Re: Aspen Times

I keep harping for someone to post a real circuit problem... you know, something more invigorating than "My LED won't blink" ;-)

But it ain't gone'a happen :-(

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Both right and left wingnut are at least ten years old. Try searching GG for Widewing.

Right. We don't need an more blinkin' LED problems.

Yours won't either?

They have a pill for that. I've seen the spam.

My nose keeps running ;-)

...Jim Thompson

You didn't swallow it fast enough.

That's bad, it should be your feet.

Everyone is missing my joke about certain drug ads ;-)

...Jim Thompson

...even worse; his feet smell.

Or maybe i am making a point of teasing you, or maybe not. Humor should not be too obtuse.

. . .

Harp no more. I just built a prototype of this circuit:

but I can't get the microphone amplifier to work. I have access to an oscilloscope (Telequipment D54!!!) but don't have SPICE, so can't simulate it. My suspicion is that there is too much gain for a single stage amp.

The whole circuit seems rather more complicated that it needs to be and any help to simplify it would be greatly appreciated.

Certainly qualifies for "weird" ;-)

Check the bias ("Q" points) and report.

...Jim Thompson

I'm pressed for time right now, but it looks like it should be using an ELECTRET microphone??

...Jim Thompson

It's basically a clone of the Clearcom intercom system, and their circuits are always this messy, they do strange things with DC signaling. All the capacitors are to fiddle the response of the hybrid, I assume they got it wrong in the first place. You should use an electret mic, (or even carbon can be catered for)

Despite the wierdness, their system does work quite well, I've used it on many shows. They have/had many circuits/ service manuals on their site.

Why are you trying to build this particular circuit?

martin

Ah, I didn't think of that. I have a dynamic mic attached at present but have a couple of cheapo PC headsets that I can try.

. . .

I'm trying to build a couple of extra beltpacks for a Techpro system, which gets used in several of our village halls. It seemed like a good idea at the time, but is proving to be more of a challenge than I imagined.

I did try searching for suitable schematics, but this is the only one I could find. I've tried it with an AV headset and a standard Techpro one, both of which use dynamic mics; but hadn't thought of using an electret. I've got a PC compatible headset with an electret mic, so I'll try that next. If that works, I'll stick a common base impedence buffer on the input and see what happens with the dynamic mic.

I thought the frequency shaping around the mic amp and the hybrid was a bit overcomplicated. However the DC signalling part does work with both Techpro and Stonewood beltpacks. I don't have access to a Clearcom one to try that.

Try the electret first,before replacing with a tranny

You could also just get the boards, save a lot of hassle

martin