Adding a 1/4 speed circuit to an existing Fisher audio cassette recorder.

[John L. Perry]

What I would like to do as shown in the title, is to have a 2 way switch that would allow me to change from normal speed to 1/4 speed which would increase the recording, and playing of a standard 45 minute tape on one side, to over 3 hours running time. I have a " CCRANE VERSACORDER" that does exactly that. I would like to do that on my "Fisher Audio Component System" MC-723BK .

I would appreciate it very much if someone out there could supply a schematic diagram of the best way to do that. Thank you very much. John from Chesterfield Twp, Michigan.

 

[ronv]

It's probably not as simple as just slowing the speed down (though that wouldn't be easy). The recording density will go way up and the read write electronics probably won't support that.

 

[canadaelk]

You need to change the record emphasis and play-back de-emphasis to something like you have on the Versacorder. Than you would have to find a motor that has enough torque at the 2 speeds to give you low wow+flutter. After that, you find out that Muzak sounds like HiFi....E

 

[crutschow]

Why are you recording things on an old cassette recorder?

 

[John L. Perry]

crutschow

My thinking is this. The Fisher MC-723BK is a great machine that has discreet components, which should be easy to work on. Why I want to use it is to save wear and tear on the "Versacorder, which has the capability of timer recording for up to 4 hours on one side of a 105 minute tape, which I use for recording "Coast To Coast AM" that is on in the middle of the night 1:00 am to 5:00 am. Its a good program that's on 7 days a week. Very good talk radio that records well at 1/4 speed.

I do have 2 different schematic diagrams that I found on the internet that uses a cmos 555 timer, 500k potentiometer, and other components to make the pulse width variable, thereby controlling the speed of a dc motor. one has a capacity of 2 amps maximum, and the other is 1.5 amps maximum. The first operates with 6 volts, and the 2nd with 12 volts.
If I don't get another schematic with a switch, then I will use one of these 2 that I have. Then I will tie it into the cassette motor. That's what I hope to do. John from Michigan

 

[carbonzit]

Your PWM approach would probably work; certainly it could be tweaked and made to work.

Don't worry about the objections you've heard here regarding emphasis, etc. The recorder will still record and play back at reduced speed. It obviously won't have the same fidelity as normal speed, but you didn't mention that in your query, so I'm gonna ASS-U-ME (you know how that works!) that that's OK with you. After all, you say you're recording an AM radio broadcast, probably mostly speech, so I don't imagine high fidelity is a crucial issue here; am I correct?

Y'know, sometimes you can just answer the questions people ask without cross-examining them ... just a thought.

 

[John L. Perry]

carbonzit

You are absolutely correct. High fidelity is not an issue when listening to talk radio. If I can get it to work on the Fisher, as well as it doe's on the Ccrane Versacorder, I'll be a happy camper. Thanks John from Michigan

 

[carbonzit]

carbonzit

You are absolutely correct. High fidelity is not an issue when listening to talk radio. If I can get it to work on the Fisher, as well as it doe's on the Ccrane Versacorder, I'll be a happy camper.

Whoa, wait a minute: I didn't say, or mean to suggest that it would work as well as your other recorder, because I have no idea how well that unit works. But I'm confident that it will work well enough for your purposes.

 

[ronv]

I'd love to just stand back and watch - but I just can't.
Think about what happens when the diameter of the reels change?

 

[carbonzit]

I'd love to just stand back and watch - but I just can't.
Think about what happens when the diameter of the reels change?

What are you talking about?

Do you mean what happens when tape winds from supply to takeup and the diameter of the spool changes? That happens as is, so why would changing the speed of the transport affect anything in that regard? ASS-U-MING, of course, that there's still enough torque to drive the takeup reel. I suppose if there wasn't you might get some tape spillage, true. So maybe the O.P. shouldn't invest too much $$ in this until he gets a proof-of-concept trial running.

 

[canadaelk]

Fidelity is not the issue in this case. It will be the pits (apologies to one and all who live in Pittsburgh) anyway. Without proper emphasis correction you will not get much above 1500Hz (or is it 1507Hz?). The spoken word will not be inelligeble.

carbonzit: ......without cross-examining them....! This is a forum. People come here for info, no one was lecturing!

A good friend of mine, an icon in the audio industry, had this to say: I met a man, we exchanged a dollar. We each had a dollar. I met a man, we exchanged ideas. We each had two ideas.

Cheers, E

 

[crutschow]

Reducing the motor voltage to control the speed may work, but only if the motor is dc and there is no motor feedback control that regulates the speed.

 

[ronv]

What are you talking about?

Sorry, don't take it personal.
But, this won't work on so many levels I hate so see someone spin their wheels.
Recorders have servos to keep the speed constant - a simple PWM does not.
The gap in the write head will be to big, same with the read head.
The write current will be to high.
The output from the read head will go down with the reduction in speed.

 

[carbonzit]

Sorry, don't take it personal.

Thanks, I didn't.

But, this won't work on so many levels I hate so see someone spin their wheels.
Recorders have servos to keep the speed constant - a simple PWM does not.

I agree this could be a show-stopper. However, not all cassette decks have servos. Does his use one? I don't know.

The gap in the write head will be to big, same with the read head.
The write current will be to high.
The output from the read head will go down with the reduction in speed.

Not show-stoppers. Again, I think he understands there's going to be some degradation in quality.

Here's a thought: assuming for a minute that he can use PWM to reduce the speed, then certainly he can build his PWM controller so the speed is adjustable, no? So try 1/2 speed first, see how that works. Then he can try reducing the speed more. Nothing to lose. I don't think he has to have 1/4 speed; he just wants to get more stuff on a cassette, as I understand it.

 

[colin55]

MOTOR SPEED CONTROLLER
Most simple motor speed controllers simply reduce the voltage to a motor by introducing a series resistance. This reduces the motor's torque and if the motor is stopped, it will not start again.
This circuit detects the pulses of noise produced by the motor to turn the circuit off slightly. If the motor becomes loaded, the amplitude of the pulses decreases and the circuit turns on more to deliver a higher current. You can get to half speed but 25% speed is very slow.

 

[rogs]

To be honest, it would probably make more sense to splash out $40 on something like this:
**broken link removed**

Then simply use a couple of resistors, to attenuate the line output from your source, to match the sensitivity of the external mic input.

No worries about 'wear' then, and lots of hours of recording, at AM radio quality!

It would certainly avoid all the potential problems mentioned, and leave your Fisher cassette machine working as it should.

Just a thought.....