Introducing MixTape, our very first fully analog Eurorack module!
MixTape is designed to make it easier to use a tape machine for tape delay/echo within a Eurorack system. Specifically, it adjust for Eurorack and Line levels when going to/from Eurorack and tape. It also includes a non-resonant low-pass filter in the tape return path with a cutoff frequency of around 16 KHz. Th efilter is there to help with tape decks which have a problem with bias bleed on the outputs (such as my own Marantz PMD221). While the filter doesn’t completely eliminate the bias bleed problem, it considerably helps.
Here is a short demo of what it sounds like (poorly recorded on a phone):
This patch uses an A-110-2 VCO as the main voice with the PWM being modulated by an LFO into the A-106 filter which is also being modulated by another LFO. The WMD ADSRVCA is the combined envelope/VCA. The output of the filter then goes to the MixTape which send the audio to my Marantz PMD221 in low speed mode with the pitch knob all the way to the left (the slowest delay I’m able to get with this deck).
The module has 3 knobs for controlling the input to tape, the amount of feedback, and the dry/wet mix. There is no way to control the input level directly and this is by design. My thought was folks can adjust that in other ways within the rack and controlling the input to the tape felt more important to directly control to help with gain staging.
The other reason for not having a global input is that I wanted to keep the module small – targeting 4HP or less. Keeping the module at 4HP while being skiff friendly also meant that I had to opt for using mostly surface mount (SMD) parts. This means it is not as DIY friendly, but also means the cost should hopefully be reasonable. One place where I spluged in terms of cost was with the op-amps. I opted to use OPA1679 OPAs instead of the usual TL047s common with Eurorack gear. Given how it sounds, I think I made the right call there.
Cost is perhaps somewhat relative since folks using this will need a tape deck capable of echo. That means, at minimum, a 3-head deck but having the ability to adjust the tape speed during recording is also important. Decks which can do this aren’t exactly cheap. One route is to consider a new-old-stock UHER 4400. I bought mine from here. MixTape also isn’t wholly unique – there are other tape echo helper modules in the wild, but mine I think takes a unique spin on it with the tape input and addition of a filter. Plus I quite like that it is only 4HP.
The prototype has a few minor issues which will require another PCB revision. The dry/wet knob works backwards and the feedback gain was originally way too high. I had it set to a comical 3x whereas unity gain (1x) is plenty. Fixing the feedback on the prototype was easy enough (removing a few resistors and adding a bridge wire), though the dry/wet requires cutting traces and things (hence the need for a PCB update). There are also some minor layouts changes I would like to make as well as decide on a proper color scheme.
That means at present, MixTape isn’t available it but I do hope to at least do a small production run soon. If you are interested in picking one up, let us know!
And watch this space for some other prototypes we’re working on as well as some exciting WaveBoy updates coming soon!
