How to modify a Technics turntable to play 78 rpm

On an SL-D2 could a pot be used in place of the resistor so that you can vary the speed + or - in the 78 rpm position?
I just saw this. Yes, you can. I think I mentioned it before, but one of the ways to narrow down the resistor you might want to use in this method is to use a pot as a rheostat (just two of the three terminals) so you can dial in resistance to speed up stuff. Using a multimeter you figure out the value you need by where 78 hits measuring the pot's resistance. But, if you just used the pot, the value of the pot would be the range of resistance you could dial in. I did find I could dial in some speedy stuff, well beyond 78. By removing the resistor off the board and subbing in a pot it messes the speed up all the way - slow like 16rpm or nutso fast. Seeing as the range of magic is in the 22k-56k area, a 100k pot might be all you would want. I have thought instead of a dpdt switch using a mono 1/8th jack to plug and unplug an external pot would be another method of modding speed. That might be fun for old 78s and Edison discs which weren't exactly 78 but sometimes 80 or around there. Edison discs need you to mod the wiring on the cart too I recall, like hotwiring (using both pos ) it or something.
 
If I'm not mistaken, for vertically cut records like Pathe and Edison DDs, you wire one channel out of phase at the cartridge (just reverse the + and - wires on either the left or right).
 
I did the mod on a 1800 mk1. I also had to solder onto R10, but I used a 100K pot and a switch. Put both up through the case for easy access on the top. Disassembly was a little tricky and requires persevering. It seems like a PITA until you get it apart and back together once and then it seems easy once you've done it. Don't be squeemish about taking stuff apart. I also use a shure 44 cartridge with a 78 needle (forget which one). Results are excellent with some fiddling. While it's apart spray contact cleaner in the factory pots and lube the spindle.
 
I did the mod on a 1800 mk1. I also had to solder onto R10, but I used a 100K pot and a switch. Put both up through the case for easy access on the top. Disassembly was a little tricky and requires persevering. It seems like a PITA until you get it apart and back together once and then it seems easy once you've done it. Don't be squeemish about taking stuff apart. I also use a shure 44 cartridge with a 78 needle (forget which one). Results are excellent with some fiddling. While it's apart spray contact cleaner in the factory pots and lube the spindle.


Cool! I did the pot version mod to a Pioneer belt drive. It's like the pitch pot really but your range is pretty wild. I like using Shure carts. There are lots of 78 needles that will fit in most of them on eBay and they're cheap. I had great results using a Realistic Shure R25 cart which was aimed at changers with heavier tracking range. I paid $20 for that and found a real Shure 78 needle for $5.
 
The 100K pot probably isn't the most elegant solution but it got the job done and makes it all easy to adjust. I put 6 inches of wire from where r10 is to the pot & switch combo so I could mount it anywhere (I put them over near the on/off switch). It made it convenient and saved some time. I soldered to the bottom side of R10. I also set the 100K pot at 56K before I put it back together so I'd be close when I put the 60hz strobe disc (just googled it and printed out a paper one and used it with the flourescent lights we already had in our kitchen). I've still got to sit down and nerd out and figure out how to match the headshell/cartridge/needle weights between my 33/45 setup and my 78 setup so I don't need to rebalance but it's not far off so not too much for weight should be needed. I do have to adjust the skate when I go from the 33s to 78s.
 
The rebalancing is easy enough to do, but that is why I started using similar carts and tack-on 2gm weights. If I track my main headhsell/cart set up at 2gms, and have a sticky 2gm weight on my 78 headshell/cart, it ups the tracking to a more 78 ready 4gms. No spinning the counterweight after that. Not better or worse either method, but I like it.
 
Can you show pics or a drawing of how you wired up the sl-1800 please, I just tore one down today to clean so while it is apart I might as well mod it.
 
For any body with a Philips GA 212... think 312 also... just put the belt over the outside diameter of the motor pulley and it rotates at 78 rpm. Use a strobe disc if not sure but I know it works. Select 33 when you do it.
 
For any body with a Philips GA 212... think 312 also... just put the belt over the outside diameter of the motor pulley and it rotates at 78 rpm. Use a strobe disc if not sure but I know it works. Select 33 when you do it.
That is a good tip. These are great machines, and like the Technics the speed control is electronic, so you can do the same kind of mod to these. There was a guy doing that on ebay for a while, and like people using the mod I put up here way back, making some good gas money on ebay. There is also the sleeper Philips Norelco GA-202 - precursor to the famous 212 - that had three speeds.
 
That is a good tip. These are great machines, and like the Technics the speed control is electronic, so you can do the same kind of mod to these. There was a guy doing that on ebay for a while, and like people using the mod I put up here way back, making some good gas money on ebay. There is also the sleeper Philips Norelco GA-202 - precursor to the famous 212 - that had three speeds.

Yes... on the 212, if it's adjusted for 33 it is correct for 78 with the belt over the rim of the pulley. The floating suspension was a great selling point, that and the back lighted green touch controls.
 
Just a quick update to let you know that I FINALLY got hold of a clean Techinics SL-B5 belt drive stacker turntable. I've wanted one for a while, and the closest I got was missing out on one at an estate sale but got to buy the owners manual. A few years later one shows up at the local thrift - with the stacking spindle! At any rate, the mod was simple enough, and I have a belt drive 3 speed stacker with a 10" set down option.

The mod is similar, but the speed set up is a bit different vs direct drives. The SL-B3 schematic is on vinyl engine and very much the same. A single resistor is on a sub-board inside with 2 trim pots. The trim pots feed into the motor via a yellow wire so I soldered a tap there, and the 45 circuit feeds into those via the sub-board with the external pitch and speed selector, so I tapped into the 45 there with my second wire for the regular dpdt switch method. Using a 1k pot I dialed in 78 and hit it about 500 ohms, so I used a 470 ohm resistor from rat shack. That was it, and so close I barely have to adjust when switching from 45 to 78, and the son of a gun is quiet and stable as anything could be. I'm a fan of the mini slide switch underneath these days, so with the fiberboard bottom it's a cinch. Done!

Have at 'em, ladies and gents.
 
Hello Guy's can anyone help me out doing the trick of making my SL1700MK2 suitable for playing 78rpm.!
Please give me a clear way to adjust this circuit. I would be much gratefull if I got the golden tip.
(I've uploaded the circuits so you can point me out easely)

Thanks!

Robbert (Netherlands)
 

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Hello Guy's can anyone help me out doing the trick of making my SL1700MK2 suitable for playing 78rpm.!
Please give me a clear way to adjust this circuit. I would be much gratefull if I got the golden tip.
(I've uploaded the circuits so you can point me out easely)

Thanks!

Robbert (Netherlands)


Been there, done that for the SL1300MK2 family! See http://audiokarma.org/forums/index.php?threads/sl-1300-mk2-78-rpm-mod.647136/ Unfortunately, it doesn't look like I ever posted my complete write up of the full mod but the thread does show how to implement 78 mode using a simple switch. The SL1300MK2 uses the DN860 chip that supports 33, 45 and 78 (and was used on the SP10 MKIII, a somewhat rare beast for all three speeds.)

Unfortunately, I do not believe the chip set AN6680 on the SL1700MK2 has an unused 78 mode so there is no easy solution. Since this is a phase locked loop version there is no simple resistor mod to do this like there is on the SL1300 (non MK2). As mentioned the SL1300 MK2 has a chip that does support 78, just the needed switch was not added.

However one could do something like program an arduino or other microcontroller to do the job of the AN6680 and generate clock signals appropriate for 78 but don't know how well this will work for this model.

To make a long story short, I am not aware of a simple way to do this with this model.
 
TOUPS-INFO Thank you very much for responding on my question and giving me a direction to search for a sollution!!
 
Has anyone performed this modification on a Technics SL-1500?
My main board is SFDP 130-1

I just purchased an Ortofon 2M 78 and have the parts to do the mod... Looking forward to hearing some 100+ year old music...
 
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Does anyone know if this will work with the SL-3350?
Or which of the above models discussed are similar?
Thanks
 
Does anyone know if this will work with the SL-3350?
Or which of the above models discussed are similar?
Thanks
The 3350 is in the vein of the 1950. I'd have to double check but I'm thinking the 56k tap in will work.
 
SL-1200 MK2 mod possibilities

I downloaded the service manual and schematics for the Technics SL-1200 MK2 and have been staring at the motor control logic diagrams for the past couple of days. This TT uses a Panasonic AN6680 (IC201) chip to handle the phased locked loop for control of the rotational speed of TT. The speed is selected by grounding one of two pins on this chip. That in turn sets how fast the table spins based on the generated frequency pulse rate and the output of the position detection coil. The actual physical control of the speed of the TT is handled by the AN6675 (IC101) chip, but the IC201 chip tell that chip how fast to go. Unless the IC201 chip has some un-described pins that can be used set the 78 RPM speed, I do not see any way to modify the logic with the IC201 without a chip change. There apparently is no magic changing of a resistor that can effect a primary speed change to anything other than 33 or 45 RPMs as existed on the Technics SL-D2. It would be nice to have more information about the chips used in this TT.

That being said, there may be a way to do this with the pitch control logic associated with the AN6682 (IC301) chip and the various related resistors. The question is whether or not the pitch control login has enough range to made the TT spin at or near 78 RPM.

We shall continue out investigations... :music:

Bill

For this one, you spend your money, send it to KAB and get it done correctly. And it is 3 speed when done.
 
BACK FROM THE DEAD!!!!

So, has anyone thought of approaching this through the pitch slider on a 1200mkii? Maybe a small circuit attached to a mini toggle that allows the slider to use its entire throw to achieve the desired speed?
 
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