Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Preamps and Effects => Topic started by: benzer on September 26, 2007, 05:10:56 AM

Title: tone frequencies
Post by: benzer on September 26, 2007, 05:10:56 AM
at what frequencies should we boost the bass/treble/midrange in the tone control circuit of a guitar preamp for best tone?
i read somewhere that the midrange should be between 300hz to 500hz
,,is it true?
Title: Re: tone frequencies
Post by: tonyharker on September 26, 2007, 02:30:18 PM
If you check out and download the Tone Stack Calculator on this page http://www.duncanamps.com/software.html It may give you some ideas.

Tony.
Title: Re: tone frequencies
Post by: benzer on September 26, 2007, 04:57:52 PM
yea its a nice program,but the you cant change the resistor/cap values to get better responses,,for example :
the fender response when it boosts the treble there is a gain of -3 db
and when it boosts the bass the gain is about -7db
i would like some resistor/caps values which gives me a gain of almost 0 db at each highest boost,, any idea?
Title: Re: tone frequencies
Post by: teemuk on September 26, 2007, 06:22:47 PM
That's the nature of the circuit: It has very high insertion losses. We are talking about a passive circuit so it essentially doesn't boost anything. The "boost" is achieved by attenuating other frequencies.

You can decrease the insertion losses by driving the circuit from a low impedance source, having a high impedance following stage and by decreasing the "sweep" resistor's value. (In "Fender" stack it's R1). You'll have to tweak other values accordingly to maintain proper response. Basically, you scale the circuit to lower impedance. The default values are taken from tube circuits.

However, I think you'll never get rid of the inherent "lossiness" of this circuit (and it's variants) - at least not without seriously decreasing the range of controls or messing up the characteristic response.

The way I see it you have two choices: 1. Convert it to an active circuit or 2. Use another tone control circuit.

Be warned: TSC's "Vox" stack gives invalid results. Duncan Munro has been informed about this issue years ago but so far he has not corrected the errors. I think that particular software is too limited anyways. You can edit component values alright but that's about all you can do. SPICE is soooo much better.
Title: Re: tone frequencies
Post by: benzer on September 26, 2007, 06:34:10 PM
Quote
decreasing the "sweep" resistor's value. (In "Fender" stack it's R1). You'll have to tweak other values accordingly to maintain proper response.
true but how would i know how to change the other values??
the transfer function for the fender stack is very complicated
Title: Re: tone frequencies
Post by: teemuk on September 26, 2007, 07:36:06 PM
You'll have to experiment with that. If you would have read my post more carefully you would have catched the important point: You can't tweak that circuit too much without messing up either the range of controls or the characteristic response.

You may get a fair compromise between frequency response, control range and insertion losses but you can't replicate the "default behaviour" with lesser insertion losses; for that the circuit is just too damn "interactive". If you are not happy with that then try another circuit or convert it to an active one.
Title: Re: tone frequencies
Post by: benzer on September 27, 2007, 08:23:42 AM
expirementing values using matlab is hard unless you have the transfer funcion.. does SPICE do it easily? and what version are you using?
Title: Re: tone frequencies
Post by: teemuk on September 27, 2007, 08:53:28 AM
It is definitely easier with SPICE-based software once you'll learn how to use it. I tried various SPICE softwares few years ago and ended up using LTspice/SwitcherCAD III; it's freeware and very intuitive to use.

http://www.linear.com/designtools/software/#Spice
Title: Re: tone frequencies
Post by: benzer on September 27, 2007, 04:41:02 PM
thnx 4 the link,, lookslike its got another good softs too