# Speaker signal to Audio convert?

#### mariojl

Joined Sep 12, 2017
3
Hi you all.
I' not a tech but can follow some diagrams. I'm trying to hook up a stereo Pionner amp/equalizer to a car radio.
The problem is the Pionner has various input, but all in low signal level and radio only has speaker output signal level.
May any of you help in how do I convert such a speaker signal to a proper input audio signal??
Thank you in advance.
Mario

#### Ian0

Joined Aug 7, 2020
3,785
It claims to give a "dual 4.5 Volt line level low distortion RCA output", and I suspect that the signal level for the equaliser would be 0dBm, so it still needs attenuating by another 15dB.
And is the radio output from a Bridge-Tied-Load amplifier?

#### mariojl

Joined Sep 12, 2017
3
Yaakov: in my country (Argentina) we have very hard & expensive rules to import (if not imposibble) any item; thats why I'm looking for a DIY circuit.
Ina0: like I said I'm not a tech, frankly don´t know about BTL Amp. Below is the circuit of the radio, please lighten me up.
TIA
Mario

#### sghioto

Joined Dec 31, 2017
2,441
IC401 appears to be a single ended headset amp. Maybe you could use those outputs shown on CN410, pins 1,2 and 3.
If the output is still too high a simple resistor divider will bring the level down.

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#### Ian0

Joined Aug 7, 2020
3,785
BTL = Bridge Tied Load.
If you look inside the amplifiers that drive the speakers (IC402/403) you'll see two amplifiers (labelled AMP1 and AMP2), and the speaker is connected between the two output, not between one output and ground.
Each amplifier can produce a signal with a maximum output that goes from 0V to 12V, so the speaker can get ±6V peak, which gives 9W peak into a 4Ω load, an average audio power for a sinewave of half that (4.5W)
Using two amplifiers together, when one is at 0V the other is at 12V and vice versa, you can get ±12V across the speaker, giving 36W peak and 18W sinewave.
For your purposes, as neither speaker connection goes to ground, and you need a ground-referenced signal for the next stage, it's not suitable.
Fortunately as @sghioto noticed, there is a headphone output, which does give a ground-referenced signal. It is probably not too high a voltage to use directly as your input. Start with the volume control turned down and increase slowly, unless it gets very loud immediately and starts to distort as soon as you rotate it, you probably don't need anything else.

#### MisterBill2

Joined Jan 23, 2018
9,905
IFF the radio does have a headset output that would be the very best place to start. And if the Pioneer amplifier has a "tuner" input that would be the very logical one to use with any higher level signal. A voltage divider attenuator may still be required, if the signal level is too high causing distortion.
It might also work to tap the audio off of the volume control terminal. That will require more information.

#### Audioguru again

Joined Oct 21, 2019
3,872
Since a BTL output has two outputs then one of them can be used with a coupling capacitor to give a ground-referenced output.

#### MisterBill2

Joined Jan 23, 2018
9,905
Connecting to a speaker output will provide both the desired audio plus all of the noise and distortion products from the power amplifier.