tone control schematics please

[preludefan]

hi all,

after building a few small tube amps i am now having a go at building an integrated amplifier, and have tried out a few circuits on the net but they all sound horrible!

i was wondering if any of you have a schematic that i can use in conjunction with half of a 12ax7 (to make up the losses in the circuit)?

this circuit is going to be used in my 4w+4w single ended el84 amp that i listen to down in the mancave...

its set up to use 1 12ax7 per channel (half driving the el84 and the other half allocated to the tone control)

i dont need alot of adjustment, just some so i can tweak things here and there to compensate from old/dry recordings and if possible, to use with 100k pots as these are the only ones available to me without having to order in from the internet!

thank you all in advance,

mike

 

[mickeymoose]

Here is one from 1959. E

 

[chrispenycate]

100 k linear pots, or audio taper/logarithmic? That circuit's for log, with different value pots for high and low. And driven from what impedance? That one uses the first tube as an impedance buffer, which is nice but means you can't do a feedback style Baxandall circuit, as that needs quite serious drive, much easier to arrange round two halves of a tube.

Hm. that's from '59 and they were using solid state rectifiers? Most designs had tube rectifiers back then…

 

[irwanks]

you should try apex ml3. thank you. http://www.diyaudio.com/forums/analog-line-level/167363-mic-line-eq-preamps.html

 

[mickeymoose]

The rectifier would be a selenium bridge. Quite common than. E

 

[preludefan]

thank you so far for your inputs

 

[chrispenycate]

The rectifier would be a selenium bridge. Quite common than. E

Yes, and I remember the smell when one burnt out. But they (for me) were more for preamps, radios and small mixers than power stages.

I like the little amp circuit (that is I don't, because I'm a push-pull fanatic and consider running continuous current through a transformer a crime, but ignoring that) but the passive tone controls rely on the pots being down 20dB at centre point (and having different value pots to get the same amount of lift and cut at treble and bass frequencies, but perhaps we could bodge that). Is there any way of loading the pot, even if this loses overall gain, so as to finish with flat frequency response in the middle? Or perhaps accept reduced control range and use equal value components.

I was considering putting a Bandaxall in overall feedback, but to get the necessary three phase inversions this would mean the input impedance was a bit low, and variable; the passive is much more reasonable (and changing the values from 1Meg to 100kΩ child's play).

All the apex circuits seem a bit modern – op amps and transistors. When his basic tone control has four active elements – more than in this entire project – it doesn't translate across to tube mentality very well.

 

[mickeymoose]

Attached the frequency response of the circuit. Interesting, it is in V gain and loss. I am just glad it is not in Neper! E