Cassette tape delay

Rorut · Dec 19, 2017

Im going to try and do this modification on my cassette player from this instruction/schematic (two images linked below)
https://experimentalistsanonymous.c...Samplers/Echo-matic cassette delay page 1.gif

https://experimentalistsanonymous.c...Samplers/Echo-matic cassette delay page 2.gif

In this video the guy have a low pass and a high pass filter (variable).
https://m.youtube.com/watch?t=10s&v=zjpe45XjXpg
Is the filters on the in or out signal? Also want the filters but unfortunately they are not included in the instruction schematic above.

Any ideas/schematics/product boards that can help me with the filters

Cheers

schmitt trigger · Dec 19, 2017

hmmmmm............
The capacitors in parallel with the feedback resistors (C2, C3 & C11) will perform some low pass filtering at about 15 Khz, presumably to filter out the hiss inherent in tapes.
I would increase the 100 pF caps to 150pF caps to lower the frequency to about 10 Khz.

You may want more complex filters ( I would advise at least a 2nd-order Butterworth).

Also, the virtual ground supply comprised of R7, R8, C7, buffer it with an opamp like the LM358. These opamps are dirt cheap and will provide a lower virtual ground impedance.

dr pepper · Dec 19, 2017

Better or should I say intermediate cassette players have Nab Eq, however for an echo you might just get away without unless you want super bright or hifi quality echos.
I like the idea of this project, a long time back I repaired a couple of copycat's, they were a tape echo that used 1/2" tape at 3 3/4 Ips and had multiple heads, quite something in their time, I beleive there was a 'special' version for movies that played echo's backwards.
If you scavenge around you might be able to find an 80's telephone answering machine that has an endless tape and can run infinitum, I think they were just like a compact cassette but with just 1 reel, might even work on a standard deck.

Rorut · Dec 19, 2017

Thank you very much. Would these work as low and highpass filters. Would be nice if I could replace a resistor om them with a pot the make them adjustable..
Lowpass:
**broken link removed**

Highpass:
**broken link removed**

Googled for schematics but was not sure what to choose

dr pepper · Dec 20, 2017

Yes you could, you'd need a dual or stereo pot as there are 2 r's to adjust.

Rorut · Dec 20, 2017

dr pepper said:
Yes you could, you'd need a dual or stereo pot as there are 2 r's to adjust.

Great, thanks!
So a dual linear pot wired to R5 and R6?
What value could be good and should there be a resistor in series with the pot if it gets at zero?

Rorut · Dec 20, 2017

Something like this?

dr pepper · Dec 20, 2017

Yup, the listing mentions R5&6 as tuning resistors.
The listing says 8k2 min so leave 8k2's in circuit & wire pots inline, I havent done any calcs however maybe a 100k would be a start, ought to get at least 5:1 ratio.
Edit with a fixed R of 8k2, a 22nF cap and a pot of 100k you'd get from 60hz deep bass to about 1kc female vocals.

schmitt trigger · Dec 20, 2017

Pots are available linear taper and log taper. Get the ones with a log taper.

Rorut · Dec 20, 2017

dr pepper said:
Yup, the listing mentions R5&6 as tuning resistors.
The listing says 8k2 min so leave 8k2's in circuit & wire pots inline, I havent done any calcs however maybe a 100k would be a start, ought to get at least 5:1 ratio.
Edit with a fixed R of 8k2, a 22nF cap and a pot of 100k you'd get from 60hz deep bass to about 1kc female vocals.

Thank you very much! This sounds perfect
Guess I have to desolder one of the ends of the 8k2? And connect that end to the pot. Another thing, there is two vcc on the circuit?

dr pepper · Dec 21, 2017

Yep on the 8k2 and the 2 vcc's are probably just connected to the same track on the board.
Unless it has a + and a - rail, you have a schem?

Rorut · Dec 21, 2017

dr pepper said:
Yep on the 8k2 and the 2 vcc's are probably just connected to the same track on the board.
Unless it has a + and a - rail, you have a schem?

Sorry no scheme. Almost every scheme I googled had It with both positive and negative voltage. Feels easier for me with only one power source.
Or maybe there is something like a dual-output supply -+5v ?
Or a circuit that can do this that I can put inside the unit

Edit
Something like this that can support 5v +/- ?
https://vi.raptor.ebaydesc.com/ws/e...=181993&pm=1&ds=0&t=1513889992026&cspheader=1

Rorut · Dec 21, 2017

Dont really understand the difference between the two I linked (lowpass and highpass) as they both has the same cut off frequency 3khz?

dr pepper · Dec 22, 2017

One filters out high end above 3khz, and the other filters out low end below 3khz.
Loosely put if you turn the bass on an amp (with others at zero) up you are creating a low pass filter, if you turn the treble up your creating a high pass.

Rorut · Dec 22, 2017

dr pepper said:
One filters out high end above 3khz, and the other filters out low end below 3khz.
Loosely put if you turn the bass on an amp (with others at zero) up you are creating a low pass filter, if you turn the treble up your creating a high pass.

Ofcourse! Thanks
Where would be best to apply the filters? On input or output?

dr pepper · Dec 22, 2017

Deffo output, then you have the option to bring detail back by twiddling a pot, if you did it on the input then there wouldnt be anything to bring back.

Rorut · Dec 25, 2017

dr pepper said:
Deffo output, then you have the option to bring detail back by twiddling a pot, if you did it on the input then there wouldnt be anything to bring back.

Thanks. Does it matter if signal goes through Lpf or hpf first?
And would it be difficult to add a potentiometer(s) for wet and dry to the circuit?
Separate dry
As always Im really grateful for all your help!

dr pepper · Dec 25, 2017

Like I was saying output.
The only time you'd use eq on the input to the tape is if the tape itself couldnt handle it, like a kick drum for example.
Its a bit heath robbo, however if you feed unfiltered audio to one end of a pot say 10k (input to the filter), and filtered audio to the other end, then you could twidlle the pot from unfiltered to filtered on its wiper, you'll get some frequency anomalies, dips half way, and volume differences but it'd do for this project.

Rorut · Dec 25, 2017

Yes, just thought about the two linked boards above for lowpass filter and highpass filter and if it does matter if the output from the player first is connected to the lowpass and then to the high pass or the other way around. Or if output connects to both lowpass and highpass at the same time and then connect the outputs together (joining) from the lowpass and highpass boards. Im sorry if I misunderatood/misunderstand what you explained
thanks

dr pepper · Dec 25, 2017

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.

Cassette tape delay

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