Need help with my TB loop-pedal

[vikko98]

Hi,

New here and I'm finding all this DIY-stuff very exiting. Everything from building fx-pedals to guitars. But I have no deeper knowledge regarding electronics, just enough to understand some stuff. Story of my life, I know a little about alot of stuff but there are only a few things that I know really well.

If this topic is posted in the wrong section of the forum please move it to it's right place.

By the way, I'm also very good at making short-stories into a novels but please, bear with me.


Anyways...

I'm just about to get finished with my pedalboard. It has taken awhile to get there but now I have everything I need. Well, almost...

I had been looking around for a switching system until I settled for a Carl Martin Octa-Switch. It has alot of good stuff (like 8 TB programable loops) but a few drawbacks like no tuner out and there's no way to disengage the loops although it's true bypass. If you don't know anything about the Octa-Switch you can read more here: http://www.carlmartin.com/product_octaswitch.htm

If you want a tuner out/mute and a clean sound you have to give up two banks. Which to me is kinda disturbing 'cause there are only eight programable banks and I want to use them all. To combine my FX-pedals in as many variations as possible.

Therefore I decided to build a TB-loop with a tuner out/mute function. My idea was to put the Octa-Switch in the loop so I could be able to bypass it going straight into an A/B-box I have at the end of my signalchain (choosing between going to Amp 1 or 2).

So I built it and right from the start I got problems. It put a cloth over the sound even with short cables. So I thought that I had soldered something in the wrong place or that there were cold solder joints. So I started over and measured everything with a multimeter. No disturbances and no Resistance anywhere.

But still the same problem arose so I decided to skip the TB-function and put in a buffer circuit. Well, that solved the problem. It removed the cloth and my guitars sounded clear and beautiful. So began hooking everything up. Cables (good ProCo ones), put the pedals in the loops of the Octa-Switch, and fixed everything to my pedalboard. Whoohoo!!!...finally...

So I began programming which pedals should be at which bank on the Octa-Switch. I was ready but, what the f**k!!! What's wrong with the Maxon PT999 Phaser (a really old one) and the BYOC Mouse (RAT-clone)? There's a really huge loss of volume in those two pedals.

At first I thought it was the Octa-Switch that was malfunctioning 'cause it had already been sent away for repairs (the buffer didn't work). I have been in contact with Carl Martin and they made me do some more troubleshooting and I discovered that my own loop-pedal was the bad guy again.

If i plug my guitar straight into the Octa-Switch the before mentioned pedals work as they always have. No volume drop. So I tested putting just the Phaser and the RAT-clone in my loop-pedal and there it was, the same volume drop.

So I thought that I should try disconnecting the buffer, making the pedal TB again, and use the built-in buffer in the Octa-Switch instead. But the cloth was back and the pedals still dropped in volume.

And this is where I'm at now, I really don't now what to do. Since the Octa-Switch is TB (except when using the buffer) there shouldn't be any problems. I know it isn't the buffer circuit 'cause I put one just like it in the A/B-box. A guy at a swedish guitar forum thought that the circuit design of my loop-pedal wasn't compatible with the pedals (incl. the Octa-Switch). I know that the wires in the pedal make for some signal loss but isn't a buffer circuits function to "remove" the them?

Well, I found the schematic/layout at http://www.singlecoil.com/tb-strip/dia12.html and my pedal looks like this (UT means OUT in swedish):



The signal is routed like this:

Loop and tuner/mute disengaged: signal between IN hot and OUT hot.

Loop engaged: Signal between IN hot and SEND hot + RETURN hot and OUT hot + if i connect the SEND and RETURN jacks with a cable I got signal between IN hot, SEND hot, RETURN hot, and OUT hot in all different combinations.

Tuner/mute engaged: Signal between IN hot and TUNER hot. It doesn't matter if the loop's engaged or not.

I can't find anything that doesn't ground properly.

The buffer circuit looks like this:



IC: TL071
C1: 1K63
C2: Jamico 22 uF
R1,R2,R3: 14k

If someone could shed some light I would be a thousand times grateful.

/Niklas

[vikko98]

I've written the values on the resistors wrong for the buffer circuit.

It should be like this:

IC: TL071
C1: 1K63 / 100 nF
C2: Jamico 22 uF
R1,R2,R3: 2M2

Sorry for double posting.

/Niklas

[dmc777]

Not trying to hijack your thread but I have a similar question involving the EXACT same buffer. I have a dual loop TB pedal and was thinking about adding the buffer for now and possibly adding volume and blend controls controls to it.

I first want to accomplish how to add the buffer. Any suggestions?

[jkokura]

What I would suggest is that you build a buffer splitter instead, have that right at the beginning of the signal, and then simply set the first switch to a mute, and then the second switch as the bypass loop for the Octaswitch. So the signal path would go like this:

Guitar In  > Buffer/Splitter > (output 1) Mute Switch > Bypass switch > Octaswitch > Bypass Switch > Ouptut
                                      > (output 2) Tuner output

Here's a thread about the buffer/Splitter over at BYOC's forum: http://www.buildyourownclone.com/board/viewtopic.php?f=41&t=18466. There may be a layout in the gallery here, I haven't looked. I've built the perf version of this into a volume pedal and it works for splitting the signal to the tuner and having no tone loss.

Jacob