Searching \ for '[EE] Simple op-amp mixer design' in subject line. ()
Help us get a faster server
FAQ page: techref.massmind.org/techref/index.htm?key=simple+amp+mixer
Search entire site for: 'Simple op-amp mixer design'.

Exact match. Not showing close matches.
'[EE] Simple op-amp mixer design'
2004\10\19@020129 by

Hey all,

I've been in a major "clean-up" mode lately and as part of this, I decided to
have just one pair of speakers on my desk, but still use them from all 3
computers.  So I need a *simple* 4-channel (1 extra for future use) stereo
line-level mixer.  I'd appreciate some help with this design...

My initial (and hopefully final :-) thought is to do this with a single op-amp
per channel, with a gain of greater than 1 (I'll just experiment to find the
right level), and each input would be connected to this via a resistor and a
decoupling capacitor.  I'll also use a single-supply from a wall wart.

However, how do I calculate the correct values of the input resistor and
decoupling caps?  I don't need individual volume controls, nor any switches
etc.

Finally, I intend to do this with parts I have laying around here (already
have enclosures, stereo jacks, PCB's, resistors, caps, and op-amps), but
which op-amp should I use?  My choices are LM741, TL072, LF353.

Thanks,
-Neil.

____________________________________________
PicDude wrote:

{Quote hidden}

Use the TL072 or LF353. 47K input resistors in series with a 100n capacitors
go to the inverting input of the opamp. A 47K goes from inverting to output.
This will make the gain unity. The non-inverting goes to Vcc/2. Use a
couple of
10K resistors and a 10u cap to get your Vcc/2 point. Add a 47u output cap in
series with a 100R resistor on the output. Run the whole thing from +12V.
David...
____________________________________________
part 1 929 bytes content-type:text/plain; charset="iso-8859-1" (unknown type 8bit not decoded)

> Hey all,
>
> I've been in a major "clean-up" mode lately and as part of this, I decided
> to
> have just one pair of speakers on my desk, but still use them from all 3
> computers.  So I need a *simple* 4-channel (1 extra for future use) stereo
> line-level mixer.  I'd appreciate some help with this design...
>
> My initial (and hopefully final :-) thought is to do this with a single
> op-amp
> per channel...

Hi Neil,

How about just doing a zero-voltage summing bus? The quality should be
fine(when compared to the ground loops you'll likely have with three
computers), and you can do stereo with just a dual opamp, or use a quad if
you want to uninvert the signal. Attached is a diagram of the left or
right channel. If you run it single supply you'll need t provide vref and
also use an output cap.

Cheerful regards,

Bob

part 2 4485 bytes content-type:image/gif; name="mixer.gif" (decode)

part 3 79 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

____________________________________________
> Attached is a diagram ...

Note that "CW" on the pots is shown on the wrong end of the pots, oops.

-Bob

____________________________________________
Neil,

What's wrong with handling the connectors manually?

Mike.
____________________________________________
Mike Singer wrote:

> <>Neil,
>
> What's wrong with handling the connectors manually?

Well, he did ask for guidance on a circuit and we happily gave it.
Maybe he gets sick of friggin' around with those connectors!
David...
____________________________________________
On Tuesday 19 October 2004 12:05 pm, Bob Blick scribbled:
> Hi Neil,
>
> How about just doing a zero-voltage summing bus? The quality should be
> fine(when compared to the ground loops you'll likely have with three
> computers), and you can do stereo with just a dual opamp, or use a quad if
> you want to uninvert the signal. Attached is a diagram of the left or
> right channel. If you run it single supply you'll need t provide vref and
> also use an output cap.
>
> Cheerful regards,
>
> Bob

Hy Bob,

I'm not familiar with the terminology "zero-voltage summing bus", but your
circuit is very straightforward.  I'm also wondering why you didn't use
individual capacitors on each channel, so I'm assuming that's the point of
the zero-voltage summing bus?

And noticing that it's inverted, I'm not sure why I was adamant to make my
circuit non-inverted.  As long as both channels are inverted, all should
sound fine.  The non-inverted design also makes the calcs for the resistor
values pretty simple, so I'm good there as well.

Question:
As for power, I was thinking earlier today, that I wanted to run it off of a
wall wart, hence the single supply, but I thought of doing this instead for a
split supply:

Vin+ >-------'\/\/\,------o--------------> V+ to mixer
|
R        `-,
^  Zener
/_\
|
o--------------> Gnd to mixer
|
`-,
^  Zener
/_\
|
Vin- >-------------------o--------------> V- to mixer

I can't see why it won't work.  I'll use 12V in from the wall wart, and 5.1V
zeners for z +/- 5.1V supply.  Of course, filter caps etc will be added.

Thanks,
-Neil.

____________________________________________
Hi Mike,

Not sure exactly what you mean here.  Since all 3 PC's are usually on at the
same time, I want them all to be output from the same set of speakers
simultaneously without changing connections.

Cheers,
-Neil.

On Tuesday 19 October 2004 03:09 pm, Mike Singer scribbled:
> Neil,
>
> What's wrong with handling the connectors manually?
>
> Mike.
> ______________________________________________
On Tuesday 19 October 2004 06:22 pm, David Duffy scribbled:
> Mike Singer wrote:
> > <>Neil,
> >
> > What's wrong with handling the connectors manually?
>
> Well, he did ask for guidance on a circuit and we happily gave it.
> Maybe he gets sick of friggin' around with those connectors!
> David...

Pretty much.  But also because I am sick of having 2 sets of speakers on the
desk, and having to listen to the laptop's crappy speakers, which are mostly
muted since my palms rest on the speakers when I'm typing.

Speaking of cleaning up, one of my computers is Mini-ITX based, and small
enough that I mounted it on a keyboard tray under the desk.  Nice stealth
setup!

Cheers,
-Neil.

____________________________________________

On 20 Oct 2004, at 6:09 AM, Mike Singer wrote:

> What's wrong with handling the connectors manually?

Now that would not be much of a 'mixer' then, would it?

____________________________________________
Hi Neil,

The reason for the zero-voltage summing bus, it means you get no (well, in
a perfect world, but pretty much almost no) crosstalk between channels,
and the gain of one channel doesn't change with another channel, you can
even add or disconnect channels from the bus with no change to the other
channels.

> I'm also wondering why you didn't use
> individual capacitors on each channel, so I'm assuming that's the point of
> the zero-voltage summing bus?

Just for simplicity, there's no need to use individual capacitors. If you
run a dual supply and all your inputs have no DC on them, you can run with
no capacitor at all. But make the capacitor plenty big, shoot for a 5
Hertz rolloff.

> And noticing that it's inverted, I'm not sure why I was adamant to make my
> circuit non-inverted.  As long as both channels are inverted, all should
> sound fine.  The non-inverted design also makes the calcs for the resistor
> values pretty simple, so I'm good there as well.

Most consumer gear pays no attention to signal inversion anyway.

For a split supply, lots of devices use an AC output wall wart, like this:

*-------*------>|------*  positive output
|
|------|<------*  negative output

*----------------------*  ground

Wall wart goes in at the left side, and of course you'll need filter caps.

Cheerful regards,

Bob

____________________________________________
David Duffy wrote:
<<<<<<<<<<<<<<<<
Well, he did ask for guidance on a circuit and we happily gave it.
Maybe he gets sick of friggin' around with those connectors!
David...
>>>>>>>>>>>>>>>>

Neil wrote:
<<<<<<<<<<<<<<<<
Not sure exactly what you mean here.  Since all 3 PC's are usually on
at the same time, I want them all to be output from the same set of
speakers simultaneously without changing connections.
>>>>>>>>>>>>>>>>

Sean Alcorn wrote:
> > What's wrong with handling the connectors manually?
>Now that would not be much of a 'mixer' then, would it?

Neil,
You've got a mixer with each computer's sound system.
Why not connect speakers to some central computer and other computers
to its spare sound system's inputs (some inside computer case)?

Regards,
Mike.
____________________________________________

On Wed, 2004-10-20 at 16:03, Mike Singer wrote:
> Neil,
> You've got a mixer with each computer's sound system.
> Why not connect speakers to some central computer and other computers
> to its spare sound system's inputs (some inside computer case)?
>
> Regards,
> Mike.

Agreed, in fact that's exactly what I do, except I do it in a daisy
chain fashion. Computer 1 output connected to computer 2 input. Computer
2 output connected to computer 3 input. Computer 3 output connected to
home theatre.

Works quite well. Only limitation is every machine down the chain has to
be on (not a problem since I never turn those machines off).

The multiple sound cards in the chain does lead to some extra noise, but
I've never been bothered by it. I never use my PC for anything hi-fi
anyways. TTYL

-----------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

____________________________________________

You could also do a passive mixer. If, for example, you tie one end of
three 10k resistors together and drive the other ends with voltage
sources, the voltage at the common end will be the average of the three,
or the sum of the three divided by three. You can compensate for the
divided by three by turning up the gain of the amplifier.

Harold
(The ideal design has zero parts)

--
FCC Rules Online at http://www.hallikainen.com
____________________________________________

More... (looser matching)
- Last day of these posts
- In 2004 , 2005 only
- Today
- New search...