Adding a blend knob to a stompbox

[Widows]

I was talking to a bassist friend the other day who suggested that any pedals I build for bass would benefit from a blend knob to allow the user to balance the effect/dry sounds.

Am I right in thinking this would be as simple as including a pot with one lug wired between the on/off stomp switch and the input of the board, and another lug wired to the output jack? Essentially in much the same way as you would connect a pot to two different caps to act as a tone control. Or is there more to it than that?

[armdnrdy]

We'll go with the much more than that statement.

The level of difficulty introducing a mix control varies from circuit to circuit.

[Widows]

yeah I just breadboarded up a Bazz Fuss circuit n did exactly that n got results that I wasn't looking for :-( Damn!

I want to add a blend onto a Rat pedal that's being used for bass. How would I go about that?

[armdnrdy]

There is info on adding a Blend/Mix control at R.G.'s site. Geofex

[pappasmurfsharem]

http://www.runoffgroove.com/splitter-blend.html

You can use this to split and or blend

I'd put it in a separate enclosure so you can use it with anything

[mth5044]

Check out the Buff n' Blend circuit. I've added that to a bunch of pedals and it has worked pretty well. May be trouble with pedals that don't enjoy the fine, crisp taste of buffer.


schematic from Beavis Audio

[Widows]

Thanks guys :-)

[MrStab]

just curious: in the few times ive done this, ive always used a lazy clean opamp buffer fed into one lug of a 50k lin pot with the effect going into the other, but what would be the advantage of using a log pot as outlined in this schematic? guess i always thought blending between 2 (ideally) even signals was linear by concept.

[GibsonGM]

I'm gonna make an assumption: that since the human ear hears in a logarithmic fashion, blending the signals this way will seem more natural and each increment of rotation of the pot will give you an "approximately equal" sensation of blend, rather than an abrupt and hard to control situation that a linear pot may produce.

IOW, you may get very little going on in the 1st half of rotation of a linear pot (or last half), and then the action occurs from 1/2 to full.   A log pot will correct that.  It's not about absolute signal level, but how we perceive it as humans.

[nosamiam]

just curious: in the few times ive done this, ive always used a lazy clean opamp buffer fed into one lug of a 50k lin pot with the effect going into the other, but what would be the advantage of using a log pot as outlined in this schematic? guess i always thought blending between 2 (ideally) even signals was linear by concept.

Yeah, I've seen that schem before and been curious. I thought that logarithmic curve GibsonGM is talking about only applies to perceived loudness. It makes sense that a volume knob should be log, but a blend?

[duck_arse]

the "w" curve is probably the one. it has a flat, slow middle, and goes quick either end. think stereo balance control.

for some ideas .....
go here, look for the gruntbox:
http://hammer.ampage.org/?cmd=lt&xid=&fid=&ex=&pg=1

mark speaks! here:
http://www.diystompboxes.com/smfforum/index.php?topic=88080.msg749956#msg749956

a bunch of circuits on bass and fuzz:
http://www.diystompboxes.com/smfforum/index.php?topic=102430.0

[GibsonGM]

^ Yup.  Maybe "W" tapers are hard to come by where they designed it??   Someone should try the W and A tapers to see what the heck the diff. is.   I think it's in the 'how fast' you get blend, as I stated above, but yeah - seems a little odd. 

Linear would be 'too slow and bunched up' I think, but not sure...

[SISKO]

I build this blender circuit http://seanm.ca/stomp/images/fet-minblend1.png but replacing the jfet with a bjt and reducing the 2.2M resistors in a Big Muff but never could get ride of the squeal it generated.

I will mod it to the beavis version and see how it works

[Kipper4]

I built the buff and blend and made R4 switchable.
Great little circuit. Its about time I boxed it up.

[John Lyons]

I usually use something like this (as posted above)



but with this one circuit I have been working on lately (Foxx tone machine)
I get a crackly clean signal when set to the clean side of the blend pot.
Anyone have an idea why?

It's not a fault of either circuit, they both work well when separated.
I've had oscillation issues with this one

so I've taken the input to the fuzz
from the input of the emitter follower as shown in the first image.

[duck_arse]

john, yr crackle (not ok) pot may have dc on it between the "return" and "out" connections, ie the other circuits.

if yr buffer is oscillatoring, you could try the noiseless bias method on the gate, and perhaps a ~10k? series resistor between C1 and the bias point. might work ......

[jubal81]

I made up some boards that have a blend circuit on a 3PDT board. Works pretty well.

http://www.madbeanpedals.com/forum/index.php?topic=8427.msg73062#msg73062

[closetmonster.]

http://imageshack.us/f/9/circuit6ei.png/

Here's a schematic for the VL Sparkle Drive. Might be some good reference material depending on what you're adding the blend circuit to.

[MrStab]

i totally forgot i had asked a question on this thread, sorry if i seemed to just ignore it.

IOW, you may get very little going on in the 1st half of rotation of a linear pot (or last half), and then the action occurs from 1/2 to full.   A log pot will correct that.  It's not about absolute signal level, but how we perceive it as humans.

i understand the point of log/reverse-log pots generally, i just couldn't compute how it would be of benefit in this situation. thanks for the info, though. linear seemed to be fine whenever i used it, but granted that was using a circuit which had been designed with that in mind (presumably).

It makes sense that a volume knob should be log, but a blend?

my thoughts exactly! the W taper thing seems interesting - would it be do-able with a resistor hack? my interest is purely theoretical, but you never know when this knowledge could come in handy.