Systech Harmonic Energizer - Mods/Analysis

[Barracuda]

So lately I've been playing around with wah circuits and twin t's (thanks R.G. for the Geofex article) to make a frequency boost pedal, and the Harmonic Energizer is actually exactly what I wanted to make (because it has bandwidth control).

But I've been having trouble understanding completely what IC 'c' and 'd' do in the circuit.
I've considered modding this to suit me more if I could, but I need to understand what their purpose is and how they work if anyone has any info?




Thanks!

[robthequiet]

I have a qq about how the expression pedal is implemented. Is it just a matter of adding an outboard pot in a wah-type treadle or is there some extra hardware involved?

Edit: Never mind, I found it at the manufacturer's website:

http://www.godlyke.com/_literature_95293/Schematic_-_EV-5_Expression_Pedal

[PRR]

IC a and IC d are integrators. Two integrators in a loop forms a resonance. IC c changes the loop gain which *probably* changes where the loop resonates in frequency. Various connections and taps give LP, BP, HP and notch filter responses. I would assume that added drek around IC shifts the narrowness of the resonance action. I can't say I have seen quite this scheme before.

What is it not doing for you?

[Mark Hammer]

Consider plopping a pair of diodes and treble-limiting cap in the feedback loop of IC1B.  You'll have a resonant overdrive.

[Digital Larry]

Look up "state variable filter design".

[Barracuda]

Hey guys thanks for the replies. I'm going to research a bit into what you have mentioned as I'm a bit unfamiliar with some of it. It's not that it isn't doing the right thing for me, I'd just like to know how it works to see if I could expand on it, or incorporate it into something. But more for knowledge for future designs, thanks for the help I'm gonna go read up a bit now!

[amz-fx]

That schematic in the first post looks wonky around the TIS97. There is no dc path from the base of the transistor to either power or ground. It is probably in error.

The junction of the 22k/240k probably should be jumpered across to the junction of the 1k/10uF. 

regards, Jack

[Mark Hammer]

That schematic in the first post looks wonky around the TIS97. There is no dc path from the base of the transistor to either power or ground. It is probably in error.

The junction of the 22k/240k probably should be jumpered across to the junction of the 1k/10uF. 

regards, Jack

I built the Madbean version, using his layout, and can confirm that it works.  So unless there was an error in the drawing that was rectified on the board, that you point out regarding the TIS97 appears not to be a problem, for whatever reason.

But you are correct in noting the missing jumper between the 22k/240k pair and the 1k/10uf pair.

FWIW, the Madbean version uses a 2N5088 for the transistor without any problems.

[nick d]

        Built this on perf , replaced the power supply section with a stock diode/cap filter section .
     
         Works fine , but it will not make you sound like Frank Zappa , although I have just found that I have Stinkfoot !

[Mark Hammer]

A little green rosetta, will make that stinkfoot betta.

[bool]

        Built this on perf , replaced the power supply section with a stock diode/cap filter section .
     
         Works fine , but it will not make you sound like Frank Zappa , although I have just found that I have Stinkfoot !

Lucky you it works fine.

Imagine it was a HORMONIC Energizer instead and it would malfunction. The things it'd do to you ... oh, my!

[snk]

Hello,
I built it today, and it sounds great. I would like to add an expression pedal to control the frequency(with a switched closed jack tied to the freq pot), but my attempts failed : I tried with several expression/volume pedal (2 of them have a 50K pot, so it should match), but i'm getting only noise and squealing while moving the pedal...
Would anyone have a clue how it should be done (or did anyone manage to make such a mod) ?

[Mark Hammer]

Chances are pretty good that the volume/expression pedal is wired up a little different than you think.

You will want to use a stereo switched jack, like what gets used to turn speakers off when a headphone plug is inserted, and make sure that the pot in the expression pedal is NOT connected to ground.

Many expression pedals will assume that the effect being controlled will be providing a supply voltage of some type, which is divided down by the expression pedal pot.  Since you are going to be subbing an external 50k variable resistance for the normally-internal 50k, you will have audio flowing through the cable between effect and expression pedal.  This recommends use of 3-conductor shielded cable (2 hot + shield).  HOWEVER, the pot being foot controlled should NOT be grounded, but simply be a free-floating variable resistance wired up to the other two conductors.

[snk]

Hi, Mark,
Thank you for your answer (and your knowledge).
I have used a stereo switched jack.

make sure that the pot in the expression pedal is NOT connected to ground.

This might be the issue (and all my expression pedals behaved the same : Moog EP3, Boss FV300, Behringer FV100...).
The only way to be sure is to open them and check them, right ? If they are all connected to ground, is there a way to make them work (without modding the expression pedal) ?

[Mark Hammer]

Much like gate/trigger pulses in analog synthesizers, there are several standards when it comes to expression pedals.  Sadly, it's one of those areas where we could all benefit from a database that lists the protocol used for each.  Two years back, I bought myself one of those Source Audio Hot Hand controllers.  It outputs two different formats for controlling Source Audio pedals and Line 6 devices.  The Line 6 protocol is simply a 0-10k variable resistance to ground.  The Source Audio protocol is 0-3.3V.  Given how many pedals that use 9V supplies have an expression-pedal jack, I don't know which among them expect a variable resistance to ground, expect a 0-9V control voltage at either the tip or ring contact of a TRS plug/jack, expect a 0-5V cv or even a 0-3.3V cv or something else.  If a voltage, is the voltage to be provided by a source in the expression-pedal (e.g., 9V battery), or coming from the effect?  If coming from the effect, does it come in via the tip or ring contact?

It's certainly not chaos, but there is enough variation that one needs more know-how for oneself and from music store staff (and forums!), and perhaps clarity in the user manuals, and probably a few different distinctively-marked patch cables to run from the expression pedal to different effects.  So, for instance, one that simply provides the wiper and ground for controlling Line 6 type pedals, one that uses TRS but tip for output and another TRS using ring for output, and so on.

If the expression pedal you intend to use employs a TRS jack, then I'll suggest that you mod it by installing a toggle to lift/connect the ground side of the internal pot.  The patch cable you would then use for controlling your Harmonic Energizer frequency would use the tip and ring contacts for the variable resistance, as well as the shield, but the shield would simply "protect" the audio path, without making any contact with the expression-pedal's internal pot.

[snk]

Much like gate/trigger pulses in analog synthesizers, there are several standards when it comes to expression pedals.  Sadly, it's one of those areas where we could all benefit from a database that lists the protocol used for each.

Thank you, Mark.
You confirm what i suspected when i tried to understand if a standard existed for vintage analog synths allowing for CV control of their filter using an expression pedal. None of the schematics i have read gave any kind of useful information, and what was working with one synth didn't work (or half-worked) for the other.

If the expression pedal you intend to use employs a TRS jack, then I'll suggest that you mod it by installing a toggle to lift/connect the ground side of the internal pot.  The patch cable you would then use for controlling your Harmonic Energizer frequency would use the tip and ring contacts for the variable resistance, as well as the shield, but the shield would simply "protect" the audio path, without making any contact with the expression-pedal's internal pot.

Yes, I want to use a pedal with a TRS jack. I'm quite reluctant to modify the pedal itself (as i will use it with other instruments), but i guess i could build such a toggle on the cable itself, isn't it ?

[Mark Hammer]

I don't know how easy it is to pop a hole in the expression pedal you're planning to use.  I doubt that a ground-left toggle would be either difficult to wire up, or detract from the resale value, since it would increase the usability and flexibility of the pedal.  A simple toggle-flick means you can use it with this OR with that.  But, you're the boss of your own gear, so do what you feel is best and are comfortable with.

[snk]

Hi, Mark. It is not that it would be difficult to drill a hole in the pedal, it is that i am still unsure about which pedal i might use with this Harmonic Energizer (the one which i know for sure is using a 50K pot, and which i used for the test, is used daily with another instrument). So, if possible, I would have liked a more "universal" solution, so i could use the Energizer with any spare pedal (given that the pot has the right value).
From a technical point of view, isn't it a good idea to add the switch directly on the TRS cable (or in a tiny box), or am i missing something ?

[Mark Hammer]

Nah.  You're not missing anything.  It's just a different perspective on what "convenient" consists of.

[snk]