Powering the Zoom F8

I picked up a Zoom F8 recorder to improve my on-location recording experience. It seemed like the right time, the F8N is now out and shops are selling off the F8s much cheaper even though the new version is 99% the same (and certainly not worth 50% more). I even got a free bag.

Having bought a F8 a gentleman’s thoughts will turn to how to power it.

A world of batteries

Between the 12V barrel connector and the Hirose connector there are certainly plenty of options, including V-mount and Sony L-type batteries with cradles, plus various 12V output Lithium packs and even good ol’ lead-acid.

The Tracer batteries seem like a solid option, but are relatively expensive. A 4Ah pack with Hirose connector is about £150 and 8Ah is £185. At the cheaper end there are Talentcell batteries, 6Ah here is only £40, but they’re clearly lower-end products. For example, there’s no output stabilisation so the voltage will vary quite a bit over the discharge cycle, but with a barrel-to-Hirose adaptor (£20) the F8 should cope.

An interesting alternative is a Maxoak K2 general purpose USB/Laptop battery which includes a 12V output and provides about 16Ah for £110. 4 times the capacity of the small Tracer unfortunately means four-times the weight (1.2kg), and it’s a big, awkward shape for packing.

How big is big enough

The next question is how much capacity is needed. Zoom provide some example runtimes for different scenarios, and from the times given for the NiMH batteries with a stated capacity we can get an idea of how long a nominal 4Ah battery would last. The calculations are a bit rough but it comes out that a 2-channel recording should last 16 hours. This lines up reasonably well with this experimental test which ran for 14 hours, but that was with condenser microphones so a lower runtime would be expected.

The only phantom power scenario Zoom provide is 8-channels at 192KHz and with headphones. The calculation here gets very approximate as Zoom appear to be rounding down their times to the nearest hour, so the 2 hour quote for the NiMH batteries could be anywhere between 2 and 3 hours. However, worst case for this implies a runtime of 3h off a 4Ah battery. Another factor is that Tracer state their battery will be down to 70% of original capacity after 300 charges, dropping the runtime to 2h. This is starting to get short for my usage as even if I don’t produce final recordings of this length, there are likely to be many takes and the recorder would be on for additional time during setup and soundcheck.

Powering from USB

Another power option is to use a USB-to-12V step-up adapter. These are dirt-cheap and would allow the use of a common USB battery bank. All the adaptors I’ve found are only rated for 0.8A output at 12V (9.6W) and the Zoom data with pessimistic assumptions imply a draw of 1.2A (14W).

I thought it was worth a test so picked up one of the step-up adaptors and a plug-in USB power meter and collected some data.

USB power meter

The Zoom was setup the way I’d likely be using it:

  • Condenser microphones, so phantom power on (3 x vocal, 3 x DPA4099, 2 x NT5)
  • Headphones plugged in
  • Recording to both SD cards
  • Backlight on

Channels

Sample rate

mAh (2 min)

Amps

Watts

Amps @ 12V

4Ah runtime (h)

70% runtime (h)

8

192

55

1.65

8.5

0.71

5.6

4.0

96

52

1.56

8.0

0.67

6.0

4.2

48

51

1.53

7.9

0.66

6.1

4.3

6

192

46

1.38

7.1

0.59

6.8

4.7

96

45

1.35

7.0

0.58

6.9

4.8

48

43

1.29

6.6

0.55

7.2

5.1

4

192

39

1.17

6.0

0.50

8.0

5.6

96

38

1.14

5.9

0.49

8.2

5.7

48

37

1.11

5.7

0.48

8.4

5.9

2

192

28

0.84

4.3

0.36

11.1

7.8

96

27

0.81

4.2

0.35

11.5

8.1

48

26

0.78

4.0

0.33

11.9

8.4

The mAh hours was the actual recorded value, all others derive from that. I used 5.15V for conversion to Watts as that was reported as the voltage by the meter. The F8 reported an input voltage of 11.7V.

The runtime figures here may be low for a true 12V source as I’m measuring the power going into the step-up adapter rather than out of it, i.e. these times include the ‘cost’ of running the adapter. On the assumption that 10W into the adapter (5V, 2A) produces 9.6W out (12V, 0.8A), the converter appears to be 96% efficient which, from my limited understanding of these things, seems optimistic.

Stability

The average consumption was below the capacity of the converter but the consumption did swing second-to-second, and wattages of just over 9W were observed for the 8-channel, 192KHz recording.

I tried some longer recordings to test stability. The recorder wasn’t stable at 8-channel and 192KHz and failed within 10 minutes, presumably as some momentary power demand went beyond what the step-up adapter could supply. At 96KHz the recording ran successfully until I stopped it after almost an hour, and similarly 6 channels at 192KHz was fine.

The F8 does include an internal AA battery sled. Using this as the main power source would be irritating, but it can function usefully as a UPS if there’s sudden failure of external power, or in this case to cover those split-second occurrences where the step-up adaptor runs of current. I reran the 8-channel test at 192KHz with internal batteries added and the recorder was again stable for almost an hour.

It’s a shame I can’t seem to find a step-up adaptor rated at 2.4A input (now common on USB power banks) rather than 2A. At the same conversion efficiency this would provide 0.96A at 12V and that might give enough headroom to avoid leaning on the AAs at all settings.

Conclusions

The USB-to-12V adapter can work even with 8 channels of condenser microphones, but at 192KHz it’s right on the ragged edge of what it can handle. With AA batteries as a backup it is usable, but how much time it spends on AA batteries vs external power may depend on exactly which microphones you use. I personally would be a bit wary about relying on something so close to its limits, and depending on AA batteries which are invisibly discharging.

However, I wouldn’t record at 192KHz anyway as it’s excessive[1], and the adapter arrangement appears stable otherwise.

Going to have a ponder on whether a proper 12V battery is justified, but either way I will keep the step-up adapter in my kit, because why not? I’ll be carrying a USB battery anyway as my Tascam recorder will be serving as a backup for the F8, and that has decided it only wants to work off USB power. I already have a (claimed) 10Ah USB battery which would be roughly the equivalent of a 4Ah Tracer, and it’s not expensive to get more.

  1. In the studio I only work at 96KHz and drop to 48KHz when I need more than 6 channels. [Back]