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PostPosted: Sun Feb 13, 2011 9:09 pm 
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They do work in the LED clipping section, I shorted the base lead to the emmitter lead, oriented the collector lead in the positive LED eyelet. Doesn't sound bad.


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PostPosted: Tue Jul 12, 2011 6:42 pm 
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can the mosfets handle 18v if placed in the clipping section????


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PostPosted: Mon Oct 24, 2011 10:27 am 
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Great info - thank you!
CEW


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PostPosted: Mon Nov 28, 2011 12:10 pm 
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Hi,
My OD2 is built according to the original setup, no mods made.
I´d like to change the LED clippers to Mosfet bs170. Will it be enough just to take out the two LED:s and put in two bs170 mosfet transistors in the designated spots next to them (backwards), or do I have to make other adjustments as well?


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PostPosted: Mon Nov 28, 2011 12:20 pm 
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Meugel wrote:
I´d like to change the LED clippers to Mosfet bs170. Will it be enough just to take out the two LED:s and put in two bs170 mosfet transistors in the designated spots next to them (backwards), or do I have to make other adjustments as well?

Yup, that's all you need to do. No other changes needed.

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PostPosted: Wed Mar 14, 2012 9:41 am 
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duhvoodooman wrote:
Because of this tonal similarity between the LEDs and the diode "lift", I prefer to build my OD2's with BS170 MOSFETs in the second clipping position.

I take it that installing MOSFETs in the second clipping position is different than the mod with MOSFETs in the boost channel?

And if it is how can i achieve the MOSFETs in the second clipping position? Do other parts of the circuit need to be built MOSFET or can it be done just by switching out the clipping position with MOSFETs instead of LEDs?


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PostPosted: Wed Mar 14, 2012 10:03 am 
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tom474e wrote:
I take it that installing MOSFETs in the second clipping position is different than the mod with MOSFETs in the boost channel?
Yes, completely different. For the clipping mod, you're just utilizing the internal "body diode" of the MOSFET's to function as a signal clipper. The additional MOSFET modifications are totally different in what they do.

tom474e wrote:
And if it is how can i achieve the MOSFETs in the second clipping position? Do other parts of the circuit need to be built MOSFET or can it be done just by switching out the clipping position with MOSFETs instead of LEDs?
This is covered quite clearly in the posting in this thread immediately preceding yours.

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PostPosted: Sat Mar 17, 2012 6:06 pm 
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In your opinion which would be the better way to build the OD2, with the boost channel converted to MOSFET or with only switching the LEDS for the MOSFET transistors, like you discussed earlier?

Thank you


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PostPosted: Fri Apr 05, 2013 10:13 am 
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tom474e wrote:
In your opinion which would be the better way to build the OD2, with the boost channel converted to MOSFET or with only switching the LEDS for the MOSFET transistors, like you discussed earlier?

Thank you
I just received the OD2 kit as well and am wondering the same thing.

Thanks!


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PostPosted: Fri Apr 05, 2013 11:16 am 
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flashtilley wrote:
tom474e wrote:
In your opinion which would be the better way to build the OD2, with the boost channel converted to MOSFET or with only switching the LEDS for the MOSFET transistors, like you discussed earlier?
I just received the OD2 kit as well and am wondering the same thing.

This is a very subjective judgment, guys, so the following should be taken only as my personal preference:

I like to build the OD2 kit with the following configuration:

  1. MOSFET clipper pair instead of the LEDs, since the latter don't sound much different than the middle "diode lift" position of the clipping toggle switch, due to their high voltage threshold.
  2. JRC4558D op amp for a bit warmer, grittier sound, or the Burr-Brown OPA2134PA if you want a bit more clarity. (Doesn't make a lot of difference.)
  3. MOSFET input buffer for somewhat better retention of the highs in the incoming signal.
  4. Stock BJT output buffer for its stronger drive characteristics (a Jack Orman recommendation that I endorse).
  5. Stock LPB-style boost stage for more available output and better low-end.
  6. Switchable effect order modification.

As they say, "YMMV"!!

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PostPosted: Tue Feb 11, 2014 3:27 pm 
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I have been trying to understand the inner workings of guitar pedal circuits and since I've built the OD2 I have been looking at its schematic. I know it's not the simplest circuit but I'm "somewhat" familiar with it.

From the input I can see that that R1 adjusts the impedance so it doesn't load the guitar. Then C1 and R2 are a high pass filter. Let me know if I'm wrong here.

The question I have is regarding the input buffer. It looks to me like there's a voltage divider as the 9 volt supply goes down to 4.5 volts after the 511K resistor. What I don't see is what I've understood to be a voltage divider.

Hopefully someone can explain this to me or link me to an explanation.

if this is the wrong place to ask this please let me know too.

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PostPosted: Tue Feb 11, 2014 3:42 pm 
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Resistors R17 & 18 (2x 10K) make up the voltage divider. They are part of the power supply circuitry that consists of the two resistors, C12 (100uf) and C13 (47uf).

Image
Image

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PostPosted: Tue Feb 11, 2014 3:48 pm 
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Oh wait, I found this: http://www.geofex.com/article_folders/t ... sxtech.gif

I can see the voltage divider now in that schematic. I haven't found it in the OD2 schematic yet.

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PostPosted: Tue Feb 11, 2014 3:54 pm 
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It's right there at the bottom between the MOSFET input buffer and MOSFET boost circuit diagrams.

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PostPosted: Tue Feb 11, 2014 3:55 pm 
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Thanks Stephen,

I was writing my last post while you were posting. I see it now. So I guess that anywhere in the schematic where it shows +4.5v or +9v it would be connected by a trace to the power supply circuitry.

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PostPosted: Tue Feb 11, 2014 4:49 pm 
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bondsong wrote:
So I guess that anywhere in the schematic where it shows +4.5v or +9v it would be connected by a trace to the power supply circuitry.

Yes, per diagram below. The voltage splitter resistor pair is the side-by-side 10K's at the top of the PCB. The 4.5V trace goes down the middle of the back side of the board (shown in orange), while the main 9V power trace runs primarily around the perimeter of the front side (shown in yellow).

Image

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PostPosted: Tue Feb 11, 2014 4:57 pm 
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Thanks a lot duhvoodooman,

So those are not just pretty pictures then. :D

I'm starting to get this stuff figured out thanks to the help here. The schematic is looking a lot simpler.

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PostPosted: Thu Apr 03, 2014 11:43 pm 
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Hello, I've just ordered OD2 kit and waiting for delivery...
I don't want to install trimpots and want to use resistors at stock values. Can someone point to me, which holes should I use for solder them?


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PostPosted: Sun Apr 06, 2014 9:27 pm 
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You can use either of the pairs of horizontally opposing holes for each of the trimpots, i.e the installed resistor should be oriented horizontally on the board. Stock TS values are 51K for the MIN position, 4.7K for the MAX position and 1K for the LOUDER.

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PostPosted: Mon Apr 07, 2014 3:40 am 
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duhvoodooman wrote:
You can use either of the pairs of horizontally opposing holes for each of the trimpots, i.e the installed resistor should be oriented horizontally on the board. Stock TS values are 51K for the MIN position, 4.7K for the MAX position and 1K for the LOUDER.

Thanks


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PostPosted: Wed May 07, 2014 3:14 am 
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there are an error in current instruction on page 27 (lug 8 of right footswitch suggested to wired twice)
Quote:
Step 2:
· Cut 7 x 3/4 pieces of wire. Strip 1/8 off each end. These will be used to connect
lugs/eyelets 1, 7, & 8 of the footswitch on the left and lugs/eyelets 1, 2, 7, & 8 of the
footswitch on the right.

· Cut 4 x 1 pieces of wire. Strip 1/8 off each end. These will be used to connect
lugs/eyelets 2 & 5 of the footswitch on the left and lugs/eyelets 5 & 8 of the
footswitch on the right.


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PostPosted: Wed Aug 19, 2015 6:51 pm 
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Is it only the MOSFET opamp that can't handle 18V? I.e. can I safely run the Burr-Brown opamp with MOSFET clippers and MOSFET input buffer at 18V? Thanks!


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PostPosted: Wed Aug 19, 2015 7:00 pm 
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Page 35 of the OD2 instructions (last page before the schematic) is very clear on answering this question:

"18 volt operation? - This can be a little tricky. Because the standard spec overdrive circuit can run just fine at 18v. But the standard silicon boost circuit cannot. 18v will not hurt it, but it will be distorted. The MOSFET boost can run at 18v. But the MOSFET overdrive circuit cannot. Anymore than 9v will fry the MOSFET op amp. So if you want to run the pedal at 18v, you'd need to build the overdrive portion of the circuit to standard specs and build the boost to MOSFET specs."

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PostPosted: Wed Aug 19, 2015 8:19 pm 
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Quote:
"18 volt operation? - This can be a little tricky. Because the standard spec overdrive circuit can run just fine at 18v. But the standard silicon boost circuit cannot. 18v will not hurt it, but it will be distorted. The MOSFET boost can run at 18v. But the MOSFET overdrive circuit cannot. Anymore than 9v will fry the MOSFET op amp. So if you want to run the pedal at 18v, you'd need to build the overdrive portion of the circuit to standard specs and build the boost to MOSFET specs."


This is exactly the paragraph that's got me confused. So the entire overdrive circuit must be built stock in order to run at 18V?


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PostPosted: Wed Aug 19, 2015 9:00 pm 
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Wild Goose wrote:
So the entire overdrive circuit must be built stock in order to run at 18V?

No. It's just the MOSFET op amp that can't be used at 18V. Just use one of the other two. There's no significant tonal difference.

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