

I wouldn't have the amplifier board & transformers in the same casing as the preamp supply (or the same casing as the preamp, for that matter), but aside from that I think it should be fine.

I don't think there's any problem with having the oscillator board in the same casing as the preamp, because the signal voltages on the oscillator are really very low - a 50Hz (clean) sinewave at a couple of volts. Bearing in mind that your cartridge & cartridge wiring are only a few inches away from wiring carrying full (dirty) AC line voltage and the motor, it's a non-issue in comparison.

[willbewill]

Audioblazer put me for 2 instead of 1 .
thanks

Done

[doctorhugocat]

List updated please check your entry and location.

Many thanks, all correct for me!!
Bruce

[Pete_fi]

Hi, first post here! Please one board for me.

I've tried to get another speed controller schematic (similar than found from this thread, the Francois 110V version) working but not getting enough speed with my PTP II.

Best regards,
Pete

[nigel]

Sorry folks, for the lack of news. Bear with me, impossible workload at the moment.

That said, I thought I had another nightmare on my hands and will just share it with you briefly ...

Since the mini-meet at Piero's a few weeks back, my prototype controller has been with Colin. All was going well, until I got this PM from Colin (I don't think he'll mind me quoting it here) -

I have been using the speed controller for a couple of weeks with no problem, but on Sunday I switched it on and after a second or two the led went out and there is no output.  The only thing I can think of as different was that the Lenco was left in the on position from the previous session - I had up till then only turned the controller on when the Lenco switch was in the off position.  This time I did not notice it was left on.  

When using the controller at Piero's his Lenco was always left on and actually switched on/off by the controller, so I don't think it should have been a problem .....

 

OH no! Another dead controller!! Immediately I thought that we had another case of exploding chip amps and was almost ready to abandon the project.

Thankfully, that isn't what happened. Colin returned the controller to me and in fact all that had happened, was that the fuses on the supply transformer secondary had blown. I fitted new fuses and it is now working perfectly again.

So, why did the fuses blow? Well, I think it's due to the large inrush(surge) current which will be drawn when the unit is powered up with a turntable connected and switched on. That's not to say that you shouldn't do that - it's bound to happen occasionally, even if unintentionally. So, the fuses I have used are not adequately rated for the job.

Fuses come in various "flavours" - quick blow, semi-delay, anti-surge, etc, etc and I will need to either change to a fuse with a longer delay, or else increase the current rating a little. This is a pretty trivial detail, I will look into it.

(The reason that Colin saw a one second delay, before the LED went out, is because the amplifiers are held in mute for about a second after power-up, by the way.)

Meanwhile, there is ONE final detail that I need to resolve, before I can start taking PCB orders and I will need some input from all of you. No time to write about it now, though. I'll get back to you ....