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Author Topic: Two guitarist in ona amp using a DIY mixer  (Read 8784 times)

pyromaniac_

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Two guitarist in ona amp using a DIY mixer
« on: December 11, 2009, 08:37:06 AM »
Hi, I'm thinking of a way to use two guitars in the same amp. Of course a simple 2 mono to 1 mono cable splitter can be use, there are some donwsides with this solution I've heard though. Sometimes some tones from one of guitarist totaly takes over the signal and playing with heavy distortion may also sound weird then a Y-cable is used.

But why not use a simple mixer cicrcuit like "Mini-Mixer" at generalguitargadgets.com? A better solution in my opinion, coluden't siounds worse than the Y-cable solution anyway. However I don't know if it will solve the problems mention before, I'll have to try I guess.

So, have anyone else done something similiar and want to share their experience before I start maybe? If there's a better mixer-circuit for guitar, please post.

phatt

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Re: Two guitarist in ona amp using a DIY mixer
« Reply #1 on: December 11, 2009, 09:26:46 AM »
Welcome Pyromaniac,
                             That circuit is for pedal mixing, No good for passive joining of 2 guitars.  You need two hi Z isolating buffers for the job your asking.

The 4x 10k pots will serverly limit the usefulness unless both guitars have active pu's OR both guitars go through pedals that are always ON or have the last pedal in the chain with a dedicated *Buffered* bypass.

I did know of a simple circuit but for the life of me can't remeber where. I'll head scratch ,,see if I can track it down.

Some advice,
If you where mixing two acoustic players into one input the concept has merit but if one player has lots of pedals and the other player has none then you really need to use 2 Amps.
Phil.

pyromaniac_

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Re: Two guitarist in ona amp using a DIY mixer
« Reply #2 on: December 18, 2009, 02:27:30 AM »
Ok, I know there was I hatch. But if using to pedals with the guitars could solve the problem, wouldn't it be enough to use a cleean booster/buffer circuit like the MXR microamp or  AMZ MOSFET booster (found on tonepad.com I think) in line with the guitar before the mixer? A such circuit could easily be built in the mixer, at the input of every channel, just skipping the volume control for the buffer circuit using the pots in the mixer-circuit for volume instead*. Maybe it was something like this that cicuit you thought about was designed. This way you'ld have a mixer ciruit this insultated high Z inputs or? (yeah my english maybe sucks but I hope you'll understand that i mean anyway)

* Just checked the schematics, Ithought the level controll at the booster only was an regular log pot at the and as in most stompbox design, but it's not. Looks more like an gain control or I don't really know. Maybe it's better to remove the pots at the input of the mixer instead or maybe both is needed, cause I it looks like they're actually doing to different things. Anyone got an Idé?
« Last Edit: December 18, 2009, 03:42:43 AM by pyromaniac_ »

phatt

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Re: Two guitarist in ona amp using a DIY mixer
« Reply #3 on: December 18, 2009, 07:20:22 AM »
Hello pyromaniac,
Just look for something that *isolates* ie Hi Z buffer.

They should look something like this below.
Drawn off the top of my head , so I may have missed something but enough eyes on here to correct it or refine it for you.
I assume you know how to develop a *bias supply*? If not I'll draw it when I have time.

Don't worry about the language,, you are doing just fine. ;)

Have fun, Phil.
« Last Edit: December 18, 2009, 10:12:06 AM by phatt »

pyromaniac_

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Re: Two guitarist in ona amp using a DIY mixer
« Reply #4 on: December 20, 2009, 06:06:16 AM »
Yes, what I need is of course a high Z BUFFER circuit, don't know why I was taking about boosters. Your circuit (thanks btw) looks good to me, I'm thinking of building it actually, just need to know a few more things before a start....

I can fix a bias supply for the op amp, just a simple voltage divider you was thinikng of or? But that 10 v connection at your schematic makes me a bit confused. Why, and what op amp runs on 10 volts? Don't know what op amp I'm going to use yet, but at least some that runs on 9 v, since the mixer circuit also runs at 9 v. There's a lot of op amp that runs at 9 v, so which one should I choose? Is there any special features needed, or will the TL072 do the job? (the one used in the buffer circuit at generalsguitargadgets.com)

phatt

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Re: Two guitarist in ona amp using a DIY mixer
« Reply #5 on: December 20, 2009, 10:11:00 AM »
Actually there is a bias voltage on the "mini mixer", so just run off that bias point.

Don't worry about 9 or 10 volts as a lot of these opamps run anywhere from 6 to 30 volts. 9 volts is a little low actually and you tend to waste a lot of battery life because some opamps suffer when the 9v batt runs down to below 6 volts.

From memory a TL062 is a good one as it still works at 4volts, or there abouts, not as high speced as others but still a very usefull chip for low voltage battery situations.

The best bet with these circuits is to run 2 x 9volt batts in series giving 18 volts and you will probably tripple battry life.
Just remember to use 25volt rated electro caps and you will be fine, 16volt caps will likely explode or leak if run at higher that rated voltages.
Rule of thumb for caps is allow a 25% margin of safety and they will last a long time.
So if you have a 9volt battery and your caps are 10 volts then you have no margin for error and the caps will certainly fail sooner or later.
Phil.

 

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