Roland Micro Cube Effect Loop add-on

[kmos]

Thomeeque, I have a quck follow-up question:

Since I am planning to get rid of the Master pot, I can also lose the C6 capacitor, right? Do I need to change the value of C5 then?

Nevermind the horrible quality of the second schematic, it is because I imported the project into Altium.

[Thomeeque]

Good news, I got the readymade boards of the currently latest (v1.1) revision. I will solder the board and run the first tests soon.

To whom it might concern: since I ordered 3 boards, I will end up having spares, which I am happy to send away for free, shipping price not included.

Nice boards and nice offer!

Bad news is that the vertical board-mounted jack socket that Thomeeque has used seems to be the only model that can fit nicely inside the Micro Cube casing. Mine doesn't fit inside, unfortunately (notice the long scratch parallel to the edge of the chassis - it represents the casing edge):

I have checked other available socket models as well, and their width is still over 16mm, which is the physical limitation of the casing.

So, I will have to probably cut away a small region of the casing edge (marked on the photo). It is made of MDF, so shouldn't cause much trouble:

Hmm, I was little bit worried about that. Compactness is one of the reasons I like to use these jacks. I would probably try to modify the jack first (bend legs, cut out some unnecessary plastic etc.), but if would not help, little cutout from that MDF part as you plan should not make any significant harm to the MC imo.

While reflecting on this, I have realized several things:

• Master Pot at max setting is supposed to give unity gain (0dB), so it gives no real gain (pun intended) in terms of driving additional effect loop cirquit.
• My looper pedal has its own "Loop Volume" knob and I am quite happy to operate two knobs, MC volume and Looper volume to mix the output sound.
• I really do not want to drill more holes than absolutely necessary in my Micro Cube.
• I like the way Thomeeque's board is mounted to the chassis using Master Pot's threaded nut, and my model of jack socket allows me to do the same.

So I came up with a solution of my own: I will solder the jack socket directly onto the board and will use the socket nut it as a mounting point. Here is a rough mockup:

Yup, this may work for you, it really depends on many aspects, you'll see Btw. on my looper there is also rhythm section with it's own pot, so I would have to dial three pots

While this solution will require me to trace a new board, it will at the same time lower the number of loose wires from seven to four (C32+, C32-, AGND, 11V) as well as keep the original neat outlook of my MC. And since I am already planning to cut the chassis edge, the board will fit right into the cutaway. And of course, I will be able to add a Master pot in the future, if I ever need one.

So I am looking for ways to trace and produce a new board. Meanwhile, to make sure that I really can do without a Master pot, I am going to solder a Thomeeque v1.1 board and try it out.

Good luck, keep us posted please

Thomeeque, I have a quck follow-up question:

Since I am planning to get rid of the Master pot, I can also lose the C6 capacitor, right? Do I need to change the value of C5 then?

Nevermind the horrible quality of the second schematic, it is because I imported the project into Altium.

Yes, you can do that, value of C5 should stay. I am not sure about polarity though. Both ends should be on the same potential (I expect there is half of A+8 also at C32- pad), so it probably does matter, but if you want to be sure, measure DC voltage at both ends (IC1B output and C32- pad) and orient C5 accordingly.

Cheers, T.

[Thomeeque]

One small note on version number, as it is obviously confusing: "v1.1" was actually the original published circuit, revised version is just "Rev1". It *is* stupid , I should have go either with "v1.2" now, or with "v1.0" before when publishing original circuit (as v1.0 was just something what happened at my home and nobody needed to know), but it is too late now. Sorry

[gnels]

Hi Tomas,

Boy do I wish I had found your excellent post when I was struggling with exactly the same problem a couple of months ago!  I also have a BOSS RC3 and wanted to plug it in the (non-existent) FX-LOOP. Lockdown gave me plenty of spare time so...

I have tapped into C35 rather than C32, using a few bits of wire and two 1/4 jack plugs. As you and kmos  point out, the looper pedal has its own rhythm and loop volume controls so I haven't included a separate master volume circuit - it's 'passive'.

Anyway, here's a link to what I did! Any comments welcome. It works really well but I'm not an engineer so I might be slowly frying it, who knows.

https://microcubemod.wordpress.com/

Cheers,

Gnels

[deadastronaut]

excellent....very simple.   

[kmos]

Gnels, as you have probably seen, a solution like yours had already been discussed here, along with the possible risks. Hope that yours works okay in the future. 

Meanwhile, the virus lockdown helped me finish my own project as well.

As I have previously written, I decided to use two tricks that I picked up from Thomeeque: using the socket as a mounting point for the board, as well as using L/R channels in a stereo socket as Send/Return respectively, thus having to drill only a single hole in the chassis.

So, first of all, with the help from a friend, I have retraced Thomeeques board to make it same 20mm width as the socket body:

I have dropped the Master pot as well as the C6 capacitor along the way, because I didn't need them. Also, with Thomeeque's help, I have figured out that C5 polarity should be reversed in this setup. Being 20x78mm, the resulting board stayed one-sided, except for a small jumper cable near the jack socket (marked red).

After that, I had to produce the board. I had never chemically processed a board before, so I chose to go with the tools I am familiar with and engrave the traces on a CNC router that I have access to. Turns out, getting a CNC G-code from Altium PCB project is a non-trivial task, which I solved using a free web-based Rapid PCB to GCode tool, that I just cannot recommend enough. This tool takes regular Gerber and NC drill files and turns them into code for a wide variety of CNC machines.

Lighter for scale
As a bonus, routing gave me nice guide indentations for drilling the board. Unfortunately, I had no ability to drill the board on the router itself.

After assembly and soldering the board looked like this:


And this is how it fit into the chassis:


I had to make a cutaway in the case MDF though, to give the board some clearance:


Finally, I have engraved the "Send/Return" markings with a Dremel tool both on the chassis and the custom cable that I had made:


This is the fully assembled Micro Cube after the mod. As you can see, there are no visible changes whatsoever, except for the FX loop jack socket itself:


If tuned correctly, the board sounds indistinguishable from the stock Micro Cube. I did the comparison test using a bypass toggle that switched the signal to the original C32 capacitor.
The only circumstance under which I could tell the difference was when I put dead batteries (7.5 volts) inside the Micro Cube. At that voltage, the Micro Cube's speaker power amp started shutting down, so I had to use headphones to hear the barely audible distortion at high frequencies.

Overall, I am very happy with the mod. It allows me to loop using Micro Cube's native sound, which I find quite pleasant for a small room.
I want to thank Thomeeque for all the help and guidance he provided during this project, and wish you all luck in yours.

[Thomeeque]

It works really well but I'm not an engineer so I might be slowly frying it, who knows.

Hi Gnels, there should be capacitors in series at both SEND and RETURN signals, so only AC part of signal gets out and in. It will probably not fry anything but it may cause some weird pops when switching etc., depending on what you will plug into the loop. So if you measure some steady DC voltage at signal not going thru original C35, put there also capacitor, similar value, with + pole at MC side.

T.

[gnels]

Thanks Thomeeque. Yes there is a pop when plugging jacks in and out, though no more so than my Marshall Valvestate which has an FX loop designed in. But it sounds like that's the solution, thanks! 

Also, perhaps I should move the insert point to c32 rather than c35, as perhaps that is upstream of the REC OUT/PHONES jack? Capacitor c35 seems to be downstream meaning the FX LOOP occurs after the REC OUT/PHONES socket. Annoying but not a major problem for me. Having a lot of fun layering different amps and effects onto the looper still with dry RC3 rhythm tracks. Such a difference.

Again, I wish I'd discovered this thread a couple of months ago. Keep up the good work!

Gnels.

[Thomeeque]

Small update to this thread - to make my tiny guitar corner tidier (to get rid of power cord and extra PSU brick), I have created PSU power splitter (or how to call it) to feed also my additional setup (wah and looper) with MicroCube PSU. PSU states 9V/500mA output, but it is not stabilised, under no load there are 14VDC (it drops to 12V when all is powered). Also MicroCube does not need all those 500mA, at least on living room levels (I measured only around 60mA consumption; same for looper, wah I did not measure, but it will be few mAs):







12V (-drop on diodes) is little bit on the edge for good function of those regulators, but it works quite nicely, I am happy with it (for gig or something I would definitely pack proper PSUs or at least test it properly first). Grounds to FX pedals must not be connected, otherwise it will introduce hum (they are already grounded thru signal cables, additional grounding thru power cables creates ground loops). 9V branch is meant for digital fx, 10V for analogue (closer to full battery voltage) - just to explain those crazy symbols at the outputs

Schottky diodes are used to minimise voltage drop. I don't know exact type number (I have recycled them from some prehistorical small stepper motor drivers), for these small currents and voltages any would do, I guess..

T.

[deadastronaut]

Excellent, i had to rebox my roland cube psu a few weeks ago,

So i will be doing this,  to add extra outputs, for no hum etc...

Which diodes did you use?

And when you say' grounds not connected'  on what?...

Cheers man .

[Thomeeque]

Oh, good questions, thanks, I have updated original post.

[deadastronaut]

excellent , just what i needed to know thanks thomas...

so i,ll go with 1n5817's then.

and only have the + coming out of the extra dc sockets ...got it.

i tried a daisy chain from the reboxed roland psu, and yes it hummed like a mutha when using other pedals

connected... nice one. i will knock up a vero to put in the psu enclosure. 

[deadastronaut]

[Thomeeque]

Nice, good job! Maybe just instead of Q I'd use IC prefix and for 10V branch (Q4) it is 7810 (or just leave both on standard 9 volts, maybe safer regarding relatively small input voltage). T.

[deadastronaut]

ahh i thought that was a misprint...

ok i will amend.

EDIT: DONE