Input impedance of wireless audio transmitter - Page 1
Forum section: electronics / projects

author: PanSam1986
author_rank: Contributor
timestamp: April 23, 2023, 07:09:19 pm
content: Hi,I apologise in advance for rambling on but also because I am completely clueless to the electronics behind audio equipment which is what I need help with.I have the Boss Waza Air 'personal guitar amplification system' that I have used with my Zoom G1X four multieffects pedal in the past. I stopped using this setup because of an issue I had. I think the pedal outputs too much power for the transmitter to handle and every 5 minutes or so it turns off, which I guess is some kind of built in protection. The Zoom pedal outputs line +2dBu and according to the manual the output impedance is 10KOhm or more (which I don't really understand what they mean by "or more"). Also, what does line +2dBu mean? Does anybody know or have an idea of what the input impedance of a guitar transmitter might be? I assume the impedance is not really what's causing the issue but rather as I mentioned earlier the output power being too high. I seem to recall having found some information on professional guitar wireless systems and that they have built in various selectable line attenuators since they can be used with varying output guitar pickups. If my assumption is correct then I obviously need a line attenuator that I thought I would just build myself with a couple of potentiometers. Does the resistance required to attenuate the line signal have any effect on the output impedance of the pedal or the input impedance of the transmitter? To me it seems that the impedance seen by the pedal should be greater than the 10KOhms 'or more' so as to not load it and the impedance seen by the transmitter should not be greater than its input impedance again so as to not load it, in which case would I be wrong to assume that something in the range of 50kOhm to 100KOhm should be OK?Again sorry for rambling on. Any help would be greatly appreciated.Panos

author: donlisms
author_rank: Frequent Contributor
timestamp: April 27, 2023, 02:29:52 am
content: Audio connections made between devices with reasonable impedances are all about voltage. Your notions about "too much power" and so on are a little off the point, and I would suggest you either abandon those thoughts, if you just want to solve the problem, or dig deeper and learn a lot more stuff about audio signals and impedances, if you want to understand things in greater detail. In the meantime, yes... check impedances if something seems terribly unusual, but generally speaking, those will be in the ballpark of where they're supposed to be, and all you need to think about are voltage levels, either in volts, or dBu, or whatever other units you prefer.To convert dBu to volts, use 10^(dBu / 20) * sqrt (0.600). So if dBu is -10, the voltage is .245 volts. To convert volts to dBu, of course, you would use log10(voltage / sqrt (0.600)) * 20.The Boss website says the transmitter input expects a maximum of -10dBu into 1 Megohm. That's very reasonable for guitar, though it might not be that hard to clip the thing once in a while. If it clipped, it sound funny, but the transmitter would not be harmed. One important point here is that all we really care about is the voltage.The Zoom can produce a voltage (-2dBu) higher than the transmitter would expect (-10dBu). This is only going to happen if you have the pedal output set very high. In such a case, you would hear clipping (on a clean patch, of course!). The solution is much simpler than the ideas you're exploring... just turn it down, until you don't hear clipping any more. If you already don't hear clipping, the level is fine where it is.Then... the only audio devices I'm aware of thatmightturn themselves off with a bad signal are big power amplifiers. I've used many hundreds of audio devices, and I've never seen one that turns itself off after 5 minutes of clipping. I suppose there could be some kind of side effect, e.g. the clipping is overheating an amplifier somewhere or something like that, but... I'm doubtful that's it. My bottom line is this: if you're not clipping the transmitter, the shutoff problem is somewhere else.All of this is based on an assumption that it's the transmitter that's turning off. It's not completely clear from your original post, but I assume that's it. I would wonder if it'sexactly5 minutes, i.e. if it's the same every time. That would speak of something digital; analog electronics are more approximate than that! So signal path stuff is unlikely to do that.I would read all of the documentation, assuming they are respectful enough to provide some. All of it. Yes.I would look for any clues about the shutoff. We use some of the little Senheisser transmitter/receiver pairs, and they have a behavior where if they can't find a device to pair with after five minutes, they shut off. So if you turn one off, the other will eventually go off, that sort of thing. That's just an example; there are lots of seemingly clever ideas you could build into a system like this. And before I read the pages, it was more in the "What's it doing and why?" category. And I tested it to confirm the exact behavior, given the vague and incomplete notes in the "documentation."

author: floobydust
author_rank: Super Contributor
timestamp: April 27, 2023, 04:39:30 am
content: Check theWaza Air firmware versionyou have is up to date.

author: PanSam1986
author_rank: Contributor
timestamp: April 27, 2023, 07:16:34 pm
content: Admittedly I haven't tested the waza air after the latest firmware update. I'll give that a go, thanks.

author: bdunham7
author_rank: Super Contributor
timestamp: April 27, 2023, 07:35:17 pm
content: Quote from: PanSam1986 on April 23, 2023, 07:09:19 pmI would take that to mean not that the output impedance is 10k (it is probably much lower) but rather that it expects the input impedance of whatever it is driving to be 10k or higher. That's the only explanation that makes sense to me just generally knowing how audio equipment generally works.

author: PanSam1986
author_rank: Contributor
timestamp: April 27, 2023, 07:45:55 pm
content: Like I said in my post, I am clueless when it comes to audio electronics so thanks for your reply, I appreciate it.Funnily I had a conversation with a colleague where I mentioned that audio equipment is all about voltages and not currents (even more so guitars with passive pickups) but I totally forgot about it when I posted my question. Admittedly I am not the best when it comes to reading documentation. simply because I despise reading but also because reading gives me a headache. I tried finding information on the waza air transmitter but couldn't (although based on your reply it's evident that I completely missed this info when browsing the Boss website).Yes, it's the transmitter that keeps turning off. To be honest I don't really hear any clipping, but maybe it's just too subtle for me to notice. And yes, the output of the zoom pedal is set to max so I will definitely test my setup by turning it down. As for the duration between the transmitter turning off it's just a ballpark, I've never really measured the time.Boss doesn't seem to provide any kind of documentation unfortunately other than the user manual. The only technical information they give you is what is written on their website.

author: PanSam1986
author_rank: Contributor
timestamp: April 27, 2023, 07:50:48 pm
content: Also, just a correction, the zoom pedal outputs +2dBu not -2dBu according to the manual. Makes no difference I guess but thought I'd let you know.

author: PanSam1986
author_rank: Contributor
timestamp: April 27, 2023, 08:00:34 pm
content: Quote from: bdunham7 on April 27, 2023, 07:35:17 pmCould you elaborate on your answer, like I said I am no expert on audio. I thought the output impedance of an amplifier is made up of a 'real' component (resistance) + the 'imaginary' component which is frequency dependent. Your explanation definitely makes sense since you don't want anything lower than 10k and risk loading the output amp.