Hi BEN.

21-Dec-02 17:05:03, BEN RITCHEY wrote to ALL


 BR> I have a Stereo Audio feed for 2 Watts {at} 8 Ohms (per channel) that
 BR> I need to convert to "Line" level (I'm assuming this is around 1
 BR> Vac Peak-to-Peak at a much higher impedance) in order to pass the
 BR> signal through an Equalizer, then back thru a secondary Amplifier
 BR> (probably 5-10 Watts per channel, not built yet). Can this be done
 BR> with a simple Voltage Divider like dual Pots and would the pot(s)
 BR> need to be Audio-taper?

2W into 8 ohms is  4V (RMS)  (so about 12V  peak to peak)
so a 11:1 divider would be about right

most line level inputs aren't too fussy about source impedance (AFAIK) so
something like this should do it.

   input
       ----[7.5R 2W]---+
                       |
       +--[0.75R 1/4W]-+----- output
       |
   ----+-------
  ground

 or if you want it variable something use a 1K pot (dual for sterio)
 and stick a 8.1 ohm resistor in parallel with the input.


 BR> Are there any industry standard Audio Amp ICs that deliver approx.
 BR> 10W/RMS per channel I should use for the last stage? I have a
 BR> couple of National Stereo Amps (Lm4755) rated at 11W/channel with
 BR> low noise/distortion specs, I think.

11 looks close enough to me. if you've got thwm you may as well use them.

 BR> I dismantled a very expensive TV to develop the Line-level outputs
 BR> but could only work out speaker taps

Whoa... if the TV didn't have external speaker terminals, be very careful,
some TV sets operate with a live chassis ("ground" on the TV chassis
could be a few hundered volts away from the mains Neutral)

If you still want to tap in you should install isolating transformers
(with two 8 ohm windings) on the speaker lines. before your diverter (did
you use something like a switched headphone socket)

 BR> (no schematic :( they go for
 BR> over $50) and cannot risk/afford to cause any damage by playing
 BR> around . My old TV had Audio/Line-out taps that sounded
 BR> incredible through the Equalizer. :)

you could chase the specifications for the chip that drives your TV's
speakers... quite possibly there's line level near it somewhere.
OTOH there may be a spot in the circuit board marked for line-out sockets
:)

Again you may need isolating transformers.

Equaliasers are fun... I used to run my ZX spectrum's sound (one bit
ooutput under software control - more primitive than a PC speaker) through
a 5 band equaliser - it could make the sound FX sound more real...)

AFAIK the easiest way to tell if a TV has a live chassis is to measure the
resistance between the antenna socket and the chassis. if you get 0 Ohms or a
low reading it doesn't, if you get 10K or more it probably does.

 -=> Bye <=-

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