Zoom F8 teardown

Since I posted photos of the internals of a MixPre 6 before, thought it might be fair to display the guts of SD’s main rival in this market, the Zoom F8…

The differences in layout between F-series and MixPre are telling, to say the least. The F-series is a serious puzzle box, I wasn’t sure I’d be able to get everything put back together, all the little modular boards and ribbon cables crisscrossing with one another and tiny slots for each board to fit together (I did, and it still works). That being said, the actual footprint for audio stuff is shockingly small, like not much more real estate than the analog stages in an H6. All the puzzle-making seems a product of someone’s insistence that they be able to fit that bulky battery box inside, and everything else is crammed in around it. I understand the F8n has a battery box on the bottom, so I’m curious how (if at all) that has changed the internals. [My guess: not much.]

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  pop the hood!

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  A/D converters

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  accessory mic a/d, and d/a converter

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  clocking and FPGA

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  slate mic preamp

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  underside of top board

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  “anyone down there?”

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  secret screws under footpads

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  puzzlebox nightmare

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  1 of 2 preamp boards, bottom view

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  1 of 2 preamp boards, top view

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  “oh, that’s how it opens…”

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  D/A analog section –– NJM4556 (headphone), NJM4580 (sub out), NJM2114 (balanced out)

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  underside of D/A analog section (HP out nearest)

Main A/D converters are AK5388, and D/A AK4359. These are totally fine choices, the only issue being that “ground” is ca. +2.5VDC, so capacitors must be used to block DC from incoming/outgoing analog stages. Capacitors are bulky and take up a lot of space, even surface mount types, so I found it telling there are no opamps anywhere on the preamp boards. The preamps themselves are THAT1583 chips, high quality digitally controlled designs and perfectly reasonable in this setting (the sort of “off the shelf” preamps SD keeps referring to in their advertising for the MixPres), but rather than running their outputs to a set of buffer opamps (like the OPA1662s used in the MixPres) which would then drive signal into the A/D converters, it seems the preamp chips drive the converter inputs directly (with capacitors in between). There’s nothing wrong with this, the preamp datasheet demonstrates it as a “low-cost” solution, but it won’t get the best distortion performance from either preamp or converter as a circuit using low-noise opamps to buffer the signal. My guess is they figured it would be cheaper to fill the board with capacitors than to add copious buffering stages, never mind analog limiters.

Plus, if you ever wondered why the MixPre devours batteries for breakfast and the Zoom is still only sipping coffee late into the afternoon, this is why. There is at least twice the analog circuitry in the MixPre 10 (and perhaps even the 6) than the Zoom F8.

I am also going to guess this is why the headphone amp on the Zoom (which I don’t think actually sounds that bad, despite the many negative reviews I read) is a touch edgy and thin compared to the MixPre. The driver isn’t bad, NJM4556 (I’d use something else, though diminishing returns eventually kick in), but there are some small, no-name caps upstream blocking DC from the D/A converter. Not to be a snob, but to my ears the best capacitor is almost always no capacitor, and the D/A converter in the MixPres (where ground is 0V) drives the headphone amp directly.

This probably sounds like I’m taking this opportunity to crap on the F8, but I’m really not. I should just say that I absolutely love the ergonomics of the menu controls, and the fact that so many things SD has been pressed to include in subsequent firmware releases (or as payware plugins) are just sitting in utero in the F8. This is only to demonstrate a big difference in design attitude: Zoom is clearly fine cutting corners with analog stuff to emphasize user experience and functionality; SD has pretty much cut zero corners with analog stages (much to the chagrin of your battery budget), but every firmware release is a bit like a new version of Windows where fun surprises lurk around every corner…

Could the F8 be modded? Maybe, but there is really not much to be done, and it would be a puzzle nightmare (take it from someone who modded an H5). There is almost no room for better (/bigger) capacitors, very few opamps to replace (the D/A stage is really the only candidate, plus some op amps around one of the converters which I think are for the “dual record” mode), and pretty much no room for more robust power supply filtering for the converters.

Whatever, life’s short, get out and record. The talent should have rehearsed more anyway.

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