Single opamp bass/low boost only?

[screamersusa]

More amp related than pedal.
I need to compensate for changes in the od section of my hybrid amp.
I have one unused half tl072 in the right spot to insert a low compensation boost
either before or after the hi-gain volume (output).
Is it possible with only one op amp?
Worst case, I dont need the reverb (currently disabled) which uses a whole opamp.

Details...
I changed the od tube gain to Engl spec and added a switch to change the
decoupling cap between the drive opamp and the tube. Values are currently
22n,44n,100n. I would like to compensate for this low cut after the passive opamp eq.
Looking for 80hz, 100hz or 120hz with a variable level.
It's a bipolar +-15v supply.

In actuallity, I could use this in some of my pedal builds as well.
TIA

[Johan]

You could implement a resonance filter. ..study the dod distortions from the nineties such as the grunge pedal. ... One opamp, one transistor and a few passive components could probably do the trick
J

[Mark Hammer]

http://www.muzique.com/news/frequency-booster/

[wavley]

http://www.muzique.com/news/frequency-booster/

I like that, I'm going to have to keep this in mind.  It's such nice and simple design.

[Mark Hammer]

And the nice thing is you can cascade them.  Just remove the 100k terminating resistance from the output when feeding it to another similar stage.  You can also skip the redundant 2u2 input cap.  Note that each boost stage can be essentially cancelled by lifting he 10uf cap along the ground leg.  Though pop-free performance would likely be facilitated by sticking a 1M-2M2 resistor between the 10uf cap and 10k resistor, and using an SPST to bridge/unbridge the added resistor.

Imagine a quad op-amp.  First stage provides a nice unity-gain input buffer.  Its output feeds one booster stage whose resonant frequency is set to one of three different bass frequencies via a DPDT on-off-on toggle.  That feeds another stage, geared towards three different mid-range boosts, and finally a stage oriented to 3 different treble boosts.

Build it into a 1590BB, oriented with the long side facing you, and three DPDT stomps to enable/disable each of the booster stages and provide status LED.  Three pots for adjusting frequency boost (maybe a 4th to adjust overall final output level since the boost adds volume, and three boosts adds more), and three toggles for frequency selection.  Badda-bing-badda-boom, you have a very simple-yet-flexible device for adding a little bit of this or little bit of that, in highly repeatable fashion, with minimal fuss.  Kinda like the old Maestro FRB-1 Full Range Booster...but with more flexibility, less distortion, and foot-switching.

[wavley]

Has somebody on this forum told you that they love you yet today?  If they haven't, then let me be the first.

And the nice thing is you can cascade them.  Just remove the 100k terminating resistance from the output when feeding it to another similar stage.  You can also skip the redundant 2u2 input cap.  Note that each boost stage can be essentially cancelled by lifting he 10uf cap along the ground leg.  Though pop-free performance would likely be facilitated by sticking a 1M-2M2 resistor between the 10uf cap and 10k resistor, and using an SPST to bridge/unbridge the added resistor.

Imagine a quad op-amp.  First stage provides a nice unity-gain input buffer.  Its output feeds one booster stage whose resonant frequency is set to one of three different bass frequencies via a DPDT on-off-on toggle.  That feeds another stage, geared towards three different mid-range boosts, and finally a stage oriented to 3 different treble boosts.

Build it into a 1590BB, oriented with the long side facing you, and three DPDT stomps to enable/disable each of the booster stages and provide status LED.  Three pots for adjusting frequency boost (maybe a 4th to adjust overall final output level since the boost adds volume, and three boosts adds more), and three toggles for frequency selection.  Badda-bing-badda-boom, you have a very simple-yet-flexible device for adding a little bit of this or little bit of that, in highly repeatable fashion, with minimal fuss.  Kinda like the old Maestro FRB-1 Full Range Booster...but with more flexibility, less distortion, and foot-switching.

[Mark Hammer]

Aw, shucks! 

Incidentally, I've been using the frequency booster circuit for years, in different ways.  I have a plain vanilla one using a 2P6T rotary.  I also included a single stage with a 3-position toggle in the Forty-Niner, and also threw in a similar 3-choice stage in a silly little "instant Slash" thing I called the Boost-N-Scoop.  It's a great little circuit.  Throw a little love Craig's way, and also in Jack's direction for keeping it alive.

[wavley]

Aw, shucks! 

Incidentally, I've been using the frequency booster circuit for years, in different ways.  I have a plain vanilla one using a 2P6T rotary.  I also included a single stage with a 3-position toggle in the Forty-Niner, and also threw in a similar 3-choice stage in a silly little "instant Slash" thing I called the Boost-N-Scoop.  It's a great little circuit.  Throw a little love Craig's way, and also in Jack's direction for keeping it alive.

They always get some love from me, I don't get much chance to interact with them though!  Both of those guys have taught me sooooo much about this little hobby of mine.

[GibsonGM]

Have you guys found that this thing (the modified Anderton boost by Jack) oscillates like crazy??  Dunno what I did wrong, but I've got motorboat with no input/output, and high pitched wail if I plug cords in for guitar and amp.

I've tried more decoupling...100u bypass cap in ref supply, bypassing the TL071 pins with 221pF and .1u caps, I've put a BFC in parallel with the 10u to ground...nada.  Tried another TL071, and even an LM741.   I've upped the 5.6K resistor, nope.    Cannot get this to stop feeding back.   Using a power supply, and then tried battery...nope...tried hooking the 10u cap to Vr instead of ground...no.  Different freq. selecting caps (.022 now) - nope.   Pulling one of them raises the feedback pitch, BTW....lifting the input cap does nothing.

I've built a lot of things, but this one has me stumped!!  I recall having issues with the original, too.   This is a brand new breadboard, too.  Seems like a VERY useful circuit, if I can get it going, Grrrrr. 

[Mark Hammer]

Just looked at the original GP article, and where Jack shows a 10uf going to gnd, the original shows the 10k resistor going directly to vref, without any cap.  There are some other things stemming from the inclusion of an input buffer stage but that would be the big difference.  I built that version and experienced no difficulty.

[screamersusa]

THANK YOU THANK YOU THANK YOU!!!!!!!!!!!!!!!!!!!
It seems to work after the OD eq/output buffer. I added a dpdt to switch
two 100nf across two 154n for about 80hz and 140hz or so.
Does resonate at full gain but adds the thump I was trying to put back.
My crate GXT-100 is now a "BENGL" and back in its casing.
Thanks for the finishing touch!

[GibsonGM]

Just looked at the original GP article, and where Jack shows a 10uf going to gnd, the original shows the 10k resistor going directly to vref, without any cap.  There are some other things stemming from the inclusion of an input buffer stage but that would be the big difference.  I built that version and experienced no difficulty.

Thanks, Mark. Looks like others are using Jack's schematic with no issues.  Personally, I've never doubted anything he puts out, always top-notch.   I'm wondering if my new Chinese breadboard might be to blame?  Some kind of parasitics or something, who knows?
Going to rebuild it on an old and good one, just for grins. 

[Mark Hammer]

I trust Jack implicitly too.  Undoubtedly, your problem is going to come from something small.  Doesn't it always? P  

[GibsonGM]

Yup!  Knock out a small tube amp like an 18W, or an Easyvibe in a weekend, and have a 10 part, 1 opamp circuit misbehave like this.
It's doing it on a different breadboard, too, on battery.   It has to do with the pot and 5.6K I think....if I lift it, it passes signal at about unity.
Very Very Odd.  

Now I have to make it work, or I won't be able to sleep tonight, ha ha!  

***EDIT:  yeah, I build things way too compactly on the board...once i moved the pot away I got it under control.   Can't believe I fell for that one!  lol  **