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DC blocker audio cable (to block 2.5v PiP)

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Chanher:
I still want to try to use a Zoom F2 mono recorder to record mono sbd feeds but you can’t turn off the 2.5v PiP that comes out of the 1/8 input. Not wanting to risk any damages of any kind, I’ve been trying to research DC blockers; there do not appear to be any products that fit my needs.

Does anyone here have any knowledge of this or can you recommend a forum that would know about this?

There’s coaxial DC blockers, but for tv antennas etc. I’m considering building a cable. I’ve read about electrolytic capacitors with DC blocking capabilities. There’s concerns of bass rollofs. Has anyone had Ted build something similar? Thanks in advance for any knowledge.

wforwumbo:
The theoretical DC blocker is a high pass filter. You won't get good performance out of anything passive built in to the cable, you'll get far too much attenuation of bass frequencies from passive designs, and you'd have to *shudder* solve the transmission line equations for your cable's RLGC impacts.

Your best bet is to google an active op amp based higher order DC blocking circuit powered off of a USB or 9V battery. If you're handy with a soldering iron, you can build one yourself. Again, you want an active high pass filter, and given that you have two channels you probably want a dual op amp. Something with a corner frequency of 10 Hz should do the trick.

Chanher:
That’s excellent info specific to our hobby, thank you. I was afraid of this. I may have to scrap this idea of the F2 as a mono sbd recorder. Maybe just buck up and buy another F3.

I did come across these XLR phantom blockers. Wouldn’t one of these stop 2.5v? I could always order one of Amazon and test with a multimeter. I’m curious about high pass filtering….

https://a.co/d/cc4repc

mjwin:
I don't think you'll find an off-the-shelf solution to this. However,  to block the DC pip voltage you really just need a simple capacitor.   I managed to endure the dreadful Zoom website for long enough to check the spec of the Zoom F2, and the input impedance is specified as a minimum of 2k ohms.  In this case you could use a commonly available 10uF electrolytic capacitor  in series with the input from the sound board to block DC. This will, of course, form a high pass filter, but at around 8Hz, I don't think this will cause any audible issues! Any capacitor will do, and one rated at 6.3V or 10V (or more) will be fine.  The + (positive) end should go to the F2.

I'm actually more concerned by the maximum input level of the F2. It's designed for a mic input, and Zoom actually specify the maximum level as -5.5dBu. That's 5.5dB below 0.775V, which works out as 0.412V, which is way less that you will likely get from a soundboard feed. Pro audio levels are typically +4dBu (1.2V), so unless you can vary the level of the SB, the F2 inputs will clip.

You could introduce a series resistor (say 10k) to reduce the levels, but maybe that's getting a bit further into electronics than you wish to go. It's also complicated by the fact that Zoom specifies the input impedance as a minimum of 2k (seems reasonable for plug-in-power), but give no maximum...

Personally, I'd try a 10k resistor and a 10uF capacitor in series & give it a go.  You can easily mount the components in a1/4" jack or XLR plug which goes to the soundboard. Of course you'll need to be reasonably comfortable with soldering electronics stuff, or know someone who is.

Hope this is of some use!

Chanher:

--- Quote from: mjwin on October 11, 2023, 01:44:53 PM ---I don't think you'll find an off-the-shelf solution to this. However,  to block the DC pip voltage you really just need a simple capacitor.   I managed to endure the dreadful Zoom website for long enough to check the spec of the Zoom F2, and the input impedance is specified as a minimum of 2k ohms.  In this case you could use a commonly available 10uF electrolytic capacitor  in series with the input from the sound board to block DC. This will, of course, form a high pass filter, but at around 8Hz, I don't think this will cause any audible issues! Any capacitor will do, and one rated at 6.3V or 10V (or more) will be fine.  The + (positive) end should go to the F2.

I'm actually more concerned by the maximum input level of the F2. It's designed for a mic input, and Zoom actually specify the maximum level as -5.5dBu. That's 5.5dB below 0.775V, which works out as 0.412V, which is way less that you will likely get from a soundboard feed. Pro audio levels are typically +4dBu (1.2V), so unless you can vary the level of the SB, the F2 inputs will clip.

You could introduce a series resistor (say 10k) to reduce the levels, but maybe that's getting a bit further into electronics than you wish to go. It's also complicated by the fact that Zoom specifies the input impedance as a minimum of 2k (seems reasonable for plug-in-power), but give no maximum...

Personally, I'd try a 10k resistor and a 10uF capacitor in series & give it a go.  You can easily mount the components in a1/4" jack or XLR plug which goes to the soundboard. Of course you'll need to be reasonably comfortable with soldering electronics stuff, or know someone who is.

Hope this is of some use!
--- End quote ---

Awesome, thank you! I always enjoy trying to find different solutions. (and thanks for tolerating the Zoom website, a chore in itself).

I am also concerned about the max input level; I've read online about people successfully recording out of a professional mixer into a F2 and there are roughly the same amount of people reporting that attenuation is necessary. Numbers are numbers though and I will attenuate.

Since I've always wanted to get into soldering and cable construction, I think this is the perfect time to try it. If any of you advise that this is a bit too advanced for a beginner, I may seek a local electronics professional. I found this youtube video about wiring in a resistor and I'm curious if this method will work for both. I definitely have read that the positive end of a capacitor should go towards the power source.

https://www.youtube.com/watch?v=DXkvTWweacE

Can anyone advise different resistors for audio use? I don't mind doing research so I will also look this up myself. I hate ordering off Amazon but I may end up doing just that...

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