Thorens TD125: 78 rpm conversion

[fiddlefye]

Found this and wonder if anyone has tried it? I'm never going to play anything at 16 rpm, but 78 would be really useful. It applies to the MkI which is what I have.

THORENS TECHNICAL BULLETIN # 4 (dated 5/19/69)
SUBJECT: TD 125 CONVERSION TO 78 RPM
The conversion of the THORENS TD 125 Electronic Turntable to 78 rpm may be accomplished two ways:
1. Direct replacement of the16 rpm speed with 78 rpm, whereby the speed selector sequence becomes: 78, 33 1/3, 45.
2. Interchange of speeds, whereby the 45 rpm speed position becomes 78 rpm and 33 1/3 and 45 rpm are moved to the left, eliminating the 16 rpm speed. The speed selector sequence then becomes: 33 1/3, 45, 78.
NOTE: The introduction of the 78 rpm speed will result in an alteration of the phase relationship for the motor. Erratic starting may occur. Always start the turntable at the 45 rpm speed then switch the speed selector to 78 rpm.
PARTS REQUIRED:
2 0.033 ufd/200v
1 50 ufd/70v
METHOD ONE (1):
CHANGE: PART NO. FROM TO
C 4 250 ufd 50 ufd
C 8 0.2 ufd 0.033 ufd
C 11 0.2 ufd 0.033 ufd
METHOD TWO (2):
CHANGE: PART NO. FROM TO
C 4 250 ufd 100 ufd
C 5 100 ufd 75 ufd
C 6 75 ufd *50 ufd
C 8 0.2 ufd 0.1 ufd
C 9 0.1 ufd 0.075 ufd
C 10 0.075 ufd *0.033 ufd
C 11 0.2 ufd 0.1 ufd
C 12 0.1 ufd 0.075 ufd
C 13 0.075 ufd *0.033 ufd
* Additional parts
ALIGNMENT:
FOR METHOD ONE (1):
a. Connect an AC-VTVM, on 30 v scale, to the Blue and Black motor connections on the printed circuit board. Adjust A-16 for maximum reading, approximately 12 VAC.
b. Set the fine speed control to the mid-position, place a 78 rpm stroboscope disc on the turntable and adjust F-16 for a stationary stroboscope pattern.
FOR METHOD TWO (2):
a. Connect an AC-VTVM, on 30 v scale, to the Blue and Black motor connections on the printed circuit board. Adjust as follows:
A 45 Maximum, approximately 12 VAC.
A 33 8 VAC.
A 16 5 VAC.
b. Set the fine speed control to the mid-position and place a 78 rpm stroboscope disc on the turntable. Adjust as follows:
F 45 Stationary strobe pattern at 78 rpm on strobe disc.
F 33 Stationary strobe pattern (lower) in illuminated turntable viewer.
F 16 Stationary strobe pattern (upper) in illuminated turntable viewer.
NOTE: The stroboscope pattern is best viewed under fluorescent light. The adjustments should be made with a non-metalic alignment tool such as a nylon TV alignment screw driver.

 

[ddarch]

Yes, have done that. Motor on the unit we tried was a tad noisier at the 78rpm speed. However, the choice of a useless 16rpm vs a slightly noisy 78 was easy one to make.

 

[fiddlefye]

Yes, have done that. Motor on the unit we tried was a tad noisier at the 78rpm speed. However, the choice of a useless 16rpm vs a slightly noisy 78 was easy one to make.

So it went relatively painlessly then? Good to know and thanks for posting. If it doesn't stress the motor too much then it is well worthwhile. I read some notes about possible phase issues starting the motor. Did you encounter this when you did it? You're absolutely right about 16 rpm being useless. I don't have any transcription recordings and am not into "talking books" so I've never used it, not even once. A bit of motor noise shouldn't be audible when you're actually playing a record, so as long as that doesn't indicate overstressing it is all good.

 

[ddarch]

Our theory was the noise would eventually dissipate as it run-in. Unfortunately, it was sold to someone who wanted to play 78s but so far hasn't done so extensively, so we don't know.

 

[KentTeffeteller]

Transcriptions did not use 16 2/3 RPM. Never. Always 33 1/3 RPM. There have been not one broadcast table ever made with a 16 2/3 RPM speed except for the Thorens TD 124 line.

 

[fiddlefye]

Transcriptions did not use 16 2/3 RPM. Never. Always 33 1/3 RPM. There have been not one broadcast table ever made with a 16 2/3 RPM speed except for the Thorens TD 124 line.

Ah, so it was just the "talking book" recordings then. I've only recall seeing the 16 rpm setting on European tables, so maybe it was more popular there? So there wasn't an equivalent to the 1 7/8ths RTR setting for such uses.

 

[fiddlefye]

Our theory was the noise would eventually dissipate as it run-in. Unfortunately, it was sold to someone who wanted to play 78s but so far hasn't done so extensively, so we don't know.

No problem with starting then? In that Thorens list it mentioned having to always start in the 45 rpm setting and then switching to the desired speed. Did you find that was necessary?

So glad you've actually done this and it was successful. If I weren't needing an extensive rebuild of the electronics I might not bother, but given I do play and transcribe 78s from time to time it would save me needing a second table in the set-up and so worth considering.

 

[Charlie S]

Yes, but ...

When the TD125 was designed there were some extra-long-play classical music albums available at the 16rpm speed, notably on the Vox label. I suspect that was the reason for including this speed, not for talking book records. Poor fidelity soon killed that idea.

I did this mod years ago on my TD125 (Mk I), substituting the 78rpm parts for the 16rpm ones. It works but won't start up at 78 without either a push or first running at 45.

When running at 78 the motor emits a fairly loud hum/buzz acoustical noise which is mildly distracting. There is less torque at this speed and the table slows down when using a record cleaning brush. So far no damage, but I don't use the 78 speed much. I wouldn't recommend the TD-125 for heavy duty 78rpm use.

A friend who is heavily into 78s bought a Numark TT200 turntable (with optional offset arm tube). The relatively inexpensive Numark serves this purpose well, even though it doesn't have proper audiophile credentials.

 

[fiddlefye]

When the TD125 was designed there were some extra-long-play classical music albums available at the 16rpm speed, notably on the Vox label. I suspect that was the reason for including this speed, not for talking book records. Poor fidelity soon killed that idea.

I did this mod years ago on my TD125 (Mk I), substituting the 78rpm parts for the 16rpm ones. It works but won't start up at 78 without either a push or first running at 45.

When running at 78 the motor emits a fairly loud hum/buzz acoustical noise which is mildly distracting. There is less torque at this speed and the table slows down when using a record cleaning brush. So far no damage, but I don't use the 78 speed much. I wouldn't recommend the TD-125 for heavy duty 78rpm use.

A friend who is heavily into 78s bought a Numark TT200 turntable (with optional offset arm tube). The relatively inexpensive Numark serves this purpose well, even though it doesn't have proper audiophile credentials.

So it is only at 78 that the starting issue rears its head then. It wasn't clear from the Thorens service memo. Interesting that the motor noise doesn't go away over time as was previously suggested might be the case.

I wouldn't be doing any really heavy 78 duty as I don't have that many of them and am unlikely to. I do have another table or two that do 78 rpm well so if I were to really get into it I could sub one of those in. The Elac Miracord will probably do a go job once set up for the purpose I think. On the other hand having the 125 set up so I can just change the cart and go would be really handy!