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cassette recorder circuit guitar effects

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the cracken

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im trying to make an effects pedal. the circuit needs to record on one head then pick up the signal on the other head and input it to the original sound making an echo. i have bough some tape recorders but they are too complicated does anyone have a simple circuit or an idea
and it has to be analog :)
thanks
 
It's called a 'Copicat' they were made by WEM (Watkins Electronic Music) back in the 60's and 70's, but used an endless tape loop, not a cassette mechanism.

The electronics is simple enough, it's the mechanics which is the only problem - and making it small and cassette sized will only make it more difficult.

The Watkins / WEM Copicat

It's still available as well :D

WEM Copicat page.
 
that's what i was looking for but is there a transistor copicat? and do you know of a circuit diagram? i found the valve schematic.
thanks :)
 
the cracken said:
that's what i was looking for but is there a transistor copicat? and do you know of a circuit diagram? i found the valve schematic.
thanks :)
Click to expand...

As far as I'm aware most of them were transistor ones, I certainly repaired plenty back in the 70's :D

A simplr google instantly finds this:

WEM Copicat Mk4 Schematic

And this:

http://www.vintagehofner.co.uk/britamps/watkins/schematics/copicatmk3ss.html

And even this:

http://www.vintagehofner.co.uk/britamps/watkins/schematics/copicatsup1c.html
 
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The mechanics should be easy enough. Use the transport from the old tape deck. Open up the cassette, remove the tape, unwind it, cut to length, splice the ends together, and place back in the case so that instead of winding at each end it simply loops back. Probably a bit limited in terms of how long you can make the tape though. :)

Hm. Maybe you could get some extra length by using the old Space Echo trick of having a bunch of extra slack just wibbling around inside.


Good luck,

Torben
 
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i just made some measurements and it takes about a volt to the head to record which is easy enough but i have to amplify 5mV to about a volt any suggestions??? thanks
(i forgot they were peak to peak readings)
 
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the cracken said:
i just made some measurements and it takes about a volt to the head to record which is easy enough but i have to amplify 5mV to about a volt any suggestions??? thanks
(i forgot they were peak to peak readings)
Click to expand...

I posted you three circuits above, two with transistor amps, one with opamps - what's wrong with the amps from those?.
 
i do appreciate it and i have looked at the circuit's but i haven't a clue how it works there are a few transformers which has completely thrown me. i think as long as i know how to amplify 5mv to 1v i would be ok. is it possible to do it with a single opamp. all i know is that it will need a gain of 200 but i dont know what else i have to look for in an op amp!
thanks :)
 
the cracken said:
i do appreciate it and i have looked at the circuit's but i haven't a clue how it works there are a few transformers which has completely thrown me. i think as long as i know how to amplify 5mv to 1v i would be ok. is it possible to do it with a single opamp. all i know is that it will need a gain of 200 but i dont know what else i have to look for in an op amp!
thanks :)
Click to expand...

You need to do a LOT more than that it's not a linear amplifier for a start, it has to follow specific record and playback specifications - you also must provide erase and bias signals, that's what the transformers are for.

I would imagine it's trivial to rip the actual reord and playback amps from the WEM circuits, it's the erase and bias that's the problem.

EDIT:

Having said that, the opamp version doesn't seem to do much in the way of frequency correction, although tbe transistor one does. For the opamp version the playback amp is the bottom left opamp and associated circuitry - but both still use AC erase and bias.
 
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The erase problem is solved lol in the recorders i want to use (normal 1/4 inch cassette) (cheapo cheapo of the cheapo clan) they had no circuit for it. all it is is a small magnet and when the recode button is pressed the magnet is brought into contact with the tape. what is the bias for??
i can record. i used my signal generator and put 1v onto the head and it recorded perfectly. all i need to do is amplify the signal and then stick it into the input.
i wish i new as much as you do about electronics :)
 
the cracken said:
The erase problem is solved lol in the recorders i want to use (normal 1/4 inch cassette) (cheapo cheapo of the cheapo clan) they had no circuit for it. all it is is a small magnet and when the recode button is pressed the magnet is brought into contact with the tape. what is the bias for??
i can record. i used my signal generator and put 1v onto the head and it recorded perfectly. all i need to do is amplify the signal and then stick it into the input.
i wish i new as much as you do about electronics :)
Click to expand...

The bias is to stop it been heavily distorted, have a look at:

Tape bias - Wikipedia, the free encyclopedia

Your cheap recorder probably uses DC bias - which is FAR poorer, as it magnet erase.

I would suggest you draw out the existing circuit of the record output of the cassette, to see how the head is driven and the biasing done. Notice in all the examples I posted the head is driven through a resistor, this drives the head with a current - not a voltage. I would suggest you will find the cheap cassette does the same.
 
couldn't i use a 555 timer to produce an ac bias. do you think its a 0v to 1v ac signal or a + - signal? i looked on the net but couldn't find any more info apart from the fact that they started to use it to decrease distortion and improve low frequency response. ill have to make afew measurements on the tape recorder but its 12:32AM ;0 so ill have to do it tomoz. can't i use an opamp to amplify the signal then?
thanks for all the help :)
 
the cracken said:
couldn't i use a 555 timer to produce an ac bias. do you think its a 0v to 1v ac signal or a + - signal? i looked on the net but couldn't find any more info apart from the fact that they started to use it to decrease distortion and improve low frequency response. ill have to make afew measurements on the tape recorder but its 12:32AM ;0 so ill have to do it tomoz. can't i use an opamp to amplify the signal then?
thanks for all the help :)
Click to expand...

You can't use a 555 because it MUST be a sinewave, and a reasonably decent quality one - you also need 90V or so to bias the record head.
 
i took a look at the signal to the head and there was a very small dc bias and a small ac signal im guessing the ac is just static. i did some experimenting and although its not perfect i think i can get away with not using a bias at all. i attached the head to my sig gen and varied the voltage and frequency while recording to give me an idea of what it would sound like. although its not a prefect replication of the signal i think its good enough for what i want. but i still don't know how i can amplify 5mv to 1v!!! would a normal opamp with a gain of 200 work or do i need a special opamp? thanks for the help!!!
 
the cracken said:
i took a look at the signal to the head and there was a very small dc bias and a small ac signal im guessing the ac is just static. i did some experimenting and although its not perfect i think i can get away with not using a bias at all. i attached the head to my sig gen and varied the voltage and frequency while recording to give me an idea of what it would sound like. although its not a prefect replication of the signal i think its good enough for what i want. but i still don't know how i can amplify 5mv to 1v!!! would a normal opamp with a gain of 200 work or do i need a special opamp? thanks for the help!!!
Click to expand...

As I've already told you, just look at the opamp circuit posted above, and copy the record amp - it's simple enough.

As far as I can remember you also don't feed 1V to the head, but considerably less (for distortion reasons, and to keep it in the linear region set by the bias) - but bias is absolutely essential.
 
is the amplifier the two opamps on the top left? i wasn't referring to the circuit i want to know what op amps i should use (741) it doesn't say the op amps used in the circuit diagram.
your totally right about the bias :p i recorded some guitar with the output of my laptop and it was way too distorted. the dc bias that i measured on my cassette recorder was very small ill try to put up some pictures and there was an ac signal i dont know if its just static though.
 
the cracken said:
is the amplifier the two opamps on the top left? i wasn't referring to the circuit i want to know what op amps i should use (741) it doesn't say the op amps used in the circuit diagram.
your totally right about the bias :p i recorded some guitar with the output of my laptop and it was way too distorted. the dc bias that i measured on my cassette recorder was very small ill try to put up some pictures and there was an ac signal i dont know if its just static though.
Click to expand...

The record amp is the top two opamps, playback is the bottom left, bottom right is the mixer.

Can't you draw out the required part of the original bias circuit in your cassette recorder?, it will probably just be a resistor feeding DC to the head, but you really need to know how it was done, what value, and copy that.
 
iv tryed to copy the circuit but its too difficult. here's an image of whats sent to the head. there was no tape in the tape recorder and it was playing. i used the - on the battery as earth.<**broken link removed** 10ns and 2mv if you couldn't see it.

and here it is not playing.
**broken link removed**
 
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