78 RPM on a Thorens TD-125 Mod

[JonL]

I'm busily refurbishing my recently acquired TD-125 Mk.I and got to thinking about the possibility of altering the motor speed control circuitry to change the 16 RPM setting to 78 RPM. It seems like it should be technically possible, though I don't know if it would overtax the motor. A deep search of the Vinyl Engine site revealed detailed instructions for doing this modification, possibly originally provided by Thorens themselves. Here's a link:

http://www.vinylengine.com/phpBB2/viewtopic.php?t=6029

I'm wondering if anyone here has tried this mod, and/or if anyone has enough electrical engineering background to say if this mod puts the motor at risk.

I have very few 78s, but I'd love to be able to play them occasionally and if this mod works I might start to pick up more.

Thanks!

 

[hifi_nut]

You are aware you´ll need a different cartridge / stylus for 78´s, aren´t you?

Which tonearm do you have on your TD-125? can you swap headshell easily?

 

[JonL]

Yes, I am aware that a different stylus will be required. One of the reasons I'm particularly excited about this table is because it will give me the ability to use various cartridges and styli for different circumstances. My primary table (a B&O TX-2 linear tracker) won't allow me to do that. I'd like to get a true mono cartridge as one of the options, and a 78 cart or stylus is definitely on the list.

I'm taking this one step at a time. I'm going to be changing out the electrolytic caps as part of the basic refurbishment, so I may as well do this mod at the same time. The current tonearm is a Thorens TP25 with a removable headshell. Unfortunately headshells for these are rather pricey, so I'll probably stick with one cartridge for now - still won't be able to play 78s yet! I'm considering upgrading the tonearm (SME 3009 possibly) in the future when budget allows. An important feature will be a removable headshell. Or I may decide that I like the Thorens arm, and put the money into headshells instead. That's all months away at best.

 

[eb2jim]

I haven't done this to a Thorens, but I have done simillar mods to belt drive and dd turntables. The machine I am currently using - MCS/Technics 6700 -
is one I did it to, and the mod works perfectly. I found my mod for DD in the April 1982 issue of Popular Electronics.

The theory looks to be the same - you add in resistance to speed up the motor. I stuck a dpdt on the back of the machine, so it plays normally, or 45 becomes 78rpm with the flick of the hidden switch. If I were you, and you were handy enough, then I would do it. I use my 78rpm every few weeks. Since mine uses a standard headshell, I keep a 78 cart on one seated at the back of the deck. Takes a second to swap, and then I spin Charlie Parker, or some Doo Wop. Sounds wonderful.