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Signal Mixer/Summing circuit

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I have never heard it called a virtual ground.

Personally I've always called it a 'virtual earth' point, but 'ground' is more normal in the USA than 'earth' - but it's a completely standard opamp term, as others have mentioned long predating IC's.

I have always know it to be called the summing piont were all of the voltages are summed (added ) together.

If I have been doing it wrong all of these years then how come the little mixer I have made works perfectly as you have yet to explain where I was 100% incorrect.

Adding extra unneeded parts doesn't stop it working, it's just a waste. However, for many applications you would have a buffer before the mixer section anyway, but not for any of the reasons you claimed.

I have built all of my own equipment through the years and they have worked flawlessly until I could afford to by a commercial mixing board (mackie 32-8) in which my DIY version still rivals it today (30 years later) as far sound quality goes.

So apparently your terminology may different than mine so there is know reason to insult my intelligence or abilities as a circuit designer.

In the schematic it states pedal so I am assuming Stompboxes.

If you recall (from the 70's) that usaly DPDT (sometimes just a SPDT but improper) switch , Switches the effect in an out of the circuit and when it is switched out the input is directly connected to the output.

Since all of the inputs are tied together should one the Pedals be a delay unit for a slapback type of echo(For an example) it will continue to echo instead of being a single slap back and evenualy start to oscillate profusely if its gain is set high enough.

I am not trying to start any flaming war here I don't know how to explain it any simpler than that.

If you don't understand the bypass switch arrangement then I can put up an example if needed, But I am sure that you do understand its configuration and should not be necessary.

I've no problem with understanding the bypass switching on stompboxes, although I would disagree with the way some manufacturers do it - but I don't see any relevence between that and this simple mixer circuit?.
 
"I did not say that it wouldn't work at all, Just that there is a possibilty of feeback problems the way it has been shown."

This is all I have to say about this issue.

jer :)
 
"I did not say that it wouldn't work at all, Just that there is a possibilty of feeback problems the way it has been shown."

This is all I have to say about this issue.

And it still makes no sense, there's no feedback issues with that circuit - it's a pretty standard line level virual earth mixer circuit.
 
Maybe you haven't had a situation like that happen to you ,But I have with with simple circuits like that.
I know that it is a standard circuit and I am just sharing my experiences with it as there are ways to make it better and it shall be up to the builder as to his choice if the extra parts count will be worth the while as it doesn't take a bank loan to add a few extra opamps.

I had built that same circuit for somebody and they had brought it back because it was sqealing as to the way they had hooked it up and I had redo the inputs with buffers in order to solve the problem.

Good Luck !

jer :)
 
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Maybe you haven't had a situation like that happen to you ,But I have with with simple circuits like that.
I know that it is a standard circuit and I am just sharing my experiences with it as there are ways to make it better and it shall be up to the builder as to his choice if the extra parts count will be worth the while as it doesn't take a bank loan to add a few extra opamps.

But your suggestion wasn't 'making it better' it was adding extra components for no advantage, I can only imagine you have been making some strange error in your designs that required buffers to cure - but I can't imagine what it might be?.

Do you have any circuits for any troublesome mixers you've built?.

I had built that same circuit for somebody and they had brought it back because it was sqealing as to the way they had hooked it up and I had redo the inputs with buffers in order to solve the problem.

Either designed/built wrongly, or wrongly connected in some strange bizarre way (connecting outputs back to inputs?).

If it's connected wrongly, then non-inverting buffers "shouldn't" have any effect on feedback.
 
No,I have not had any issues with any of my designs except that one time and that I had solved the issue.
It was 20 years ago and I don't remember exactly how they were hooking it up or what they were hooking to it,as the mixer worked flawlessly the way it was designed to do.
Except for their situation I added the buffers and it solved their problem because it forces the signal to flow only oneway through the circuit.

jer :)
 
I maybe stand corrected as I have been doing some reading and the way it is shown is the way I build mixers.
But my confusion/concern may have some realevance as of section 2 of this page,

**broken link removed**

as I had stated I use a inverting type of mixing I do not remember which method was used on that very first mixer it may have been a non-inverting type of configuration.

It helps people to explain to them why they are wrong, rather than just telling them they are wrong and thats it !

jer :)
 
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I maybe stand corrected as I have been doing some reading and the way it is shown is the way I build mixers.
But my confusion/concern may have some realevance as of section 2 of this page,

**broken link removed**

as I had stated I use a inverting type of mixing I do not remember which method was used on that very first mixer it may have been a non-inverting type of configuration.

Possibly?, but I can't comment on what it might cause, I wouldn't ever dream of attempting a mixer with a non-inverting (not virtual earth) configuration.

I do have some circuits somewhere, from old cheap commercial products, which are quite crude transistor designs - if I can find them I'll post one.

It helps people to explain to them why they are wrong, rather than just telling them they are wrong and thats it !

It wasn't, and still isn't, possible to do that, as we've no idea what you must have been doing wrong - the 'passive' mixing examples on the Elliott Sound Products site (which is a site I really like - though I've not read that page before) is truely horrible :D

Figure 4 though is of course a 'normal' mixer, and essentially the same as the one in this thread.
 
well I am glad to see that we are on the same page now and I may have used a non-inverting configuration on that particular project.
Because, From what I do remember is that it was used in the tape in/out loop of a stereo reciever for the guys kid to be able to play his guitar through and still be able to hear the music going through the stereo system because he could not afford a guitar amp at the time.
This again is a big no-no in my book as well but it was what he wanted.

Soon I will be messing with opamps again and I will recheck the scenerio but other than the two mistakes and the missing of DC Blocking caps on the inputs I see no reason that the circuit should not work.

jer :)
 
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