Wi Digital JM-WAL35 successful use so far.

[Jay Massengill]

I have a few of those type of transformers from the old days (another Radio Shack reference). I'll have to dig them out of storage and try one.

The cable and adapter I used was an XLR wired correctly for balanced to unbalanced on a single RCA.

The adapter is a single RCA splitting the signal equally to the tip and ring of the 3.5mm TRS.

I'll have to try two mics converted and connected in stereo on the 3.5mm stereo breakout cable and record the results to see what happens.

[Greg Miller]

Ah, so you didn't really try a mic test in stereo mode, because you used a mono cable plugged into the transmitter. So it might be capable of transmitting stereo mics after all.

Try using a common stereo converter cable, with a 3.5mm TRS feeding two separate RCAs (one for each channel). Connect the same mic (with its signal on a single RCA) to the two transmitter channels, one at a time. Monitor the receiver output on stereo phones. If you hear the mic first on one channel, then the other, then the transmitter is still maintaining stereo throughput.

Yes, you might find a really good deal on a mic impedance matching transformer, if you find a Radio Shack store that's on the hairy edge of closing. The transmitter specifications (p.34 of the manual) state that the input impedance is 1 Megohm. If that's true, then you could safely use a transformer with a secondary impedance of 50 kohms (or even greater) without excessive loading. That would give you significantly more voltage and a better S/N. For example, a transformer with impedance ratio of 200 : 50,000 ohms would have secondary voltage that's 16x the primary voltage, in other words a voltage gain of 24dB.

[Jay Massengill]

I connected two self-powered mics simultaneously this afternoon to the model 35 transmitter input, set to the guitar preamp mode, using a stereo breakout cable.

I can confirm that only the signal on the tip of the 3.5mm TRS connector gets transmitted in this mode.

Switching the mic connections resulted in the same outcome.

Sorry Greg!


I also tested the model 55 Pro receiver's mic/headphone breakout adapter again. This time using a pair of self-powered mics running into a passive BeachTek to defeat the mic voltage that's present in this jack.

It does work, allowing wireless recording back through the transmitter connected to USB while monitoring playback. Interestingly, both mics get transmitted even with the BeachTek set to keep them separate on the tip and ring of the 3.5mm TRS, but I didn't have time to determine if I could keep them separate in the computer audio routing to the software tracks.

However I haven't hit on the right combination of impedance, levels and connectors yet. The overall quality of the transmitted signal was poor. I need to experiment further, but this wasn't going to be a major intended use for me.

I will try an active BeachTek preamp tomorrow if I have time and see if more gain does the trick to improve the signal quality. I wasn't working in as quiet a space as I should have been and will set up in the studio tomorrow.

[Greg Miller]

Jay, thanks for the additional testing. I'm disappointed to learn of the result, but at least I know what I'm up against.

I think I read somewhere that the WAL35 can accept line level as high as 3 volts. Not sure whether that's RMS or P-P. In any event, it should be possible to achieve that with an op-amp running on a +9 volt supply rail. I'll have to ponder a bit.

Hopefully putting the right level into the transmitter will improve the S/N, if that is the problem with your "poor" audio. I'm not sure which transmitter mode you were using, but I would guess that using it in "line input" mode, preceded by a good preamp, would give the best results.

Thanks again for the report, and good luck with your further tests!

[Jay Massengill]

According to the spec sheet the transmitter input can take 3Vrms.

In all my "normal" uses for transmitting a signal from the Tx to the Rx, I've had excellent results.

It's only when trying to use the Pro receiver in transceiver mode that I've had poor audio. And I think that will just take some additional experimentation and/or equipment to iron out.
But as I said, that's not what I normally will be using these sets for.

I think if you can build a satisfactory miniature stereo preamp, the model 35 in stereo line-level input mode will be fine for transmitting.

[Richard Crowley]

So it appears that this is a 1-to-1 system and cannot be used for "broadcast" (one transmitter to multiple receivers). But that is typical of digital systems.

[Jay Massengill]

That's correct for these very small sets.

The same company does make a larger multicast system with 1 Tx and 2 Rx, with extra receivers also available separately, but I have no experience with those.