Project I'm planning- EHX Frequency Analyzer mod

[SpectralJulian]

Well, if I made ground be the tip connector, +15 be sleeve, and the output be ring, that would lower the chances of the +15 volts being grounded substantially wouldn't it?

[arnehepp]

Sounds like fun.


Why add a tune expression pedal jack?  You can just use the CV in and use a CV pedal to control the frequency.
-Colin

is this also appliable for the mod you posted in the tutorial department?

[expanoncolin]

Well, if I made ground be the tip connector, +15 be sleeve, and the output be ring, that would lower the chances of the +15 volts being grounded substantially wouldn't it?

It certainly would, but you still gotta be careful

is this also appliable for the mod you posted in the tutorial department?

Yeah, it's true that if you add a CV in to the FA prior to doing that mod you could do this...

-Colin

[SpectralJulian]

So, I think instead of doing one big cumbersome project, I'm going to do it in steps.  

1. Add an expression pedal jack, carrier in/out jacks, and a square wave switch.

    I just wanted to make sure with you how you do the square switch, I think you wire a 15k resistor from pin 9 of the wave generator and also run pin 9 and pin 2 to a selector switch to select square/sine right?  

  Problem: I have an old keyboard volume pedal that I used to use as an expression pedal for my now destroyed johnson analog delay.  I was thinking about rewiring it to work with the frequency analyzer (it is actually wired to ground the signal I believe    The pot in there is twice the resistance of the shift pot (which is 250k).  I think the best solution to that would be to add a 500k resistor in parallel with it to make it closer to the range of the 250k shift pot.  Am I right to think that, or am I overlooking something?  

2. Add a sequencer in jack and build an external 8 step sequencer (3 is a little too much now that I think about it!)  The box would have several stompswitches- one that bypasses the original pot and switches to the sequencer, one that switches from step to auto, and one switch that steps through.  

  Problem here is I have to make 4 connections from the sequencer to the frequency analyzer, so I'll probably use some other kind of connector besides audio cable (so I can keep it to one cable going inbetween these two boxes)  If I wired the 2pdt that changes from the shift to the sequencer into the frequency analyzer, I could do it with a stereo cable, but I don't want to mess up the layout of my frequency analyzer with big ugly stompswitches.  Messing the sides up with tons of jacks and little switches does not bother me though.  
 

 Any suggestions of the kind of cable to connect the two?  

3.  Add an LFO to modulate the pitch of the VCO.  I'm not exactly sure how to do this or which LFO schem to use here.  Or if I can even use an LFO since technically it is not CV that is controlling the VCO.  I could always make a vibrato with a square/sine switch on it, and put it between the carrier out and carrier in.  

4.  Add more synth module type stuff.  I'm thinking a sample and hold sort of thing would be cool, but I am not sure if I quite understand how sample and hold works.  I read the Moog control processor manual (I don't own one, but it is nice for the ideas) and it didn't really explain it very well.  

Well I'll explain how I think it works and then you can correct me hopefully.  

It has two inputs, one for LFO, one for the signal getting modified, and the output.  Everytime the LFO rises above 0V, the S+H samples the signal getting modified, and holds the output at where that signal currently was, until the LFO passes by again.

[expanoncolin]

Sounds like a big project... let's see.

1) You could just replace the pot-buying/making replacement wah pots isn't too hard, just take a look at how the volume pedal is made.  Wiring 500k resistors in parallel between the center lug and side lugs works, but bugs up the response a little.

2) If I was you, I'd either use two stereo jacks and ground the sleeve conductor on both, or I'd wire directly.

3) For an LFO, my favorite schem is this one:

From there, you can modulate the pitch via a DIY vactrol (there is a good howto thread in the articles/tutorials section).  That being said though, you could reduce the amount of connections you need for the sequencer by simply making its output a CV, and having one simple stereo jack with an output supply voltage, ground, and an CV input, which then goes to this CV->resistance vactrol, which you could then use for teh sequencer AND the LFO...

4) Sample and hold takes some varying voltage, and at some rate "samples" that voltage and holds it at that point until the next time it samples.  The easiest way to think of it is as a triangle wave being converted into a staircase wave.  A sequencer can do S+H sounds... I wouldn't say you needed one that much.

Good luck...

-Colin

[SpectralJulian]

Oh cool, I didn't even think of that.  I'll have to redo my schematic some, but I've got time.  My current project is building a cab for my fender bassman, and the frequency analyzer mod will be right after that.  

I think my volume pedal's stuff works so that you can unscrew the resistor and put another normal same sized one in.  A lot easier than getting a wah pot.  

I think I'll put the expression pedal project off a bit, because I want to make a switch box so that I can control all my effects pedals with one expression pedal.  I'm going to have to read more into the vactrol, but it seems that if I converted my volume pedal into a CV pedal that the resistor inside wouldn't matter too much.

[SpectralJulian]

Let me think outloud for a minute.

I'm going to have to modify the sequencer schematic portion back to a CV controller sequencer, which is easy, I'll just change the pots to 100k, and wire them back the way that Dnny had in his sequencer schematic.  I'll make it output voltages from 0 to 5 volts as is usual for a CV controller (I think) I'll also mesaure the ampere draw.  It will run off its own power source ov 9volts, and I'll use a voltage divider to bring it down to 5 volts power, so I'll have to know the amps to find the correct resistance.  

I'll get some LEDS and LDRs and try making a vactrol that has similar response to a 250k log pot, and figure out what range of voltages it likes and at what current for the LED.  Then I'll have a voltage divider from the CV input to the LED so that it functions correctly.  

I'll wire the LDR half of the Vactrol in parallel with the stock 250k pot and probably make an external footswitch to switch between them.  

When I add the LFO, I'd have to make a simple CV mixer with one pot, and I believe that would control the intensity.


One question though, did I get the square wave mod for the frequency analyzer VCO right or was I missing something?  

I just wanted to make sure with you how you do the square switch, I think you wire a 15k resistor from pin 9 of the wave generator and also run pin 9 and pin 2 to a selector switch to select square/sine right?

[expanoncolin]

It sounds like you're making the sequencer part a little overcomplicated-with CV outs on a sequencer, you could just choose the proper resistor value for one of them, use it over and over again, and wire it to an LED.  (sorry if I'm misunderstanding).  I would wire the LDR and pot such that you could switch between the two, rather than in parallel.  You could put another pot on the LDR side if you wanted some sort of depth control.

I'm not sure about the square wave mod as I don't have one in front of me, but find the square wave out of the function generator and use a resistor divider network to get it to the proper level, if it's not.  Then just put it to your carrier in point.

-Colin