madbeanpedals::forum

Hello everyone, and thank you for accepting me here  ;D

Total noob on the forum, so forgive me if i break the rules from time to time  ::)
I've been working on this for a couple of months and i think it's time to show it around, get some feedback, do some troubleshooting etc. It's a pedalboard switcher, a bit different than what we usually find on the market. I wouldn't say it's got brand new features, but the whole thing is very easy to use

First things first, a BIG thank you to bryan for sharing so much info and marshall arts for the guidance with this project so far. It's built around the arduino mega, and features:

• Separate boxes for controller and looper, this means you can have it all set up on your pedalboard somewhere far away, and only use the controller with the foodswitches in front of you.
• 10 loops, the last 2 of which have trails/spillover option (thank you guys)
• midi control with 7 different parameters stored per patch. that includes program change, CC and other stuff
• 4 amp switches, which can also be used for tap tempo input for pedals that support it
• expression pedal support right next to the controller. It can control any midi parameter real-time
• switchable pre-gain on guitar input, post-gain on guitar output, i intend to give it a +/-9dB range
• 100 presets stored in banks of 10
• tap tempo stomp (green led blinking)
• bank up/down stomps
• patch/stomp mode stomp (when active, you can directly control any of the loops via the 10 stomps. for improvising situations)
• Color LCD resistive touchscreen. Yes i wanted to have a capacitive touch, but could not find something that fit the project. It works just fine though!
• The whole setup/programming is done on the screen. This makes it very easy to understand and fast to configure, even if you've never seen it before!

The relays box is under heavy construction/design, the prototype of the controller is already here and working (attachments)

So what do you think about it guys? Any features worth adding?

Looks gorgeous, but what does "HVYGBJI" mean?

Quote from: rockola on November 27, 2019, 02:50:15 AM
Looks gorgeous, but what does "HVYGBJI" mean?

hehe it's just random gibberish i wrote for the program name
I will post the menu screens with all the settings later so we can see how deep this thing can go  ::)

Very cool. I like having bpm shown on screen. I don't have any midi capable delays but would be cool to do presets and my Nova delay is annoying at best to preset.

Some eye candy from the design:

And here is my spillover problem, breadboarded.

I'm sure there's something else wrong with my setup, not the schematic itself. I have been swapping caps and op amps to see if i spot anything bad, but i get the same behavior: from bypass to fx on, no pop. From fx on to spillover, huge pop. From spillover to bypass, huge pop. Measuring from ground to output jack, when spillover is on, i get about 1V DC. I have everything powered from an isolated supply, so i have separate supply for the delay, the audio signal of the looper, and the relays/arduino, just to make sure the pops don't come from the relays themselves. I followed Marshall Arts fantastic looper schematic for loop 7, exactly as it is, the only difference is i replaced all 100K resistors with 150K (that's what i had in hand), and the Vb resistors of 10K replaced by 18K. My op amps under test are all TL072. I know the breadboard pics won't help, it's a tiny mess... ::)

I also tested another mixer a couple of days ago, but still get that annoying DC which gives the huge pop... i also attach a hand drawn schematic of that one.

The BOTY competition hasn't even opened yet and we have the winner...

Quote from: Willybomb on November 28, 2019, 02:28:16 AM
The BOTY competition hasn't even opened yet and we have the winner...

:-X :o

As promised, here are a few of the main screens/menus on the controller. I finally got to embed pics in my posts, yay..!  ::)


Hope i didn't make your eyes bleed!  ;D

Nice. I am very much interested in the technical details. Schematic, Display, code :-)

The code is of dual nature. the screen is a Nextion 4.3", which happily does all the heavy weight lifting, running its own code for the menus buttons etc, and reports stuff to the arduino via serial port. The arduino on its turn sends its own data to the screen. it's simple, but it's like writing the same thing twice. I'd love to share schematics and some sample code, heck might even make a kit or tutorial :)
But i have to get over the spillover problem first so i can complete the relays box. And i'm also in the research for volume control via digital potentiometers. The MCP41010 (10K) has some basic circuit in the datasheet and that's where i'll begin. I also note that, even if i do the 10ms mute while changing patches, i think i'll need to do the same on the inputs of the spillover fx (9+10), since the pop will be repeated inside the delay, should there be one at its input.

Summarizing some points for your debugging endeavor concerning the pop:

I see no reason in the hand drawn schematic of the mixer above for a DC on the output. For the spillover circuit used in Eoo3 I provide a simplified view of the relevant part of loop 7:
(https://i.postimg.cc/W481L29f/191129-Spillover-Excerpt.jpg)

It's hard to image, where the DC on the output should come from in bypass mode (that's the mode the schematic shows): C27 should block all DC coming from the circuit, if R52 is connected to GND, there is no chance for a potential difference on the OUT.

In FX mode, Return is directly connected to the OUT Jack, so if the FX itself has DC in it's ouput, that would be the source (unlikely, but easy to measure). The IN signal is fed to the FX in AS WELL as towards C28. It is directly fed to the Output via C30, where it is mixed with the return signal (this is where phase issues might occur with the direct signal part of the fx return, but I did not care, as I never had any issues).

On the input, the send is grounded in bypass mode. Switching to FX mode should not create any popping. The output switch has pulldowns on both sides, this should not create any popping either.

If I fully understand my approach (it's been a good year now...), the direct signal in fx mode coming through C30 should not cause any issues. I think I tested that as well, but to be 100% sure, you could test the following:

Pull R60 (any trails would disappear)
Switch from bypass to FX mode
If the pop is gone the phase inverted (IC1A!) direct signal does not go well with the non-inverted signal from the return path (RET7)

Can you try that?

P.S. This is an impressive work, if you get all of this to work. Having designed Eoo3, I know about the effort. Having a display and other digital components in such a unit can induce some serious HF noise in the audio path, and fixing that is a PITA. I had issues with the 7-segment display driver... my goodness!

If I should ever design a 3rd version of this, I would try to add a WIFI Chip (ESP-wroom) and make the unit configurable via smart phone. Other features I failed with were configurable fx order and configurable displays/label on the fx buttons.

For the digital potentiometer: It does not work for continous volume control, it's just not discrete enough. It's ok for setting a static volume, though. You will have to mute the output for the volume change time, though, because it creates some nasty artefacts during the change... They are available in 50k and 100k (recommended)as well.

Damn, I'm looking forward to getting back home to the bench now.

Yes i've done some research on digital pots and i don't intend to use them to change the volume continuously, only once when the patch changes. Continuous changes of the MCP digipots creates zip noise, i've tested it. There are special digipots that detect zero crossing, but i think my choice is more than enough for this application.

Also, here's some fresh new pics of the controller and relays units, side by side, and how  they are connected via serial cable:
(https://i.imgur.com/oQx1jkS.jpg)

(https://i.imgur.com/f1ItUgU.jpg)

I will research the schematic you proposed again tomorrow afternoon when i get back from work. Yes it is quite an amount of work and man-hours invested in this! Weeks, if not months...

As for the LCD, i don't know about any EMI from it yet, i'll find out soon when i connect the guts of these 2 units :) But i'm counting a bit on the 6 foot long cable that might get rid of any possible digital noises on the way... yes i've been through hell with all kinds of digital noises too! Imagine this: making a digital tremolo with patches, with an LED and LDR. Even after changing the PWM frequency above the audible range, the LED emits something that the LDR picks up as noise, it was totally WTF? Unexplainable noise, optical fibres also carry it with them... it's like part of the optical wave. Something i'd like to develop further one day when i have more time  ;D Long story short, i had to apply a sallen-key low pass filter to the LED, the only way to make it go away...

P.S. Are you using KiCad for the schematics?

I am using eagle for schematics :-)

Where did you get the enclosure from? It's great as well. And yes, having a separate patch box will help with HF interference.

The enclosures for the controller and looper are 1mm stainless steel sheet metal, and the top part of the controller looks like this:

(https://i.imgur.com/AOQMs9I.png)

Lucky me, i've been working on CNC programming for a while now! But the stainless steel finish is not easy to paint, takes special primer and i didn't have time to deal with the decals yet.
I tested the schematic you sent me about the blend/fx on, and i must say though i don't get huge pops anymore, there's quite a lot of noise when the blend is activated. Maybe it's my digital delay pedal that somehow gets its own noise in the circuit, will keep on testing this whole week on different schematics and ideas and let you know. I remember i had built a couple of years ago a nice programmable bass guitar looper, 3 loops,  5 patches, phase reversal, blend and volume stored in patches, was dead silent and all the nice frequencies came through. This was the schematic:

(https://i.imgur.com/X2uBDBv.png)

it was a modified version of a K&R blender and now that i see it again i have a lot of changes to suggest to myself haha  ::)

Good morning everyone, the project is progressing slowly but steadily. Today i got the first chance to test it all out, basic functions like simple switching and MIDI. It all works fine, but the midi creates a ground loop (midi cable and audio jacks on the same pedal), is this normal? Should i get rid of the midi ground, or  add a small switch to lift it?

PS: the LCD makes no noise at all, the whole setup is dead silent!  8) But one thing i wanted to avoid that i totally can't avoid: connecting analog and digital ground together at some point. without it, this thing like a noise beast! Why does this happen?   ???

Thank you all for the support and ideas, i'll keep posting progress  ;D

Hello!

Glad to report, the rig is working quite well, a demo video might be coming soon  8)

I use an expression pedal to control midi CC for digital pedals, and even though it works fine, if i plug in the jack while the unit is on, the board gets reset. This is because expression pedals use a TRS jack with T=analog input, R=+5V, S=Ground. So i guess the +5V and ground get short-circuited momentarily and the unit gets the reset. Any workarounds for this?

Thanks everyone!

Wowzer this project is cool! Are you gonna be making the code and schematics available for it? This would finally give me a reason to use my nextion lcd...

note to self and everyone else interested: Yes, as Marshall Arts guessed in a previous post, the nextion DOES produce noise and feeds it back to the audio signal. In my case, playing really loud with the amp last night in a studio made me notice the tiny buzz. The 3 meters long cable from controller to relay unit might be helping to attenuate this noise, but i will try the following as suggested on other nextion audio projects:

• connect a 2mH inductor between LCD and +5V power feed
• weld a 220uF between +5V and Gnd on LCD.

This fix allegedly removes almost 90% of the noise, so it's test time! i will report soon with results!

Watching this with interest.  I've built a lot of MA's projects so I know how savvy he is.  He's a great resource and I suspect between you both you'll get this sorted out.

it's really interesting to me too yes :)

I would like a couple of suggestions on this:
Pre/post gain: the range is +-dB and when used at +dB it will act as a buffer. But i've been reading a lot lately online that a booster can be a buffer when set to unity gain (SHO?), while there's also the exact opposite theory:

http://www.muzique.com/news/boosters-are-not-buffers/ (http://www.muzique.com/news/boosters-are-not-buffers/)

i was thinking about incorporating the Boost and buffer 2 from here: http://www.muzique.com/tech/op-amp.htm (http://www.muzique.com/tech/op-amp.htm)

but i'm not a specialist and i don't know if this is the right or wrong direction... i'll use a digital potentiometer to control the gain upon loading of each patch.
any ideas are welcome!

The direction is OK....I tried buffers in various locations in the signal chain (up to four in my rig) and eventually decided that one on the I put (post fuzz/wah) is enough for me... YMMV. I usually build the Klon buffer (OP amp based). Using a double OP amp for buffer and boost is a great approach. Your pcb will invert the signal (no big deal, just in parallel chains to be aware of). And: Every OP amp adds a bit of noise (noticeable!), so I recommend to use as much as it takes, but not more (as always in life). :-)

Quote from: Marshall Arts on December 15, 2019, 01:19:39 AM
The direction is OK....I tried buffers in various locations in the signal chain (up to four in my rig) and eventually decided that one on the I put (post fuzz/wah) is enough for me... YMMV. I usually build the Klon buffer (OP amp based). Using a double OP amp for buffer and boost is a great approach. Your pcb will invert the signal (no big deal, just in parallel chains to be aware of). And: Every OP amp adds a bit of noise (noticeable!), so I recommend to use as much as it takes, but not more (as always in life). :-)

Affirmative! Breadboarded the AMZ buffer/booster last night and does it sound terrific! Though i have one more question: what is the use of buffering the signal before boosting it? Wouldn't just an inverting amplifier to the trick directly? Does the order of them matter impedance-wise? Buffer->Amplifier or Amplifier->Buffer?

here's also a teaser pic from the upcoming complete project of a custom pedalboard case  ::)
(https://i.imgur.com/SpCwrCJ.jpg)

There is no set rule for the use of buffers, unfortunately. Try and decide. Trust your ears. As I said, one buffer at the start of the signal chain worked for me. But I don't use fuzz, a lot of people do...

Hello pedal gurus, merry Christmas!!!
:) project is on a small halt, but I'm designing the rest of the stuff to complete it. I don't know if I'll make it on time for the ΒΟΤΥ, but it's ok :)
I have 2 questions that would be really helpful to clarify:
1) Amp channel switching. Most switchers provide a TRS jack for dual switching. But looking at schematics, many footswitches have less with diodes and momentary or latching switches. Is it enough to use relays for the switching? Should I include optional simulated momentary action? Does this cover most of the amps?

2) about tap tempo, the pedals that support external footswitch, let's say I want to sync 2 of them, again using relays. Is it ok to use a TRS for 2 tap pedals, or will the common sleeve cause problems? So I'll need to use 2 mono jacks instead of one stereo? Sorry for asking this, I never owned any tap tempo pedals and can't think about the complications...

Thank you!
Vangelis

Nice project, waiting to see more!

Hey Vagos, is this project still going?
Would love to see a video or some more pics!!

Have you made any progress?
I am very curious about the result.