[DaveC[_2_]]

I want to connect the audio out (headphone jack) of 2 computer sound cards to
a desktop & woofer speaker-amp combination. (The original input was via USB
only and I'm modifying this for analog audio input.)

This is my guess at the necessary resistors to mix down these 4 outputs to
the 3 inputs in the amplifier (L, R, sub):

http://i41.tinypic.com/97mpud.jpg

The data sheet for the Philips TDA8510J amp IC shows an application for 2
channel input:

http://i40.tinypic.com/5ets9w.jpg

Suggestions welcome.

Thanks.

[DaveC[_2_]]

If I'm on the right track, what are the suggested values for resistors?

Thahks.

[Tomi Holger Engdahl[_4_]]

DaveC writes:

If I'm on the right track, what are the suggested values for resistors?

10 kohms for all fixed resistor should work...


--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/

[DaveC[_2_]]

10 kohms for all fixed resistor should work...

Hi Tomi. Thank you for your advice. I have enjoyed your creative designs for
many years.

Do you have any comments on my revisions of the circuit (ie, are caps
recommended? should I be concerned about cross talk if I take resistors from
all 4 channels to drive the sub woofer? etc...)

Cheers,
Dave

[John Fields]

On Sat, 29 Oct 2011 00:49:32 -0700, DaveC wrote:

10 kohms for all fixed resistor should work...

Hi Tomi. Thank you for your advice. I have enjoyed your creative designs for
many years.

Do you have any comments on my revisions of the circuit (ie, are caps
recommended? should I be concerned about cross talk if I take resistors from
all 4 channels to drive the sub woofer? etc...)

Cheers,
Dave

---
Why not go active and get rid of the caps altogether?


..LA-+---[10k]-+-[10k]-+------------- -(LA+LB)
.. | | |
.. | | +V |
.. | | | |
..LB-|-+-[10k]-+--|-\ |
.. | | | -+ 10K
.. | | +--|+/ +-[POT]-+
.. | | | | | |
.. | | GND -V | +5 |
.. | | | | |
.. | +------[10K]---+---+-|-\ |
.. | | | --+-- -(LA+LB+RA+RB)
.. +--------[10K]---+ +-|+/
.. | |
.. +--------[10K]---+ GND
.. | |
.. | +------[10K]---+
.. | |
.. | |
.. | |
..RA-+-+-[10k]-+-[10k]-+
.. | | |
.. | | +V |
.. | | | |
..RB-+---[10k]-+--|-\ |
.. | -+------------- -(RA+RB)
.. +--|+/
.. | |
.. GND -V

Seems to work pretty well...

Version 4
SHEET 1 880 968
WIRE 112 -544 48 -544
WIRE 224 -544 192 -544
WIRE -96 -448 -528 -448
WIRE 32 -448 -16 -448
WIRE 48 -448 48 -544
WIRE 48 -448 32 -448
WIRE 112 -448 48 -448
WIRE 224 -432 224 -544
WIRE 224 -432 176 -432
WIRE 256 -432 224 -432
WIRE 112 -416 80 -416
WIRE -96 -352 -432 -352
WIRE 32 -352 32 -448
WIRE 32 -352 -16 -352
WIRE 80 -352 80 -416
WIRE -528 -240 -528 -448
WIRE -416 -240 -528 -240
WIRE 64 -240 -336 -240
WIRE 112 -240 64 -240
WIRE 240 -240 192 -240
WIRE -432 -192 -432 -352
WIRE -352 -192 -432 -192
WIRE 64 -192 64 -240
WIRE 64 -192 -272 -192
WIRE -272 -144 -336 -144
WIRE 64 -144 64 -192
WIRE 64 -144 -192 -144
WIRE -176 -96 -240 -96
WIRE 64 -96 64 -144
WIRE 64 -96 -96 -96
WIRE 128 -96 64 -96
WIRE 240 -80 240 -240
WIRE 240 -80 192 -80
WIRE 272 -80 240 -80
WIRE 128 -64 96 -64
WIRE 96 0 96 -64
WIRE 112 112 48 112
WIRE 224 112 192 112
WIRE -336 208 -336 -144
WIRE -96 208 -336 208
WIRE 32 208 -16 208
WIRE 48 208 48 112
WIRE 48 208 32 208
WIRE 112 208 48 208
WIRE 224 224 224 112
WIRE 224 224 176 224
WIRE 256 224 224 224
WIRE 112 240 80 240
WIRE -240 304 -240 -96
WIRE -96 304 -240 304
WIRE 32 304 32 208
WIRE 32 304 -16 304
WIRE 80 304 80 240
WIRE -528 688 -528 -240
WIRE -432 688 -432 -192
WIRE -336 688 -336 208
WIRE -240 688 -240 304
WIRE -144 688 -144 656
WIRE -48 688 -48 656
WIRE -528 832 -528 768
WIRE -432 832 -432 768
WIRE -432 832 -528 832
WIRE -336 832 -336 768
WIRE -336 832 -432 832
WIRE -240 832 -240 768
WIRE -240 832 -336 832
WIRE -144 832 -144 768
WIRE -144 832 -240 832
WIRE -48 832 -48 768
WIRE -48 832 -144 832
WIRE -528 928 -528 832
FLAG 144 192 +5
FLAG 144 256 -5
FLAG 80 304 0
FLAG 144 -464 +5
FLAG 144 -400 -5
FLAG 80 -352 0
FLAG -528 928 0
FLAG -144 656 +5
FLAG -48 656 -5
FLAG 160 -112 +5
FLAG 160 -48 -5
FLAG 96 0 0
SYMBOL Opamps\\LT1007 144 160 R0
SYMATTR InstName U1
SYMBOL voltage -240 672 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value SINE(0 1 1000)
SYMBOL res 0 192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 0 288 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 208 96 R90
WINDOW 0 -43 58 VBottom 2
WINDOW 3 -37 60 VTop 2
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL Opamps\\LT1007 144 -496 R0
SYMATTR InstName U2
SYMBOL res 0 -464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL res 0 -368 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL res 208 -560 R90
WINDOW 0 -43 58 VBottom 2
WINDOW 3 -37 60 VTop 2
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL voltage -48 784 R180
WINDOW 0 -50 102 Left 2
WINDOW 3 24 16 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 5
SYMBOL voltage -144 672 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 5
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 160 -144 R0
SYMATTR InstName U3
SYMBOL res 208 -256 R90
WINDOW 0 -43 58 VBottom 2
WINDOW 3 -37 60 VTop 2
SYMATTR InstName R12
SYMATTR Value 5k
SYMBOL voltage -336 672 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V4
SYMATTR Value SINE(0 1 1700)
SYMBOL voltage -432 672 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V5
SYMATTR Value SINE(0 1 2300)
SYMBOL voltage -528 672 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V6
SYMATTR Value SINE(0 1 4260)
TEXT -562 952 Left 2 !.tran .005


--
JF

[DaveC[_2_]]

Why not go active and get rid of the caps altogether?

Thanks John. Good simple design.

Can you suggest a good op amp for such an audio application?

Is it possible to use single-supply amps throughout?

Thanks,
Dave

[NT]

On Oct 26, 7:58*am, DaveC wrote:
I want to connect the audio out (headphone jack) of 2 computer sound cards to
a desktop & woofer speaker-amp combination. (The original input was via USB
only and I'm modifying this for analog audio input.)

This is my guess at the necessary resistors to mix down these 4 outputs to
the 3 inputs in the amplifier (L, R, sub):

http://i41.tinypic.com/97mpud.jpg

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.


NT

[Don Pearce[_3_]]

On Wed, 26 Oct 2011 08:50:55 -0700 (PDT), NT
wrote:

On Oct 26, 7:58*am, DaveC wrote:
I want to connect the audio out (headphone jack) of 2 computer sound cards to
a desktop & woofer speaker-amp combination. (The original input was via USB
only and I'm modifying this for analog audio input.)

This is my guess at the necessary resistors to mix down these 4 outputs to
the 3 inputs in the amplifier (L, R, sub):

http://i41.tinypic.com/97mpud.jpg

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.


NT

Is there something wrong with my browser? I can't see any of these
component references. Actually I see what you mean. One problem here
is that R9 and R10 are going to cause crosstalk. Without some active
electronics there is no way around that apart from taking the sub from
one channel only. This is actually quite common.

d

[DaveC[_2_]]

Is there something wrong with my browser? I can't see any of these
component references.

Sorry. They didn't make onto the jpg file. Added he

http://i40.tinypic.com/5ets9w.jpg

Actually I see what you mean. One problem here
is that R9 and R10 are going to cause crosstalk. Without some active
electronics there is no way around that apart from taking the sub from
one channel only. This is actually quite common.
d

OK, can do that.

Suggested values for resistors?

Thanks.

[Michael Moroney]

(Don Pearce) writes:

On Wed, 26 Oct 2011 08:50:55 -0700 (PDT), NT
wrote:

On Oct 26, 7:58*am, DaveC wrote:
I want to connect the audio out (headphone jack) of 2 computer sound cards to
a desktop & woofer speaker-amp combination. (The original input was via USB
only and I'm modifying this for analog audio input.)

This is my guess at the necessary resistors to mix down these 4 outputs to
the 3 inputs in the amplifier (L, R, sub):

http://i41.tinypic.com/97mpud.jpg

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.


NT

Is there something wrong with my browser? I can't see any of these
component references. Actually I see what you mean. One problem here
is that R9 and R10 are going to cause crosstalk. Without some active
electronics there is no way around that apart from taking the sub from
one channel only. This is actually quite common.

I don't see component references, either. However, assuming R1-R4 are
the resistors from the inputs to ground, they may be necessary to provide
a proper impedance to the source driving them.

To reduce crosstalk, I'd replace the two resistors from the 220nF
cap junctions to the pot with four resistors from each of the four inputs
to the pot. Presumably, the output impedance of the amps is low compared
to the resistors reducing crosstalk.

For mixing signals there is a method using amps and feedback where the
connection between multiple sources is at a virtual ground, eliminating
crosstalk.

[NT]

On Oct 26, 5:09*pm, (Don Pearce) wrote:
On Wed, 26 Oct 2011 08:50:55 -0700 (PDT), NT
wrote:

On Oct 26, 7:58*am, DaveC wrote:
I want to connect the audio out (headphone jack) of 2 computer sound cards to
a desktop & woofer speaker-amp combination. (The original input was via USB
only and I'm modifying this for analog audio input.)

This is my guess at the necessary resistors to mix down these 4 outputs to
the 3 inputs in the amplifier (L, R, sub):

http://i41.tinypic.com/97mpud.jpg

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.

NT

Is there something wrong with my browser? I can't see any of these
component references. Actually I see what you mean. One problem here
is that R9 and R10 are going to cause crosstalk. Without some active
electronics there is no way around that apart from taking the sub from
one channel only. This is actually quite common.

d

I was hinting that the OP might decide to add numbers to the
components, otherwise its sufficiently tedious to talk about them that
people often just wont bother.

Yes the caps are necessary, but for the amp IC, not for the mixer.
House them together and its the same difference, house them apart and
the distiction matters.


NT

[DaveC[_2_]]

Yes the caps are necessary, but for the amp IC, not for the mixer.
House them together and its the same difference, house them apart and
the distiction matters.
NT

This is unclear to me.

Do you mean that if the mixer resistor matrix is housed close to the amp IC
that the capacitors won't be needed? And if they are separated and connected
by shielded audio cables that the caps will be needed?

Thanks.

[NT]

On Oct 27, 5:17*am, DaveC wrote:
Yes the caps are necessary, but for the amp IC, not for the mixer.
House them together and its the same difference, house them apart and
the distiction matters.
NT

This is unclear to me.

Do you mean that if the mixer resistor matrix is housed close to the amp IC
that the capacitors won't be needed? And if they are separated and connected
by shielded audio cables that the caps will be needed?

Thanks.

Nothing like that, no. The amp IC requires the caps, so theyre needed,
no question about it. But theyre needed for the amp, not for mixing
purposes, so if the 2 circuits can be disconnected by the end user,
then the caps need to be with the IC amp part, not the mixer part.


NT

[John Fields]

On Wed, 26 Oct 2011 21:17:16 -0700, DaveC wrote:

Yes the caps are necessary, but for the amp IC, not for the mixer.
House them together and its the same difference, house them apart and
the distiction matters.
NT

This is unclear to me.

Do you mean that if the mixer resistor matrix is housed close to the amp IC
that the capacitors won't be needed? And if they are separated and connected
by shielded audio cables that the caps will be needed?

Thanks.

---
Since the chip is being powered by single positive DC supply, The
only way to get signals which swing below ground into and out of the
chip is to use capacitive coupling.

--
JF

[DaveC[_2_]]

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.
NT

Callouts added:

http://i40.tinypic.com/5ets9w.jpg

R11 provides some adjustment for sub. Otherwise no way to have any difference
between L & R channel volume and sub volume.

The caps are suggested on the data sheet example:

http://i40.tinypic.com/5ets9w.jpg

Why would you do away with them?

What values for the resistors do you suggest?

Thanks.

[Don Pearce[_3_]]

On Wed, 26 Oct 2011 10:10:12 -0700, DaveC wrote:

Lose Rs 1-4, keep 5-8, lose R11, and lose C1,2,3, then itll be good.
NT

Callouts added:

http://i40.tinypic.com/5ets9w.jpg

R11 provides some adjustment for sub. Otherwise no way to have any difference
between L & R channel volume and sub volume.

The caps are suggested on the data sheet example:

http://i40.tinypic.com/5ets9w.jpg

Why would you do away with them?

What values for the resistors do you suggest?

Thanks.

For that particular circuit with that chip, the caps are necessary
because those inputs are not at ground potential. If you are feeding
normal hi fi unit inputs the caps aren't needed. Resistor values
around 5 to 10 k would be what you need.

d

[DaveC[_2_]]

For that particular circuit with that chip, the caps are necessary
because those inputs are not at ground potential. If you are feeding
normal hi fi unit inputs the caps aren't needed. Resistor values
around 5 to 10 k would be what you need.

And the value for the potentiometer?

Thanks.

[Don Pearce[_3_]]

On Wed, 26 Oct 2011 11:18:39 -0700, DaveC wrote:

For that particular circuit with that chip, the caps are necessary
because those inputs are not at ground potential. If you are feeding
normal hi fi unit inputs the caps aren't needed. Resistor values
around 5 to 10 k would be what you need.

And the value for the potentiometer?

That depends entirely on the input impedance of the subwoofer. You
could try a 100k pot and connect it as a normal volume control - one
end to the incoming signal, the other end to ground and the slider to
the subwoofer.

d

[The Ghost In The Machine[_2_]]

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