Systech - Overdrive

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Systech - Overdrive

Postby Dr Tony Balls » 31 May 2011, 17:39

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:

Image

Image

Image

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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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celadine (02 Jun 2011, 03:07), Crumbchildz (01 Jun 2011, 14:04), D-Day (31 May 2011, 23:11), Greg (31 May 2011, 23:24), grizzlytone (31 May 2011, 18:55), jrod (01 Jun 2011, 14:31), lolbou (31 May 2011, 19:02), roseblood11 (02 Jun 2011, 13:43), Steven_M (31 May 2011, 19:22)
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Re: Systech - Overdrive

Postby grizzlytone » 31 May 2011, 20:03

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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Re: Systech - Overdrive

Postby jrod » 01 Jun 2011, 14:31

Hey thanks for tracing this one out! Looks like an interesting unit.
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Re: Systech - Overdrive

Postby Dr Tony Balls » 01 Jun 2011, 14:51

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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Re: Systech - Overdrive

Postby Dr Tony Balls » 01 Jun 2011, 14:58

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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Re: Systech - Overdrive

Postby Dr Tony Balls » 01 Jun 2011, 17:03

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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Re: Systech - Overdrive

Postby mictester » 01 Jun 2011, 19:04

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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Re: Systech - Overdrive

Postby Dr Tony Balls » 01 Jun 2011, 19:10

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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Re: Systech - Overdrive

Postby mictester » 01 Jun 2011, 19:19

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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Re: Systech - Overdrive

Postby Dr Tony Balls » 01 Jun 2011, 19:28

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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Re: Systech - Overdrive

Postby tube-exorcist » 01 Jun 2011, 22:57

mictester wrote:The IC needs to be a bipolar type ......


Really ?

Systech_Overdrv_TL022.jpg
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Re: Systech - Overdrive

Postby Dr Tony Balls » 02 Jun 2011, 13:06

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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Re: Systech - Overdrive

Postby roseblood11 » 02 Jun 2011, 13:49

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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Re: Systech - Overdrive

Postby Dr Tony Balls » 02 Jun 2011, 14:29

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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Re: Systech - Overdrive

Postby lolbou » 02 Jun 2011, 15:03

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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Re: Systech - Overdrive

Postby roseblood11 » 02 Jun 2011, 19:44

Tonefrenzy has a sound sample
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Re: Systech - Overdrive

Postby roseblood11 » 02 Jun 2011, 19:47

...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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Re: Systech - Overdrive

Postby mictester » 02 Jun 2011, 20:49

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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Re: Systech - Overdrive

Postby Dr Tony Balls » 02 Jun 2011, 22:35

crap, didnt realize the image link had changed:

Image
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Re: Systech - Overdrive

Postby RnFR » 03 Jun 2011, 02:03

Q2 looks a bit off.
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