Barber Tone Pump schematic

[David Barber]

I got around to drawing up a schematic of the Tone Pump for a discussion I was having, I thought maybe some people here might find seeing the schematic as something useful, if so, have at it! 



And a pdf link here. http://www.barberelectronics.com/tone_pump_schem.pdf

[dedguy]

Hey David are you using a JRC 072BD like in the LTD Silver or something else .....PS your Dirty Bomb is AWESOME!!!!!!!!!!!!!!!!!!!!!!!!

[Ripthorn]

You, Mr. Barber are the man.  Thanks for sharing with us, it really is too kind of you.

[chi_boy]

Well I considering the age of this topic, I guess nobody cared much for this circuit.  It has a lot that is similar to the LTD, but has anyone actually built this?

[WGTP]

I haven't built it, but it contains several ingenious design elements and should sound as good or better than most Tube Screamer clones.  The Presence control in the first op amp and the mid and bass controls in the second should allow for lots of flexibility.  Also a good place to start for mods, if you want to mess with the diodes and/or frequency response. 

[ayayay!]

I think I horsed around with it when it first came out, but I didn't do the mid & bass control.  It was more about tinkering with that tone control that wasn't blended into...  I remember what it was now:  Is that tone control supposed to go to ground or connect to the NFB like the TS? 

[Mark Hammer]

Nah.  It's simply used as a variable resistance to form a single-pole lowpass in conjunction with the 2200pf cap.

[nocentelli]

Old thread, I know.... Can anyone explain how the bass+mid controls work? It seems like a really simple but effective way of doing EQ with a single opamp and sounds good on the breadboard, but I haven't seen this method used before.

[Mark Hammer]

These are essentially different rolloffs.

Let us say that the mid control is set to zero ohms.  In that case, the .01uf cap is irrelevant.  The gain of the stage is then essentially set by the ratio of the bass control (50k) and the 3k resistor to Vref.  At max resistance, the gain of the stage is 53/3 or 17.7x.  But with the control set to 50k, the treble rolloff begins around 38hz.  Reduce the pot resistance to 10k, and the gain is reduced, but the rolloff begins around 194hz. 

So the general principle is that as the bass control is "increased" there is a gain boost but it is selectively applied to only the lowest content.

Okay, let's set that knob to zero ohms, rendering the .082 cap irrelevant, and look at the other pot and cap.  With the mid control set to max resistance, we have a stage gain of 28/3 = 9.3x.  The treble rolloff, however, begins around 637hz.  Drop that mid control by half to 12.5k and the gain drops to a little under 5.2x , and the rolloff starts around 1273hz.

For both those caps/pots, the treble rolloff is at 6db/oct, so there is still some treble coming through, just not very much.

The "Tone" control also produces a general treble rolloff at 6db/oct, but has no impact on the level.  In contrast, the bass and mid pots in the feedback loop compensate for what they take away, by adding some gain.  A much simpler (and more cost-effective) version of the circuit might skip the bass and mid controls, and replace them with a 12k fixed resistor and a 3300pf cap (stage gain = 5, treble rolloff beginning around 4020hz), and just use the tone and presence controls to vary the bite.

There, make more sense to you now?

[nocentelli]

Excellent as ever, thanks Mark.

[PRR]

> how the bass+mid controls work?

They work WITH the networks in the clipper stage.

Capacitor is "open" at some low frequency and "short" at some high frequency.

Therefore the bass+mid stage is unity gain at high frequency but higher gain at low frequency according to the resistor (pot) values.

It boosts lower freqs an adjustable amount.

So where's our highs??!

Look at the clipper stage. Again we have caps but in the other leg of the gain setting network. This stage is unity-gain for low frequencies but high gain at high frequencies. This treble boost, plus the added overtones of clipping, create an excessively bright signal. The tone network shaves the worst of this off, the bass+mid network trim-up lower frequencies, for a "balanced" (or musically unbalanced to taste) sound.

These two circuits probably will not work well each in isolation.

[pinkjimiphoton]

nice to know you're still "one of us" dave!!
thanks man!!

[mth5044]

He was a little over four years ago, anyway 

[aron]

Dave contributed stacked op amps among other things. I love those stacked op amps!!!!!