Safe to merge line-level outputs?

S

Steve Reinis

Guest
I have a computer system with an older SoundBlaster ISA sound card. It has
line-level RCA inputs and I'm currently feeding a component-style Yamaha
tuner to it. I'd like to also feed the line-output of my DishNet receiver
to the sound card using a pair of "Y" adaptors. Since both outputs are
line-level and not amplified, would I end up frying anything? I'm just
trying to avoid throwing a switcher into the mix...

Thanks,
-Steve
 
Steve Reinis wrote:
I have a computer system with an older SoundBlaster ISA sound card. It has
line-level RCA inputs and I'm currently feeding a component-style Yamaha
tuner to it. I'd like to also feed the line-output of my DishNet receiver
to the sound card using a pair of "Y" adaptors. Since both outputs are
line-level and not amplified, would I end up frying anything? I'm just
trying to avoid throwing a switcher into the mix...

Thanks,
-Steve
Click to expand...
It's unlikley to do any damage, but you might have problems caused by
the changes in impedance.

Better to insert resistors in the lines, 4.7k should do, to isolate
the sources from each other. Put a resistor in the signal line from
the sources, with the feed to the amplifier taken from the junction of
the two.



--

rgds
LAurence

.... Keep the streets safe: Run down a cyclist today!
begin the search for better software
 
"Steve Reinis" <noemail@all.com> writes:

I have a computer system with an older SoundBlaster ISA sound card. It has
line-level RCA inputs and I'm currently feeding a component-style Yamaha
tuner to it. I'd like to also feed the line-output of my DishNet receiver
to the sound card using a pair of "Y" adaptors. Since both outputs are
line-level and not amplified, would I end up frying anything? I'm just
trying to avoid throwing a switcher into the mix...
Click to expand...
Use a switch. It can just be something simple, doesn't need
active circuitry, just a switch for the signal.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: The email address in this message header may no longer work. To
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"Steve Reinis" wrote to "All" (20 Jul 03 23:08:28)
--- on the topic of "Safe to merge line-level outputs?"

Don't do this! Source device outputs tend to be taken directly from a
little buffer amp and though they are very low power it is still
possible to blow something. Both source devices may very well have
enough series resistance to mix the signals but unless you know for sure
then better not take a chance.

Since the input impedance of the card is around 47Kohms, a safe solution
might be to include a 10Kohm series resistor in each hot leg to the Y so
it will function as a simple line-mixer. At least this way each source
device sees about 20K ohms which won't likely strain anything. Use clear
heatshrink tubing around each individual resistor and cable to isolate
and support it.


SR> From: "Steve Reinis" <noemail@all.com>

SR> I have a computer system with an older SoundBlaster ISA sound card.
SR> It has line-level RCA inputs and I'm currently feeding a
SR> component-style Yamaha tuner to it. I'd like to also feed the
SR> line-output of my DishNet receiver to the sound card using a pair of
SR> "Y" adaptors. Since both outputs are line-level and not amplified,
SR> would I end up frying anything? I'm just trying to avoid throwing a
SR> switcher into the mix...
SR> Thanks,
SR> -Steve

.... You may be a tech if you're entertained by a 6-pack and sparking HV.
 
I'm tempted to try the resistor deal offered, but I'll probably just get a
switch to be safe... I knew there must have beebn some technical reasons it
wasn't safe (for the equipment).


Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in message
news:6wy8ysrt7z.fsf@saul.cis.upenn.edu...
"Steve Reinis" <noemail@all.com> writes:

I have a computer system with an older SoundBlaster ISA sound card. It
has
line-level RCA inputs and I'm currently feeding a component-style Yamaha
tuner to it. I'd like to also feed the line-output of my DishNet
receiver
to the sound card using a pair of "Y" adaptors. Since both outputs are
line-level and not amplified, would I end up frying anything? I'm just
trying to avoid throwing a switcher into the mix...

Use a switch. It can just be something simple, doesn't need
active circuitry, just a switch for the signal.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work.
To
contact me, please use the Feedback Form at repairfaq.org. Thanks.
Click to expand...
 
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