The Trux'O'Flux - An Analog Echo Machine morphed from an old Cassette Recorder

The TRUX'O'FLUX MK1! A Cassette tape echo/delay machine made from an old Cassette Deck...

This project was merely a figment of my imagination for many years, and having searched the inter web many times for a proper "how-to" on it I always thought that it would just be a waste of time and a waste of a good cassette deck. Well I took a notion one day this October to start experimenting with cassette and loops etc. I had found a few cassette decks in our local recycling centre so the only thing I had to lose was time :-). 

To Cut A Short Story Long Long Long!...

My first prototype is shown below which used a double cassette deck and modified cassettes. The deck is put into A-B copy mode where one deck plays while the other records. The cassettes have only one roll of tape shared between them and holes cut in the sides to allow the tape to pass from one cassette to the other. You get quite a long delay as there is a large distance between the head of deck A and deck B. This deck had high-speed dubbing which meant I could get a shorter delay when this was selected. I found the point on the board where the signal was coming out of deck A (right) and injected my signal there.

It already has it's own feedback path as signal that gets recorded on Deck B (left) is then played back a certain time later through deck A and that signal then goes back to Deck B to be recorded again, and so on. The reason it was controllable was due to the loss from recording onto old tape and then playing from it again.

Although this is a workable concept, I don't like it for a number of reasons; Firstly double decks are mostly found in all-in-one stereos which are huge and rather low quality. You also need to find one with not much between the two decks! Otherwise you can't get the tape across. You also need to modify a pair of cassettes, and after a while the tape will wear out and you'll need to replace it. And lastly, you have to turn around or rewind the tape whenever it reaches the end! This can happen quite quick when you use the High-Speed Dubbing mode ;-).

Enter The TRUX'O'FLUX! Flux! Flux! Flux!....................................Sorry, I'll stop that now :D

My dream in Cassette Echo Magic was to have a machine which took standard, unmodified cassettes so that I (or any other analog freak!) could change them easily and also be able to try a loop cassette designed for Answering Machines (They usually come in 30 seconds,  45 seconds and so on and are still available on ebay! :-)). So the key to doing this was to be able to fit three heads in the tape transport. I then discovered that Auto-Reverse decks have their rec/play and erase heads condensed into one rotating unit. BINGO! All I needed to do was to remove the heads themselves from the rotating thingy and make them fit in place of the Erase head in my Test Subject/Victim Deck :D. I found an old Rec/Play head in my junk box which had a removable bracket. I think this might only be found on very old heads as all my modern ones were spot-welded together. This allowed me to wedge the new heads into it with the ability to adjust their position, while always keeping them still. Here's some photos before I bore the arse off you with more text...

TINY! A rotating Rec/Play head (right) and Erase head (left) from Auto-Reverse Deck

Erase-Record head in the place of the original Erase head

A Word of Warning!>>>

Beware that some decks use differential wiring to the red-play head while others use single-ended. Differential means that neither end of each head coil (L & R) is permanently grounded (0V), whereas with single-ended you will see that one side of each head coil is always connected to ground/0V. this can usually be seen at the head itself. There are usually four pins under the head; a pair for the Left coil and a pair for the Right. In a single-ended setup two of these pins will be connected together and soldered to the screen of the cable and the other two will have wires (usually white and red for L & R), all going back to the PCB. In a differential setup there will be four wires connected to the head, all to their own pins. Just MAKE SURE that your new head is compatible with the Electronics that you intend to use before hacking stuff apart! ;-) (I learnt that the hard way...)

The exact position of the new head is crucial to the success of this venture! My method was to first make sure that the tape path on the new head (left in pic) lined up with the existing head (right) when looking from above. The next step was to make sure that the new head fitted ok inside the cassette when the play button was pressed. This took a bit of messing about but once it fitted I could start testing.

Now for the tricky rewiring! One option (which most other youtube videos use) is to use another deck for the Erase-Record electronics and connect your new Erase-Record head to this (Or Vise-Versa). Then use the deck you are building within for the playback electronics. This is a quick solution but leaves you with two units, strung together with bits of wire. That's what I didn't like, so I started studying schematics of various Cassette Decks to see if I could do it all in one unit...

My test victim was a Technics RS200 HiFi Deck that had been laying in a dumpster in the rain for a week! After drying it off it surprisingly worked with just a muffled sound on the right channel being the only issue. Most decks of this shape and size have mic input jacks on the front panel. They also have Record Level controls and Bias/Tape Type switches which you will see later come in very handy indeed! What I needed to do in order to record and play back at the same time was to enable the Record EQ/Amp section while also enabling the Playback (P/B) EQ/Amp section. This is not possible with cheaper decks/ghetto blasters/dictaphones as the same EQ and Amp is cleverly switched for both tasks. But in a HiFi deck there are dedicated circuits for each, with the P/B Amp being used as a Mic amp when recording with mics. But we don't need mic inputs as we can just use the line inputs on the rear. I won't get into schematic details here as every deck will be slightly different, but the main place you need to rewire is the big long silver switch on the PCB that gets pushed by a mechanism when you hit the record button. This switches everything; the heads, the amps, the inputs and outputs etc. In my deck I forced the P/B Amp to stay in playback mode and connected the original Rec/Play head directly to this. Confirm that this is working by playing a normal cassette which you know has music on it and you should get audio out. Then I connected the new Erase/Rec head to the original head connections on the PCB. Now the new Erase Head should Erase, the new Rec/Play head should Record, and the original Rec/Play head should play! With all this modifying it is a good idea to use the same connectors for both rec/play heads so then you can interchange them during testing (see Align notes below)...

Ready, Set, ALIGN!

After confirming that your deck still plays fine, you are now ready to align the new "magic" head! :-) One way of doing this is to first connect the new Rec/Play head to the P/B Amp and play a tape with music on it. If all is working then when you move the new head up and down and tilt it with SLIGHT movements the sound should change. It will be very muffled at first and only when you find the exact position will you then get clear sound from the output. Note that it is best to do this with the transport removed from the housing and with the tape drawer removed, but still connected with all cables. You can mess with this forever if you want perfect reproduction from the delay, but alas, you are aligning a head that was never meant to fit in this machine, so don't expect wonders ;-).

Tape Transport out in the open for head alignment

The next step is to test the new head in Record mode. To do this you need to feed constant audio into the line input (I recommend music which you won't mind hating afterwards due to hearing it so many times ;-) Cheesy 80s Pop worked for me). Load the deck with a new, blank cassette. Don't bother using an old Whitney Houston tape from your Mum's car as it's probably so over-played that it can't hold music anyway! You set the deck into record mode. Now it should be recording that 80s Pop with all the sparkle of gated snares and cheesy synths. As before, you now need to monitor the playback signal from the P/B amp. But because the deck is in Record mode the line output will just be outputting what is coming in on the line input (via the Record Level control of course). To monitor the P/B amp output directly I just wired up two RCA cables straight to the output points of the amp which in my case were at the "Playback Gain" preset pots on the PCB. 

New "delayed" output RCAs fitted between line in and line out RCAs

If the first test has proved a success then you should be getting SOMETHING out, even if it is muffled and very low in volume. At this point, a nice inspiring trick to pull you out of the frustration is to cut the audio coming in and see how long it takes to cut on the output. This is your delay! You have successfully managed to delay audio ON TAPE! YES! It might sound like shit and it might be 80s Synth Pop but hey! It got delayed!!!!

Don't be so... BIASED!?

OK so back on track after that excitement... You now need to play with the bias level. And no this has nothing to do with political discussions over dinner with your in-laws... For those of you who don't know, Bias in magnetic tape recording is a high frequency signal which is put into the head(s) along with the audio signal when recording. It sort-of shakes up the ferrous grains on the tape so that they can align to the music easily. This same bias signal is also fed to the Erase head (at a much higher level) and this randomises the magnetic fields on the tape leaving it blank before it gets to the record head. Bias levels will be different from one head to another, and even change depending on tape formula (Normal, Metal, Fe02 and all that). This is another great thing about using a HiFi cassette deck as your Frankenstein. Most if not all of them have adjustable bias pots inside as well as playback gain and record gain. While listening to your muffled yet delayed signal from the P/B amp start adjusting the bias pot(s). You will notice the sound changing from nearly nothing at minimum bias, all the way to quite harsh and hopefully loud sound at maximum. Find a happy medium and leave it for now. If need be you can also adjust the record gain, but if you aligned the new head properly you should not need to increase this much or even at all. The playback gain will adjust the output level of your delayed signal. Play with this as you wish too :-).

A bad photo of the PCB. If you look close you'll see the preset pots for Playback Gain, Record Gain and Bias

Now that the time(delay) machine is working, how do we control the damn thing!?

Adding A Feedback/Regen control

coming soon! I promise

Making the delay time variable

coming sooooon!

Adding a Wet-Dry mix control

also coming soon!