Build Your Own Clone Message Board

Ok, so I need some more opinions here. If I understand this all corectly, the stock 808 Screamer uses the .047uf cap in that position, right. The common "Mid-Hump" mods involve using either a .1uf, or a .22uf cap in that position. That will REDUCE the mid hump, right?

I have also seen people use a .022uf cap there? Will that fatten the mid up more than stock? If I am understanding all this properly, how come more people don't use this mod?

Also, will using different types of caps (metal film vs. poly film, etc.) in this position really change the tone at all?

Any thoughts or ideas on this?
Thanks,
Dan

Hey Dan,
I've been using .22/.047 with an on/on toggle. What it actually does, is give a big fat bottom, that was never there. It does remove a bit of the highs. I use Wima's, or AVX caps there, and in the 1uf non polar positions, so you retain the clarity and articulation of the guitars character.

Geek

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Thanks Geek.

So what would a .022 cap do in there?

Also, what model caps do you use? AVX "BQ" series or some other AVX? What voltage rating?

Dan

581-BQ014D0224K is the avx
505-MKS20.22/63/5 is the wima

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The 0.047uf cap in conjunction with the adjacent 4.7K resistor determine the bass rolloff frequency of the pedal. Frequencies above that value will get the full gain of the clipping stage, while those below the rolloff point get progressively less gain/distortion. For those stock component values, the rolloff point is 720Hz, well up in the audible range (middle C, i.e. C4, is about 262Hz). Changing to a 0.1uf cap will drop the rolloff to 338Hz, increasing the bass distortion, and 0.22uf takes it down to 154Hz, increasing it even more. You asked what a 0.022uf cap would do--it would raise the rolloff point to about 1540Hz, taking out even more low end.

My modified Screamer pedal has switchable 0.047, 0.1 and 0.22uf caps, and they definitely have the intended effect. I find the 0.1 and 0.22uf caps to be quite usable on single coil pickups, but the 0.22uf sounds pretty muddy to my ears with humbuckers. The 0.1uf cap is, IMO, the best "compromise" value for retaining clarity while still boosting the low-end distortion a bit. Polyester film caps work very well for this purpose; I use the Xicon PM sub-mini series caps, same as the BYOC kit. I only go with the metallized ones when the cap ratings are higher than 0.22uf, because polyester film caps get too bulky.

For the 1uf NP electrolytic cap replacement that Geek mentioned, I use an AVX BN series metallized polyester film cap. This particular cap happens to fit the holes on the BYOC Screamer board exactly.

Got it! Thanks again guys. I think I finally have a grip on what I want to do with my 808 kit.

Dan

Lead spacing on the 1NP caps is 15mm. You need to be pretty exact with that when dealing with the metal film box caps.

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Please do not PM me. email is prefered. keith@buildyourownclone.com

Excellent point, Keith. These metallized film caps have short, stiff leads that require a very close fit. The AVX cap I'm referring to has that same 15mm lead spacing, so it fits the Screamer board like it was made for it. Mouser P/N is 581-BN154E0105K. Here's a photo of two of them (the large gray boxes) installed on a Screamer board:

what calculator do you guys use to determine theses values/frequencies?

You can calculate the cutoff frequency (f[sub]c[/sub])of a high-pass filter from the values of the resistor/capacitor pair as follows:

f[sub]c[/sub]= 1/(2*pi*R*C)

where R is in ohms and C is in faradays. For the stock TS components, R = 4,700 and C = 4.7 x 10[sup]-8[/sup]

Oh crap. nobody told me there was gonna be math involved. :lol

Dan

LOL.... yeah, no math homework!

Voodoo, there are software calculators that do tone stacks etc. I just wondered if you were using one of them.

I just set up the formula in an Excel spreadsheet (my favorite calculator!), and then I can just punch in different values to the variables as I please. I'm kind of an Excel junkie from using it extensively in my work....

can you tell me how to do that in excel? that sounds awesome...i dont use excel much but i might now!

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N.O.C.3 Effects!

I'll post a copy of the spreadsheet on my website, and you can download it and check it out. The sheet is set up to do the calculation three ways--with the three parameters of resistor value, cap value and cutoff frequency, if you know any two, you can calculate the third.

Will have to wait until this evening, 'cuz I can't do it from here at work....

Thats really cool!

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OK, below is a link to the filter calculator spreadsheet. The sheet is protected so that only the cells containing the variable values can be edited. This is to prevent Excel novices from accidentally deleting key formulas or information. If you know your way around Excel, you won't have any problem unprotecting the sheet, if you want to make other changes.

Note that, while the formula requires the capacitor value to be in farads, the sheet also displays the value in microfarads (uf) and picofarads (pf), since these are the units in which most capacitors are rated. The farad entries are usually small decimal fractions with lots of zeros, and it's easy to get confused. Displaying the value that's entered or calculated in these other two units should help you keep things straight.

Here's the link:

http://duhvoodooman.com/musical/filter_calc.xls

sweet! thanks Voodoo