Adding bass post op amp overdrive

[Zbridges01]

Hey guys, I've learned so much from your forum, I thought I'd ask my first question. I'm working on a fairly simple soft clipping overdrive circuit. Currently powered by single op amp, obviously clipping diodes are in the feedback loop. I've had to drop the bass in the loop to get my desired overdrive flavor, however I am running into issues adding bass back post op amp.  Any suggestions on our way to do this without switching to a dual op app?  I have a simple low pass filter that works well on the highs, but bass is lacking.  Experimenting with an eq pedal after the overdrive yields great results with a 200hz boost post pedal but I'd like to figure out a way to boost it in the circuit after clipping to avoid fuzziness.  Anything helps, Thanks!

[Oolooloo]

In my experience, the way the Way Huge Green Rhino does this works superbly, but it uses two op-amps.
It gives you a boost/cut control, centred around 100 Hz. It uses an op-amp gyrator if I'm not mistaken.

If you want minimal extra parts, you could try a passive high shelving cut (looks like a low shelf boost, with gain loss) - two resistors and a cap, it depends on what the rest of your circuit looks like.
Tacking this directly on the output of your circuit would increase output impedance.

[Zbridges01]

Great thanks, I'll check out both these methods.  I'm super happy with the result I'm getting with a smaller cap to ground in the feedback loop of the opamp, so I'm looking for a remedy that adds bass post clipping section.  I can always change to a dual but I thought I'd check with you guys first.  Learning everyday!

[Zbridges01]

I also had the thought of adding a transistor like a 2N5089 to power a simple bass boost. Anyone have any advice on this?

[iainpunk]

try an cap in series with the clipping diodes, and experiment to taste.
depending on the rest of the component values, it could be best anywhere from 100n to 330p, and i suggest starting small and lowering the ammout of bass from there until you have the right sweetspot.

cheers

[Zbridges01]

Oh interesting.  So is that creating essentially an active low pass filter?  I'll try it out on the breadboard tonight, thanks!  I've got a 100p cap in parallel to knock off some harshness but I never thought about caps in series...

[iainpunk]

what the series cap does in preventing the low frequency's from getting clipped, since the low frequency resistance is higher, at super low frequency's there is no clippin due to the super high resistance of the capacitor.

cheers

[Jarno]

An alternative might be to use a clean blend, and blend some clean signal (which can be bass boosted), more elaborate for sure.

[antonis]

So is that creating essentially an active low pass filter?  I'll try it out on the breadboard tonight, thanks!  I've got a 100p cap in parallel to knock off some harshness but I never thought about caps in series...

100pF parallel cap forms a LPF together with feedback resistor/pot..
(it reduces high frequency gain without dealing with diode pair..)
Diode pair series cap is also set in parallel with feedback resistor/pot, preventing low frequencies to be shunted through diode(s) hence enhancing bass gain..
(just like Big Muff diode pair + cap inside NFB loop.. - see page 10 - 13 in http://www.guitarscience.net/papers/bigmuff.pdf as very well and comprehencively analyzed by Jarmo..)