Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on March 26, 2012, 07:55:12 am

Title: can one approach a diy build this way?
Post by: bakerlite on March 26, 2012, 07:55:12 am

Anything is possible I know but what i would like to do in the realm of my capabilities is build a preamp for my bass.
After messing with many eq's and bass amps/preamps  I would sure like a tube preamp that had the following tonestack?

Lows         ->        100Hz,   A = 2, Q = 1.4
Low mids   ->        500Hz,   A = 1, Q = 1.4
High mid    ->        2.5kHz,  A = 1, Q = 1.4
Highs         ->        5kHz,     A = 2, Q = 1.4

this is the real important part - after that i would like to add a mid cut switch, effect loop and grind(gain) control but i want to start off small and try and hammer out a layout that encompasses my required tone controls first.

Any thoughts and general musings gratefully appreciated!

Thanks

Title: Re: can one approach a diy build this way?
Post by: bakerlite on March 26, 2012, 08:17:51 am

Sorry I should have added that I am looking for the tonestack to be flat when all controls are at their centre point.

Title: Re: can one approach a diy build this way?
Post by: jjasilli on March 26, 2012, 10:49:18 am

You are describing a Baxandall tonestack, or EQ circuit, common to the hi-fi world.  This has flat tone with the knobs at 12:00 o'clock.  If you don't have it already, you should download the Duncan Tonestack Calculator.  Checkout the James and the Bench circuits, which are Baxandall circuits adapted for guitar amps.  Also Ampeg has built circuits similar to what you describe: 12:00 o'clock flat tone with cuts switchable at 300, 1000 or 3000Hz.  See Ampeg V4, e.g.

Title: Re: can one approach a diy build this way?
Post by: tdvt on March 26, 2012, 12:18:17 pm

I would like to have something similar (also for bass) & have done a few searches regarding mid-range and the James-style tone controls as I don't know enough to design one myself.

The James stack does boost/cut mid depending on your settings, but more as a by-product relative to your hi/lo & you can tweak your mid-center with component values.

From what I've seen so far, when there IS a dedicated mid control, it seems the regular treble/bass James stack (like the Duncan tone stack calculator has it) is used first in the signal path, then the mid-range is manipulated in a separate circuit. You might check out this thread (with links back to EL34world by loudthud) as it has a couple other links as well.

http://music-electronics-forum.com/t25669/ (http://music-electronics-forum.com/t25669/)

The Marshall example has a pretty extensive mid control after the James stack.

I'm finding myself gravitating toward a B15 pre-amp circuit but with 2 separate outputs (cathode follower maybe?) that are each adjustable for level. The treble/bass only may actually be fine, as I do like simple.

I will be interested to see what you turn up.

Title: Re: can one approach a diy build this way?
Post by: JayB on March 26, 2012, 03:25:45 pm

How about designing it within a feedback loop.