Coron - Over Drive  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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Dingleberry
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Post by Dingleberry »

Hi.
I got a Coron Over Drive pedal for maintenance from my friend. It's a quite nice sounding low gain overdrive. One fet (k86A), two tant. caps (100nf, 3,3uf) one film cap (47nf) and three resistors (10K, 22K, 510K).
At the input there is a 1MC pot wired as a variable resistor (gain control, labeled "emphasis") and output vol pot is 50KA. Beautiful, simple, classic.
I will document it and post pics and schematics when I get into it, although there is some pics and one schematic floating in the net. The funniest part is that it runs on one AA-battery (1,5Vdc.)
I always thought that Maestro FZ1-A was the only one that runs on 1,5Vdc until I opened the Coron.

My friend wants to hook it up to his existing pedalboard and he only has 9Vdc outlets. My question is: What is the best way to drop the voltage to 1,5Vdc? Should I use lm317 regulator?
Should a simple voltage divider do the trick? Zeners?

-T
Simplify before you amplify.

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phatt
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Post by phatt »

This is often missed;
Unlike a lot of later pedals which draw insane amounts of electrons to run,,,
This unit (with only one active element) likely has such a low power draw the battery will last a very long time, which was the whole idea of pedals when I Wus young.
So running from a supply is hardly worth the trouble and add needless complexity.

A wise man would simplify,,,Just buy a battery and go play the guitar. 8)
Phil.

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The G
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Post by The G »

You should measure the current drawn by the pedal. Then it'll be easier to choose:
- if the drawn current does not vary a lot, you could use a single resistor with a value big enough to cause the needed voltage drop.
- there are no 1.5V Zenners that I know of, you could use a green LED or 3 1N4148s.
- a LM317L (TO-92 case) circuit should be almost as small as any of the other variants and provides more voltage regulation and more curent capability.
- if your friend does not care that much for the overdriven sound, you could also have him try the pedal at 9V; I couldn't find the datasheet for K86A (the Toshiba 2SK series?), but I seriously doubt that it cannot stand 9V.

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Dingleberry
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Post by Dingleberry »

phatt wrote:This is often missed;
Unlike a lot of later pedals which draw insane amounts of electrons to run,,,
This unit (with only one active element) likely has such a low power draw the battery will last a very long time, which was the whole idea of pedals when I Wus young.
So running from a supply is hardly worth the trouble and add needless complexity.

A wise man would simplify,,,Just buy a battery and go play the guitar. 8)
Phil.
That is totally true my friend, but you missed the whole point of my question... My friend wants to hook it up to his existing pedalboard and 9Vdc is the only voltage his pedal board power supply delivers so my goal is to make it happen.

The current draw for that fet will be nearly nothing but I decided to go with the LM317 route, mostly because I've never fiddled with one before. Only have experience with LM78- and LM79-series regulartors. I already made a tiny board for it and probably get the pedal done this evening. Got to change the jacks too because they are broken and install DC jack and make it true bypass with led. It's gonna probably be a little pita because he had already tried to "mod" it and drilled hole without thinking it any further and regular dc jack is probably not going to fit between input and output jacks... we'll see how's it gonna turn out.
Lm317 being variable voltage regulator it will be interesting to try it with higher voltages also and see how it changes the character of the the pedal.

-T
Simplify before you amplify.

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fuzzbunny
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Post by fuzzbunny »

I look forward to seeing a schematic for this!

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Nocentelli
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Post by Nocentelli »

fuzzbunny wrote:I look forward to seeing a schematic for this!
Dingleberry wrote:One fet (k86A), two tant. caps (100nf, 3,3uf) one film cap (47nf) and three resistors (10K, 22K, 510K).
At the input there is a 1MC pot wired as a variable resistor (gain control, labeled "emphasis") and output vol pot is 50KA. Beautiful, simple, classic.... The funniest part is that it runs on one AA-battery (1,5Vdc.)
With so few parts, there are a fairly limited number of different ways of connecting them that would produce overdrive: This is my best guess until dingleberry gets around to tracing it -
coron OD perhaps.bmp
coron OD perhaps.bmp (21.84 KiB) Viewed 2671 times
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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fuzzbunny
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Post by fuzzbunny »

Thanks for your fine help Nocentelli!

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Dingleberry
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Post by Dingleberry »

Just switch the input and output caps Nocentelli and it's correct.
Mild overdrive/pre amp booster, good Texas tone with strat and didn't sound bad with humbuckers either.
Simplify before you amplify.

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Dingleberry
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Post by Dingleberry »

This is the schematic. 100nf and 3,3uf are tantals. 47nf is film cap.
All resistors carbon film. And only 2 lugs of the 1Mc pots were used (actually mislabeled in the scheme... should be lugs 2 and 3 connected)
Attachments
Coron Over Drive.png
Coron Over Drive.png (5.37 KiB) Viewed 2457 times
Simplify before you amplify.

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johnk
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Post by johnk »

I drew up a pcb for this one, etched it, built it, and tested it and IMO, it's a decent low gainer.
I used an LM317LZ and an NTE458 since I couldn't find a K68.
layout:
Image

PCB:
Image

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Bill_Mountain
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Post by Bill_Mountain »

Are there any other FETs that would work? MPF102? 2N5457?

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johnk
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Post by johnk »

probably a J201 but mind the pinout.

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