bjfe sea blue eq q's

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bjfe sea blue eq q's

Ravenswerld
    Hello all, want to say thnx for all the great work going on here. I built a bjfe sea blue eq a few back and am using it with my acoustic rig. Which works really well! I was wondering if anyone could help me figure out which cap to change to decrease the bass response? Also, I used MPF102's in it and sounds really good. I just want to see if I can get a little more volume out of it? I used Johnk's layout with the mid control. Which works great thnx john. Anyways, thnx for the help and keep on playing!!!!
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Re: bjfe sea blue eq q's

IvIark
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The SBEQ uses a James tone stack for treble and bass as you can see in the schematic here:



If you want to tweak the response to your own taste I'd suggest downloading the Duncan Tone Stack Calculator, tweak the values and see how it affects the response:

http://www.duncanamps.com/tsc/index.html

Of course this is put out of whack to some extent by the inclusion of the mids pot but it will at least show you how altering the component value around the Bass pot will affect the basic response and so give you a good basis to work from.
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Re: bjfe sea blue eq q's

Ravenswerld
Cool, thnx mark!!!
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Re: bjfe sea blue eq q's

Frank_NH
I've been looking at this schematic, trying to understand how the FETs work.  It appears they are in a low current mode of operation, but since this circuit is not intended for much gain (except to drive the EQ), it seems to work.  I may simulate this in LTSpice to further my understanding.
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Re: bjfe sea blue eq q's

nocentelli
It's a lossy passive James tonestack, so there is boost (via the electro's on source) to compensate. You could probably use a mosfet booster circuit in place of the JFETs and get a similar sound without the potential drawbacks of using JFETs.
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Re: bjfe sea blue eq q's

Frank_NH
In reply to this post by Frank_NH
I played around with this in LTSpice which appeared to confirm the bass heavy response.  Here are the James Tone Stack mods I came up with for a hopefully more even response:

C9 = 4.7n
C10 = 6.8n
C11 = 47n
C12 = 47n
R13 = 10K
R14 = 10K
R15 = 6.8K

Treble = B100K
Bass = A100K

Let me know if this works better.
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Re: bjfe sea blue eq q's

Ravenswerld
Wow!! Thnx...ill give it a try in a few and let you know!!
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