Systech - Harmonic Energizer

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Re: Systech - Harmonic Energizer

Postby snk » 15 Jun 2019, 13:22

Thank you, Zokk. There is a lot to investigate here, I will take the time to read the schematic, and understand how i can deal with it.
What surprises me, though, it that Tim Hulio from Fredrich FX said he made a version with expression input, and i don't think he used any vactrol/ldr. He posted a layout some years ago (page 7 of this thread), but i don't see the exp. input, and the circuit needed to make it work.
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Re: Systech - Harmonic Energizer

Postby Zokk » 16 Jun 2019, 14:06

:roll: well maybe they have simply used a switched jack to connect the expression pedal in place of the pot like you tried before.
You need an isolated stereo switched jack socket, so you can swap the Sleeve and Ring on the expression pedal to change the sweep direction.
Remember the Tip is the cursor (exp pot pin2), and the Ring and Sleeve are Pin1 and Pin3 of the exp pot.
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Re: Systech - Harmonic Energizer

Postby snk » 19 Jun 2019, 23:10

Hi,
Thank you for your answer, and sorry for my somewhat late reply.

I really appreciate the advices you gave me about using LDR. But for this project the expression input would be only icing on the cake :the circuit is already boxed, and space is lacking, so if it's technically possible, i would like to look for the simplest way to achieve this. But i am quite a filter freak, so i think that your advices will be very handy on some other projects :thumbsup

I tried to use a TRS jack with the sleeve (ground) disconnected on the pedal's side (a friend gave me this advice this afternoon and i wanted to try) : it works, but the effect self-oscillate quite easily (the Harmonic Energizer is quite wild, but here it is meta-über wild, much prone to self-oscillation than when i only use the knobs). Also, i noticed that the filter range is quite different when using the pedal or when using the knob.
The pedal is a Moog expression pedal, so its internal pot should have the same value (50K) than the Harmonic Energizer.

I will try with your wiring tomorrow :)
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Re: Systech - Harmonic Energizer

Postby Zokk » 20 Jun 2019, 08:24

Have you disconnected the onboard pot when trying your TRS jack? This won't work if the expression pedal is in parallel with the pot, it should totaly replace the pot in circuit.
If you have tried with an isolated socket you should be fine, the Sleeve is one end of the pot. So you can try to use the (Sleeve and Ring connected) + the Tip, or (Tip+Ring connected) + Sleeve. But in theory only two points are needed to vary the resistance.
If the pedal oscillate because the resistance is too low, maybe try to add a resistor in series (or a trimmer then take a measure and replace it by a fixed R).
To be sure, take a DMM and check what you get between the Sleeve and Tip, that's the expression's pot value.

Yes to control filters you'll need more parameters to adjust the sweep to the real mechanical limits of the expression pedal; that's why I prefer the LDR trick.
I find nothing more boring than a fixed filter 8)
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Re: Systech - Harmonic Energizer

Postby Zokk » 20 Jun 2019, 08:28

Sorry still no edit: I've messed the pin numbers in my previous message.
So to be clear here is what I take as standard wiring for an expression pedal:
Image

To correct myself:
try to hook (Tip and RIng) + Sleeve
or (Ring and Sleeve) + Tip

And pot's resistance will be between Ring and Sleeve.
Sorry for the confusion :oops:
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Re: Systech - Harmonic Energizer

Postby Zokk » 20 Jun 2019, 09:00

Here is an example with the correct pin numbers, use an isolated jack socket:
systech exp.jpg
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Re: Systech - Harmonic Energizer

Postby snk » 21 Jun 2019, 11:00

Thank you so much, Zokk, that is very helpfull. :thumbsup

One thing which is holding me down of digging deeper with this circuit, is that it is not true bypass, and i noticed that when bypassed, moving the expression pedal was chaing the dry sound...
I guess this is because the audio is actually going through the filter pot, even when bypassed, so the expression pedal is NOT "doing nothing" when the pedal is bypassed. Maybe it is due to my wiring (which might be incorrect), but maybe also it is the way the pedal was designed.
I will investigate further this week-end, and let you know what happens.

Have you disconnected the onboard pot when trying your TRS jack? This won't work if the expression pedal is in parallel with the pot, it should totaly replace the pot in circuit.

Yes ;)

I find nothing more boring than a fixed filter 8)

Well, it depends :) I work a lot with synths, so i know what you mean.
I like the way the Energizer works as a rough "color shaper" (so this is the reason why i will be happy even if i can't manage to have the expression pedal work).
But with some setting is sounds so much like an extraordinary wah, that i wish i could use it like that with an electric piano :D
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Re: Systech - Harmonic Energizer

Postby Zokk » 23 Jun 2019, 16:07

snk wrote:One thing which is holding me down of digging deeper with this circuit, is that it is not true bypass, and i noticed that when bypassed, moving the expression pedal was chaing the dry sound...
I guess this is because the audio is actually going through the filter pot, even when bypassed, so the expression pedal is NOT "doing nothing" when the pedal is bypassed. Maybe it is due to my wiring (which might be incorrect), but maybe also it is the way the pedal was designed.

You're right this pedal is known as a tone sucker in bypass; I've had to convert 3 original units to "true bypass" because of this.
If I had to do these bypass mods again I would use an optical bypass like this one:
https://cdn.shopify.com/s/files/1/0022/3952/9069/files/Opto-Tron-BOM.pdf?14931847358987224012
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Re: Systech - Harmonic Energizer

Postby snk » 23 Jun 2019, 20:01

Thanks for the further feedback.
I may try with different wirings at the end of the week, but maybe that i will just keep this one as it is, and build a new one in a couple months, when i will have more knowledge and experience with vactrols and LDRs.
I think it is a great "quick and dirty tone shaper" kind of pedal, which really brings attitude and help any instrument to be heard in a mix.
It could become something a bit more advanced, with more features (like optical bypass and a LDR circuit for the expression pedal, etc) in a near future ;)
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