Baxandall-based Single Tone Control

[jbefumo]

Would have posted this as a reply to the existing Baxandall discussion, but it has no reply button, so ...


Needed a tone control for my 6BM8-based reverb unit, and came up with this -- Fiddled with the values in MultiSim until the curves looked like something I wanted and built it right on a 1M linear dual-ganged pot.  It's basically the same layout as given in the Adam's Amp Page article for building on a dual CONCENTRIC pot, but I reversed the connections on one of the pots so turning turning one up turns the other down. Haven't compared it to other single-tone controls with respect to loss, but the range seems pretty pleasing to my ear.  Prior to this, I've always used variations on the BMP control, but I think this sounds better.  (Will post my schematic for the entire reverb unit elsewhere.)

[tubeswell]

Cool

[PRR]

A "slope" control. Though +/-18dB at both ends of the band is more than usual, perhaps extreme. (Though some extremes of other happy tone-controls are just as severe.)

[xm52]

You may want to search for a tilt control circuit. This goes back to the early hi-fi days.


http://tubecad.com/2013/08/blog0267.htm

[jbefumo]

Thanks to all -- will definitely work on refining this, as I tend to favor single tone controls when panel space is limited.  Liked the way it sounded for the reverb, but ... once I get my hearing aids fixed, I may change my opinion ... 

You may want to search for a tilt control circuit. This goes back to the early hi-fi days.


http://tubecad.com/2013/08/blog0267.htm

[jbefumo]

A lot of great stuff at that site - THANKS for the pointer!

You may want to search for a tilt control circuit. This goes back to the early hi-fi days.


http://tubecad.com/2013/08/blog0267.htm

[jbefumo]

I'm looking at this slope/tilt control for another application, and since it's a stereo device, I'm wondering if I might put it after the phase inverter -- any reason this wouldn't work, or wouldn't be a good idea? Whether it sounds good is another question -- right now I'm just wondering if there's some catastrophic event lurking in the shadows.  Thanks,


Joe

You may want to search for a tilt control circuit. This goes back to the early hi-fi days.


http://tubecad.com/2013/08/blog0267.htm

[HotBluePlates]

You could put it after a phase inverter; it might be easier to drive from a different circuit earlier in the preamp.

It will present a 100kΩ impedance to ground, but cannot take the place of the tubes' grid reference resistors, so this board will be in parallel with those. Together that's a fairly heavy load for the inverter to drive, so you'll likely need 47kΩ or lower load resistors at the phase inverter (and a corresponding low-rp tube in the circuit).

If you opted to move the control to that place earlier in the preamp, you could use only one side of it and save the cost of half the caps & resistors for the same end result.

[jbefumo]

Thanks! Yeah, my first thought was 'hey, I can just use in place of the grid reference..." but then looking at the schematic I saw that in some positions a capacitor was in the path to ground, so scratch that.  Wasn't certain from a cursory scan of the article what the actual load was.  Was thinking, alternatively, that I might be able to replace the DP5T with an SP10T and adjust half the components for finer granularity if I'm using in in mono in a more traditional location. 


Joe

You could put it after a phase inverter; it might be easier to drive from a different circuit earlier in the preamp.

It will present a 100kΩ impedance to ground, but cannot take the place of the tubes' grid reference resistors, so this board will be in parallel with those. Together that's a fairly heavy load for the inverter to drive, so you'll likely need 47kΩ or lower load resistors at the phase inverter (and a corresponding low-rp tube in the circuit).

If you opted to move the control to that place earlier in the preamp, you could use only one side of it and save the cost of half the caps & resistors for the same end result.

[shooter]

but cannot take the place of the tubes' grid reference resistors

sorry for jumping in, I'm using a nearly identical setup in the amp I'm "tuning" and I am using it as a grid reference, can someone explain why, how you loose R?
thanks

[drgonzonm]

but cannot take the place of the tubes' grid reference resistors

sorry for jumping in, I'm using a nearly identical setup in the amp I'm "tuning" and I am using it as a grid reference, can someone explain why, how you loose R?
thanks

The person who answers this request, please provide a schematic.  thanks   Drgonzo

[jbefumo]

Well, what caught my eye immediately was that in position 5 (left to right), the power tube is seeing only C4 (as far as DC is concerned), which will look like an open circuit to ground, so zero R.  In the other positions, the resistance will change depending on the values of R2, R4, R5, and R6, which could potentially exceed maximum datasheet specified values.  I think it will get even worse if you're fixed-biased instead of referencing to ground, but I'm sure more experienced folks on this board will identify other issues as well.

but cannot take the place of the tubes' grid reference resistors

sorry for jumping in, I'm using a nearly identical setup in the amp I'm "tuning" and I am using it as a grid reference, can someone explain why, how you loose R?
thanks

The person who answers this request, please provide a schematic.  thanks   Drgonzo

[kagliostro]

Ciao Jbefumo

I don't know if you have read this previously but if you didn't it worths to spend 10 minutes

http://www.muzique.com/lab/tone3.htm

Franco

[jbefumo]

I have, and thanks -- the BMP is my go-to single-tone control, though I haven't tried any of the AMZ variations. I just may do so on my next build. I particularly like the BMP because it lends itself to building on a push-pull pot and hence doesn't take up any board space on cramped circuits.

Ciao Jbefumo

I don't know if you have read this previously but if you didn't it worths to spend 10 minutes

http://www.muzique.com/lab/tone3.htm

Franco

[kagliostro]

Here a link about single knob tone controls (if there is interest)

http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/

Franco