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Old 17th March 2006, 03:20 PM   #11
Brion55 is offline Brion55  United States
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I'm afraid I don't have any photos at the moment, but maybe I could take one in the next few days. I used dry transfer direct etch on the ones I etched and made a few on copper clad perfboard too. both ways are pretty simple. The most difficult thing was to find a place for the battery before they came out with the externally accessible battery holders. I usually just routed a cavity behind the pickguard for it.

As far as the 10K pot, I get most of my electronic supplies from Mouser Electronics. http://mouser.com/

Actually, the value of this pot isn't critical and a 50K would probably work. It should be audio taper though, while the tone pots should be linear.
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Old 22nd March 2006, 10:02 AM   #12
Scummer is offline Scummer  United Kingdom
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Default Questions Questions Questions

Hi All,

I am building a Les Paul type thing, I am thinking of using the three band EQ version of Brion55's design, so I use all four pots (for vol, bass, mid and treb), with a push switch on one pot to dial in extra gain

The alternative is the two band version with a variable gain pre-amp (so the pots would then be vol, bass, treb and gain)

So my questions are:-

For the first alternative above, could you have a switchable gain level on the pre-amp, so you can flick a switch and dial in additional gain (for soloing)?

For the second, could RG2 be a pot so you can vary the gain level? If so, would any other modifications be required?

Any help and advice appreciated.

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Old 22nd March 2006, 11:16 AM   #13
sangram is offline sangram  India
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Default Re: Questions Questions Questions

Quote:
Originally posted by Scummer
For the first alternative above,
use the switch to change resistor value in the feedback network.

Usually dropping another resistor in parallel with the feedback resistor (-in to ground, not the o/p to ground) should give you a gain boost, but it shouldn't overload the opamp or anything, so keep the value sensible.

If you're trying to vary gain using a pot you would need to ensure that if the pot decides to go to heaven at any point in time (wiper not conducting or wiper turned fully one way or the other) the minimum feedback ratio is maintained through fixed resistors, usually in series and parallel with the pot.
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Old 22nd March 2006, 03:57 PM   #14
Brion55 is offline Brion55  United States
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A volume "boost" switch would be very useful. You would still have control over the volume with the volume pot, so I would think another pot would be redundant. Please keep in mind that the input circuit can provide a HUGE amount of gain by just changing the resistors. Be careful not to go too far, or all you'll have is distortion - not a very nice distortion either. Another useful alteration is a "Mid shift" to select the center freq of the mid control. Or even a "Mid sweep" control if there is room. I have included the schematic below.
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File Type: gif guitar para eq.gif (9.9 KB, 1450 views)
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Old 23rd March 2006, 10:37 AM   #15
Scummer is offline Scummer  United Kingdom
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Hi

I have added a DPDT switch to let you choose between two different gain levels, and have worked out how to fit it all onto a bit of 21x21 veroboard (approx 5.25cm x 5.25cm) which should fit in the space available. As you can see, I am not using the version with the mid-sweep (not enough space for all the pots.....)

Any advice on:-

1) RG1A and B values? I need a small but significant boost for soloing, but I am not sure if Vg is a linear measure (i.e if the value is doubled, does this actually mean the thing will be twice as loud?)

2) As I am not using the mid-sweep, what are the suggested values for the two resistors?

In both cases I can just experiment with different values, but I would appreciate any suggestions.

Cheers
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Old 25th March 2006, 05:17 AM   #16
Brion55 is offline Brion55  United States
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I just noticed an error in the gain equation. here are the revisions
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Old 25th March 2006, 05:20 AM   #17
Brion55 is offline Brion55  United States
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3 band
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Old 25th March 2006, 03:14 PM   #18
Brion55 is offline Brion55  United States
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Here's an idea for the boost. It would probably be best not to switch the feedback resistor.

Example:

RG1 = 10K
RG2 = 1M
RG2b = 2.4K

Boost off = unity gain (0)
Boost on = 12db gain (voltage gain of 4)
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Old 25th March 2006, 03:21 PM   #19
wxn is offline wxn  Lithuania
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Am I getting old, or that output jack in "3 band" version really is wired incorrectly
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Old 25th March 2006, 03:28 PM   #20
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Quote:
Originally posted by wxn
Am I getting old, or that output jack in "3 band" version really is wired incorrectly
No, you're not wrong, the tip and ring are reversed.
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