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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Re: Systech - Harmonic Energizer

Postby snk » 19 Sep 2019, 09:47

Hi, Zokk.
I played a bit more with the Energizer, and ended up manually turning the freq knob all the time, so i guess i should try to make a vactrol daughter board for an expression pedal or a CV input :)
I made this quick & dirty veroboard layout (from the schematic you posted). I am not sure that it is good and accurate yet (i have to give it a fresh new look and closer inspection later this evening). If it is ok, i will build it soon.
Vactrol Expression Pedal.jpg
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Re: Systech - Harmonic Energizer

Postby Zokk » 19 Sep 2019, 15:03

Hi
it seems you've forgotten the LED and the LDR 8)
Also the 1K resistor in the bottom right corner should be adjusted to suit the LED (but here it's connected to nothing).
The LED should be connected to the emitter, by the way here's a standard pinout:
Image
The LDR should be in parallel with the 50K resistor.
If you need I can draw a perfboard/pcb layout too.
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Re: Systech - Harmonic Energizer

Postby snk » 19 Sep 2019, 17:39

Hi, Zokk
Sorry, I was a bit in a hurry when i posted the layout, and i forgot to mention that the blue rectangle should be a vactrol (embedding a led + ldr).
I will check my layout more accurately in a couple hours.
If you are willing to make a veroboard layout, please be my guest : i think yours should be less prone to error than mine :)
(but i will try to improve mine anyways, it's a good way to learn)
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Re: Systech - Harmonic Energizer

Postby snk » 19 Sep 2019, 19:56

Zokk wrote:Hi
it seems you've forgotten the LED and the LDR 8)
Also the 1K resistor in the bottom right corner should be adjusted to suit the LED (but here it's connected to nothing).
The LED should be connected to the emitter
Vactrol Expression Pedal (w led&ldr).jpg

The LDR should be in parallel with the 50K resistor.
If you need I can draw a perfboard/pcb layout too.

I'm still a basic user with DIY layout creator :)
I didn't find the right icon for the vactrol, so i just used a blue rectangle shape. I updated the layout with the green led, and (as i didn't find a LDR icon either) a resistor icon for the LDR.
I didn't either know how to enter a variable value (1-10K) for the resistor labelled "1K" at row #17.
The 2N3904 was not in the right orientation.
This is the updated schematic (displaying a led and "ldr" instead of the vactrol) :
Vactrol Expression Pedal (w led&ldr).jpg
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Re: Systech - Harmonic Energizer

Postby Zokk » 19 Sep 2019, 20:50

Nice!
I've drawn a quick perfboard layout with its schematic/parts:
Systech exp pedal3perf.png

Systech exp pedal2.png


Let us know if it works :D
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Re: Systech - Harmonic Energizer

Postby snk » 19 Sep 2019, 21:11

Excellent ! Thank you :D
I have a friend who can make PCBs from time to time, so if your circuit is somewhat "universal" with some tweaks, it could be a good idea to have a batch of them...

Do you think that vero layout seems correct ? If there is no obvious mistake, i might try it tonight... ;)
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Re: Systech - Harmonic Energizer

Postby snk » 19 Sep 2019, 23:36

Hi,
I would have 2 further questions :
- How should i adjust R3 (1-10K) ? (I mean, while i understand that the 100K trimmer should be adjusted to set the "amount" of modulation sent by the expression pedal or CV, what does C3 do to the led, and when do i know that i have set the right value ?)
-
use an isolated jack socket:
: I guess I should also use a switched jack socket, right ?
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Re: Systech - Harmonic Energizer

Postby Zokk » 20 Sep 2019, 09:11

Hi
yes it could be interesting to have a multipurpose vactrol board, to hack existing circuits!
Let me know if you need the tracks only to make small pcbs.
Your vero seems ok.

The idea with the LED resistor is that when the CV input is at minimum the LED should just be at the right current to be near active, or just starts to glow.
You'll need a minimum current before the LED starts to glow, if the CV IN is 0V your LED will be off, but the LED will remain dark until the CV jump above the threshold of the LED (usually around 2V).
This is not really "musical" and you'll hear clearly a step. Plus the light curve just above the light threshold is not very linear, could be ok, but not always.
So the trick is to always feed the LED with some current, to reduce the "step" or completely remove this behaviour. And simply this resistor will also set the LED consumption, so be careful to not use a too low value.

As example, a regular Vactrol uses a LED which is around 1.5V but the specs to achieve minimum resistance on the Vactrol are crazy: 20mA!!!
So those LEDs start to emit light early, but they are not efficient at all, or the LDRs are not very sensitive: take a modern lo power clear 5mm led an feed it with 20mA , it's simply too bright for most LDRs, and too much current draw for a pedal.
This is how they achieve a nice response curve.

You'll need to experiment first with your vactrol and a simple variable voltage source (potentiomenter as voltage divider + 9V battery) to know what is the minimum acceptable value for this resistor according to your LED
I'd say this resistor could be called "offset", and the trimmer "range". You can use a trimmer in place of the fixed resistor, could be useful if you change the LED type in your vactrols.
And it's a good idea to measure the resistance on the LDR legs while doing this, you should see what happens when the LED starts to conduct.

Everything is tricky with the LED/LDR, you'll have to find a good balance between several parameters:
LED specs
LDR specs
offset and range of the modulation (LED resistor + Trimmer )

All the trick is to achieve a nice sweep between the minimum modulation (avoid a step between 0V and the threshold of the LED) and max modulation, and have an acceptable "center" when using your expression pedal.
Plus in the Systech you want to have a very low resistance on the LDR at max, but only 50K at minimum; so you should be able to set the LED resistor so the LED is always on but the LDR is still limited by the 50K resistor.

:hmmm: sorry I'm not sure if it's clear.

Concerning the jack:
you can use a non switched, non isolated stereo jack socket to add the expression pedal if you use the "vactrol" board.
I was suggesting an isolated and switched stereo jack to completely replace the onboard Frequency pot. without any vactrol trick.
Like that:
Image
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Re: Systech - Harmonic Energizer

Postby Zokk » 20 Sep 2019, 09:15

Sorry I forgot about C3, it's just a small buffer/filter on the +9V rail for the transistor power.
I'm used to always put a small cap on power lines.
You can use a ceramic, or anything cheap 8)
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