Hi all, I built the AES am transmitter a few years back and I am noticing a problem with it. For mono songs it does fine, but on true stereo songs there is distortion. I am running my Ipod into it using a "Y" connector to go from the Ipod's earphone jack to 2 RCA connectors to one RCA into the transmitter. Any ideas? Also is there a way to reduce the noice that the Ipod's charger generates?
Thanks!

I would use two 1k resistors instead of using a straight Y connector; that is, do not run the left and right channels together.

The only suggestion on the adaptor I can think of is try another one that is not switch mode (a transformer type adaptor).

You can build a charger which is easily done by getting one of those car phone chargers that plug into the cigarette lighter socket with one or two USB ports on it then build a 12 volt 2 amp power supply. Add a panel mount cigarette lighter socket and you're all set. You can then use it as a noise free way to charge things like cellphones or other electronic devices that use a USB cable for charging purposes.

A straight Y connector is a no-no because you have two active outputs tied together. When 'mono' they're doing the same thing, so it appears okay, but with stereo you have one trying to forcably drive the other in a different direction than it's trying to drive things.
You need a resistive mixer (or other but a resistive is easiest) and. as someone else suggested, series 1k would probably work on a headphone output but 10k is more in keeping with tradition (line level).

OK thanks for the help; I understand the issue. So if I am understanding right can I run 10K resistors from the center posts of the 2 RCA connectors to the common input of the transmitter? And I can just "tie" the shields of the RCA connectors together to the ground of the transmitter?

You are absolutely correct.

Yep.
Now, "just in case" I would also cap isolate the input since line outputs are not always perfectly ground referenced (I have a notebook that isn't, for example) but that's not terribly common so you might get away with a direct connection.
My schematic of the AES transmitter shows a 100k grid leak so a .1uF 50V film after the 10ks would be fine.

Would that cap be in series between the ouput of the 10K resistors and the input of the transmitter?

Yep, you got it. Two 10ks and one .1uF cap.

Thanks for all the help!

Ok, So I built the resistive mixer and I still have the stereo distortion problem. There is no problem with the Ipod hooked up to my Kenwood amp or the headphones, just when I try to use the transmitter (problem with it?).

Maybe the signal level is too high when being fed by a stereo signal?

Well, a resistor mixer is run of the mill bog simple and as Spock and McCoy explained about their tranquilizer grenade "nothing can go wrong." They said that just before it didn't work

The first obvious thing is to make sure it really is wired right. Nowhere should the outputs be tied to each other. Each one goes only to its corresponding resistor.

Are you over-driving the transmitter? Volume up too high?

If neither of those 'fix' it try playing a stereo MP3 but with only one channel connected to the transmitter. Try left alone and then right alone. Do each, by themselves, sound ok?

I have doubts the "stereo" input would cause transmitter problems... I regularly connect a computer to experimental 6GY6 & 12CS6 Tx on the bench with a "Y" cable with no matching resistors at all, I've not had a issue... Possibly the problem is created within the I-pod when the channels are connected... If you have a scope, check the waveform at output of the I-pod when the channels are connected...


Tom

It depends on the output and, for example, maybe yours inherently has a series resistance, or other means, for 'protection' or to cater to variable headphone impedances. However, it's intuitive that two active outputs should not be directly connected to each other because if one goes 'high' while the other goes 'low' then who wins?

You are probably right, there was one 'puter here that didn't like the outputs connected together... Still I've done it countless times without issue...

Tom

The problem is there's no way to know, it being virtually impossible to get 'specs', much less schematics, for these things, so I can't give what the 'odds' are. But even if it doesn't blow an output that doesn't necessarily mean it works right either.

But, back to his problem, he shouldn't have distortion with a mixer and the only time I've seen anything remotely resembling that was with Winamp playing something that had 'surround sound' content. For some reason it didn't seem to 'add' right and showed up as obscure background distortion (till I told Winamp to disallow 'surround sound') so I suppose it would be worth checking to see if he has some problematic 'equalizer' setting. In particular, any kind of '3d effects' or 'stereo enhancers' as those manipulate phase and could cause odd effects when added back together.

Flipperhome wrote: "But, back to his problem, he shouldn't have distortion with a mixer and the only time I've seen anything remotely resembling that was with Winamp playing something that had 'surround sound' content".



He will need two separate channels outputed to the AES transmitter to start out with, and he will almost certainly need a mixer if he has any hopes of delivering AM stereo to his receiver. Virtually all of the ARF AM transmitter designs (including the AES AM transmitter) do not incorporate a stereo mixer.

He's not doing "AM Stereo," he just Yd L and R into a mono transmitter and had distortion. So we told him how to make a resistive mixer, which he did, and he's still got distortion.

You're correct, but he might end up going through that route in any case.