syncing / adjusting motor speed between two tandberg decks (64x & 65) - diyAudio
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Old 4th August 2010, 03:38 PM   #1
diblet is offline diblet  United States
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Question syncing / adjusting motor speed between two tandberg decks (64x & 65)

i have a tandberg 64x and a model 65 playback deck. i am not sure which one is playing closer to "correct speed," but would like to figure out how i can get them to playback at the same pitch. i am a musician using the pair of decks for creating music. i would like to be able to move something recorded on the 64x to the 65 to play back to play along with the previously recorded tape, adding new layers and re-recording to the 64x. it doesn't matter to me what the correct speed actually is, just that they play in sync with each other.

it is a benefit to have the playback deck running a little bit faster when using the two decks together making long tape echos (keeping good tape tension). however, the problem comes when playing along with a tape playing back on the 65. the 65 runs a little faster (and thus tonally sharp) so the playback sounds out of tune compared to my instruments.
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* is there a way to modify the speed of the 65 playback motor to sync up the two decks? i would rather do any modifications to the 65 deck, as there is plenty of room in there, and not as many downfalls if something gets messed up.

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my understanding of motors is limited, but the service manual for the 64x states it is a hysteresis synchronous motor motor (and appearances are similar in both decks). if i understand correctly, the speed of this motor type syncs up with the 60hz ac and is subsequently hardwired in for each motor.

if that is the case i can only think of two options for getting the speeds to sync up:

1.) carefully modify (or re-machine) the pulleys on top of the motor that contact the idler wheel to slow the 65 down to the same speed as the 64x. i can see some problems here, especially if there are screw ups...

2.) change the motor out for one that has the ability to dial in the speed. this is probably the best option as i could have it run a little faster when doing long tape echos, or have it run in sync when wanting to play things back. but the downside being a lot of work (and i would need help figuring out exactly how to do it electronically)

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i attached a shot of the schematics & mechanics above the motor (simple stacked pulleys of differing sizes for differing speeds driving an idler which in turn spins the idler wheel/capstan)

any thoughts would be appreciated! thanks so much

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Old 4th August 2010, 03:49 PM   #2
kevinkr is offline kevinkr  United States
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What you propose is non-trivial, the fact that the two machines run at noticeably different speeds indicates that there may be a problem with one of them or that they are worn out or their speed tolerance was by design somewhat imprecise to start with. (Not surprising for low/mid range domestic tape decks.)

The deck you are discussing is locked to the line frequency so speed tolerance is a matter of mechanical tolerances in the capstan drive assembly- it may be possible to use an external power amp and highly stable (probably synthesized) oscillator to nudge this deck onto speed with the other one..

The best solution if you have the coin would be to look for an old 8 track open reel studio recorder - then the issues you talk about go away. Look around and see what you can find..
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Old 4th August 2010, 04:00 PM   #3
diblet is offline diblet  United States
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thanks for the reply - i am guessing that the speed tolerances are just imprecise - the decks are in great shape. i went over both of them with regards to their path to the capstan and everything checks out.

where could i go to learn more about the power amp / oscillator approach?

i understand this is complicated, i would just like to know what options i have. i really enjoy learning how these things work (otherwise the playback deck is just limited to doing long tape delays, no big deal i guess, just limits what i can do with them together).
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Old 8th August 2010, 01:58 PM   #4
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Getting two analogue tape machines to run at the same speed is something that has occupied a lot of minds over the years!

As the machines are locked to mains frequency the errors from the "right" speed are due to mechanical differences - capstan diameter being the most important. If you measure the capstans accurately, and they are the same diameter, then the differences are caused by tape slippage at the capstan

Tape slippage at the capstan is caused by the pinch roller, mechanical drag from the feed spool and mechanical drag from the takeup spool

Many simple mains-synchronous machines run at a different speed depending where they are in a roll of tape so setting the "right" speed by mechanical tweaking won't be easy

Machines with externally-clocked speed control use a crystal reference and an idler with a detector to feed back the current speed & control the capstan motor. Mains-synchronous machines use a heavy capstan flywheel but that is generally incompatible with externally-clocked speed control as the hysteresis created by capstan intertia makes speed control difficult

So: some tweaking may make your existing machines run better in sync. Converting them to external speed control probably won't work for you. More modern speed-controlled machines may be better for your purposes

A pair of older professional machines, like the Studer A80, would work well for you if they were in good mechanical condition. A slightly later generation would give you more accurate and repeatable speed control. The later A800 multitrack was impressively speed-stable, even with 14" reels of 2" tape. I don't remember if there was ever a two-track version

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Old 2nd January 2011, 08:02 PM   #5
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If thees decks are to have any chanse to obtain the same speed, the following MUST be done first:

The intermediate drivewheel must be of exactly same productionlot and stored together.
The capstan press-rollers must be of exactly same lot and stored together since production.
The surface of the capstan-wheel where the intermediate wheel rolls on it must be thoroughly cleaned for any residues of oil or grease. Also the main motor wheel should see the same treatment. The pressure roller pressure must be alligned to exact similar pressure on both decs. The bearings on the capstan need to be cleaned and lubricated equally.

NOW we have two decks tat should run at similar speeds.
BUT why isn't it so?
Just because there is margins in the production of the flywheel, the capstan itself, the main drive wheel and other components in the mechanism.

To illustrate this I know quite a few attempts to get two 10XD-decks to run at exactly same speed. I never heard of any who have succeeded in doing this.
And those deks had quite a good capstan-motor regulator.
With feedback directly on the flywheel itself.

Note: Wow and flutter is very good on all theese machines, but the speed deviation of less than a tenth of a percent is still noticeable when using theese for recording music.
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Old 3rd January 2011, 01:59 PM   #6
diblet is offline diblet  United States
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well it is good to know no one can get two tape machines perfectly within tolerance - i have since gave in and worked within the limitations of having to play back music only on the machine on which it was recorded.
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