DIY Tape Delay

[bigtex]

Yeah, like that. An adjustable regulator. I was going to search for something like that to point you to, but I was feeling lazy. I'm glad you found such a straightforward example.

As far as Ohm's Law goes, voltage, current, and resistance are all kind of intertwined. Since you have two resistances in that equation (the motor itself and the resistor you were using) the voltage across the motor actually did decrease as the voltage across the resistor increased (higher value resistor means higher voltage drop across resistor). Less voltage potential across the motor means less current being pulled through the motor. Higher total resistance in path of current flow means less current flow is possible. It's not just one or the other, as changing one variable will effect the other two.

[kokoon]

hmm all of that is really hard to visualize/imagine... i know those are the bare basics but... any good short articles for a newb like me?

[blue hell]

A lot of casette transport motors have a built-in RPM control and then it's not much use to try to control them externally. What could be done is to try to open the motor and see if it has an internal trimpot. If so just bring that one out, that will work much better.

[kokoon]

the motor is sealed quite well... i'll get me a LM317 tomorrow and see what happens. it does slow down for more than 50% before it dies as it is right now (with just a ~0.5k pot) so i guess it can be done... or not?

[blue hell]

For what I've seen the outer casing nearly always was bent inwards at three points around the inner casing. For that some magic with a screwdriver (not too large) and a hammer has always worked, but I can imagine you don't want to try that as the first thing

Hope the LM thing will work for you, if not you could try current control instead of voltage control - which should work better even. See http://www.uoguelph.ca/~antoon/gadgets/sccs.htm to see how that could be done with the same LM317, but the resistors would need adjustment for your purpose.

[blue hell]

The battery charger on http://ourworld.compuserve.com/homepages/Bill_Bowden/page7.htm might give some better ideas about how to make a current source,

[kokoon]

hmm i can't see any drastic difference between your first link and the one i found... are you sure the LM317 isn't doing the same thing in both cases?

[kokoon]

uh oh the voltage regulator doesn't change anything and i decided to open the motor. but i'm having a really hard time.

this is how it looks:


the left is (i think) the motor that lifts the heads. the middle one is the motor i'm trying to open and the right one is for ejecting. now apparently those 2 holes are for opening the sucker but i can't do it. i have tried twisting the lid both ways, bending the outer rim of the casing, bending the lid, ... but it's so hard i can't do anything.

and taking the motor completely out of the machine is nearly impossible unless i unsolder ~30 wires first... shit.

any ideas?

[bigtex]

Um... mechanical speed control? It might wear out or break the thing, but you could probably install a little tab or rubber stopper to apply friction to the motor. Not very elegant, though.

If the regulator doesn't work, then it probably does have internal speed correction. Shucks. Have you measured the voltage across the motor and the current running through it when you try to adjust the regulator? If the voltage goes down, the current goes up, and the motor speed stays the same, you'll definitely be dealing with a stubborn one-speed-only beast.

[kokoon]

i have measured the voltage but not the current. the voltage drops and the motor slows down. the problem is that when it slows down to a certain level (not slow enough for me) it just dies like it's too weak to pull the tape. that's what i was hoping to sort out.

[bigtex]

The next step here is to try pulse width modulation. You will be feeding it a constant voltage, but in pulses. As you narrow the width of the pulses, the equivalent DC voltage that the motor sees will decrease.

A google search will turn up many, many sources of information on PWM motor speed control. Give that a try.

The idea with PWM is that you are always giving the motor the voltage it wants to make it go, so it will always go. When you decrease the voltage with the adjustable regulator, it gets down to a voltage that is insufficient to make the motor turn. If you take the voltage that the motor wants to see and then turn it on and off repeatedly, the motor will always turn, but at a lower speed. You can then vary the ratio of on time to off time, hence modulating the pulse width.

So hunt around for a schematic for an oscillator with pulse width control, but a fixed frequency. A good PWM frequency for motors will be above 1kHz. I usually use 2 or 3kHz. Then all you'll need is a power transistor or MOSFET to trigger with the oscillator's output. When the pulse goes high, the motor will receive power. When the pulse goes low, the motor will not receive power.

I don't think I'm doing a very good job of explaining this... but just do a search. You'll find something.

[nisios]

Does anyone know how to interact with the tape heads?
I have opened an old cassete recorder and i would like to make a tape delay........in the copycat fashion. With filter in the feedback. But i have no idea how to interact with the heads.

[the19thbear]

as said earlier: you need a three head casette player or a reel to reel recorder. It has to be able to record and playback at the same time.
then do this:
use a small mixer, connect a mic to the mixer( say.. channel1), send the mic signal from aux1 to the tape desk that is recording and playingback at the same time.
connect the line out of the tape deck, back to another channel ( say.. channel 2) on the mixer.
you can now control the amount of feedback by sending the returned tape signal(channel2) back to the tape deck via aux1. and even do eq'ing (filtering, like the copycat)

If you have no experience with mixer/audiorouting, then buy a cheap behringer mixer, and you'll soon understand..
hope that helps!

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[Peake]

Cassette tape loops- that brings me back. Have not done one in years nor wished to

I've been giving a lot of thought to tape delay, and am interested to try something like Ken Stone's tube VCA in the feedback loop, with some inverted envelope following driving the gain down ala' compression, as well as an analog filter and/or EQ. A filter at 20KHz and up, with increasing resonance, should provide some nice air.

BTW, in high school I experimented with this stuff a lot. Inserting an SPDT between the erase head and its other connections is enough to freely turn it off and on, for that nearly infinite echo (dependent upon tape speed). Sound on the tape gradually darkens, as you'd expect and may have experienced with existing lengthy tape delays (one of the Rolands has sound on sound capability, right?)

Good thead! And good advice regarding the archival value of vintage recordings. The first stereo recording was discovered a bit back; two mono recorders had been set up in different parts of the same room, and when sync'd, gave stereo. I don't know if this was the intent, but that's the result. It took someone finding and noticing the "extra" tape's characteristics for this to come to light.

True documents of time passed are important. There are museums, or even the government archive, that would be interested.