Tape speed, motor control, LFO, help!

Discussion in 'The Projects Forum' started by zowno, May 15, 2014.

  1. zowno

    zowno Thread Starter New Member

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    Hi everyone, I'm new around these parts and I have a project I'd like some help with.

    I am building an effect unit using a reel to reel tape machine. It is a take on an effect created by Ken Townsend for the Beatles called ADT. It used a oscillator to control the speed of the tape machine. It had one large knob to manually vary the speed by small amounts to create the effect. I want to reproduce this effect but I want to be able to set the initial speed manually and have an LFO control the small variations in speed. The motor is a four pole induction type, 100VAC. The motor currently moves tape at 7.5 inches per second. I need to be able to set the speed to between 24 and 118 ips and then vary it with the LFO at a rate of say 1hz to more extreme setting of 100hz or more to vary the IPS by milliseconds. If I can clarify anything any more please ask. I have electronics experience, just not in this area.

    Many thanks in advance,
    Zowno
  2. AnalogKid

    AnalogKid Active Member

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    Excuse me - 118 ips?!?!? At that speed you will have serious aerodynamic problems, plus that is way outside the bandwidth of the tension mechanism, not to mention that a motor designed for 1/15th that speed probably will not be happy.

    Separate from that, the capstan probably has a flywheel on it, there specifically to *prevent* the flutter you are trying to induce.

    I'm familiar with ADT; where do the high tape speeds come in?

    ak
    Last edited: May 15, 2014
  3. zowno

    zowno Thread Starter New Member

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    I admit that I was taken back with the high tape speeds when I did the calculations. It was merely trying to push the unit into flanger territory as I was run the unit in line like a guitar stomp box with the gap between the record and play heads acting as the delay.
  4. wayneh

    wayneh AAC Fanatic!

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    If you just want the effect, why not do it electronically instead of mechanically? Much easier and much more control.
  5. Alec_t

    Alec_t Well-Known Member

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    Did Townsend really increase the tape speeds that much? I'm surprised the motor and take-up mechanism etc survived. Like AK, I don't see how (or why) you'd overcome the flywheel inertia.
    Another option might be to use a fixed 15ips tape speed but have a servo-mounted playback head which can be moved very close to the record head or further away along the tape path.
  6. zowno

    zowno Thread Starter New Member

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    I could just do it all electronically, but there is something romantic and better sounding about tape.

    Townsend did not increase the speeds that much, but in the way they used ADT they did not have to use the tape in the same way. They used multiple machines during the mixdown stage. I only have one machine and it needs to be an in line effect for live use.

    I have done the maths and conceded that the tape speeds I want are impossible to achieve. I am happy just to increase the speed by say 2 times. There are plenty of 30ips machines and indeed the townsend machine was 30ips. I am not trying to directly copy ADT, so changes, concessions and improvements are welcome. If at some stage I can make a sliding head, much like in the echoplex tape delay, that could work as well.

    So, with the concessions I am making I now require: Being able to double the current running speed and then have the ability to vary this speed by up to 10ms at a rate of around 2hz and below to maybe 0.25hz or so. At some stage I may add a sliding playback head, but not until I have worked out the fundamentals.

    Thanks for the help, lets keep it going :)
  7. Alec_t

    Alec_t Well-Known Member

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    Is that a permanent doubling? Or switchable at will? How rapidly must the doubling/halving occur?
    Methinks even that is a hard ask for a mechanical system. I assume this is a tape loop system rather than one with supply and take-up spools. The conventional flywheel would have to go, and the most suitable motor to replace the ususal induction one would perhaps be a BLDC type. Without the flywheel, tape flutter will be an issue.
  8. AnalogKid

    AnalogKid Active Member

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    Actually, if you think about 10 ms shifts in tape speed at a 2 Hz rate, flutter is the goal. My guess is that the original was a capstan motor driven by a power amplifier. All videotape machines of that era had them to facilitate genlock to external sync. Vacuum tube motor drive amplifiers in the 50's, quasi-complimentary solid state amps in the 60's, power hybrids in the 70's. But those systems had a fairly low bandwidth (lock could take 10 seconds) and they still had a flywheel because the audio was linearly recorded along the tape edges.

    ak
  9. Alec_t

    Alec_t Well-Known Member

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    True, but only when the effect is wanted. Is the tape unit disconnected at other times? Not being a music-maker I have no real feel for how this unit is going to be used.
  10. wayneh

    wayneh AAC Fanatic!

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    Romantic? To who? :eek: Just kidding - it's one of those things that's in the eye of the beholder.

    Better sounding? I don't think there is anything in the analog world that cannot be reproduced digitally. Figuring out how to do it might be a hurdle, but in theory you can do anything you can imagine.
  11. zowno

    zowno Thread Starter New Member

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    Okay, so the doubling would be permanent. The tape machine has a 3 3/4ips and 7 1/2ips switch already so by doubling the speed I'd still have the 7 1/2 but I'd also have 15ips.

    It will be a tape loop system, but these are the specs that the original machine used and I know it's not impossible. To use and LFO instead of a manual knob seems totally within the realm of modern electronics.

    Flutter is indeed the goal and any random flutter will be welcome. The unit will have a "dry" through signal that will remain unaffected to be blended with the effected signal.

    In the case of audio and specifically, music technology you will struggle to find someone who will think digital is better than analogue. You need look no further than Daft Punk's latest album to understand that. But this is not a place for such arguments. This is more a building exercise to design something interesting rather than perfect.
  12. wayneh

    wayneh AAC Fanatic!

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    That depends on what "better" means. ;)
    The market has spoken, and digital wins. This from a bluegrass fan.
  13. zowno

    zowno Thread Starter New Member

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    Tape flutter would actually be a nice quirk. It wouldn't be anything that wouldn't add to the effect.

    Currently the machine runs at 7 1/2 IPS. I would want the double in speed to be permanent. I could later use a servo system to move the playback head, but for now nailing the effect is more important.

    You think that I should replace the original motor?

    What is the likely hood of being able to implement an LFO to vary the speed?
  14. wayneh

    wayneh AAC Fanatic!

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    Are you certain that the motor directly drives the tape? Sometimes there are pulleys and belts. Maybe you could just change a pulley?
  15. Alec_t

    Alec_t Well-Known Member

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    We don't know what motor/drive system you have. I was guessing 'domestic tape recorder = small induction motor driving capstan/flywheel via stepped pulley system'. Is yours different?
    Wayneh's suggestion offers one possible solution; otherwise you would have to double the motor speed by doubling its drive frequency (which the motor might not like).
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