Spectra Audio

[Spiffy50]

So, I've read everywhere that it is a cardinal sin to connect Spectra audio leads to anything other than a speaker for fear it might let out some magic smoke. I want to connect one to my computer for audio logging purposes. I came across a device at a local electronics toy store called a Pyramid NS-60 Hi/Low Impedance Adapter. It says it takes 10 ohm audio and converts it to 10k line level. It is intended to let you connect a car AM/FM radio to an amplifier by means of the speaker wires.

Inside all that happens is each line of the speaker goes through a resister and into a transformer, then out to a variable pot (presumably to adjust levels) and into an RCA jack. It says it provides "Full DC isolation".

Would it be safe to use this to connect the Spectra to a computer's line in? It seems to me as though the transformer would provide the protection required so as not to tick off the audio amp in the Spekkie.

[Bill_G]

I'm not familiar with the product, but it sounds like it will do what you want.

[maxkelley_kc2spy]

A little research found this on Mike Blenderman's Spectra site...

SLN6435A - 8 Ohm Audio Isolation Transformer $ 85.50

So 10 ohms is close... but not exactly the 8 that Motorola uses.

[Will]

Most of the later Spectras are happy with 4 ohms up to 16 ohm speakers.
We even run a couple with 2 ohm speakers to over come high ambient noise.

The early Spectras did not like anything but 8 ohm speakers, the audio stage went into oscillation that you do not hear.

[Bill_G]

Couldn't hear it, but you could light your cigarettes off them. It was a great feature. Too bad they fixed it.

[desperado]

As long as you measure an open to ground on both the speaker level inputs it will work.

Most all of those level converters are floating due to any grounds introducing noise in the amplifier that they are designed to connect to.

[RADIOMAN2002]

Float the lines with .01 caps and should work fine. Use to do that to interface with older series sirens like the Federal PA 200 which didn't have a floating ground input to the radio function. Now as far levels, start with 1meg ohm and work your way down. Don't want to smoke the input to the sound card.