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Default Mixing 4 audio channels to 3?


In article ,
DaveC newsgroups wrote:

Only a single supply (in the amplified speakers) is available to power this
circuit. I can tap this supply for my circuit:


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.

--
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Default Mixing 4 audio channels to 3?

Latest rev:

http://i40.tinypic.com/35m026h.jpg

What needs to be reference to the new "ground"? Everything between the
input
caps and output caps?


Pretty much... each of the op amps' noninverting inputs, and the
"bottom ends" of the potentiometers, as you have drawn them. *NOT*
the V- input to the op amp(s), of course.


You do mean each of the op amps' *inverting* inputs, yes?

You might want to add "pop preventer" resistors at the inputs and
outputs... say, 100k to DC ground, from the "outside" end of each of
the DC-blocking capacitors.


Is this what you mean (see link)?

Thanks.


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Default Mixing 4 audio channels to 3?

On Tue, 8 Nov 2011 21:07:44 -0800, DaveC wrote:

Latest rev:

http://i40.tinypic.com/35m026h.jpg

What needs to be reference to the new "ground"? Everything between the
input
caps and output caps?


Pretty much... each of the op amps' noninverting inputs, and the
"bottom ends" of the potentiometers, as you have drawn them. *NOT*
the V- input to the op amp(s), of course.


You do mean each of the op amps' *inverting* inputs, yes?


---
No.

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.

--
JF
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Default Mixing 4 audio channels to 3?

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.
JF


Thanks guys. Fixed:

http://i44.tinypic.com/r1k8qa.jpg

All else looks good?

Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?

Thanks.

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Default Mixing 4 audio channels to 3?

DaveC writes:

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.
JF


Thanks guys. Fixed:


http://i44.tinypic.com/r1k8qa.jpg


All else looks good?


You still have the signal go to the non-inverting input. The way the
schematic is, U1-U3 will throw their output hard to a rail or oscillate
with positive feedback from R13-R15.

Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?


I worry that the RC time constant would have the reference be not at the
1/2 way point while C8 charges on powerup. I don't see a C9. Might do
something not so good to the subwoofer.



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Default Mixing 4 audio channels to 3?

You still have the signal go to the non-inverting input.

The current version of the drawing has signal going to the inverting input

Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?


I worry that the RC time constant would have the reference be not at the
1/2 way point while C8 charges on powerup.


Suggestions?

I don't see a C9.


That means you're not looking at the right version of the drawing. Copy &
paste this into a browser:

http://i44.tinypic.com/r1k8qa.jpg

Might do something not so good to the subwoofer.
[M. Moroney]


Suggestions?

Thanks.

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Default Mixing 4 audio channels to 3?

On Wed, 9 Nov 2011 09:07:15 -0800, DaveC wrote:

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.
JF


Thanks guys. Fixed:

http://i44.tinypic.com/r1k8qa.jpg

All else looks good?

Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?

Thanks.


What does U4 do?

d
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Default Mixing 4 audio channels to 3?

In article ,
DaveC newsgroups wrote:

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.


Agreed.

Thanks guys. Fixed:

http://i44.tinypic.com/r1k8qa.jpg

All else looks good?


Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?


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 AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
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Default Mixing 4 audio channels to 3?

I'd eliminate C9. Some op amps aren't able to drive capacitive loads
without exhibiting instability.


OK, done.

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.


Sound like basic good advice. :-)

Remember to get the polarities of C1-C7 correct when you install them
(+ to the op-amp side, - to the outside world).


I presumed that such coupling caps should be non-polar. No?

Thanks.

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Default Mixing 4 audio channels to 3?

What does U4 do?

Provides a Vcc/2 local "ground" so I can use these op amps with a single
supply voltage.



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Default Mixing 4 audio channels to 3?

On Nov 9, 5:07*pm, DaveC wrote:
Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.
JF


Thanks guys. Fixed:

http://i44.tinypic.com/r1k8qa.jpg

All else looks good?

Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?

Thanks.


First you can replace C1-5 with 1uF each. Replace C8 with 220uF, and
omit U4 & C9 entirely.
You dont want to use a 50k pot followed by a 10k load (R5-12). I'd go
with 10k pots and 100k for R5-12, adjusting the nfb Rs accordingly.


NT
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Default Mixing 4 audio channels to 3?

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.


Since the V- pin is already PS ground, I need decouple caps only on the V+
pins, yes?

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Default Mixing 4 audio channels to 3?

First you can replace C1-[4?] with 1uF each. Replace C8 with 220uF, and
omit U4 & C9 entirely.


Leave C5-7 as is?

You dont want to use a 50k pot followed by a 10k load (R5-12).


Teach this man to fish: why don't I want to use 50K pot & 10K load
combination?

I'd go
with 10k pots and 100k for R5-12, adjusting the nfb Rs accordingly.
NT


"adjusting" means replace those with 100K's also?

Thanks.

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Default Mixing 4 audio channels to 3?

On Wed, 9 Nov 2011 12:10:19 -0800, Bob E. wrote:

What does U4 do?


Provides a Vcc/2 local "ground" so I can use these op amps with a single
supply voltage.


More useful to let it oscillate as a square wave generator at 100kHz
or so, and rectify the output into a negative 15V rail. That way you
can run the op amps the way they are meant to be run.

d
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Default Mixing 4 audio channels to 3?

More useful to let it oscillate as a square wave generator at 100kHz
or so, and rectify the output into a negative 15V rail. That way you
can run the op amps the way they are meant to be run.

d


Suggest a circuit...?

Thanks.



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Default Mixing 4 audio channels to 3?

In article ,
DaveC newsgroups wrote:

Remember to get the polarities of C1-C7 correct when you install them
(+ to the op-amp side, - to the outside world).


I presumed that such coupling caps should be non-polar. No?


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 AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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Default Mixing 4 audio channels to 3?

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.


Since the V- pin is already PS ground, I need decouple caps only on the V+
pins, yes?


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 AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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Default Mixing 4 audio channels to 3?

On Nov 9, 8:31*pm, DaveC wrote:
First you can replace C1-[4?] with 1uF each. Replace C8 with 220uF, and
omit U4 & C9 entirely.


Leave C5-7 as is?


1uF

You dont want to use a 50k pot followed by a 10k load (R5-12).


Teach this man to fish: why don't I want to use 50K pot & 10K load
combination?

I'd go
with 10k pots and 100k for R5-12, adjusting the nfb Rs accordingly.
NT


"adjusting" means replace those with 100K's also?

Thanks.


that would work


NT
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Default Mixing 4 audio channels to 3?

I was going to suggest that, since the mixer is going to be external
to the amp, he use a couple of wall-warts to get the dual supplies,
but I like your solution a lot better. :-)


Enough to suggest a nice circuit? ;-)

Thanks,
Dave



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Default Mixing 4 audio channels to 3?

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.
...
Dave P.


I'm learnin'! Thanks for the explanation. I'll use standard aluminum 'lytics
here, connected as noted.

Dave C.

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Default Mixing 4 audio channels to 3?

On Wed, 9 Nov 2011 12:10:19 -0800, Bob E. wrote:

What does U4 do?


Provides a Vcc/2 local "ground" so I can use these op amps with a single
supply voltage.


Hint: Don't use the chassis ground symbol as a "Vref" symbol. It's confusing
and someone along the line might get hurt. Grounds should be.
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Default Mixing 4 audio channels to 3?

Hint: Don't use the chassis ground symbol as a "Vref" symbol. It's
confusing
and someone along the line might get hurt. Grounds should be.


Yeah, I wasn't sure about that. How should I have indicated 2 separate
grounds?

Thanks.

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Default Mixing 4 audio channels to 3?

In article
,
DaveC wrote:

http://i40.tinypic.com/35m026h.jpg


Distortion performance might be better if you run the amps in inverting
mode. If you run the audio into the non-inverting inputs, the inverting
input follows and the amp has to operate throughout it's common-mode
range. If you use the amps in inverting mode, both the + and - inputs
will stay very close to ground.

Isaac
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Default Mixing 4 audio channels to 3?

What is wrong with using an op-amp to "amplify" DC? Surely they are
"meant" to do that.

Isaac


I think he means that better audio results can be achieved by providing true
dual-voltage supplies and eliminating all coupling caps.

The "DC amplifier" is a fine design, but will result in inferior audio
performance due to the caps.

Now, if someone would volunteer such a negative voltage generator circuit...
;-)

Thanks.

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Default Mixing 4 audio channels to 3?

On Wed, 9 Nov 2011 19:10:58 -0800, DaveC wrote:

Hint: Don't use the chassis ground symbol as a "Vref" symbol. It's

confusing
and someone along the line might get hurt. Grounds should be.


Yeah, I wasn't sure about that. How should I have indicated 2 separate
grounds?


It's not ground. It's Vcc/2. I generally call it Vref, or some such thing.
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Default Mixing 4 audio channels to 3?

On Wed, 09 Nov 2011 20:49:28 +0000 (GMT), Stuart
wrote:

In article ,
Don Pearce wrote:
Provides a Vcc/2 local "ground" so I can use these op amps with a single
supply voltage.


More useful to let it oscillate as a square wave generator at 100kHz
or so, and rectify the output into a negative 15V rail. That way you
can run the op amps the way they are meant to be run.


KISS


Exactly. Much easier than all these halved supplies, coupling caps and
multiple grounds.

d
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Default Mixing 4 audio channels to 3?

Exactly. Much easier than all these halved supplies, coupling caps and
multiple grounds.

d


So, how -- exactly -- would you create that negative voltage?

Dave

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Default Mixing 4 audio channels to 3?

On Thu, 10 Nov 2011 00:51:03 -0800, DaveC wrote:

Exactly. Much easier than all these halved supplies, coupling caps and
multiple grounds.

d


So, how -- exactly -- would you create that negative voltage?


---
Version 4
SHEET 1 964 748
WIRE -32 80 -176 80
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SYMBOL voltage -176 368 M0
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SYMATTR InstName D2
SYMATTR Value 1N4148
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TEXT -40 536 Right 2 !.tran .01 startup uic

--
JF


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Default Mixing 4 audio channels to 3?

On Wed, 9 Nov 2011 14:45:13 -0800, DaveC wrote:

I was going to suggest that, since the mixer is going to be external
to the amp, he use a couple of wall-warts to get the dual supplies,
but I like your solution a lot better. :-)


Enough to suggest a nice circuit? ;-)


---
Sure, a 555 charge pump.

Got LTspice yet?

--
JF
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Default Mixing 4 audio channels to 3?

On Thu, 10 Nov 2011 00:51:03 -0800, DaveC wrote:

Exactly. Much easier than all these halved supplies, coupling caps and
multiple grounds.

d


So, how -- exactly -- would you create that negative voltage?

Dave


---
Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:


Version 4
SHEET 1 1676 1124
WIRE -32 -528 -64 -528
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WIRE 16 704 -32 704
WIRE 384 704 240 704
WIRE 464 704 384 704
WIRE 560 704 544 704
WIRE 656 704 624 704
WIRE 672 704 656 704
WIRE 752 704 736 704
WIRE 768 704 752 704
WIRE 384 736 384 704
WIRE 272 768 240 768
WIRE -80 832 -80 576
WIRE 272 832 272 768
WIRE 272 832 -80 832
WIRE 656 848 656 704
WIRE 752 848 752 704
WIRE -528 864 -528 -240
WIRE -432 864 -432 -192
WIRE -336 864 -336 192
WIRE -240 864 -240 288
WIRE -80 864 -80 832
WIRE -32 864 -32 704
WIRE 304 864 304 640
WIRE 304 864 -32 864
WIRE 384 864 384 816
WIRE 384 864 304 864
WIRE 384 896 384 864
WIRE -528 1008 -528 944
WIRE -432 1008 -432 944
WIRE -432 1008 -528 1008
WIRE -336 1008 -336 944
WIRE -336 1008 -432 1008
WIRE -240 1008 -240 944
WIRE -240 1008 -336 1008
WIRE -80 1008 -80 944
WIRE -80 1008 -240 1008
WIRE 336 1008 336 576
WIRE 336 1008 -80 1008
WIRE 384 1008 384 960
WIRE 384 1008 336 1008
WIRE 656 1008 656 912
WIRE 656 1008 384 1008
WIRE 752 1008 752 912
WIRE 752 1008 656 1008
WIRE -528 1104 -528 1008
FLAG -64 272 0
FLAG 0 -448 +16
FLAG 0 -384 -10
FLAG -64 -352 0
FLAG -528 1104 0
FLAG -64 -16 0
FLAG 464 -416 LA+LB
FLAG 464 -80 LA+LB+RA+RB
FLAG 464 208 RA+RB
FLAG 0 -112 +16
FLAG 0 176 +16
FLAG 0 -48 -10
FLAG 0 240 -10
FLAG -112 576 +16
FLAG 768 704 -10
FLAG 128 -336 0
FLAG 128 0 0
FLAG 112 288 0
FLAG 224 496 0
FLAG 320 -272 0
FLAG 320 64 0
FLAG 320 352 0
SYMBOL Opamps\\LT1007 0 144 R0
SYMATTR InstName U1
SYMBOL voltage -240 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 1000)
SYMATTR InstName RB
SYMBOL res -112 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res -112 272 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 64 80 R90
WINDOW 0 -35 58 VBottom 2
WINDOW 3 -35 60 VTop 2
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL Opamps\\LT1007 0 -480 R0
SYMATTR InstName U2
SYMBOL res -112 -448 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL res -112 -352 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL res 64 -544 R90
WINDOW 0 -38 58 VBottom 2
WINDOW 3 -33 59 VTop 2
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL res -80 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL res -176 -160 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -256 -208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL res -320 -256 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL Opamps\\LT1007 0 -144 R0
SYMATTR InstName U3
SYMBOL res 64 -256 R90
WINDOW 0 -37 62 VBottom 2
WINDOW 3 -37 60 VTop 2
SYMATTR InstName R12
SYMATTR Value 6.2k
SYMBOL voltage -336 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 1700)
SYMATTR InstName RA
SYMBOL voltage -432 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 2300)
SYMATTR InstName LB
SYMBOL voltage -528 848 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 1 4260)
SYMATTR InstName LA
SYMBOL Misc\\NE555 128 672 M0
SYMATTR InstName U4
SYMBOL voltage -80 848 M0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value 16
SYMBOL cap 400 896 M0
WINDOW 0 -19 1 Left 2
WINDOW 3 -21 57 Left 2
SYMATTR InstName C1
SYMATTR Value 1n
SYMBOL diode 736 720 M270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode 672 848 M0
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL polcap 768 848 M0
SYMATTR InstName C2
SYMATTR Value 1
SYMBOL polcap 560 688 M90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 1
SYMBOL res 368 720 R0
SYMATTR InstName R13
SYMATTR Value 10k
SYMBOL res 560 688 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 100
SYMBOL sw 96 -416 R270
WINDOW 0 32 15 Left 2
WINDOW 3 32 44 Left 2
SYMATTR InstName S2
SYMBOL sw 96 -80 R270
WINDOW 0 32 15 Left 2
WINDOW 3 32 44 Left 2
SYMATTR InstName S1
SYMBOL sw 80 208 R270
WINDOW 0 32 15 Left 2
WINDOW 3 32 44 Left 2
SYMATTR InstName S3
SYMBOL res 144 352 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL cap 208 400 R0
SYMATTR InstName C5
SYMATTR Value 100n
SYMBOL res 304 -400 R0
SYMATTR InstName R15
SYMATTR Value 1000
SYMBOL res 304 -64 R0
SYMATTR InstName R16
SYMATTR Value 1000
SYMBOL res 304 224 R0
SYMATTR InstName R17
SYMATTR Value 1000
TEXT -296 1040 Right 2 !.tran .01 startup uic
TEXT -488 1080 Left 2 !.model SW SW(Ron=1 Roff=10Meg Vt= 8 Vh=0)
--
JF
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Default Mixing 4 audio channels to 3?

Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:
[J. Fields]


Thanks John. Nice design.

What part is used for SW1-3? Purpose? If these are "anti-thump" turn-on
suppression switches, I think the main amp is similarly turn-on delayed. Of
course it's important to know the timing of these to avoid any window through
which the sub's cone could launch (or lunch?)...

Thanks,
Dave

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Default Mixing 4 audio channels to 3?

Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:


John, what's the reason behind choosing 6.2K for the feedback R on U3 (sub op
amp)? And if that is to be a pot (the original idea), is 10K appropriate?

There should be some kind of sub volume control...

Thanks,
Dave



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Default Mixing 4 audio channels to 3?

C2, C3 are polarized, so I presume electrolytic?

What type should C1 be?

Thanks.

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Default Mixing 4 audio channels to 3?

On Fri, 11 Nov 2011 09:20:22 -0800, DaveC wrote:

C2, C3 are polarized, so I presume electrolytic?


---
I put in polarized from habit, (and, BTW, C2 is in backwards, oops)
but there's no real reason for them to be.

Ceramic or polyester would also work.
---

What type should C1 be?


---
Polyester or ceramic.

--
JF
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Default Mixing 4 audio channels to 3?

On Fri, 11 Nov 2011 09:03:36 -0800, DaveC wrote:

Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:
[J. Fields]


Thanks John. Nice design.

What part is used for SW1-3?


---
A 4066 would work well.
---

Purpose?


---
Anti thump
---

If these are "anti-thump" turn-on
suppression switches, I think the main amp is similarly turn-on delayed. Of
course it's important to know the timing of these to avoid any window through
which the sub's cone could launch (or lunch?)...


---
The output delay, from turn-on, is determined by R11 and C5.

--
JF
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Default Mixing 4 audio channels to 3?

WHAT COMPLICATED CRAP SHOTS......HAVE YOU TRIED APPLYING ONE SET OF
STEREO OUTPUT CABLES TO THE STEREO PORTION, THEN THE OTHER TWO TO THE
SUBWOOFER SECTION AS IS????
WHAT CAN POSSIBLY GO WRONG?
DON'T YOUR SPEAKERS HAVE A CROSSOVER NETWORK ALREADY ???
THEN ADDING ANY COMPONENTS TO THE MIX WILL ONLY DISTORT THE SIGNAL
COMING FROM THE SOUND CARDS AND YOU WILL HAVE TO RE-ATTENUATE IT ALL
OVER AGAIN BEFORE YOU ENERGIZE THE COMPLETED "REVAMPED" AUDIO SYSTEM
YOU PROPSE, NEEDLESSLY.

TGITM
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Default Mixing 4 audio channels to 3?

On Fri, 11 Nov 2011 09:18:16 -0800, DaveC wrote:

Here's the whole thing; DC coupled mixer with a charge pump for a
negative supply:


John, what's the reason behind choosing 6.2K for the feedback R on U3 (sub op
amp)?


---
It makes the output of the sub channel approximately equal to the
outputs of the other channels with 1VPP inputs from the four sources.
---

And if that is to be a pot (the original idea), is 10K appropriate?


---
Yes, if all the other resistors are 10k.
---

There should be some kind of sub volume control...


---
That'll work.

--
JF
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