At 08:35 AM 2009-04-14, Curt Olson wrote:
>Richard Hess wrote:
>
> > I have taken some time to characterize the line inputs of the H2 and
> > have written it up here:
> > http://richardhess.com/notes/2009/04/13/zoom-h-2-line-input/
>
>Good stuff, Richard. Very helpful.
Thank you!
> > The -10 dBV input spec only allows about 3-5 dB of headroom above
> > -10 dBV. This is why, I think, some reports have indicated that the
> > device shows some clipping.
> >
> > Don't ever run down the digital level control on a line input--it
> > serves absolutely no purpose. The H/M/L switch does not work for the
> > line input, which is too bad.
>
>Okay... I think I'm finally tracking with you. You're saying the H2's
>level control is downstream from the A/D conversion, and not before
>it? And of course, it stands to reason in a device so inexpensive. Now
>everything you're saying here is clicking for me.
Without an actual block diagram, I can't say for sure, but it is
behaving that the level control is downstream of the input preamp and
that the preamp is clipping. It has been said that many of the
less-expensive digital recorders have digital (i.e. after A-D
conversion) level controls and the H-2's behaviour is in keeping with
that topology.
> > Remember, when we normally say a -10 dBV line level, we're referring
> > to a lineup tone referenced to a VU meter and the meter lets through
> > peaks of typically 10 dB (but can be more on some program material),
> > so the input gain structure is a little bit too "hot" in the H2.
> >
> > I would use some sort of external pad so that if you set the H2 to
> > 100 and then set an alignment tone at 0 VU and set that to at least
> > -12 dBFS on the H2, preferably -18 dBFS.
>
>I have a couple nice inline pads here. Will give them a try.
Rob Danielson and I have been discussing this off-list and while the
MixPre has features of a small mixer, if you use it as a plain
preamp, you might be able to forego the pad.
Set the H-2 gain to 100 then run up the MixPre gain while watching
the H-2 meter, ignoring the MixPre meter. This means that your
headphone output on the MixPre will be lower, but it will give you
another 12-14 dB of gain which might be useful.
If you opt for the inline pad, it should be about 14 dB, but should
not be a "mic" pad, only a line pad. What pads do you have? I think a
mic pad with XLR connectors might be a bit low impedance for the 2k4
output impedance of the MixPre.
Since the output impedance is high enough not to load anything, I'd
give a quick try to putting shunt resistors of about 600 ohms from
each of the two hots to ground. You can do that easily by slitting a
mini-stereo-plug to mini-stereo-plug cable in the middle and
carefully stripping the two hot wires, soldering in the resistors,
and then taping the resistors and the rest of the cable. Or you could
do a neater job with a box and connectors, but that would make more
potential failure points. Also, the nice thing about using the source
impedance of the MicPre as part of the pad is this cord is still
non-directional--you can plug it in either way. Once you add series
resistors to the cord, you have to mark which end goes to the MixPre
and which to the H-2.
If the MixPre has a true 2k4 output impedance, then that, coupled
with the 600 ohm shunt resistors would provide roughly14 dB of
attenuation. 620 ohm resistors are easier to find and would work just
fine, providing roughly 13.75 dB of attenuation (both calcs ignore
the input impedance of the H2 which is 10 k ohms. WIth the 10k load,
the attenuation is 14.4 dB and 14.2 dB, respectively. Please try this
out and tell me how it works, but I think if you just ignore the
attenuator and take 14 dB more overall system gain you might be
better off--just ignore the meters on the MixPre.
While I did my tests in dBV, the Zoom is rated at -10 dBm nominal
line input which is about 2 dB lower, so their specs are a bit better
than I recently noted with two dB more headroom than published, but
still less than 10 dB. It is odd to have a consumer -10 device to be
rated in dBm.
>Thank you much!
You're welcome much! It was something I needed to do in order to
comfortably use the device.
By the way, you're previous comments about using the H-2 as a "bit
bucket" are partially true, but you're also using it to do the
analog-to-digital conversion. Others have attempted to provide
external preamps that would totally bypass any analog electronics in
early recorders. Zefiro/Denicke (sp?) made a device they called the
"InBox" that had two mic pres and an A-D converter and would go in
the SPDIF input of a DAT Walkman. Core Sound has done things like
that, too, I think.
Certainly the MixPre is an excellent preamp and coupled with the H-2
is about 44% of the cost of the SD702. In reality you'll spend more
on accessories for the 702 than the H-2, but the ratios stay about
the same as you accessorize. With that in mind, I'm not sure I'd want
to stand behind this solution, even though I am impressed by it and
think it clever for doing this on a budget.
I think it's a good, creative solution and if it gets you into the
field faster, that's great. On the other hand, I think the
convenience, reliability, and sound quality improvement of the 702 is
(at least to me) probably worth the money.
Don't get me wrong, I think if you've done this, it's great, but I'm
not sure if it's the solution for everyone with the 702 out there and
32 GB flash cards now reasonably priced.
Honestly, I think where the H-2 really shines is in its ability to
gather sounds all on its own to a level we never before thought
possible in a $200 (or less) box. I also think it makes a great
ingest station for making digital audio files in a fixed
installation, be it church services or cassette digitization. I'm not
sure I'd rely on it and its mini-phone plugs out in the boonies, but
that is a decision each person needs to make for themselves. I
certainly would not have bought the SD722 if I was making the choice
today after what has happened to the economy and since I don't make
any money off of it.
Cheers,
Richard
Richard L. Hess
Aurora, Ontario, Canada http://www.richardhess.com/
Detailed contact information: http://www.richardhess.com/tape/contact.htm
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