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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

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 

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/

i was thinking about incorporating the Boost and buffer 2 from here: 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!

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!

Hello!

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

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!

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!  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 

My also newbie gut tells me it could be something between a ground loop, or input/output wires running close to each other, or the wires from the board to the pots tangled somehow causing cross-talk? The wiser people of this forum will be of much greater help 

if it's in a box, take everything out of the box, as far away from each other, and see if you still get the same whistle/noise

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



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:



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 

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:




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  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?

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.

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

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! 

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.

Some eye candy from the design:

Good morning from greece!

I don't want to ruin this beautiful thread with my own stuff, so let's continue this here:

http://www.madbeanpedals.com/forum/index.php?topic=30407.0

Marshall Arts, I visited, examined and tested everything you suggested in that link, but things didn't work out well... On the other hand, your looper schematic works perfectly in terms of tone and volume and function, it's really amazing! BUT I still get that huge pop when spillover is turned on or off via relay, it's not that innocent bypass pop, it's something else... Measuring voltage at the output Jack I get 0V when bypassed, 0V when fx is on, but 1.1V (!!) When spillover is activated (constantly). It's that big voltage difference that makes the huge pop... Any ideas on that?