Author Topic: Roland Micro Cube Effect Loop add-on  (Read 558 times)

Thomeeque

Roland Micro Cube Effect Loop add-on
« on: October 03, 2019, 06:00:13 PM »
 Hi guys,

 as I already stated in my post at pix of Custom built guitar amps/cabs board, to be able to use my Micro Cube with looper pedal, I have designed and built in effect loop circuit. In principle it is nothing special, biggest challenge was to actually get inside my MC :D (there's a rubber around chassis and it sticked to the cabinet over the years), but it had few specifics. First was that MC guts are quite complex and I could not find schematic. Luckily Cube 30 schematic is available on-line and all the critical parts of the circuitry turned to be almost identical. Second was, that basically all except the most low level functions is handled digitally inside DSP, including Volume control, so add-on also has to feature master volume pot :( But it is actually a good thing, as I realised later, because the original Volume control is quite useful when using looper, as it allows to adjust levels of different setups when layering loops. Third sort-of-challenge was placing add-on physically to the MC chassis, as there is not that much space, but it was not that bad either. I have found nice place for the Master Volume pot at the top panel (see pics) and there is some space to squeeze send/return jack(s) at the back side. For now to save some drilling I used stereo jack for both signals (requires special cable), but two jacks would fit either.

 TL'DR:

 Basic topology (blue is MC, green is add-on):

 

 Add-on replaces decoupling capacitor C32 (this capacitor has the same part name on MC and Cube 30 btw. ;)), power is taken from C107 pads (- is AGND, + is A+8), be careful not to connect audio ground (AGND) with chassis. To be able to easily find right spots, check my pics (wire colors: A, B, A+8, AGND, FX-IN /SEND/, FX-OUT /RETURN/, FX-GND).

 Add-on schematic:

 

 Circuit is quite simple, could be easily soldered on universal PCB or whatever technique you prefer, but in case you are interested, my PCB layout and Eagle files are also available at my page. Btw. for master volume linear (not audio) taper pot is used. With combination of 10k load at C32- input it works better :)

 Attenuation and Gain are set to 3x (so the TRIM_ATT is set to one third and TRIM_GAIN is adjusted to unity gain of the add-on with POT_MASTER at maximum), but this may yet change in the future, as I was not sure what would be the best value TBH. It works fine with my Boss RC-3 looper, but it would be maybe worthy to try with your pedals before putting your MC back together for good.

 

 Sample Loop

 Good luck, T.
« Last Edit: October 05, 2019, 09:23:56 AM by Thomeeque »
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deadastronaut

Re: Roland Micro Cube Effect Loop add-on
« Reply #1 on: October 04, 2019, 02:20:28 PM »
brilliant, nice one tomas....great idea making a thread for this i'm sure many others

will want to do this too... 8)
http://www.youtube.com/user/100roberthenry
https://deadastronaut.wixsite.com/effects

chasm reverb/tremshifter/faze filter/abductor II delay/timestream reverb/dreamtime delay/skinwalker hi gain dist/black triangle OD/ nano drums/space patrol fuzz//

junor

Re: Roland Micro Cube Effect Loop add-on
« Reply #2 on: October 23, 2019, 09:40:01 AM »
Great, I've been searching for instructions how to connect looper to MC!

Didn't quite understand the addon circuit and need for master volume though. What would happed if you just connect send/receive jacks to +/- of C32 and AGND? Full volume without control?

Other question if somebody knows, I'm adding speaker out but understood that there is some bass enchase circuit that would be good to bypass. Any help with this?

-J

Thomeeque

Re: Roland Micro Cube Effect Loop add-on
« Reply #3 on: October 24, 2019, 10:27:12 AM »
Didn't quite understand the addon circuit and need for master volume though. What would happed if you just connect send/receive jacks to +/- of C32 and AGND? Full volume without control?

 Yup, connecting send/receive jacks (thru decoupling capacitors at both ends) to +/- of C32 and AGND would be the absolutely most minimalistic working FX loop solution.

 Master volume would be controlled either by volume pot of the stompobox plugged into the loop (but not every stompbox has it, mostly it works only if the effect is engaged and it would be also quite clumsy) or by the original MC Volume with some limitations, based on fact that regulation would be happening at the input of connected circuit (signal level may be too small and lead to bad SNR or too big and overload the circuit or even affect it's function if it would be e.g. some envelope follower based FX).

 Input impedance at the return input would be 10k, which is also little too low.

 Add-on circuit with additional volume pot takes care of proper levels and impedances at both ends (at least principally, the exact values may need some attention yet), provides standard master volume control and also provides some electrical protection to the original MC circuitry (I did not want to expose onboard op-amps directly to the outside world).

 About second question, I read the same, I guess it happens somewhere after C32 (as it is probably common for both guitar and AUX input and also signal, I recorded by looper, does not seem to be equalised this way).

 T.
« Last Edit: October 24, 2019, 11:46:33 AM by Thomeeque »
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junor

Re: Roland Micro Cube Effect Loop add-on
« Reply #4 on: October 24, 2019, 01:25:28 PM »
Yup, connecting send/receive jacks (thru decoupling capacitors at both ends) to +/- of C32 and AGND would be the absolutely most minimalistic working FX loop solution.

About second question, I read the same, I guess it happens somewhere after C32 (as it is probably common for both guitar and AUX input and also signal, I recorded by looper, does not seem to be equalised this way).

 T.

If I would test this minimalistic setup, would those decoupling capacitors same as C32 capacitor? I will definitely build also that addon circuit but it takes a while to get to it..

About ext speaker, would filter capacitor be a easy workaround..?

Thomeeque

Re: Roland Micro Cube Effect Loop add-on
« Reply #5 on: November 08, 2019, 10:49:23 AM »
 Hello J, sorry for late answer :icon_redface:, did you get somewhere meanwhile?

 As you say, caps same (or similar) as C32, not critical for first experiments.

 About ext speaker - first I'd try connect it directly, maybe it will sound good like that? Filter capacitor could be solution, just be careful if standard (unipolar) elyt is OK or if you need bipolar type (see what's inside).

 Cheers, T.
« Last Edit: November 08, 2019, 10:51:20 AM by Thomeeque »
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