Tone Controls Poll

Graham Slee wrote: musicdude wrote: Graham Slee wrote: So this is a volume control pot and it's never going to be exact. There has to be a padding pot somewhere in a good preamp design to take up the slack (either that or plenty of waste electronic components) and that requires a preset trimmer in circuit somewhere, and that's a pot. OK, once set it's never adjusted because it's out of reach, but it's a pot. Are the two blue square the padding pots? Quite an incriminating photograph when you think of it... The big blue thing in the middle that makes so many wet their pants, having to be corrected by two Bournes conductive polymer trimmers that cost pence... But maybe they aren't... ?

Should not cost a lot. This picture is from my Chinese amplifier...

Out of interest this is a bass and treble control plot from a circuit I designed 21 years ago. I only had a calculator to work it out, and a Neutrik audio analyser and scope to measure it. The mixer it was used in sold quite well right up to recent times. This plot was simulated from the circuit diagram I kept all those years. You will see how it is shelved (the flat parts) so it goes to the level of boost or cut set by the pots and doesn't get boosted or cut any further. Cheap tone controls don't have any shelving.



By reducing the degree of boost and cut the controls can be set to emulate the response a tilt control, albeit centered on 800Hz, whilst still being able to do loudness contours. Small degrees of treble control operation can increase or decrease the presence (mid range) band and upward.




Edited by Graham Slee - 12 Jan 2013 at 7:32pm

With tone controls set flat there is always some deviation in frequency response due to both bass and treble being dealt with by the one active stage.

Each EQ circuit interacts with the other producing an emphasis either to the highs or the lows.

Correctly designed (and this was done 21 years ago without the aid of computer modelling) the set to flat deviation here, between 20Hz and 100kHz is 0.0085dB. Not even a bat should be able to distinguish any difference. Its effect on phase would be 10 times worse and that would lead to a phase error of around 3 degrees between 20Hz and 100kHz.

The plot below is in milli-dB. Each step on the left is 0.002dB

morris minor wrote - "thin sounding LPs from the 80s, or early CDs who's treble sets your teeth on edge?"

No, never experienced this. I have lots of 80's vinyl and early (1980's) c.d.s and they all sound fine to me.
Maybe I was lucky buying well recorded albums at the time? So, still no, never used or needed tone controls. I've always made sure that any past equipment, where tone controls have been fitted, there is a defeat incorporated.