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Portastudio 424 Modified for Live Performance
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Portastudio 424 Modified for Live Performance
chipaudette
Inspired by this post, where it was discussed how Alessandro Cortini was using cassette tape loops on an old Portastudio as part of his live rig, I dug out my own Portastudio 424 (the original, from the early 90's) to see what I could do with it.

First, I started by simply making my first loop tape and dropping it into my Portastudio. That alone was fun (pics and audio demo at the link below):

http://synthhacker.blogspot.com/2014/02/cassette-tape-loop.html

I'm interested in more than just pre-recorded loops, though. I want to create and mangle loops on the fly. So, I've begun to dig into the Portastudio to begin a process of modifications to make it a performance instrument.

Again, taking baby-steps, it seemed simplest to start with figuring out how to defeat the tape's erase head so that I could get gap-free live loops as well as some sound-on-sound recording. If you're interested in some pics and audio demos from that process, you can check out:

http://synthhacker.blogspot.com/2014/02/portastudio-defeating-erase-he ad.html

I'm thinking that my next step is to mod the Portastudio to enable more useful changes in motor speeds. Currently, my Portastudio has a knob enabling continuous variation between +/- 2 semitones, as well as a switch that enables you to jump +1 octave or jump -1 octave. I'd like to mod the continuous control range to cover the space between 2 semitones and a full octave.

Has anyone else done modifications on their Portastudio (or other cassette recorder) for real-time performance? I'd love to hear your stories...

Chip
ersatzplanet
I modified my PotaStudio a long time ago (an original first gen one) to remove the Dolby compression on two tracks so I could put SMPT code on them. I recently unearth a box of tapes from an old band I had back then and dug out the PS which hadn't been used in years. The main belt was stretch so it no longer works! Does anyone know of a reliable place to get spare parts for these?

As for the timing knob - I would looks for the DC motor control PCB and look for a trimmer there that sets the standard speed (the variation knob probably is connected to this trimmer if there is one. Jump over the trimmer and you should be able to take it down to almost off. I once had a full schematic for the PS and I'm sure there may be one online somewhere or you can pay for it from one of those service manual sites. That would make the erase head mode easier too. You may be able to make multiple switches, one for each track, and do some good Sound on Sound stuff that way.
jonah
when you disable the erase head how are you finding the noise because of biasing or lack thereof ? in my experience, the usually cheaper recorders that use a magnet only to erase and don't integrate the erase and bias have less noise when you disable their erase head.

i have a 424 mkii with loops and i just bounce (3 tape tracks and live audio onto the 4th) and use reverb/delay to cover any gaps. smile

also did you try to tape over (sorry no pun intended! smile ) the erase head? that's worked for me on some recorders. i like the portastudio enough that i haven't wanted to fiddle with it yet though. smile
sempervirent
I unearthed my old Portastudio recently and found that it was DOA. Power switch was broken off (sure don't remember that happening). Hopefully it can be resuscitated, because I have a bunch of 4-track demos that I want to digitize. The concept of making cassette tape loops is pretty interesting though, thanks for the idea.
ersatzplanet
sempervirent wrote:
I unearthed my old Portastudio recently and found that it was DOA. Power switch was broken off (sure don't remember that happening). Hopefully it can be resuscitated, because I have a bunch of 4-track demos that I want to digitize. The concept of making cassette tape loops is pretty interesting though, thanks for the idea.


I'm in the same situation with a box of tapes. I did dump some of them to a DAW from a standard cassette but then of course you have to reverse 2 tracks and re-pitch all four and then line them up (I recorded them from the leader so that gives a good reference) but that is WAY too much work to deal which. And of course the Dolby was weird after being pitch shifted too. Gotta find a belt for mine or work our some kind of hack.
chipaudette
I did some live looping with my Portastudio. If you're interested in the demo, you can check it out here:

http://synthhacker.blogspot.com/2014/02/portastudio-live-looping.html

This demo keeps the erase head enabled, so no per-track sound-on-sound recording.

While I'm not a huge fan of the gap that results from keeping the erase head enabled, the gap does provide a rhythmic anchor, which does provide some benefit for this kind of riff-based jam. But, if I were going for some drone-music, I'd definitely switch back to defeating the erase head.

Chip
chipaudette
Not having a schematic for my Portastudio 424 has really been annoying me...I hate poking around blindly. Surprisingly, I can't seem to find one out there for download...and I dug pretty deep and scoured a lot of unclean looking web forums. There weren't even any 424 schematics on eBay. Bummer.

I did find a service manual (with schematics) for sale on eBay for the Portastudio 464, which was out at about the same time. So, taking the chance that most of the circuits would be close enough, I bought that service manual...and it just arrived!

Let the nerdy schematic analysis begin!

Chip
chipaudette
With the schematic for the Portastudio 464, I started probing my Portastudio 424 to learn how it controlled the tape speed. I think that I've got it all figured out.

If you're interested, I've got some pics and some quantitative measurements here:

http://synthhacker.blogspot.com/2014/03/portastudio-voltage-control-of -speed.html

It looks like the capstan motor speed can be controlled by generating a negative DC voltage relative to the capstan's speed sense pin. Faster speeds result from making the voltage even more negative relative to the sense pin.

Since my goal with all of this is to make a live performance instrument, the post above also shows a simple op-amp circuit for making the correct relative voltage, assuming I've got something that can make a 0 to +5V control voltage.

My next step is to prototype the circuit, to generate the 0-5V CV, and see if I can put my theories into practice!

Chip
Groundloop
Chip, sorry to resurrect this zombie, but I was curious if you'd had any luck further modding your 424. I've got one arriving soon and definitely want to use it as a multi looper in conjunction with the modular.
ersatzplanet
Groundloop wrote:
Chip, sorry to resurrect this zombie, but I was curious if you'd had any luck further modding your 424. I've got one arriving soon and definitely want to use it as a multi looper in conjunction with the modular.


I got my PS back up and running but I wonder what draws you to using it as a looper? There are many disadvantages using one for this. Speed changes are slow. The bias oscillator becomes a hearable whine when playback speeds are slower than recorded ones. The cassette media is fragile and is already being pushed to its max by the PS. There are lots of looper modules or recording modules like the 4ms STS that can do this and much more.

Not trying to say it is a stupid idea or dissing you for wanting to do it, just curious as to what draws you to use the PortaStudio?
Groundloop
ersatzplanet wrote:
I got my PS back up and running but I wonder what draws you to using it as a looper? There are many disadvantages using one for this. Speed changes are slow. The bias oscillator becomes a hearable whine when playback speeds are slower than recorded ones. The cassette media is fragile and is already being pushed to its max by the PS. There are lots of looper modules or recording modules like the 4ms STS that can do this and much more.

Not trying to say it is a stupid idea or dissing you for wanting to do it, just curious as to what draws you to use the PortaStudio?


James, I'd be lying if I wasn't influenced at least a little by Hainbach's YouTube channel (https://www.youtube.com/channel/UCeovElJP0n0i8ADaPsRSd8g), and the music he produces, almost all of which is recorded to tape. And the video that Chip mentioned where Alessandro Cortini recorded a chord loop to each track and faded/octave shifted them. Also, at least for now I'm embracing the imperfection of analog tape, and if I want something with better quality, I have a Clouds clone in the rack. Also also? No small amount of nostalgia for sure. In the grand scheme none of this makes much sense, but it made just enough sense for me to pull the trigger on a pretty mint 424 MkI.
chipaudette
I had no practical reason for using it as a looper in place of a digital device. my goal was simply to do something that was different and unusual for myself. Basically, doing weird things sometimes puts your mind in a weird place and sometimes that makes for fun inspiration.

Chip
ersatzplanet
Groundloop wrote:
James, I'd be lying if I wasn't influenced at least a little by Hainbach's YouTube channel (https://www.youtube.com/channel/UCeovElJP0n0i8ADaPsRSd8g), and the music he produces, almost all of which is recorded to tape. And the video that Chip mentioned where Alessandro Cortini recorded a chord loop to each track and faded/octave shifted them. Also, at least for now I'm embracing the imperfection of analog tape, and if I want something with better quality, I have a Clouds clone in the rack. Also also? No small amount of nostalgia for sure. In the grand scheme none of this makes much sense, but it made just enough sense for me to pull the trigger on a pretty mint 424 MkI.


chipaudette wrote:
I had no practical reason for using it as a looper in place of a digital device. my goal was simply to do something that was different and unusual for myself. Basically, doing weird things sometimes puts your mind in a weird place and sometimes that makes for fun inspiration.


I have to admit that there is a big draw to physical machines - slotting cassettes into the tray, threading reel to reel tape, stuff like that. I don't exactly know why. I still have R2R decks, the PortaStudio, and a couple of MiniDisc recorders/players for that reason. I almost made a CV sequencer that got note data from holes in a card put in a slot, just so I could "slot them up" in a show and do something physical for a change.
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