Stereo Tool

Hi there

I was wondering if somebody can help me.

I recently purchased a relatively cheap Transmitter from China (CZE-7C), and I got it today and I configured WinAmp, and Stereo tool, and RDS was coming in perfectly, and the only issue was the Stereo encoding. Whenever I clicked encode stereo. the sound on the devices with tuners, would go loud, then soft, then loud again. Not too soft, but you could easilly tell that the sound wasn't right. The volume wasn't constant.

I've done further reading on the issue, and I've heard it's because the transmitter has a built in Stereo processor.
If that is the case, is there any way how to modify it, or disable it?

I love RDS, and Stereo sound so I would like both, not just one.

Anyone able to help?

Thanks

If you want to use MPX output from Stereo Tool (how you should) you need pure MPX input at transmitter.
Without shematics of board no one can help.

Also this is not "Stereo Tool issues" (how you call it).

Morning, sorry about the title, I corrected it.

I managed to find a schematic diagram, but unsure what's what.
It's in this manual.

http://www.fmuser.net/upload/down/month ... MANUAL.pdf

If someone can tell me what to do, it would be great.

Thanks

You definitely need to get rid of the pre-emphasis, lowpass filter and stereo generator, and the limiter wouldn't be bad to turn off too. There's nothing in the manual about how to do that though...

What about the diagram at the bottom?

Pitty I'm not that good at reading things like that, as I'd have no problem removing the components within the device that's not needed.

I have never read something like that in my life so I'll leave that to others.....

With that transmitter you can't do what you want to do. For the modifications it would need unless you have the skills to do it yourself you'd be better to look at getting one of the cheap 1 to 5 watt FM Exciters from somewhere else that has an MPX input.

http://www.tugicom.com/fm-exciter/tx180.html

Clipper

Paul and all,

I have injected composite audio into mini transmitters like this that use the ROHM FM transmitter chip. The datasheet can be found in several places, including here: http://media.digikey.com/pdf/Data%20She ... H1415F.pdf

Before I say how, first please note this BIG-TIME DISCLAIMER: 1) at best this may not work, 2) at worst, it may irrecoverably blow up your equipment, 3) it will require soldering work at a component level, including some parts removal. 4) it will void all warranties, and 5) see # 1.

Now that I've sufficiently scared you, compare the chip's internal workings in the datasheet above to the transmitter's schematic. You'll see that the internally-generated composite audio (the one that you don't want) comes out of pin 5, goes through some circuitry and then is re-inserted into pin 9 for modulation.

Exactly what that "some circuitry" does, and where the internal pilot is injected or turned off is unclear. In the older versions of this chip, I would merely lift the right side of R2, the bottom side of R20, connect those two lifted points together, and pull the 38 KHz crystal (to kill the internal pilot). Composite would then be sent into one side of the input jack.

This version appears to generate the pilot internally via division of the master clock, and they may be doing some RF work with D1 (AFC, VCO or both). Thus for this unit I would suggest lifting the top side of R17 (versus R20) and connecting R2 and R17 together. Start with your composite audio at an *extremely* low level, and increase slowly.

Again it has to be said: there are many steps and points where this can all go very wrong. It helps just a bit that I have a spectrum analyzer, modulation monitor and am a broadcast engineer.

But... if you're willing to blow up your unit in the interest of science...

Agreed Clipper...this is a good little transmitter (I have a couple of them). Put the existing one on Ebay and pick up one of these little gems and kiss your problems goodbye.