Calculating RC time constants...and why you should.

Info for maintaining and tweaking your amp to perfection.

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VelvetGeorge
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Post by VelvetGeorge » Fri Sep 02, 2005 3:59 pm

I love that quote too rjgtr. I hope you don't mind if I "borrow" it sometime. It goes perfectly with my notion that there are "guitar players" and then there are "guitar owners".

You can also use it for bad sound engineers- "pa owners".

Ok, that's far too many quotation marks.

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Post by Bainzy » Mon Nov 07, 2005 1:56 pm

so, how would I go about BOOSTING the mids in a circuit? (or cutting everything else to simulate that) :?
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Post by rjgtr » Wed Nov 09, 2005 5:18 pm

You could build a fixed tone stack with the treble and bass resistors a lower value. Mesa did this on a few amps.
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Post by VelvetGeorge » Wed Nov 09, 2005 8:26 pm

Lots of ways. Change the mid pot to 50k for example.

Have you tried the Duncan tone stack program? Check it out. That will answer lots of questions.

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Post by rjgtr » Thu Nov 10, 2005 3:28 pm

George,

Isn't there also a way to Bypass the top of the tone stack with a Cap and resistor that boosts Mids?


Re: Quote - feel free to borrow it...
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Post by Billy Batz » Thu Nov 10, 2005 6:01 pm

Raising the mid pot to 50k or 100k defionitely boosts the mids. But it also boosts the bass a bit too. I think youll find taht lowering the mid cap to .0022 really boosts the mids (and with mid boosts gain and harmonics as well) but no matter what you doo you shouyld probably go to a 56k slope resistor. Or even 100k. Your just decreasing gain by doing that especially in the low end and low mids which can get muddy when you do those things. I dont like doing either of them on a marshall because they really muddy up the low end.


Probably the best way to do it by far though is too increase your treble cap value. Switching between 2 different treble cap values is used as a mid boost control in many amps. It mostly boosts high mids but I really doubt youd want to boost low mids myself. I dont like it. I think youll find raising the treble cap value to 680p or .001 will give you a real mid boost. I especially like to do that on fenders but Ive meant to do it more with marshalls for a long time.

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Boosting Mids

Post by dcaster » Thu Dec 08, 2005 10:03 am

Put all of your tech tools away and go to your local pawn shop and buy a Peavey amp from the 80s. If that doesn't give you enough mid range, god help you!

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Post by Bainzy » Thu Dec 08, 2005 11:00 am

I don't actually have a treble cap right now, just a cap over the mixer resistor. What would change if I added one?
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Post by Billy Batz » Thu Dec 08, 2005 11:06 am

No you misunderstand me. Not bright cap. The treble cap is the 500p or 250p in the tone stack.

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Post by Brentsp » Thu Dec 08, 2005 11:23 am

Bainzy wrote:I don't actually have a treble cap right now, just a cap over the mixer resistor. What would change if I added one?
Look for the wire thats going from the treb pot to a cap on the board. That wire should be connected to a 250pf, 470pf, or 500pf cap. Thats the treble cap Dan is referring to.

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Post by Bainzy » Thu Dec 08, 2005 11:55 am

Oops!

Sorry, you're right Dan I totally misread what you said, for some reason I got it into my head that you said bright cap. I changed the treble cap to a lower value before (500pf) but didn't like the way it sounded, so I think I'll leave it at 250pf.

But still, what are the effects of having no bright cap vs. having a bright cap?
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Post by Billy Batz » Thu Dec 08, 2005 12:02 pm

It just increases the amount of high end frequencies determined by the value of the cap. On the mixer resistor it would always sound the same but on the volume controls a bright caps effect depends on how the volume is set. At about 6-7 and up the bright caps effect is no longer a factor.

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Post by Bainzy » Thu Dec 08, 2005 12:30 pm

right, I guess there's no point in adding one then as the volume is always on 10 :lol:
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Post by Bill Durham » Wed Feb 01, 2006 10:32 pm

rjgtr wrote:Resistors resist power flowing. The smaller the power the less you get. So high frequencies, which take less power to generate are easier to block. Obviously the effect is more subtle than using caps.
I don't think in the purest sense that this is correct. Adding "resistance" to a circuit doesn't effect frequency response...but...changing the impedance does effect frequency response...as George said. Resistance is a DC characteristic while Impedance is an AC characteristic. Not trying to nit pick, but you do have to be careful with your terminology.

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Post by erigm » Sat Feb 11, 2006 1:40 pm

Dan,

I wanted to add something to your "series resistance" discussion that you probably already know, but some may find helpful. If you place a resistor in series right before the input grid of a tube you will notice some treble attenuation as well, due to the internal capacitance of the tube (which is quite small). This also form a low pass filter, and is a technique commonly used to supress oscilations and stability issues.
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