Is this a dumb way to hook up a Unibass?

BarStarzBass · #1 01-27-2011, 11:28 PM

So I have a Unibass - love the concept, but hate the cheesy onboard distortion. So like many, I run the dry signal to my bass amp, then run the effected signal through a guitar distortion box or two - I've settled on a Metal Muff Nano to a Tech 21 British as a nice sound.

So far so good - the question is what to hook the British to. The obvious answer is a small guitar amp. But that's one more thing to haul to a gig. So I tried running it through a DI to our PA - but we play small places and the PA is really just for the vocals - didn't like the sound of the "rhythm guitar" through it.

So next I took an old A/B box, rewired it so it is A/A+B. My dry signal goes to A. Unibass to B. When I stomp on the switch, . it mixes the two signals and sends that to my bass amp - which is a Walkabout and actually a good guitar amp too.

Sounds good to my ears, other than a small volume drop. But is this a weird thing to do? I've read about impedance mismatches caused by mixing two signals together - but the signal only comes from one bass guitar, so do I still have a problem? And I only use the Unibass with an active bass. Am I missing something here?

walker rosewood · #2 01-28-2011, 12:02 AM

If it sounds good and doesn't hurt the gear then why not? (i don't know if that would hurt your gear or not, btw)

Quote:

I've read about impedance mismatches caused by mixing two signals together - but the signal only comes from one bass guitar, so do I still have a problem?

Once your signal hits a pedal the impedance is no longer coming from your bass (unless it is being true bypassed). And the additional pedals are likely making the signals slightly out of phase, causing the volume drop.

sry i'm not much help.

dune2k · #3 01-28-2011, 06:22 AM

Quote:

Originally Posted by walker rosewood

If it sounds good and doesn't hurt the gear then why not? (i don't know if that would hurt your gear or not, btw)

Once your signal hits a pedal the impedance is no longer coming from your bass (unless it is being true bypassed). And the additional pedals are likely making the signals slightly out of phase, causing the volume drop.

sry i'm not much help.

^ This.

bassman1185 · #4 01-28-2011, 08:22 AM

You might be better off getting a small mixer to blend the two signals together, rather than an A/B box. The volume drop you're hearing is probably phasing problems. A mixer would help alleviate that.

Ba55Man1ac · #5 01-28-2011, 09:38 AM

Yes as well as phasing problems, the 2 outputs will be 'fighting' each other - each one sinking current from the other. This can damage the output op-amps. Best get some sort of mixer. A Boss LS-2 would do the trick. Even a passive mixer like the DOD 240 would be fine.

BarStarzBass · #6 01-28-2011, 11:37 AM

Thanks for all the input, guys - this is really good. I'll look into the LS2 - I had checked it out before but for my specific setup I wasn't sure what it would do that a modded A/B wouldn't do - I think I have my answer now.

A phasing problem sounds right - in addition to the volume drop I hear a very slight "hollowness" to the sound - hard to describe, but feels like the attack is softened a little - phasing would explain it.

Thanks again.

dune2k · #7 01-28-2011, 12:04 PM

If you're handy with the soldering iron: an active mixer is pretty simple to do.
You need one dual opamp (TL072 will do), a couple of caps and resistors & if you want to be able to control the mixing further one or two potentiometers.

BarStarzBass · #8 01-28-2011, 01:10 PM

Dune2k - cool! I'm pretty good with a soldering iron - and I'm also a cheap bastard so DIY is always preferred!

Would you happen to have a link to an appropriate circuit diagram? I wouldn't even need the pots, as every input has it's own level knob and I can mix with those.

walker rosewood · #9 01-28-2011, 01:27 PM

check out the forums at http://freestompboxes.org/index.php and http://www.diystompboxes.com

they've got all sorts of projects.

or check out the 'mini mixer' from General Guitar Gadgets.
http://www.generalguitargadgets.com/...-mixer-project

dune2k · #10 01-28-2011, 01:48 PM

Quote:

Originally Posted by BarStarzBass

Dune2k - cool! I'm pretty good with a soldering iron - and I'm also a cheap bastard so DIY is always preferred!

Would you happen to have a link to an appropriate circuit diagram? I wouldn't even need the pots, as every input has it's own level knob and I can mix with those.

I'll draw something tomorrow.

BarStarzBass · #11 01-30-2011, 04:02 PM

No worries Dune2k - I followed Walker's suggested General Guitar Gadgets link and found this diagram for a simple mixer. I'm going to build an even simpler version - only 2 inputs, no pots and no LED.

But I wouldn't mind you (or anyone) looking at my proposed setup - ie. through a DPDT switch so that one side is the dry bass signal alone ("A") and the other sends both "A" and the Unibass output ("B") to the mixer. I don't think this will set up any weird phase or "fight" situations but please let me know if you see a problem with it.

Thanks!

dune2k · #12 01-31-2011, 04:14 AM

Here's a buffered (Y) splitter.

Jazz Ad · #13 01-31-2011, 04:34 AM

It's not dumb at all.
When I used the Unibass, I hooked it up to a 30 W tube amp. It worked perfectly. The SansAmp in your setup replaces the amp, so to say.

Ba55Man1ac · #14 01-31-2011, 04:34 AM

You're on the right track BSB. I can see 1 problem with your diagram. When you have the switch in the dry-only position the op-amp output will sink current from the dry signal as it is still in circuit (connected to the output jack). This will make for a distorted, low-level sound when in this position. Why not make it a 3PDT & use the 3rd pole to disconnect the mixer circuit completely when not needed?

walker rosewood · #15 01-31-2011, 01:47 PM

...and 3pdt stomp switches are easier to find anyway.

BarStarzBass · #16 01-31-2011, 01:57 PM

Walker, Ba55, Jazz and Dune2k - thanks so much for all the great input. I think I'm on the right track now - will report back once i've wired it up and tested it all. Thanks again!

BarStarzBass · #17 02-12-2011, 05:49 PM

Well, I wired it all up per my diagram, except subbing a 3PDT switch so I can pull the mixer completely out of the circuit at both ends. The bypass setting works great (of course - it's hardwired!) but when I stomp over to the mixer, I get white noise and VERY low output. I've checked the wiring three times and I'll go over it again - but does anything obvious come to mind that I should check? One thing - I used a TL082 instead of a TL072 as called for in the diagram. I understand the TL072 is a better choice but I would have thought the 82 would be close enough - are they THAT different?

dune2k · #18 02-12-2011, 06:08 PM

TL072 = low noise, TL062 = low power consumption, TL082 = the rest of the lot
So no, they're not that different.

Is the power stuff (battery, ...) wired correctly?

BarStarzBass · #19 02-12-2011, 07:03 PM

Thanks Dune2k. After some more poking and prodding and touching up some solder points, I managed to get rid of the white noise. The volume has gone up too and I can definitely hear the two signals being mixed - and they do sound better together than when i was just hardwire-mixing them - but there's still a BIG volume drop versus the bypass - like half or more. I'm running off a 1-Spot and I think the power is getting to all the points it needs to, but I'll double check that.

SteveMcB · #20 02-12-2011, 09:28 PM

I do similar with my splitting my lows and highs and processing the highs only then mixing. Obviously if you've got the skills to go the DIY route that's fantastic, but for anyone else reading this and thinking it would be cool but I don't wanna build a mixer, the Behringer MX400 is a tiny, low-noise, low-cost active mixer with 4 ins and 1 out which does this job very, very well. Only downsides are:a) something on your board that says Behringer (if that bothers you) and b) requires 12v power input and will not run on 9v (I've tested it)

Steve