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I have a TZA-4000 mixer-amplifier. It has a preamplifier output 200mV/600Ω.

I want to feed this output into several recording devices:

  • Zoom H1N audio recorder. It has a line-in/microphone input with input impedance of 2 kΩ. The manual says, "The H1N can supply plug-in power if the connected mic uses it." I don't know how it detects whether the connected "mic" uses it or not.
  • HC-X920 camcorder. It has a stereo microphone input, which provides 2.73V power. Microphone level can be configured -30..+12dB.
  • An Android phone, which is used for live streaming. Of course, it also provides some DC for the microphone.

Challenges that I see:

  • Level mismatch, which requires an attenuator for the phone. Zoom and camcorder have built-in input level regulation.
  • DC of the recording devices, which requires decoupling.

Questions:

  1. What is a proper way of splitting the source mono signal into three?
  2. How to deal with the DC provided by all the three recording devices so that it does not harm the source and each other?

Ideally, a complete circuit would be appreciated.

Related questions:

JRE
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AKd
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  • Have you tried with 1) a wire and 2) capacitors on each device to block DC? – Justme Aug 22 '22 at 14:40
  • 1) Yes I tried using a headphone Y-splitter like [this](https://amzn.eu/d/dR3oKyl) for Audio Recorder + Camcorder, and it works even without any capacitor. I'm just afraid it can ultimately harm something. 2) Not yet tried, I'm asking for a guidance here before ordering components and experimenting. I'd like to know the canonical/proper way of connecting devices in this scenario. My guess is to use a usual aux splitter (4 way), a capacitor on each line and an L-pad attenuator for the phone from https://electronics.stackexchange.com/a/620993/316022. But I'm waiting for experts' suggestion. – AKd Aug 22 '22 at 17:16
  • Hi AKd. Don't screw around trying to jerry-rig something. There's pre-engineered solutions that cost very very little available. You'll be much happier with the resulting audio quality if you go this route instead. i.e. https://www.behringer.com/product.html?modelCode=P0386 as one example – Kyle B Aug 22 '22 at 17:53
  • Hi, @KyleB. Thanks for suggestion, it helped me know such devices exist. After looking into it, I see several disadvantages that prevent me from jumping at it. (1) it is active and requires power, which I'd like to avoid. (2) My topology would actually require two fork points: at the amp where Zoom recorder is located, and then at 10-15 meters away where the camera and the phone are located. (3) It amplifies the signal, whereas I need it attenuated. (4) Probably it does not have enough output DC resistance, so the phone will not detect it as a mic. – AKd Aug 22 '22 at 18:08
  • FYI, the "power" referred to at the beginning of your question is known as "phantom power". Its a 40-48V DC bias (and almost zero current) that's applied to the input wires, used by condenser microphones. Generally when that's available, the user has to push a button to turn it on/off as it can damage some (rare) types of microphones. Most dynamic mics can handle it no problem so often you'll see that set as "always on". Now that you know what it's called, you can easily google more information about it. – Kyle B Aug 22 '22 at 19:15
  • For the signal splitting, if you can not accept a powered solution like I pointed out, and you're adamant you want these things DC-isolated (good idea), the only option you have is capacitors. The problem you'll face is each input you want to feed will likely have a very different input impedance. That will affect the relative levels going into each, and also the frequency response is going to be affected (the DC-blocking caps and the input impedances combine to make a low-pass filter... i.e. if you insist on doing this with passive components, expect some negative affect on sound quality) – Kyle B Aug 22 '22 at 19:18
  • Zoom provides just 2.5V, not phantom power of 40V. It's for an electret microphone, I believe. Thanks for your inputs on the relative levels and low-pass filter, I read about this effect (actually, about high-pass). My audio is a lecture (speech), so I don't need descent hi-fi quality. Also, the impedance of the devices seems to be close to each other: 2K for the phone, 2K for Zoom and unknown for Panasonic Camcorder. I hope to cope with the filter by using a larger capacitor as described here: https://electronics.stackexchange.com/a/521902/316022. – AKd Aug 23 '22 at 07:32
  • @KyleB: The DC blocking capacitor and the input impedance of the devices will make a high pass filter - you'll lose low frequencies. – JRE Aug 23 '22 at 09:13
  • @JRE Haha --- True, my bad :) – Kyle B Aug 23 '22 at 15:39

1 Answers1

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What you'll want is something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

  • The Zoom has line level inputs - no attenuation needed.
  • The X920 has microphone inputs.
  • The phone requires an attenuator and the 2k pull down to tell the phone that there's a microphone attached.

You'll probably need to use polarized capacitors - the plus terminal goes towards the external device, not the TZA4000.

Remember to connect all the grounds together.

I don't expect it will work all that well.

  1. The signal level will depend on which (and how many) of the devices you connect. Lowest output when all three are connected. The output impedance of the TZA4000 is 600 ohms. It forms a voltage divider with the total (parallel) impedance of all the external devices - more load, lower signal, lower signal to each of the devices.
  2. You mention a long connection (15 meters,) so I'd expect it to pick up interference easily - hum and buzz in your recordings.

The better way would be to use a small amplifier with three op-amps as buffers.

  • Adjust the gain for each stage to match the external device. The output will be low impedance, so less susceptible to interference.
  • Since the signal is buffered, it won't matter if all or none of the devices are connected - the output level will stay the same.
JRE
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  • Much thanks for the effort. Please elaborate the second proposal with amplifier and op-amps. What I understood is it's a circuit also, not an appliance. But I never worked with such components, but I can search provided I have enough inputs for the search. Perhaps it is going to become an active circuit requiring a power supply, isn't it? – AKd Aug 23 '22 at 13:41