[Richard Crowley]

It is not clear why you get noise from your Heil mic, but not from the other mics into the ZED24?
The ZED24 has mic preamps, why do you say that the Heil needs to be pre-amped before going into the ZED24?
It sounds like your computer is compatible with the ZED24, but not with the other outboard processing stuff. Does it produce the same noise with the Symetrix as it does with the Golden Gate? Are these plugged into the same mains power source as the ZED24 and the computer?

[Richard Crowley]

What happens if you plug the mic directly into the A&H?
Are you saying that you are using your (unidentified) A&H mixer as the analog to digital conversion via USB?
What happens if you just run the audio from the Symetrix or Golden Gate unit directly into the audio input of your Mac?

It seems like you have a lot of stuff there and the more you have to go wrong.

Certainly start with Mr. Wolf’s suggestion about making sure the gains are set properly on EACH and EVERY part of the audio chain.

USB inputs cannot add (or remove) noise. But different computers can have power supplies that are friendly or hostile to connecting audio devices, as your experiment shows.

Good move substituting the computer. Now do similar experiments with the rest of the system. A 24-input A&H mixer seems like vast overkill as simply an analog-to-digital converter.

[Richard Crowley]

A few pence worth of gold flash on the connector isn’t worth getting worked up over.

Film/video productions thrive on gaffer’s tape. Expensive little plastic clips can get lost or broken.

[Richard Crowley]

That Maplin cable appears to be completely adequate for your application. I suspect that “two core shielding” is simply fancy marketing speech for “two-conductor screened”.

There is no electrical difference between your Maplin cable and the fancy Rode cable. But the Rode has the coiled end, etc, and may be higher-quality plastic (maybe more flexible, longer lasting, etc.) so the Rode most likely costs more.

[Richard Crowley]

You can use a cable made as an earphone/headphone extension with 3.5mm “stereo” (tip-ring-sleeve) male on one end and 3.5mm female on the other end. But, of course you need to ensure it is shielded, as simple headphone use does not require shielded.

Your use of the UK pound sterling symbol leads us to believe that is where you are. If you were here in the US, you could visit your neighborhood RadioShack shop and pick up a cable. Perhaps you have a similar retail electronics shop nearby?

[Richard Crowley]

It does not appear that there is ANY difference between the balanced TRS outputs from the stock cable vs. the XLR outputs on the breakout box. I would be quite surprised if there was any active circuitry in the breakout box. It appears to be simply a convenience, mainly for the XLR outputs (which you don’t need with your unbalanced destination).

Certainly, if you have a ground loop or ambient EMI noise problem, a transformer like the Ebtech is a life-saver. But under controlled conditions in your own studio, the fewer links in the chain the better. And remember that people go to extreme lengths to avoid transformers anywhere where accuracy is desired. if you really must use transformers and you care about better than average sound quality I would pay the premium for something like Jensen transformers.
https://www.jensen-transformers.com/dm2xx.html

[Richard Crowley]

Ebtech makes decent products But in this application you do not need level shifting, the levels are already compatible. And you do not need impedance matching, The Apogee has a 90 ohm output impedance, and the Genelec has a 10K input impedance. And you do not need balanced to unbalanced transformers in this application. The Apogee is designed to drive either balanced or unbalanced loads.

To be sure, you might need one or more of these features in SOME OTHER applications, but putting an Ebtech box into this proposed signal path would definitely make it the “bottleneck” (or perhaps more precisely the weak link) in the chain.

Since the input of your speaker is unbalanced, using the breakout box XLR outputs doesn’t really provide any benefit over the stock breakout cable. A simple TS 1/4 inch phone to RCA cable is exactly what is needed here. I wouldn’t pay an excessive premium just to buy gold-plated connectors.

[Richard Crowley]

Remember that in North America, anything in the 700 MHz band is now illegal:

“The operation of wireless microphones and similar devices is prohibited from certain frequency bands for public safety reasons and commercial concerns. The sale of wireless microphones or similar devices intended for use in the United States in the 700 MHz Band was banned by the FCC in January 2010, and use of the devices in the 700 MHz Band was prohibited as of June 12, 2010. “Similar devices” include wireless intercoms, ear monitors, audio instrument links and cueing equipment.

The 700 MHz Band – between 698 and 806 MHz — is now reserved for use only by public safety groups, such as police, fire and emergency services, and commercial providers of wireless broadband services. Use on broadcast bands outside of the 700 MHz Band was not affected by the ban, and can continue…”

https://www.fcc.gov/encyclopedia/wireless-microphones

[Richard Crowley]

As Ty mentioned, shots longer than ~10 minutes starts getting into the area where un-synced pro-sumer equipment doesn’t necessarily hold sync all that well.

An accurate and useful suggestion would be dependent on HOW you (or your customers) are using this equipment. Perhaps if you can give us a bit more detail, we can have a better view of your situation.

1) Why do you need more than 2 channels? You mentioned not getting into the complexity of dealing with timecode, but are you already in the complexity of mixing multiple sound tracks in post-production editing? Perhaps if you could provide a better understanding for your requirements, we could understand the trade-off decisions.

2) How many channels do you need, and what kind of microphones (or other sources) are you using? The R24 has phantom power (required for condenser mics) on only 6 of the inputs (which is better than the 2 inputs on my R16).

3) What is the competence level of the people using this equipment? The R16 (and presumably the R24) has some rather fiddly multi-level menu based setup and control requirements which may frustrate casual users. You might want to get a demo to play with yourself to evaluate whether it is suitable for your typical customers.

4) What are they shooting that is that long? Typically a single video shot >10 minutes (or even 5 minutes or 2 minutes) gets dull and boring without some sort of visual variety. Reverse-angle shots of the interviewer, or wide “cover” shots of the event or B-roll inserts of details being mentioned, etc. etc. Any of these points where the video is edited is a prime opportunity to pull-up (re-sync) the video to match the audio track. With video edit points, you significantly reduce the problem with long-term “slip” between the video and audio recordings. Also, most DSLRs won’t make continuous recordings for more than 10-15 minutes, anyway because of other limitations (file size, overheating, etc.)

[Richard Crowley]

What are you shooting? 25P?
What problem are you seeing/trying to solve?
What lighting options are available to you?