Cassette tape delay

dr pepper · Dec 29, 2017

Watkins electronic music, a blast from the past, they made a load of stuff including the cry baby waa pedal, I fixed a few of those too, very popular.
I've never heard of an echo room, interesting I wonder if thats where the term 'echo chamber' came from, those 'orrid Cb mikes that had one inside back in the 80's.
I experimented a while back with an audio delay line memory, storing bits in switched audio tone bursts recycled over a mike & speaker.

Rorut · Dec 30, 2017

dr pepper said:
Hi Nige, have a look at post #3, copycat is one of the machines your talking about, I repaired a few too back in my apprentiod days.
If you have 10k rorut try it it'll probably work fine I might have been a bit too picky.
Looks like the motor speed control is onboard rather than in the motor, some tape players had a variable speed control fitted.
Have you considered modding a tape to an endless loop, or even using 2 decks with 1 tape?

This unit actually has a pitch on the front that is letting you adjust the speed but only during playback, not while recording. And I read it has a small range. But the pot mod should bypass this and giving wider control. This is only what I read from a blog post. Making a cassette loop sounds great! Good idea!

The copycat sounds interesting

Would it be an idea to clean the tape deck and demag?
Any suggestions about that for keeping it spinning for the future?

Rorut · Dec 30, 2017

dr pepper said:
Now I get it.
If the 2 have a gap ie the low pass is <1000hz and the high pass is >100hz then they can go either way around , 2 things happen, the delays can mess up the response a little however thats probably not going to be bad, this isnt a high end system, the other thing is gain, the filters will have gain which will multiply so watch out for overdriving the amp or whatever they go to, a resistor divider might be required.
Although at the time I had the wrong idea, my idea of a pot with one end of the track to low pass and the other end to high pass will still work, in the centre you'd have effectively a bandpass as desired, fading to low pass only one end and high pass the other end, an interesting concept, with the right frequencies the control would sound bright one end, bassy the other and 'nasal' in the centre.
If you have a choice bessel type filter curves would probably be best, but it'll work with various filter curves.

Would either of these work?
1.
**broken link removed**
2.
**broken link removed**
3.
**broken link removed**

dr pepper · Dec 30, 2017

I've never messed with one but I'd think the lack of speed control while recording is probably a inhibit contact on the play/record switch, usually a schadow multi contact switch, with a little knowledge it might be possible to overide said function and have variable speed while recording.

Regular cleaning and demagging is important for a tape deck, you can probably still get demag wands from china, isopropyl alcohol is usually ok for cleaning, the rubber pinch roll is the thing to be carefull of with cleaning solvents.
If you want to spend a bit more and you can still gettem you can get cleaning/demaging tapes that run from batteries.

The last of the filter circuits look the best, you'll need to wind down the output level control on the echo circuit to compensate for the gain, a 10k inbetween the pot and the op amp on the output level control will permanently drop the signal 6db.
Also you might need to solder say a 22uf cap inline with the input and output of the filter boards just in case theres any Dc on them, as there doesnt look to be any decoupling caps on the boards.

Nigel Goodwin · Dec 30, 2017

dr pepper said:
Regular cleaning and demagging is important for a tape deck.

Cleaning yes, demagging no - I've demagged countless tape decks over the years, and it's never made the slightest bit of difference.

But even more to the point, this is an echo unit, so it's recordings only have to last a fraction of a second - and perhaps a second or two if you move the play head further away, but it's difficult with a cassette.

Rorut · Dec 30, 2017

dr pepper said:
I've never messed with one but I'd think the lack of speed control while recording is probably a inhibit contact on the play/record switch, usually a schadow multi contact switch, with a little knowledge it might be possible to overide said function and have variable speed while recording.

Regular cleaning and demagging is important for a tape deck, you can probably still get demag wands from china, isopropyl alcohol is usually ok for cleaning, the rubber pinch roll is the thing to be carefull of with cleaning solvents.
If you want to spend a bit more and you can still gettem you can get cleaning/demaging tapes that run from batteries.

The last of the filter circuits look the best, you'll need to wind down the output level control on the echo circuit to compensate for the gain, a 10k inbetween the pot and the op amp on the output level control will permanently drop the signal 6db.
Also you might need to solder say a 22uf cap inline with the input and output of the filter boards just in case theres any Dc on them, as there doesnt look to be any decoupling caps on the boards.

Thanks for the good advices!
Is this the way you suggested?
**broken link removed**

dr pepper · Dec 31, 2017

Yup thats the one.
Give it a try see how it works.
Some amps might have a low input impedance and that may require a op amp follower after the pot, but most should be Ok.

Rorut · Jan 1, 2018

dr pepper said:
Yup thats the one.
Give it a try see how it works.
Some amps might have a low input impedance and that may require a op amp follower after the pot, but most should be Ok.

Thank you so much for all help!
Is there any software that can make a pcb layout automatically from a redrawn circuit layout?

dr pepper · Jan 1, 2018

Lots, but not really my scene, I work with vero and protoboard mainly.
Design spark and eagle are free design packages that have schem capture, the latter is popular with students.

Rorut · Jan 1, 2018

I can get 5 pcb for about $15 and free delivery.
I gave diptrace a try, if this looks ok im ofcourse implementing the mods aswell.

**broken link removed**

dr pepper · Jan 1, 2018

Looks Ok.
I've had many a board made, I used to run a business selling products, but for one off's I use either stripboard, padboard or metal clad dead bug.

Rorut · Jan 1, 2018

I added the components for the modification you helped me with. Did I got the components on the correct place on the PCB layout?
**broken link removed**

dr pepper · Jan 2, 2018

R17 will give you a level control for 'dry' zero to full, and R11 will give you 'wet' from zero to full.
If this is what your after then good.
I havent really checked the pcb layout proper I'm at work, but quick glance it looks Ok.
C14 and the 10k look Ok.

Rorut · Jan 3, 2018

dr pepper said:
R17 will give you a level control for 'dry' zero to full, and R11 will give you 'wet' from zero to full.
If this is what your after then good.
I havent really checked the pcb layout proper I'm at work, but quick glance it looks Ok.
C14 and the 10k look Ok.

Yes I hope it will work thank you

Rorut · Jan 4, 2018

I added some connection places for making assembly easier, does this make any sense? Hope I didnt create any problems
**broken link removed**

Rorut · Jan 7, 2018

If this look ok? Im sending it to the manufacturer this week. Really hope I have not made anything wrong

dr pepper · Jan 7, 2018

I dont see anything obvious, but dont take my word for it.

Rorut · Jan 7, 2018

dr pepper said:
I dont see anything obvious, but dont take my word for it.

Thanks that is making it more easy to move on will post the results here (video) when I get the pcb and put it together

dr pepper · Jan 7, 2018

Look forward to seeing it.

Rorut · Jan 11, 2018

Received the tape recorder a couple of days ago but ran into some problem. When opening the bottom for making the pitch modification (Slow down speed of motor) the PCB looks different from the one I linked here before. So now I dont have a clue how to connect a pot for changing that speed.
My pcb looks like this:

The one from before I found that is modded looks like this:

Cassette tape delay

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