How to get low level from high (audio)

[stuee]

I only have one line out from my head unit but want it to run 2 amps, is there any way to make a good quality volume decreaser for the high speaker out to convert it to line out?
Would be good with a volume control too.
Thanks

 

[audioguru2]

Hi Stuee,
Maybe the line out of your head unit is low-impedance and can drive many amps that have a high input impedance. Their spec's will say.

If one amp feeds the other amp, you won't have the advantages of having separate amps:
1) If you feed the 2nd amp from the output (attenuated) of the 1st amp, you lose the ability to separately adjust the levels of the amps.
2) If the 2 amps are the same, the output of the 2nd amp would have twice the noise and distortion of the 1st amp.
3) If the 1st amp clips, the 2nd amp would also reproduce the severe clipping distortion, even if the 2nd amp is turned down.

 

[MP1]

stuee,
I do not know the specs of your headphone setup, but here is an article that might interest you:
http://www.epanorama.net/circuits/speaker_to_line.html

Hope it is helpful to you.
MP

 

[hotwaterwizard2]

Here is how they do it for a Car Stereo.

View attachment 36036

 

[audioguru2]

Hi John,
That's a nice attenuating "balun" circuit.
But it provides a signal that is out-of-phase. While investigating swapping its inputs to swap the phase, I wondered what a null would sound like. Complete cancellation? Just distortion?
So I changed your resistor values and came up with this circuit that will provide an attenuated signal in-phase, a null and a signal out-of-phase. Normally you would use a ganged pot. If the pots are separate, you can have the channels in-phase or out-of-phase with themseves or with its output:

View attachment 36038

 

[hotwaterwizard2]

The resistor between the + and - puts a load across the Floating Ground and the Pot just Varies that resistance causing the gain to go up or down. It has nothing to do with Phasing since the ground always stayes the same.

 

[hotwaterwizard2]

Here is a couple of circuits without the Pot.

View attachment 36040

 

[audioguru2]

Hi John,
I am assuming that the car radio's amps are bridged without a transformer, with a + non-inverting amp and a - inverting amp for each speaker. Each amp's common is ground, not floating.
Since your circuits have the lowest value resistor in the - inverting side, their outputs are also - inverting, which is out-of-phase.
My revision of your circuit also adjusts the volume, but as an addition allows you to adjust for a + non-inverting or a - inverting output for a choice of phase, with a null position for extreme attenuation.

 

[MP1]

Good post, John. This gives stuee several choices to choose from. Hopefully, this will give him a start.

MP