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Re: Zoom H2 Line Inputs

Subject: Re: Zoom H2 Line Inputs
From: "Richard L. Hess" richardlhess
Date: Tue Apr 14, 2009 10:23 am ((PDT))
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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