Thanks I will look into that amplifier as the BT output is low.
Feeding the BT output directly into either back input forces me to raise the volume control past the loudness tap thereby thinning out the fidelity.
The only thing that almost gives me an appropriate volume (my hearing is fine) is feeding the output into the top of the volume port.
But, there goes the switched input, the EQ and level.
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Wait....I had no output, and I'm talking about audio output levels.
What, after some many hours....
Let's go to the original setup.
If you look at the BT module photo 1, I soldered a small piece of Teflon silver-plated 2 conductor shielded cable to the L-R output pins and the shield ground to the USB.
Then I mono out the radio end via 2 10Ω resistors so at least there is no phase cancelling.
Here's where everything went wrong.
After much tearing apart of that hookup, I found that there was a direct short of 10Ω to ground on the radio cable end.
I always break the problem in half........
It must be the cable, removing the resistors and unsoldering the cable from the BT output pins still left a short on only the left pin.
I had no over soldering to the ground plane.
I thought it must be the crappy 3.5 mm jack. It was removed with prejudice and some diagonal cutters.
I still had the short. I backtracked the L-R output pins and found the the audio jack interrupts the audio to the pins.
The short was in the board!
Scraping the board with a razor blade (the board is dead to me at this time) revealed that the ground-hold down pin on the 3.5 mm jack was shorted to the L output pin from the factory.
I removed that short.
The BT output comes directly from the IC via 2x 10µF 16V capacitors to the 3.5 mm jack. The 2 capacitors were outputting audio just fine.
After the butcher job I performed, I replaced the BT module with another, thus giving the levels as described in the 2nd paragraph.
I still need an amplifier, but not for the whispers or as drastic as a high gain low to high impedance transformation type.
Quote from: David Hess on Today at 04:17:24A transconductance amplifier converts its input into a high impedance output. A high impedance output is the same as a current source. The circuit you probably want is a Howland current pump.