Peter wrote:
A 1k to 8 ohm transformer is a step down one, which will hugely reduce the signal, by about 11:1.If it was wired backwards i.e. the 8 ohm side on the left in the above diagram, that would be roughly 1:11 gain (turns ratio is the square root of the impedance ratio i.e. sqrt(1000/8)) which should work.
Yes that’s how mine is wired, stepping UP. (and it works perfectly.)
Ah….Thanks, I’ll give it a try, just need mono so one transformer.
Had hoped something like that would work!
Funnily enough I bought a audio signal transformer on eBay last light, 500 ohm:16 ohm, both centre tapped so according to Peter’s formula(which I had long forgotten) using the centre tap on 16 I should get 8:1 and a few other possibilities. :-)
A 1k to 8 ohm transformer is a step down one, which will hugely reduce the signal, by about 11:1.
If it was wired backwards i.e. the 8 ohm side on the left in the above diagram, that would be roughly 1:11 gain (turns ratio is the square root of the impedance ratio i.e. sqrt(1000/8)) which should work.
I had the same matching problem between a GMA 430 audio panel (which has an input impedance of 460 ohms)
I made an impedance matcher as documented by COPA and it works perfectly. I think it would achieve satisfactory results with a PilotAware and the KMA 24.
Here are the instructions / illustrations (although I put mine in a proper little case, rather than a pill-box!):
Very old..EL84’s….Ahh!
You are either very trendy and into audio, or very old 
(I used to build with valves too, in the 1960s… EF80, ECC83, EL84… apparently some of these are back in fashion, gold plated and made in Russia of course)
I can solder but the last amp I built involved valves:-)
Only if it has a higher output – a lot more than the standard “line level” which this one does.
It would actually be very easy to birdsnest a little circuit which boosts the signal to several volts. I would use a MAX232A to generate +8V and -8V from the +5V rail, and then some common op-amp to amplify the signal. But this is easy only if you can solder competently.
I am sure others have been up this path before…
Could it be a solution to install a usb sound card?
I suggest you find a 1:5 (or similar) transformer, with a primary inductance of 30mH or more (I worked that out to make a Z of 50 ohms at 300Hz; the lowest relevant audio signal).
Ebay # 123241045604 is about 1:10 and should work.
