SL1200 at 78rpm

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RussellS
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#1 SL1200 at 78rpm

Post by RussellS »

If this is discussed elsewhere, please point me in that direction, otherwise...

I have searched the 'net for ages looking for a mod to the Technics SL1200 to give it 78rpm facility.

I KNOW that Kevin of KABUSA sells the upgrade at $175 (see here:
http://www.kabusa.com/frameset.htm?/
for details)

BUT

I don't want to spend $175 plus shipping and wait weeks for turnaround. Does ANYONE know:
(1) either what mod KABUSA uses, or
(2) any other mod that can be applied by a competent electronics enthusiast?

(Incidentally I have great respect for Kevin, he has helped me with a number of things in the past.)

I promise to share the mods with everyone if you share it with me :D
Last edited by RussellS on Thu Jan 10, 2013 3:18 pm, edited 1 time in total.
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Dave Cawley
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#2

Post by Dave Cawley »

Sorry for the overt plug, but we do one here:

http://www.soundhifi.com/78rpm.html

Thanks Dave
"if it measures well and sounds good, it is good : "if it measures badly and sounds bad it is bad" : "if it measures badly and sounds good, it could be improved" : "if it measures well but sounds bad it is bad"
RussellS
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#3

Post by RussellS »

I'm also looking for 16rpm mods for either the Technics SP10 Mk2 or the SL1200.

Any electronic geniuses out there?
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Dave Cawley
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#4

Post by Dave Cawley »

That can be done, but it's expensive, unless you ditch 33/45 and just have 16 and 78 ?

Dave
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#5

Post by RussellS »

Thanks Dave.

I'll wait a bit and see if anyone else has ideas. No need to reinvent any wheels.

But, I'm not just waiting. As something of an electronics fundi myself, I am looking at the circuits and frequency dividers to see if I can do it using my own initiative. If I succeed, this thread will be the first to know.
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Dave Cawley
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#6

Post by Dave Cawley »

The way to do it, and the way the MK4 works; is to simply switch in new crystals, it's that simple! OK you have to have them made or use a DDS from eBay ?

Don't be afraid that I'm a manufacturer, I'll talk technical to any good person!

Dave
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t-m
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#7

Post by t-m »

Very interesting because i'm looking at this mod myself at the moment to my MKII.

I have what I think is the right crystal so as proof of concept I fitted it to the deck (switching crystals can come later) , but it wasn't happy - the turntable bounced back and forth, strobe not working and the start/stop made no difference. I assume the crystal is not oscillating, anything else needed to make it work?
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#8

Post by Dave Cawley »

No, just change the crystal. Make sure it's a fundamental.

Oh ! the pitch needs to be switched off so the green light lights.

Regards

Dave
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#9

Post by t-m »

Thanks Dave, i'll take another look. Of course I could be overlooking that the new crystal could be duff. Everything went back to working fine once I replaced the original.
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#10

Post by RussellS »

This sounds interesting. Where is the crystal and what frequency does the alternative crystal need to be?
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#11

Post by Dave Cawley »

.
The crystal is obvious when you take a peek and the frequency is 78.26/45 times the frequency of the original one.

Regards

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t-m
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#12

Post by t-m »

RussellS wrote:Where is the crystal?
It's X201 in on the PCB.

The original is 4.19328Mhz. The MK4 is using a 9.844Mhz (for 78rpm) so it must be using that in conjunction with the 33rpm setting. 9.8304Mhz crystal is readily available which is what I was trying and near enough for this experiment.
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#13

Post by RussellS »

Thanks for the detail. But were you able to make it work?
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t-m
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#14

Post by t-m »

Not yet, but I haven't had the chance to investigate further. I will dust of my 'scope later and see what's going on.
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#15

Post by t-m »

Well further investigation reveals a perfect waveform with the original crystal but nothing whatsoever with the new crystal.

So either all my new crystals are faulty or the components in the SL1200's oscillator circuit are not suitable for them. Without a schematic for the AN6680 control chip its the realm of guesswork here.
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