Cheapo Bluetooth Transmitter / Receiver only output mono audio?  - Page 1
Forum section: electronics / beginners

author: WimWalther
author_rank: Regular Contributor
timestamp: November 23, 2023, 05:45:43 am
content: I have a pair of little BT TX/RX boxes that I use to send audio to a 1941 Zenith console radio and a Peavey keyboard / vocal amp. Both output analog audio to a 3.5mm TRS jack, and both the radio & amp are mono devices.As I was messing around with a stereo-mix-to-mono adapter I'd made for this stuff, I discovered that both of the BT boxes, from different mfr's, were already outputting dual-mono signals on the TRS jacks.Huh, really? Any idea why this might be? I know that BT is perfectly capable of handling stereo streams.. so I'm left confused as to why these aren't.Comments appreciated.

author: darkspr1te
author_rank: Frequent Contributor
timestamp: November 23, 2023, 01:40:19 pm
content: A lot of these BT RX units are designed for super cheap micro boom boxes that have no depth for stereo , even for a quality brand one sometimes is a mono mixdarkspr1te

author: donlisms
author_rank: Frequent Contributor
timestamp: November 23, 2023, 04:36:30 pm
content: More technical details, maybe?I'm a little curious what "messing around" actually means - how exactly did you determine the TX / boxes are mono?

author: WimWalther
author_rank: Regular Contributor
timestamp: November 23, 2023, 05:36:37 pm
content: I'd been using the BT units with a mono TS cable for output to the radio and/or amp. This meant that I was (supposedly) only hearing L-channel audio output. So I decided to make up a stereo-to-mono mixer box to do things properly, to get mixed L & R channel audio out.With the mixer in place, I played a channel identification setup track and got both L & R channels, mixed to mono, as expected. So all good. Then I disconnected the R channel input from the mixer and ran the track again - and I still heard both L & R audio! So I then re-ran the test with R channel only, and again got both L & R audio. Then, I repeated everything with the other BT box, with same results.Finally, I put the same channel ID track on a CD-R and used a CD player as my audio source, repeating all the same tests. As expected, when L was disconnected, I only heard R audio, and vice-versa.Beyond a doubt, both BT boxes are outputting mixed L & R mono.

author: WimWalther
author_rank: Regular Contributor
timestamp: November 25, 2023, 06:03:14 pm
content: Quote from: darkspr1te on November 23, 2023, 01:40:19 pmFor the record, these are both TX/RX boxes, not simply receivers. I don't know why you'd need the TX function in a boombox or headphone.But I'm curious what you mean about cheap boomboxes having "no depth for stereo". What is meant by 'depth' in this case?

author: WimWalther
author_rank: Regular Contributor
timestamp: December 05, 2023, 05:14:14 am
content: Couple of things. I found that the smaller of the two devices actually has the 3.5mm jack hardwired for mono - T & R are internally connected. So it's incapable of either inputting or outputting a stereo signal. Goofy.The larger unit doesn't have the jack hardwired, though it still doesn't produce stereo output.Here are photos of them both, for reference. I painted the power button red on the smaller unit.