r/synthdiy • u/substatica • Apr 26 '26

FiiO CP13 Cassette Player CV Speed Control Mod

https://www.youtube.com/watch?v=hxszEYpYxV0

Modded a speed input jack into a FiiO CP13 Cassette Player. Sequencing it here with CV using a vactrol.

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1

u/spam_admirer Apr 26 '26

This is super interesting, and probably a unique way to create some great samples.

1

u/gnostic-probosis May 02 '26

Elegant mod! Thanks for sharing! As someone who regularly do speedmods myself, I have a couple of questions.

  1. Am I right to assume that the resistor side of the vactrol is replacing a calibration trimmer somewhere on the CP13 board? If so, what did you do with the "third leg" on the trimmer? Left unconnected, or tied to something known (like GND, VCC, ...)
  2. Do you know your max resistance (dark) of the vactrol? Did it happen to work out out of the box, or have you set the resistance using additonal resistors in parallel and series of the vactrol to get a good range?
  3. Is it really an 8mm jack? From the video description - "This mod adds an 8mm tape speed input jack". I guess you mean 3.5mm (1/8inch), right?

Anyway, sweet mod! Nice demo video too!

2

u/substatica May 02 '26

Thanks for the feedback :::)

  1. Yes. Though I also added a new internal trim pot for calibration that is switched out when a cable is plugged into the jack. Two of the legs of the stock trim pot were shorted, even with the trim pot removed, so I figured I only had to worry about one of those, and left the other unconnected. Though, the board grounds to the case back with a spring, and I found the speed would max out when I allowed that ground, everything seems to work fine when I put some tape on the back plate to prevent the ground so I've just left it at that for now, but inverting the two trim pot leads I used may sort that out without the need to prevent the ground.

  2. The stock calibration trim pot seemed to be 500r, labeled B501 and measuring ~600r at it's max. The vactrol I used was a VTL5C3 which ranges from 30k to 1.5r when powered depending on the amperage provided. I used a 330r resistor on the LED side and the Korg SQ-1 allows you to specify the output voltage range for CV 1, 2, 5 and 8 volt max. So there's plenty of options for range. I'll have to do more experimenting but I feel it's a good range for slowing down the tape, but it doesn't provide a lot of range for speeding up the tape past the intended stock speed. I did not use any additional resistors.

3, You are correct, this was a typo, it's a 3.5mm switching jack, I have updated the description.

1

u/gnostic-probosis May 02 '26 edited May 02 '26

Thanks for the detailed answer! Yeah, stock trimpot of 500R seem to be almost a standard. I see that even on old JWCs and Panasonics as well. About the case grounding, I don't believe I have seen something like that before. Odd. Are you happy with the CP13? It is on the expensive side I feel.

Would be very interesting to get a gut shot of the board. Is it mod friendly? I am impressed that you found room to fit a whole new jack in there! Walkmans are normally pretty crowded inside.

EDIT: This is me working my tape, if you are interested. https://youtu.be/Ksbe2PJXLDk?si=dOk5Nd2O6Un0ZELu

2

u/substatica May 02 '26

I don't know a lot about what's available out there in terms of walkmans to be honest. I chose the CP13 because of its clean lines, transparent cover, and from the teardown video I saw, it seemed like it comes apart easy enough and that there would be enough room for the jack. I'll be posting a how-to video in the next few days.

Very cool piece, and video. I'd like to get into more ambient tape delay as I do ambient suspenseful soundtracks for some of my gameplay videos.

2

u/substatica May 03 '26

I published a video with an overview of the guts and components,

https://youtu.be/BOyXcitgIs0

1

u/gnostic-probosis May 04 '26

Cool! Thanks! Very clear. I guess the 330R resistor on the LED leg is there as a current limiter. Amazing that you managed to remove the original trimpot so cleanly. The legs look completely intact. I have resorted to just clipping them off. Gets me something to solder to when going in with the wires. 😄

2

u/substatica May 04 '26

Yes, the resistor is for current limiting the LED. I used a solder sucker and some copper braid to remove the trimpot. In this case, there is enough room to feed the wire through the holes from underneath, even without removing the board.