Basic Audio - Scarab Deluxe  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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storyboardist
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Post by storyboardist »

IvIark wrote:Yes that looks like the way John described it, or at least that's how I understood it.
Cool. Maybe John will chime back in and confirm. Thanks for you input lvlark. Oh, and thanks for your blog. Without it I would not be building pedals and would have zero soldering skills. :thumbsup

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Post by IvIark »

:thumbsup
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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John Lyons
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Post by John Lyons »

I meant Q4, correct.
Remove C8, put R13 between C7 and ground.
R7 should be 100 ohms.
100 ohms between C5 and ground.

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Post by storyboardist »

Thanks John! Here's the final schematic.

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roseblood11
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Post by roseblood11 »

Why is C1 so big? Wouldn't 1µF sound exactly the same? I don't like electrolytics in the signal path...

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John Lyons
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Post by John Lyons »

1uf might be enough for you. The cap stores energy as well as passes signal at all frequencies.
I like the sloppiness of 10uf. My goal is to make it as tight and responsive with the .01 and then sloppy
with the 10uf. So you set the FAT knob as you like. 10uf has a good bit of thump to it...

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Post by IvIark »

So does Q4 base and collector connect to the bias resistor? That looks peculiar to me.
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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~arph
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Post by ~arph »

Why not replace the tone pot with a 10k and leave out R13? (or am I missing something? it's still early)
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Post by IvIark »

roseblood11 wrote:Why is C1 so big? Wouldn't 1µF sound exactly the same? I don't like electrolytics in the signal path...
Get some of the 106 multilayer ceramics like these.
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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Post by IvIark »

IvIark wrote:So does Q4 base and collector connect to the bias resistor? That looks peculiar to me.
Just going back to this, I'm assuming the Bias pot just connects to Q3 collector, and Q4 collector actually connects straight to the supply. That would then be in keeping with the Hot Silicon.
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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Post by Nocentelli »

IvIark wrote:
IvIark wrote:So does Q4 base and collector connect to the bias resistor? That looks peculiar to me.
Just going back to this, I'm assuming the Bias pot just connects to Q3 collector, and Q4 collector actually connects straight to the supply. That would then be in keeping with the Hot Silicon.
I thought it looked odd, and also assume the Q4 collector is only connected to +9v. If the collector and base were shorted, wouldn't it just be a diode?
vanessa wrote: 20 Aug 2007, 17:51 You can't arrest someone for reverse engineering something.

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Post by ~arph »

storyboardist wrote:Thanks John! Here's the final schematic.

https://i756.photobucket.com/albums/xx2 ... 906ef3.jpg
Please add your name to the image, so it doesn't look like it was just me :wink:
In the quiet words of the virgin Mary: "Come again?"

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Post by storyboardist »

~arph wrote:Please add your name to the image, so it doesn't look like it was just me :wink:
I did. Team effort! 8)

Here's the schem again, hopefully in its final form, with the Bias control moved to effect only Q3.

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IvIark
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Post by IvIark »

Image
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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Post by John Lyons »

~arph wrote:Why not replace the tone pot with a 10k and leave out R13? (or am I missing something? it's still early)
The 10k/.1/2k2 is the low pass filter. The 50k pot pans between a low pass and tone network bypass (for the most part)
Imagine the big muff tone network with only the low pass side.

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Post by IvIark »

I think what ~arph was saying is that because the 10K is in parallel with the tone pot, it's just like having an 8.3K tone pot, so why not just omit the 10K resistor and use a 10K for the pot.
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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~arph
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Post by ~arph »

IvIark wrote:I think what ~arph was saying is that because the 10K is in parallel with the tone pot, it's just like having an 8.3K tone pot, so why not just omit the 10K resistor and use a 10K for the pot.
Yup
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Post by John Lyons »

Ok, I see it now. Paralleling the pot changes the taper as well.
Cheaper to use a 50KB pot rather than a 10KC...
The 10k resistor is only a couple cents. A 10KC pot is $1.50 or so.

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Post by ~arph »

Yes, you can influence taper, but shouldn't the 10k be connected to the wiper instead of the low side of the pot to simulate a reverse log action? The way it's connected now just makes the 50kB pot a 8.3kB pot.
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Post by storyboardist »

Drew up a perf and pcb layout.

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