From mgarvi–(at)–anix.com Sat Dec 2 09:27:48 CST 1995
Article: 6039 of alt.guitar.amps
Path: geraldo.cc.utexas.edu!cs.utexas.edu!howland.reston.ans.net!news.nic.surfnet.nl!sun4nl!EU.net!newsfeed.internetmci.com!in2.uu.net!panix!not-for-mail
From: mgarvi–(at)–anix.com (Mark Garvin)
Newsgroups: alt.guitar.amps
Subject: Re: Tone circuits: part 3
Date: 2 Dec 1995 05:08:07 -0500
Organization: PANIX Public Access Internet and Unix, NYC
Lines: 41
Message-ID: <49p8i7$m--(at)--anix2.panix.com>
References: <499a1r$1o--(at)--anix2.panix.com> <49df1h$87--(at)--nrp1.news.primenet.com>
NNTP-Posting-Host: panix2.panix.com

In <49df1h$87--(at)--nrp1.news.primenet.com> mike–(at)–rimenet.com (Mike Rejsa) writes:

>*Many* thanks to Mark for his in-depth treatment!

>Minor question: Is there any effective difference between the 250pf/0.1/.047
>Fender setup and the 250pf/.022/022 Marshall version? (Pots are different
>too, of course…)

Hi Mike, If the ‘slope’ resistor (100k in the Fender circuit) and the
treble pot (250k) stay the same, then the center frequency of the:

250pf/.047 circuit is around 295 hz with about a 19.7 db mid cut

250pf/.022 circuit is around 430 hz with about a 16.8 db mid cut

The numbers above are derived using simplified versions of the tone
circuit which I outlined in a follow-up post. No guarantee on
accuracy, since I’m rushing this.

The .022 circuit gives the bass control wider range, because like
all simple R/C nets, these are limited to 6db per octave. Placing
the notch frequency a bit higher affords about 2-1/2 octaves down
to the guitar’s low E string (82.4 hz). The standard Fender .047
circuit’s mid notch is less than two octaves up from the low E
string, so the low E cannot be ‘boosted’ be even 12 db.

The other (.1) cap (at the top of the bass pot) is primarily DC-blocking,
since the reactance is still relatively low down to bass frequencies.
Changing to .022 doesn’t make that much difference, esp in the Marshall
circuit with a 1 meg bass pot.

Nor does the value of the bass pot enter into the center frequency
calculation very much. It DOES work as a voltage divider against the
100k slope resistor, so values over 250k don’t do a whole lot of good.
In fact, if a 1 meg pot is used there, best make sure that it’s a
true log taper (1/10th of the value at half-rotation) rather than
a semi-log (usually around 1/3rd at half-rot.). Otherwise all the
bass boost will happen in the low range of the pot…no audible
effect with further rotation.

Mark Garvin

 

Buy the Book!

I cleaned up my tab for Sonny Boy's Help Me and made it into a short book. There's a Kindle version for 99 cents, and if you buy the paperback you get the Kindle free.

Playing "Help-Me" In the Style of Sonny Boy Williamson II: A step by step, note for note analysis of some of Sonny Boy's Signature Riffs