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Simple Audio Mixer, with volume control...?

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grrr_arrghh

New Member
Hi.

i often find myself trying to connect several differnet stereo sorces to my hi-fi. i would like to be able to connect all of these to the phono input on my hi-fi, at the same time, possibly including a volume control (using a dual gang potentiometer, one pot for each channel?), and I would like to add a switch for each input, so that i can turn each input on or off independantly, without unplugging the equipment. I wil probably be connecting things like, computer line-out, mp3 player, tv line-out.

i found the digram below on the net somewhere, but i'm not sure if it will do what I want, and if i can put a decent colume control into it.

Any help Greatly appreciated

p.s. if this is possible without an amplifier, would the output be good quality?

Tim
 

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Sebi

Active Member
Yes, this is the best quality - without active elements. If You have enough signal - min.20mV - it work fine.
 

grrr_arrghh

New Member
ok, thanks sebi - you say this is the best quality without active elements - does that mean that the quality would not be very good, but you couldn't get it any better without getting more complicated? Basically, is it worth persuing this method, or will the loss of quality be intolerable?

could I just replace the two dual gang pots with larger ones (e.g. 47K), to make an effective volume control?

also, could i just repeat the input part of the circuit several times, connecting them to the output (as shown in the diagram) to make a mixer that would mix several audio sources (more than 2)

lastly, on a 3.5mm stereo headphone jack, and on phono plugs, which connections are which?

thanks again

Tim
 

Sebi

Active Member
O.K., sorry for bad english... i want to say this is the best quality,because no contains any active elements.Transistors, IC-s, tubes have always generates noises, distortions, etc.The new and newer devices always better and better, but noises today also existiert.
Of course possible multiply this circuit for more channels, if You want use 47k potis, the serial resistor must be also 47k.
The phono-jack:
 

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Nigel Goodwin

Super Moderator
Most Helpful Member
grrr_arrghh said:
i often find myself trying to connect several differnet stereo sorces to my hi-fi. i would like to be able to connect all of these to the phono input on my hi-fi

My first thought is a possible lanquage problem? - by 'phono input' do you mean an RIAA equalised input for a magnetic cartridge in a record deck?, as it would mean in English.

If so you can't feed line level flat inputs into it. What you can do is feed it via passive filter, this corrects the frequency response and lowers the signal to a suitable level - you can find examples on the net.

Personally I find the circuit included rather crude, but it would work :lol:

Considering most CD's or records in your collection have probably gone through 100's of opamps in the recording process, adding an extra one isn't going to cause any 'loss of quality'. I would rather make a 'proper' mixer with a virtual earth mixer using a decent quality opamp, although for your simple purposes even a 741 would be good enough.
 

grrr_arrghh

New Member
hi

thanks all

language - i speak english, in england - by phono plugs, I mean the round plugs that u use to connect CD players etc to the back of an amplifier, they have a pointy bit in the middle, and a metal 'jacket' around the outside.

I would rather make a 'proper' mixer with a virtual earth mixer using a decent quality opamp, although for your simple purposes even a 741 would be good enough

My electronics knowlege is limited to what I know from GCSE stuff, and the things i have learnt on here. I had decided not to build a 'proper' mixer, as most of the diagrams i could find on the net were too complicated for me - i might as well buy a ready made mixer from maplins or similar

My knowlege of 741's is limited to using them as comparators - temp/light sensors, that sort of thing - could u expand a little on your suggestion?

Again, Thanks for everything

Tim

p.s. i have some LM358 and LM380s lying around - would they b any use, or is that gonna get too complicated?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
grrr_arrghh said:
language - i speak english, in england - by phono plugs, I mean the round plugs that u use to connect CD players etc to the back of an amplifier, they have a pointy bit in the middle, and a metal 'jacket' around the outside.

Right, Americans call them 'RCA connectors', you also said phono 'input' (which means a record deck input), do you actually mean a line level input (for a CD player or tuner).

My knowlege of 741's is limited to using them as comparators - temp/light sensors, that sort of thing - could u expand a little on your suggestion?

Have a look at https://sound.westhost.com/project94.htm for a simple opamp mixer, a 741 is just a poorer quality 'grand father' of the chips used in that. Figure 2 of that article is all you need for a mixer, simply fit volume controls on the inputs - I would also increase the values of the input resistors to 100K and the feedback resistors (R115 and R215 to 220K).
 

Styx

Active Member
Ahh the old American/English problem....
I have always called the connectors Phono's and have never had a problem when speaking at Richer Sounds (my 2nd home)

But working for an American company in Britain you end up calling things by their way since they get really confused. The funniest one had was this week

We have a new department boss from the states and he has us filling in project completness charts. Each one has a "meatball" on it and how many quarters are filled indicates how complete a projext is - sounds like a pie-chart???? We are tempeted to call them "Fagots" just for him until he comes around to our way (and the worlds way) of calling it a pie-chart.

741 I thought they could only be found in museum ?. Saying that though I am only allowed to use TL080 series of OPAMP's for aerospace.

741 were groundbreaking in their time but have been surpassed by better components. Most importantly by comparators. Designed to switch their output extreamly fast.
 

grrr_arrghh

New Member
ahh, ok - i will call them RCAs in the future - i shall explain: my all-in-one hi-fi has two 'RCA' sockets in the back for an AUX connection - that was all i meant by phono input.

in the diag you pointed me at, are you saying I could replace ALL the op amps in the diagram with 741s?

also, I am slightly confused (!), in figure 2 on that page, both diagrams are almost exactly the same, is one for left audio, and the other for right? again, if i was using stereo signals, would i have to make 2 of the input circuits (figure 1) for each channel (left or right)?

if I had three inputs (six chanels in total) would i be able to run all from just 2 9v batterys?

Thanks very much, again

p.s. 741's are still used alot in English secondary schools..., but only as comparators
 

Nigel Goodwin

Super Moderator
Most Helpful Member
grrr_arrghh said:
ahh, ok - i will call them RCAs in the future - i shall explain: my all-in-one hi-fi has two 'RCA' sockets in the back for an AUX connection - that was all i meant by phono input.

I'm English, and always call them phono plugs and phono sockets, you caused confusion by using 'phono input', which is an input for a 'phonograph' (record player).

in the diag you pointed me at, are you saying I could replace ALL the op amps in the diagram with 741s?

Yes, 741's have often been used in these sorts of designs, but it is a very old chip, and far better ones are available - probably cheaper then 741's. 741's though were such a ground breaking chip, that even today most opamps are '741 compatible' - which means you could fit sockets for the chips, and simply plug better opamps in when you wish.

Many years ago I built a complete 16 channel PA mixer, using all 741's, by operating at sensible levels it worked beautifully - I ran the PA for a rock band with it, and did disco's in between sets. If I was doing it now, I'd use better opamps - but back then 741's were cheap, others were not, and they did the job!.

also, I am slightly confused (!), in figure 2 on that page, both diagrams are almost exactly the same, is one for left audio, and the other for right? again, if i was using stereo signals, would i have to make 2 of the input circuits (figure 1) for each channel (left or right)?

Figure 2 is for stereo, as you quite rightly say. Figure one is mono, you need two for each stereo input channel - but only if you want to add tone controls. As I mentioned previously, simply adding pots on the front of figure 2 would give a working line level mixer without tone controls.

if I had three inputs (six chanels in total) would i be able to run all from just 2 9v batterys?

If just using figure 2, you could have as many channels as you liked, it wouldn't increase the current consumption. But if adding figure 1 as well, each extra pair of opamps will take more current - I don't know how much it would be, but it should be pretty low - certainly 3 stereo channels wouldn't be a problem.

p.s. 741's are still used alot in English secondary schools..., but only as comparators

Schools tend to be rather old fashioned in that respect, unfortunately teachers who know much about electronics are few and far between.
 

grrr_arrghh

New Member
Ahhhhhhh

*understanding dawns*

i know i am being both stupid and annoying (a cunning combination, almost as cunning as Balderick), but to connect the first input, would i connect the left to the 'mix 1', and the right to the other (!) 'mix 1', and the common to the gound (the ground that the output is connected to aswell)?

Also, for the volume controls connect the pots in series with the inputs? Would a 47K be large/small enough?

Thanks to everyone, very very much

Nigel, the title "Electronics God" is not misplaced.

Thanks again

Tim
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Here's a circuit for a simple mono two input mixer, using a single 9V supply. For stereo simply make two of them, for more inputs simple add extra pots (R7), capacitors (C3), and resistors (R2).

I've just made the values out of my head, they are extremely non-critical, I once built one to do a disco in about 30 minutes - using the first parts that fell into my hands!. My little brother who watched me do it, still doesn't believe it worked (even though he heard it) - perhaps my comments like "that's a pretty colour, I'll have that resistor" might have confused him :lol:

If you need a master volume control, just stick one on the output, 10K or 4.7K would be fine.
 

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grrr_arrghh

New Member
Thanks v. much for taking the time to draw the diagram, i really appreciate it

I know, i know, I can't do anything my self, but i still (!) have a couple of questions.

1, i always thought that the power connections on an op-amp had to be connected to +v and -v which would mean that you would need two power supplies, or do I connect the one connection to 0v instead of -v??

2, to make the master volume control, which of the two diagrams below is the best way to do it (or would they both work)

Again, thank you VERY much for all off your help, if you like I will let you know how I get on.

Thanks again

Tim
 

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mozikluv

New Member
mixer

:D hi,

as an added suggestion, instead of the 741 use the NE5532, or OP-27GP

:D
 

Nigel Goodwin

Super Moderator
Most Helpful Member
grrr_arrghh said:
1, i always thought that the power connections on an op-amp had to be connected to +v and -v which would mean that you would need two power supplies, or do I connect the one connection to 0v instead of -v??

R4 and R5 generate a split supply (effectively + and - 4.5V), the positive pin goes to 9V and the negative pin to 0V. If you want to use a real split supply, simply remove R4, R5, the capacitor across R5, and connect the non-inverting input to ground. Then connect the -ve supply of the chip to a -9V supply.

I used a single supply to make it easier for you.

2, to make the master volume control, which of the two diagrams below is the best way to do it (or would they both work)

The first one, the other won't work properly, and is never really used as a volume control.
 

grrr_arrghh

New Member
ahhhh, ok

I understand op-amps now, I feel I've learnt alot.

I finally have no more questions. Off I go to delve deep inside my cupboard, then (upon descovering that i have hardly any off the components I need), to Maplins.

If this circuit doesn't work, I shall be back!!

Seriously, you have been really helpful, and I really apreciate it.

Thanks very much.

Tim
 
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