Minimal blender issue.

Hauge · January 08, 2009, 01:54:10 PM

Hi.

I'm building my first stompbox and I got a little problem.
I'm a bass player and I've decided to build seanm's 90 % B. Blender since it would be useful for me and it seems like a great first build.
I've wired up the whole thing and checked all connections, but it doesn't work the way it's suppose to.
Bypassed there's no problem, but when turned on there's a loud humming, when the clean signal is dialed in. The clean signal doesn't come through. Only if I plug the strings really hard there's a 'scratchy', distorted sound but not really any notes. The looped signal sounds great so I guess the error is on the board.
Does anybody have an idea what the problem could be and how to solve it?
If I can't fix it I think I'll try over again and build the B. Blender.

Thank you
Martin

oskar · January 08, 2009, 02:26:37 PM

Tjena!

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
Vr is a reference voltage. It is supposed to be V+/2 mhich means ~4.5V. Done that?
Do you have voltages?

Hauge · January 08, 2009, 03:37:37 PM

That might be the problem. I thought Vr was just 9 volt. I guess a resistor is the easiest way to half the voltage? What about the op-amp? Does it only need 4,5 v aswell?

oskar · January 08, 2009, 03:56:56 PM

Check out this schematic. In the top left corner are two 100k resistors and a cap. The resistors are forming a voltage divider.
Two equal resistors in between two diferent voltage potentials will see half of the sum of the potentials in between.
You need something like a 1meg to V+ and 1meg to ground meeting up at the input. That will work. ( ps. no cap in your case )
What OP amp are you using?

Hauge · January 08, 2009, 04:26:42 PM

I accidently bought a dual OP amp - TL072 - since it's the one used in the B. Blender (gaussmarkov version), but I've grounded the remaining pins so I guess it'll work.
I can't see your scematic but I think I understand your explanation. Thank you.

oskar · January 08, 2009, 04:36:30 PM

Oops! Forgot to take away that comment. I couldn't link...
I have a better one though. This is one of the most common circuits there is so check out the B.Blender lower left. Two 10k and one 10u.
That's what you need.

Actually unused OP amps should not be grounded but configured like a buffer exactly like the other one and be given a reference voltage like that so perhaps you should go for the B.Blender divider cap and from that divide two 1meg resistors to each of the + (noninverting op- inputs )

- And you were just going to solder some before bedtime aight?

oskar · January 08, 2009, 05:12:33 PM

Sorry there amigo...
This is how the full circuit should look like with a dual OP amp and the divider network for the reference voltage.
Make R1 and R2 the same size. They can be anywhere between 10k - 1M.

Hauge · January 08, 2009, 05:34:07 PM

Thank you very much.
I will stop by the local parts supply on my way home tomorrow. I better buy a solder sucker aswell.

Joe Viau · January 09, 2009, 12:42:10 PM

Not to hijack this thread, but has anyone tried to build the FET version of the Minimal Blender? See the first link in this post, then scroll down a little.

oskar · January 09, 2009, 08:12:04 PM

No. I haven't tried any of them but both are just buffers whith routing and a pot, straightforward builds. The transistor version makes an even more elegant solution. Minimal is good in my world.

Joe Viau · January 09, 2009, 10:50:33 PM

Thanks Oskar. I agree that simple is good.

Hauge · January 10, 2009, 10:33:33 AM

It's now wired up as the scematic above and it works just perfect.

Thank you, Oskar.

oskar · January 10, 2009, 11:23:55 AM

Tack själv och lycka till...

Hauge · January 10, 2009, 01:42:31 PM

Tak i lige måde.

Just one more question. Right now the pot blends the looped signal into the clean. If I switch pin 1 and pin 3 on the pot, will that make the pot blend in the clean signal instead?

oskar · January 10, 2009, 02:41:31 PM

Yes. You should also note that the buffered signal will dominate in one extreme setting but, since the looped signal is not necessarily buffered, the output of that effect will effect the action of the blend knob. It the looped input comes from an F/X with a 50k output impecance, then both signals will see equal impedances with the pot turned fully to the looped signal 50k/50k each.

cab42 · January 10, 2009, 02:46:05 PM

Quote from: Joe Viau on January 09, 2009, 12:42:10 PM
Not to hijack this thread, but has anyone tried to build the FET version of the Minimal Blender? See the first link in this post, then scroll down a little.

Yes, I build it. As far as i remember it worked as it should. I was using it for blending clean bass into a bazz fuzz and it sounded terrible for some reason.

I also build the b.blender and it was just as bad. I think it is because the bazz fuzz doesn't like a buffer in front. However, there's always the possibility that I did something wrong.

The bazz fuzz sounded great on its own, both on bass and guitar.

It's not often you see a thread in this forum dominated by scandinavians

Regards

Carsten

oskar · January 10, 2009, 03:12:03 PM

Hejsan!

Perhaps the bass fuzz also inverted the signal? That would have created problems when mixing it with the clean signal. The B. blender ( and certainly not the minimal one ) doesn't have a function to choose inverted/noninverted signal which is a good thing to have because so many pedals invert the signal.

Oskar

cab42 · January 10, 2009, 03:29:18 PM

Hejsan!

Tak Oskar.

That could be the explanation.

Maybe I should recycle the components from the b.blender and build a Splitter-Blend from ROG (http://www.runoffgroove.com/splitter-blend.html). It has a phase polarity switch!

EDIT: It seems as the polarity switch in the splitter blend comes from an article by R.G (http://geofex.com/Article_Folders/polarity_reverser/polarity_reverser.htm). I could try to add that to the b.blender instead.

Regards

Carsten

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