DIYstompboxes.com

Hi friends,

So, I am pretty new to diy electronics and even newer to building effect pedals, so please pardon my ignorance on probably SOOOO many things.... that being said, there are two things that I am trying to make sure that I am doing correctly and could use any help I can get... as a sanity check, at the very least... and so I don’t screw up all my work on the other extreme.

1) I’ve been putting together this Earthquakes Disaster Transport Jr. from the layout (the original one, not the “tails” one) provided here: http://tagboardeffects.blogspot.com/2017/12/earthquaker-disaster-transport-jr.html?m=1
I have the whole board assembled and am nearly finished the off board wiring, for which I used the following as a guide: http://beavisaudio.com/techpages/stompboxwiring/
My first question is this (and I apologize if this is a really dumb question)... for the main circuit layout shown on tagboardeffects.blogspot.com for the pedal, there is one ground wire coming out of the board on the bottom left, there. On the off board wiring diagram, though, it shows the placeholder circuit for whatever you’re wiring up as having two different “ground” wires/connections.... My initial thought was that I just connect everything labeled ground together.... so the sleeve of the output, the sleeve of the input and the middle left contact of the stomp button would all feed into that one ground wire from the circuit board layout. Would that work? Or am I going about it/thinking about it wrong?

Then, thinking about all of that got me thinking about effect pedal grounding in general. I’ve read so many posts about it, but I feel like I still don’t fully grasp it.... I always thought that all grounds in an audio effect pedal connected to each other and went back to the negative of the power source. Is there more to it than that with effect pedals? Or am I completely wrong in thinking that? I am new to all of this and just trying to wrap my old man brain around it.

Thank you all for your continuing support, education, kindness and overall helpful dispositions. You’re all the best!

I see dubious solder joints. They may work when shiny-new and fail when tarnish sets in.

Hi very useful information about the resistor as old circuits are misleading. what about calculating notch filters? if I understand the circuit correctly, then a pair of 27k resistors sets the gain = 1, like a pair of resistors in other phasers on optics and transistors. Apparently 27k + 6.8n sets the cutoff frequency, but how do you calculate the changes caused by the operation of the LFO? If 27k / 1.2k is a voltage divider, then we are losing more than 20dB, 27k + 27k sets unity, where do we return the gain after the divider?

If you take a regular opamp based APF stage there are sort of two parts to it. A "unity inverting" part (from 2 equal resistors at the inverting input), and a "frequency dependent part" (a simple LPF or HPF) at the non-inverting input. These parts act together and make the overall gain 1 (or minus 1) depending on whether you use LPF (or HPF) in the frequency dependent part. Many FET based phasers will have an HPF as the frequency dependent part and so tend to invert low frequency signals (i.e. close to 180 degrees shift) and let through high frequency ones with little phase shift.  The exact amount of phase shift for a frequency depends on the RC time constant of the LPF (or HPF). An op-amp based phaser will typically vary R somehow.

With this OTA based APF there are similar parts. A pair of equal 27k resistors set inverting unity gain. But the frequency dependent part (the RC) no longer has a resistor R. Instead of R you have 1/g where g is the transconductance of the OTA (which is determined by the control current supplied from the LFO).   Don't think of the voltage divider at the OTA input as affecting the gain of the "unity inverting part". It is more to do with making sure the OTA behaves nicely.
For example, imagine you have high frequency audio input. The capacitor in the APF then acts like a short circuit, so the input goes straight to the Darlington buffer, and so to the output.  So for high frequencies, the gain is 1 and phase shift close to zero. So no signal loss due to the voltage divider at the input.

Wasn't I going to design an FV-1 board with a Teensy?  Yeah, well I thought about it and decided I might eventually do it, but I want to get back to trying to record some songs rather than invent things.  That said, I don't have a fuzz box of any sort and so have decided to build something like what's in the thread title.

I have a SparkFun ProtoPedal board.  https://www.sparkfun.com/products/13124

I'm using TinyCAD and VeeCAD to create the layout for this.  IME this is WAY better than improvising as I go or trying to do it on a breadboard first.  VeeCAD let me easily create the layout of the SparkFun board and update the netlist from the schematic as I go.  I like this part of the project as it's straight up puzzle solving. 

I only have the BMP circuitry on there at the moment but I think I will have enough room for the 3-band EQ based on a single op amp stage.

I'll publish my schematic once it's done and let you critique it.  I looked at some of the compendia of BMP schematics and notice that most of them are architecturally almost identical.  There is one variation where you take the clipping diodes off the second gain stage, which can be done with a simple SPST, which I think I will also do.

Quote from: Jarmake on Today at 04:36:23 AM

I use an old wall wart (~10V)

L074:
4: 14,7V
14: 13,7V

14V with 10V supply?

'

Yeah, that's correct. When I measure straight from the power input to the ground it's 9,85V and when measuring between ground and pin 4 and 14 it's ~14,5V and ~13,5V.

Here's a couple of pics and a bit of a video, where you can see the input voltage and 4&14 pin voltages.