Systech - Overdrive

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Dr Tony Balls
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Post by Dr Tony Balls »

Borrowed this one from a buddy and there doesnt seem to be much info on it anywhere. It's certainly not an overdrive in the modern sense of the word. Its buzzy and fuzzy and the EQ sounds like a wah. This is my first attempt at tracing, so hopefully i'm doing this right. Here's what i've got so far:

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I've got all of the component values listed out, but left them on my bench at home. I can add them shortly. The IC is a dual op-amp, as you could probably figure out by looking at the schematic. Pots on the schematic are Gain, Distortion, and EQ (L to R). I think the only really goofy thing that jumps out to me is the orientation of the FET in the buffer. You'll notice that its inverted in the schematic and the SOURCE is tied to the positive voltage with the drain to ground via R6. This seemed weird to me, but I certainly dont know everything. That FET is a 2N5458, I believe.

Also, I dont quite understand the power supply and the role of the NPN in it. Anyone have an explanation?

Please check out the schematics and let me know if you see any glaring problems. Otherwise i'll need to verify this soon by building it.

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Post by grizzlytone »

Thanks for the info!

I think the purpose of the of the power supply circuit is to have a soft start powerup, the voltage ramps up while C13 is being charged through a resistor -gives a thumpfree input jack plug-in...

What is the serial # of the unit? Is the Zip code 49001 or 49006?

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Post by jrod »

Hey thanks for tracing this one out! Looks like an interesting unit.

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Dr Tony Balls
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Post by Dr Tony Balls »

jrod wrote:Hey thanks for tracing this one out! Looks like an interesting unit.
its pretty interesting, especially given that it appears to be something different than the norm, and also something that has no circuit analysis, or even youtube clips, on the web.

Part values will be added shortly and if I get time i'll crank out a vero layout today as well.

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Post by Dr Tony Balls »

Also, can anyone tell me if they think the power supply section is necessary? It seems like measuring the voltage at the emitter of the transistor in that section would be easier, and then replace that whole section with a more standard arrangement would be easier. Something like +9V in > diode for reverse polarity protection > filter cap > trimmer for setting supply voltage to the right value.

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Post by Dr Tony Balls »

Here's the schematic with part values:

Image


The BJTs and the IC arent very standard (at least in my parts bin) but i'm thinking about a TL072 for the IC and trying 2N3904s for the BJTs.

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Post by mictester »

Dr Tony Balls wrote:
The BJTs and the IC aren't very standard (at least in my parts bin) but I'm thinking about a TL072 for the IC and trying 2N3904s for the BJTs.
The IC needs to be a bipolar type - the TL072 is a FET input type and will sound very different. Try a 4558 or NE5532 or LM833. The 5532 and 833 will be much less hissy. The 3904s will be fine for the transistors.
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Post by Dr Tony Balls »

mictester wrote:
Dr Tony Balls wrote:
The BJTs and the IC aren't very standard (at least in my parts bin) but I'm thinking about a TL072 for the IC and trying 2N3904s for the BJTs.
The IC needs to be a bipolar type - the TL072 is a FET input type and will sound very different. Try a 4558 or NE5532 or LM833. The 5532 and 833 will be much less hissy. The 3904s will be fine for the transistors.

Ahhh thanks for the input. Any advice on the power supply section? Any need for those extra parts?

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Post by mictester »

Dr Tony Balls wrote:Ahhh thanks for the input. Any advice on the power supply section? Any need for those extra parts?
They're not strictly necessary, but will prevent the IC from the risk of latch-up when the power is applied.

You don't need to be too anal about the component values - they have a 300k bias resistor for the final transistor - you can use a 330k (much more common) without detriment. They probably have a bucketful of 300k resistors they need to use up!
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Post by Dr Tony Balls »

ha...yeah I I knew that. I always laugh at the Klon that has the 399.5 k or whatever resistor.

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Post by tube-exorcist »

mictester wrote: The IC needs to be a bipolar type ......
Really ?
Systech_Overdrv_TL022.jpg
Systech_Overdrv_TL022.jpg (16.79 KiB) Viewed 5073 times
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Post by Dr Tony Balls »

Whoa! Where'd you find the pic? I was gonna socket that IC anyway so maybe i'll try some biploar types as well.

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Post by roseblood11 »

Great work, Mr Balls!

- what are the pot values/taper?

-are there any soundsamples? I wonder, if I really have to built my overdrive No 25...

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Post by Dr Tony Balls »

Pot values have been added, but I have no idea about the taper.

No sound samples yet, but maybe i'll make some tonight. Keep in mind that despite being called an overdrive its not really a typical overdrive. Much more fuzzy.

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Post by lolbou »

tube-exorcist wrote:
mictester wrote: The IC needs to be a bipolar type ......
Really ?
Systech_Overdrv_TL022.jpg
Ain't SN72L022P a TL022 equivalent? That would be bipolar as well then. (Though I did not find any datasheet for the old SN72L022P)...
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Post by roseblood11 »

Tonefrenzy has a sound sample

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Post by roseblood11 »

...but the picture with the parts values is "currently unavaillable".

I guess that Drive is rev log, Volume lin, Tone lin or log?

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Post by mictester »

tube-exorcist wrote:
mictester wrote: The IC needs to be a bipolar type ......
Really ?
Systech_Overdrv_TL022.jpg
That's what probably gives rise to the "some of these sound good and some are really horrible". The ICs will sound quite different!
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Post by Dr Tony Balls »

crap, didnt realize the image link had changed:

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Post by RnFR »

Q2 looks a bit off.
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