Mixing 4 audio channels to 3?



--
I put in polarized from habit, (and, BTW, C2 is in backwards, oops)
but there's no real reason for them to be.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

--
Version 4
SHEET 1 964 748
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DaveC <newsgroups> wrote:

Agreed.
I'd eliminate C9. Some op amps aren't able to drive capacitive loads without exhibiting instability.
If you do want some noise reduction on your reference, I'd add a small decoupling resistor (say, 47R) between U4 and C9, and perhaps use another .1 uF for C9. If you're using a good low-noise op amp, you can probably just omit the filtering here and feed U4's output directly to your "common".
I'd also recommend decoupling your 16-volt power supply, with a .1 uF located as close as practical to the V+/V- pins of each op amp.
Remember to get the polarities of C1-C7 correct when you install them (+ to the op-amp side, - to the outside world).
--
Dave Platt < snipped-for-privacy@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's largely redundant anyway.
--
Stuart Winsor

Only plain text for emails
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK, done.

Sound like basic good advice. :-)

I presumed that such coupling caps should be non-polar. No?
Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DaveC <newsgroups> wrote:

No need for that. You're going to have an 8-volt bias sitting on each cap (half of your supply voltage), and the audio signals that they see will only be a volt or two, peak-to-peak, so the caps will always be polarized in the direction I indicated.
It's entirely usual and standard practice to use polar electrolytics in this sort of situation. If you want to get fancy I'm sure you could find an exotic 'lytic (like one of the new solid-electrolyte types), but I see no need for that in this application.
You *could* use nonpolar 'litics if you have them around, but as they're usually more expensive I don't see the point.
--
Dave Platt < snipped-for-privacy@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm learnin'! Thanks for the explanation. I'll use standard aluminum 'lytics here, connected as noted.
Dave C.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Since the V- pin is already PS ground, I need decouple caps only on the V+ pins, yes?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good practics is to put the bypass caps as close to the IC leads as is practical, and run short traces (or wires) to the IC pins.
I wasn't suggesting one bypass cap from V+ to ground and another from V- to ground... since you're using a single-sided supply and V- is DC ground, that would be redundant (as you have noted).
--
Dave Platt < snipped-for-privacy@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DaveC <newsgroups> wrote:

One cautionary note with regards to this circuit, as drawn: be careful when you wire up R15. If you use a standard three-terminal potentiometer, make sure that you wire both the wiper, and one of the two ends to U3's inverting input. Don't just wire up the wiper!
The reason: pots occasionally go "open" due to dirt or wear. If you have only the wiper connected, and it goes open, you'll have no feedback path around U3, and it'll immediately and enthusiastically slam its output against one of the rails (or both in rapid succession if there's a signal present). This will let out a really unholy THWOMP from your subwoofer, and may pop the cone out of the cabinet or at last shove the voice coil out of the gap. Expensive damage.
With a three-terminal wire-up, the resistance in this part of the feedback loop will never be more than the bulk value of the pot (i.e. open wiper == wiper all the way at one end) and this will limit the maximum subwoofer volume. You can choose the maximum loudness by setting the value of the pot.
--
Dave Platt < snipped-for-privacy@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The easiest way is to take two equal value resistors connected in series across your supply (as you have done R16/17). The centre point is then connected to the + input of another op-amp which has its output strapped back to its input - terminal. this forms a voltage follower and the output is your Vcc/2 reference. This provides a low impedance source and the resistors can be almost any value you like - anything between 10k and 1M say.
--
Stuart Winsor

Only plain text for emails
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.