What are the audio input specs of the transmitter?
Is there a built-in audio modulation amplifier?
For the shortwave transmitter designed by members of this forum we incorporated an 8-Watt audio amplifier so there would be ample power to drive the modulation transformer.
Xmtr didn't come with specs. But the builder includes an info sheet, which says that it's designed to work with a typical "music device (such as a casette player or CD player)" The info sheet warns the user NOT to connect a power amplifier directly to the input, because it "may cause overloading and distortion." I also tried direct connection to a CD player using the headphones output ---- sound was better, but STILL grossly distorted, no matter where the volume control of the CD player was set ---- and no matter where the audio input level on the Xmtr was set. ????
Hi Gang -- The builder contacted me today -- he sent me the wrong version of the transmitter by mistake. It was designed to work with the naked audio output of a magnetic phono cartridge. That's MUCH LESS level than the line level of my sources. It's almost as little as a microphone. No wonder it distorted everything!
I'm sending it back and the builder has promised to send the right one upon receipt. I could modify the current transmitter, (would involve changing out 2 resistors, and removing another resistor and a capacotor) but I hate working on stuff like that -- it's why I wanted a fully assembled transmitter in the first place.
So my testing has been delayed for a few weeks, until I get the replacement transmitter. I am still most interested in hearing about others' progress with this unit, so please post! Thanks!
I am so relieved, rlkocher, that a reason was found for your audio trouble.
That is not something that would have easily been expected, so it is to the credit of the seller that he realized and admitted the reason for the problem.
What I think the builder should do in the future is label the inputs of his devices and describe the several varities in the documentation.
Receiving equipment with unanticipated mistakes is a natural hazard of working with specialized electronic equipment.
We had a factory new remote transmitter control unit installed in a rack, and one night there was a big bang and some smoke. It turns out the manufacturer had wired a large capacitor backwards and it blew up.
"I just bought the last one. Sorry 'bout that...but I'm sure he'll be building more."
...and he has. I'll be ordering one as well as I've been waiting a VERY long time for something like this.
Just placed my order!
I'm very excited about this...not sure when I'll have time to set it all up, but very excited nonetheless! 🙂
Just got mine today. Will report results of testing shortly.
I too have horrible distortion. I'm going to attempt to attenuate the signal by 40 db (I have an inline audio cable attenuator) and see what happens.
Both of the transmitters I purchased (I wanted a backup) have that horrible distortion. Attenuating the input signal does force you to crank up the input control on the front, but when you do hear the audio it is still distorted. I do hope there is a fix for this, as the transmitter does work as advertised otherwise. I've contacted the seller and we'll see what response I get.
Attenuation may not be a good solution since magnetic device signals need to be integrated (low pass filtered with a linear slope) to sound right. If this is built into the device then the audio will be missing treble. You could compensate with a RC network for the attenuator but it may be more trouble than it is worth.
Worth a try but if the results don't sound right then I would wait to hear from the manufacturer.
Neil
Wow. So at least 3 of these xmtrs were apparently designed for microvolt audio inputs, but were mistakedly marketed as music device (line level) ready units.
ArtisanRadio -- When you contact the builder, I'm guessing he'll give you the option of modifying the unit yourself, or sending it back for a replacement. If you do-it-yourself, you'll save weeks of shipping time, plus the +/- $15 shipping, and you'll be one of the first on the air with this transmitter! Plus the rest of us will know if the modification works. Hope you decide to DIY!
"1580": Sounds like you made the best deal......I'm betting this new batch of xmtrs is already set up properly to handle typical music sources. Please let us know!
Meanwhile yours' truly will be one of the last chaps on the air, since my new transmitter won't be sent out until the old one arrives in Turkey. Takes about 2 1/2 weeks each way. But even that is better than me trying to "DIY". Trust me! See you on the air in about 5 weeks, I hope!
Attenuation did reduce the volume of the audio signal, but did not eliminate the distortion.
I'm not sure what I'm going to do. This all seems a bit bizarre to me (although it may be that I'm too cynical). To have all of these built for such low level inputs, as claimed, sounds a bit of a stretch. I mean, how many transmitters do you need to accept almost obsolete phono-level inputs. But on the other hand, you'd think that if it was an error in the design, it would have been caught with the most rudimentary of testing.
I guess I'll just wait and see what the seller says.
I recieved this message this morning because I addressed the concern to the seller as I was specifying instructions prior to shipping:
"Hello again. I have good news! I shipped your transmitter today. I recommend you that running with a 9V battery it offers a very clean output. I added 2 battery clips for use with 9 or 18 Volts DC. Don't worry I sent the one which gets signals from a CD or cassette player, not phonograph. By mistake I sent phono transmitters to some of my customers which I will exchange. But yours is for CD/cassette. Normally you will receive within 3-5 weeks. Best wishes Aziz - orient100"
Also known as RIAA Equalization, the RIAA Curve is what Neil is referring to above
http://en.wikipedia.org/wiki/RIAA_equalization
Even if you attenuate the input to balance the level, the RIAA curve will continue to boost bass and reduce highs, giving line level a very muddy sound.
The EQ circuit can be removed, but it takes specialized circuit knowledge to know how to "flatten" the audio for normal results.
Carl's linked article about RIAA etc. is informative and appears to be the same effect I referenced but it is a bit different. A magnetic transducer such as a phono cartridge or microphone operates by exposing a coil of wire to a changing magnetic field which is produced by a mechanical motion. The voltage induced in the coil is proportional to magnitude of the change and the rate of change of the magnetic field which expressed in calculus is V = N (d@/dt) where N is the number of turns and @ is the magnetic flux. This translates to the voltage depends not only on the distance the mechanical device moves but also on how fast it moves. It is this increase in voltage due to increased frequency that necessitates using a low pass filter in the preamplifier. It is intrinsic in the transducer and is not just a gimmick to lower noise or record wear.
Minor pickiness on my part but the outcome is the same; namely using a preamp designed for a magnetic pickup with a source with a flat response will kill the highs.
Neil