requesting help for building a 2 channel mixer...

[JSR]

Hello guys, I'm new here...
I wanted to build a 2 channel mixer, so I can put 2 guitarsignals together in 1...
But, I my schematic doesnt work. I connected all the pieces like this:



When I set it on, the only thing I hear is brrrrrrrrrrrrrr  :lol:

The LED is just there to see when the power is on, that's the only thing dat DOES work  :wink:

So, maybe somebody can help me put the wires at the good spots.
I've already used the search-option, but my english isn't good at all, so I dont even understand the most topic-titles   :roll:  :oops:


edit: uhm... "Deze weet ik niet zeker" means "I dont know this one for sure" (or something like that...)

[Paul Perry (Frostwave)]

Power supply ground doesn't seem to connect to signal ground.
Plus, there seems to be one too few inputs for a mixer!!

[Paul Marossy]

If you can't get your circuit to work, you could always try this one: http://www.aaroncake.net/circuits/mixer1.htm

[JSR]

Power supply ground doesn't seem to connect to signal ground.
Plus, there seems to be one too few inputs for a mixer!!

exactly, I wasnt sure about the signal ground...
And I just made only 1 channel to see if it works. When this one works, I make the other channel the same, less work than struggeling ( :?: ) with 2 circuits...

[JSR]

If you can't get your circuit to work, you could always try this one: http://www.aaroncake.net/circuits/mixer1.htm

When I want to make tha schematic, I need to buy new stuff. Not that it is to expensive  :lol: , but the closest  ( :?: ) shop where I can get it is 20 km away from here and because I'm only 16 years old, I cant just jump in my car and drive to that shop.

I have the stuff for my job (what I posted above), and now I want to finish it like that    :wink: ...
But, I don't know how, so, anyone...

[Paul Marossy]

I think Paul Perry was trying to say that Pin 4 of the 741 should connect to ground... that's one thing that I see as a problem. The other thing that doesn't look right to me is that 250K pot. Usually, the signal goes to one outer lug, ground goes to the other outer lug and the output would come from the wiper (middle lug). Soemthing looks screwy the way that you have it drawn. Is that what you intended it to do, or is is supposed to be like a volume control?

[JSR]

supposed to be a volume control. I had the scematic from someone from a Dutch guitar-forum. He drawed it like this so, eventhough I thought like you, I connected it al like that.
But, ok, that's a thing I have to change. The 741 is already chanched and connected at the right way, but still a brrrrrr and no sound. Maybe because that pot, that's the thing I going to try now.

If it doesn't work after that, I will make a new drawing of how it all is connected to eachother en maybe then you guys see thàt single 1 thing (or more, I guess) and tell me what's still wrong.

[Paul Marossy]

As long as the power supply is good, my bet is on the miswired volume pot.  

[JSR]

ok, here it is, the way it all is connected now:



The brrr is less louder than it was befor this schematic, but, still no sound....

[Paul Marossy]

Your connections to the opamp look screwy. You have the output of the volume pot and the signal unit connected to the output of the opamp (Pin 6). The output of the volume pot and the signal unit should connect to the inverting and/or non-inverting input (Pins 2 & 3). The output of the opamp should be connected to an output jack.

I am also not sure that you can combine two signals with one opamp in the manner that you show. I am thinking two opamps are required. In other words, I think that you need to use a Dual Opamp.  

[JSR]

This is just 1 channel. The other has to look the same, but connected to the same power supply and "signaal uit" (signal out, to amplifier). "Gitaar in" means "guitar in"  (in case you wouldn't know... :lol: )

Uhm, but, cant you make a drawing (it's done in 1 minute) and post it here or send it to me? I'd be very thankfull...

[Paul Marossy]

Someone correct me if I'm wrong, but I believe that you need two seperate opamp input sections (with their own volume controls) whose respective outputs would be combined into a single output. Or, at the very least, you would need to have two volume pots that blend the two signals together at the input of the opamp. How else would you be able to blend the two signals?

What you have sketched just doesn't work. You must keep the two signals independent of eachother until they see the opamp input.