How to connect a Blend circuit to an overdrive ? [SOLVED]

[eh la bas ma]

Hello,

I built a Bass Overdriver from GuitarPCB a few years ago. I can't use it as much as I'd like because it cuts a lot of low frequencies.

Here is a simple blend circuit that i would like to add to this overdrive, but i am not sure how to make it work :

http://tagboardeffects.blogspot.com/2012/02/split-n-blend.html


I guess IN and OUT are going to the jacks, so there are 2 wires on each jack's tip ? the ones already there and the new ones from the Blend board ? Or is it better to connect the Blend's In and Out wires to the 3PDT's In and Out terminals, in order to bypass both boards when I switch off the overdrive ?

What about Send and Return ? Where would you connect these wires ? Are they connected to the overdrive pcb's In and out ? And the blender IN and Out should go to the 3PDT, instead of the overdrive pcb in/out pads ?

Bass overdriver :




Thank you very much for your help !

[antonis]

I'm sorry but I don't get you Jastin..

Do you want to blend some other effect with Bass Overdrive..??

[theehman]

Assuming you want to blend the overdrive with your clean signal, you'd use the in to your bass and the out to your amp.  The send goes to the overdrive input and return to the output.

[eh la bas ma]

Assuming you want to blend the overdrive with your clean signal, you'd use the in to your bass and the out to your amp.  The send goes to the overdrive input and return to the output.

Yes it's for adding some clean signal. You mean there is no way to put this Blend circuit inside the Overdriver enclosure ? It would be much easier to use it "internally" for me...

[eh la bas ma]

I'm sorry but I don't get you Jastin..

Do you want to blend some other effect with Bass Overdrive..??

No, I am not trying to blend the overdrive with some other effects, I 'd like to add more low ends to the overdriven signal, thanks to a clean blend pot. An extra Blend control to the guitarpcb Bass OD.

I am wondering if it's possible to connect the vero Blend circuit, from tagboardeffect, inside the Bass overdrive build, to achieve that ?

Edit : Guitarpcb has a similar Buff n' Blend pcb, designed to be added in a circuit. Not by itself, in its own enclosure, but inside an existing effect. I wonder if the Split 'n' Blend vero layout can be used in the same way, like in this exemple :



from https://guitarpcb.com/wp-content/uploads/2018/06/Buff-N-Blend-v2-2021.pdf

[antonis]

Why just not try to modify your Bass Overdrive..?? 

[eh la bas ma]

Why just not try to modify your Bass Overdrive..?? 

I'm open to try that too, anything that can help to bring back some bass frequencies in there is welcome. I would be really grateful if you have some suggestions.

I suppose a clean blend is always welcome in a Bass overdrive, it seemed to be the easiest way to restaure some low ends ?

I have a few other bass overdrives, and clean blend controls are very useful to shape the sound.

[ElectricDruid]

What's the value of the Drive and Volume pots in the original circuit? That makes a big difference, and it's not stated on the schematic you posted. What did you use?

Thanks,
Tom

[Mark Hammer]

Consider upping the various 200nf caps in series with the signal path to 1uf-nonpolarized.  That should help restore some of the bass you feel is not currently there.

[antonis]

Also, although C1, C3 & C5 (22μF) could be considered OK for BJT CE amps, their value should be doubled (at least) due to JFETs much lower transconductance..
(their capacitive reactance should be much lower than JFETs 1/g_m..)

P.S.
Generaly, oversize all the caps..

[eh la bas ma]

What's the value of the Drive and Volume pots in the original circuit? That makes a big difference, and it's not stated on the schematic you posted. What did you use?

Volume is A100K, Drive is B100K.

Edit : values are according to the build doc :
https://guitarpcb.com/wp-content/uploads/2018/06/BD_Bass-Overdriver-v1.pdf

Volume is usually set in the first quarter of rotation, unless Drive is on very low setting. It's very very loud with a lot of saturation when both controls are set at 12'.

The volume range is good if the circuit is used as volume boost, with Drive at minimum setting. I noticed there are more low ends in the beginning of the drive rotation, it gets quickly into distortion territory. Maybe the Drive pot is wrong ?

[PRR]

There's not a major bass-cut as drawn. Three poles near 15Hz (include the JFET internal source impedance), two near 9Hz, and one near 1Hz. About 4dB down at about 60Hz, which does shave the lowest fundamental; but a full-bass fuzz would be muddy.



If you need "all" the bass, replace the 22uFd caps with 47uFd (or tack a second 22u-33u across each one). If still bass-hungry, double the size of the 200nFd caps.

But check all your part-values first! "a lot of low frequencies" doesn't seem like a few dB at the lowest notes.

[eh la bas ma]

Thanks for your replies !

I will try to increase all 22uF caps up to 47uF, and report.

I tried non-polarized 1uF caps instead of 220n. I do have more bass but it gets muddy and fuzzy quickly. Adjusting the trimmers can also help to shape the sound, but I do loose a lot of precision in the signal with these 1uF.

I ll try to go back to 220n at C2, C4, C6, with 47uF at C1, C3, C5.

The board is starting to look overheated, I guess it won't be safe to try many values much longer.

I am still wondering about the possibility to use the Split 'n' Blend circuit as an extra Clean Blend control on this bass overdrive build ?

Do you think it can work ? If so, how can I correctly connect it ?

[FiveseveN]

I am still wondering about the possibility to use the Split 'n' Blend circuit as an extra Clean Blend control on this bass overdrive build ?

I'm surprised nobody pointed out that the output is inverted, so that's not gonna work. Try this as a quick hack:

[eh la bas ma]

I'm surprised nobody pointed out that the output is inverted, so that's not gonna work. Try this as a quick hack:

Thank you very much !

The volume pot has disappeared ? Is there a way to add some kind of volume control ?

Edit : 47uF caps are working great, it feels better than the first attempt with 1uF instead of 220n. I took a 3PDT toggleswitch and soldered all the 47uF and 22uF caps on it. Now I can toggle between standard values and bass boost.

Great mod, this will be very useful, thank you so much !

[FiveseveN]

The volume pot has disappeared ?

Look closer? Maybe down and to the right?
I think a "what value should the blend pot be" is coming so start with 100K and pay close attention to the part where I say it's only a quick hack.

[eh la bas ma]

Look closer? Maybe down and to the right?
I think a "what value should the blend pot be" is coming so start with 100K and pay close attention to the part where I say it's only a quick hack.

Ah yes, sorry !

I'll try this tomorrow and report.

[eh la bas ma]

I tried the Blend pot as you kindly suggested. Using a B100k pot.

I lifted the C6 leg connected to the Volume pot, and soldered a wire from the free leg to B100K lug 3. A second wire from R4 pad connected to C2 (without desoldering anything), going to B100K lug 1. Last wire going from C6 free pad (connected to Volume pad 3) to B100k middle lug.

It pans between clean and overdriven signal successfully. However, there are some weird oscillations in the signal when the Drive control is reaching 12'.

Both with the Blend knob fully on clean signal or fully on wet setting, once the Drive pot is set around the middle of its rotation and further, the signal gets intermittent, sporadic, like a brocken tremolo effect creating some irregularities in the signal. The noise is more in the background with Blend set on fully clean.

The issue is more prominent when I use 47uF, but it's also present with 22uF.

In the first half of the Drive pot's rotation, everything is fine. Blend sounds like it's working perfectly.

So I wonder what could cause this, and if it can be fixed ?

[FiveseveN]

So I wonder what could cause this

Having thought about it post-coffee I figured this might happen: it's introducing some of the output signal back into Q2 and creating positive feedback. A buffer along the blue trace would fix it.
Or since you're already adding a transistor you could make a separate stage similar to Q1 with whatever gain and tone shaping you need.

[eh la bas ma]

So I wonder what could cause this

Having thought about it post-coffee I figured this might happen: it's introducing some of the output signal back into Q2 and creating positive feedback. A buffer along the blue trace would fix it.
Or since you're already adding a transistor you could make a separate stage similar to Q1 with whatever gain and tone shaping you need.

Would this buffer circuit be enough ?



Edit : sorry, i guess these values are wrong...

Can I use one of these circuits as buffer ?