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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 13th May 2024, 10:00 am   #1
sourbiscuits
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Default Question about reel to reel speed control.

I recently purchased this ac motor controller online - https://www.amazon.nl/-/en/dp/B07D3R...roduct_details

My idea was to link it after the power outlet to be able to control the motor speed of my reel to reel. I only tried it out with a domestic fan and it worked fine. I still wanted to consult here before experimenting on my unit. Would changing the AC output voltage harm the machine?
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Old 13th May 2024, 1:22 pm   #2
Ted Kendall
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Default Re: Question about reel to reel

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Originally Posted by sourbiscuits View Post
I recently purchased this ac motor controller online - https://www.amazon.nl/-/en/dp/B07D3R...roduct_details

My idea was to link it after the power outlet to be able to control the motor speed of my reel to reel. I only tried it out with a domestic fan and it worked fine. I still wanted to consult here before experimenting on my unit. Would changing the AC output voltage harm the machine?
Depends on the capstan motor - if it's synchronous, as most are, changing the input voltage won't directly affect the speed until it's so low the thing drops out of lock. The usual approach is a power amplifier and a variable frequency signal generator,
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Old 13th May 2024, 6:57 pm   #3
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Default Re: Question about reel to reel

When I needed to adjust the speed of the synchronous motor of my cine projector, I used an uninterruptable power supply intended for computers that was kindly provided by a forum member. I didn't need a large deviation from mains ( about 45 to 65 Hz) , and powered it using a 26A battery charger with an old 12V SLA battery floated across its output. Modern chargers usually need to see a 12V battery before they will produce an output voltage.
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Old 13th May 2024, 11:28 pm   #4
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Default Re: Question about reel to reel

Likely to damage the machine, it's a phase angle controller. You'll probably hear nasty noises coming out of it as well. Posh machines use brushless DC motors for the capstan motor or otherwise synchronous AC motors which can't easily be speed-controlled.
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Old 14th May 2024, 11:46 am   #5
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Default Re: Question about reel to reel

Thank you for you replies! Might have been useful to mention the brand/model. So I have two units that I was hoping on controlling the speed of at the same time (I know, quite ambitious). One is the AKAI 4000DS MKII and the Sony TC377. I am not sure what type of motor they use. I only have a tiny bit of experience modifying DC motor cassette recorders with PWM modules. I remember touching on this topic a while back in another thread, and I was also told it's not that easy to achieve. Either way, I'd appreciate any tips, and obviously happy to pop in any other information you might need!
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Old 14th May 2024, 3:43 pm   #6
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Default Re: Question about reel to reel

I've got the Akai x2000 of a similar vintage that uses an AC motor, you change speeds by a combination of gears and different sized capstan sleeves. I don't know anything about the Sony.
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Old 14th May 2024, 4:54 pm   #7
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Default Re: Question about reel to reel

As Ted says, I, too, think the Akai 4000 series uses a synchronous capstan motor (mine was a 4000D).

If you want to varispeed it, then you need a variable frequency drive, not variable voltage. Depending on how much varispeed, it might not be very well behaved at excessively fast or slow speeds.
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Old 14th May 2024, 10:10 pm   #8
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Default Re: Question about reel to reel

Thank you Kevin. Yes, I do have the little spool that you unscrew from it's holder and place it on the axis above the pinch wheel. That's the standard speed change. The sony has three speeds, and they are also fixed.

Like Simondm said, I do wish to do varispeed. If I would be using a variable frequency drive, do I still use it as the main output for the units or do I need to hook it up somewhere internally (in the r2r)? Apologies for the beginner questions, I have never delved into this matter before so I know very little.
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Old 14th May 2024, 11:13 pm   #9
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Default Re: Question about reel to reel

The Revox/Studer machines use non-synchronous induction motors. They are inside-out motors with a cylindrical rotor outside the magnetic core and windings. Dual windings with a phase shift capacitor produce a multipole, rotating magnetic field. The rotor has no poles, it is a featureless iron cylinder and is driven by Lenz' law reaction to the eddy currents induced in the rotor. Varying the current in the windings controls the torque produced at the rotor. The capstan motor directly drives the capstan which is simply an extension of the motor shaft.

Speed control only works because there is a tachometer sensing the speed of rotation of the rotor feeding back to control the motor current.

Overall, it is a robust and elegant solution, but it IS a variable speed system using an AC induction motor and it's in some of the most common professional open reel machines.

These machines use similar motprs to directly drive the spool hubs on 10.5 inch spool machines. No speed feedback, the controlled current torque is OK for the basic machines, the posh ones have tape tension sensors feedback controlling the motor torque.

Look up Papst Outer Rotor Motors for more info.

A motor speed controller using variable angle firing of triacs is not going to work on any induction motor and may well do damage. They are really intended for motors with commutators and brushes.

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Old 14th May 2024, 11:39 pm   #10
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Default Re: Question about reel to reel

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Originally Posted by Simondm View Post
As Ted says, I, too, think the Akai 4000 series uses a synchronous capstan motor (mine was a 4000D).

If you want to varispeed it, then you need a variable frequency drive, not variable voltage. Depending on how much varispeed, it might not be very well behaved at excessively fast or slow speeds.
It's not quite as simple as that as the motor run capacitor is designed for a specific frequency ie 50Hz or 60Hz there is usually a switch to switch between the two. The reason is because the phase difference of the two windings is 90° and this has to be maintained.

If you want to vary the speed, you have to power each winding from a frequency generator and amplifier where the phase of the inputs to the amplifier are 90° apart throughout the frequency range.
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Old 14th May 2024, 11:48 pm   #11
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Default Re: Question about reel to reel

I can't help thinking it would be far easier to use a machine with a more suitable motor. My Philips N4515, which uses a DC motor, can be made to run at almost any speed you want just by hooking up a potentiometer to the right place.
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Old 15th May 2024, 8:36 am   #12
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Default Re: Question about reel to reel

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Originally Posted by Simondm View Post
If you want to varispeed it, then you need a variable frequency drive, not variable voltage. Depending on how much varispeed, it might not be very well behaved at excessively fast or slow speeds.
It's not quite as simple as that as the motor run capacitor is designed for a specific frequency ie 50Hz or 60Hz there is usually a switch to switch between the two. The reason is because the phase difference of the two windings is 90° and this has to be maintained.

If you want to vary the speed, you have to power each winding from a frequency generator and amplifier where the phase of the inputs to the amplifier are 90° apart throughout the frequency range.
It works for _small_ speed differences, if, for example, you only need to get a piece of music shifted back into tune (say less than a semitone). But to be honest, it's so much easier to do that kind of correction digitally these days.
But it sounds like the OP wants to do a lot of speed alteration, in which case, I agree it's not going to work.
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Old 15th May 2024, 9:12 am   #13
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Default Re: Question about reel to reel

For a lot of speed variation, even with a variable frequency drive, if you go too slow, the motor impedance falls and the current goes too high and the motor gets too hot.

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Old 15th May 2024, 9:29 am   #14
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Default Re: Question about reel to reel

I would knock the idea on the head TBH. Some professional tape echo machines from Roland and Korg that I used to service used variable speed motors but they had embedded hall sensors and a sophisticated driver board. The motors were over a hundred quid a pop way back when.

You might be able to shoehorn a microstepped stepper motor in there if you feel confident to build a power supply and driver for it that wont radiate PWM into the signal chain and can engineer the shaft and mountings so it doesn't automatically erase any tape that gets within a few inches of the pinch roller......
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Old 15th May 2024, 11:09 am   #15
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Default Re: Question about reel to reel

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Originally Posted by McMurdo View Post
I would knock the idea on the head TBH. Some professional tape echo machines from Roland and Korg that I used to service used variable speed motors but they had embedded hall sensors and a sophisticated driver board. The motors were over a hundred quid a pop way back when.

You might be able to shoehorn a microstepped stepper motor in there if you feel confident to build a power supply and driver for it that wont radiate PWM into the signal chain and can engineer the shaft and mountings so it doesn't automatically erase any tape that gets within a few inches of the pinch roller......
By the time you do that you might as well buy another machine with varispeed!
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Old 15th May 2024, 10:42 pm   #16
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Default Re: Question about reel to reel

yes I was just trying to be subtle
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Old 16th May 2024, 8:02 am   #17
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Default Re: Question about reel to reel speed control.

In the old days (seventies) a firm called Valradio produced a variable frequency drive for synchronous capstans, I think it only went about +- 15%.

The output stage was a couple of 807s if I remember correctly.

A problem with a veriable frequency drive to the capstan is that if the machine has been set up to account for hum bucking between the mains transformer, capstan motor and spool motors this will be upset by feeding the capstan from a different source.

Again, in the old days (early sixties) the Leevers Rich variable speed drive used a DC servo motor to run from about 6ips to over 40ips in a single sweep. Used a valve servo amp as well for extra audio quality........
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Old 17th May 2024, 12:57 am   #18
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Default Re: Question about reel to reel speed control.

Many but not all TEAC/Tascam reel to reel machines had front panel varispeed control as standard.
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Old 22nd May 2024, 9:31 am   #19
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Default Re: Question about reel to reel speed control.

I thank you all, for the replies. Like I mentioned, this is the second time I bring this topic up. I will consider exchanging my units, as this would be very exciting to have as an option, but I won't dive into such deep modifications. Apart from the Leevers Rich, any other recommendations for brands/models?
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Old 22nd May 2024, 10:28 am   #20
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Default Re: Question about reel to reel speed control.

Revox A77 and on accommodate varispeed, besides being cracking machines in other respects. The B77/II has 6% varispeed built in.
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