Marantz CDR300 mic input overload

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In article <d56id6$rbt$1@news1.chem.utoronto.ca>,
reedijk@hera.med.utoronto.ca says...
>
> There appears to be a major roadblock in that the mic inputs can not
> handle loud sources. For example, I recorded a piano from 10 feet
> away with a pair of BLUE Lollipop/AKG 452s and it was overloading
> very noticeably. The only way to manage it was to put in the 20dB pad
> and crank up the gains to make up!---but it hissed like a snakepit.
> External mic pres going into the line inputs seems to be just fine.

See the post on Marantz PMD660 that I just made. I had a similar
problem with my unit and I bet there are few differences in the preamp
circuits.

Problem was solved when I got a return authorization and they added or
replaced a few resistors.

As a test, record a repeatable source (possibly a test tone) with and
without the pad, then look at the levels in a audio editor. Is there a
-20db difference between the peaks of the two files? With my unit,
difference was -38db and I had to crank the gain to make up the
difference.

Eric

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Scott Dorsey <kludge@panix.com> wrote:
> Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:
>>
>>Is there anyone out there who has found away around this problem? As it
>>stands, the unit is useless without external mic preamps. I suppose
>>it could be modified in some way, but being a portable recorder
>>it is probably not a fun unit to open up and work on.

> How about a pad?

I suppose using a 10dB pad will get me less noise than the internal 20dB.
But it's still not a good solution. And I suspect I will still be able
to overload it with a 10 dB pad, if I have mics 6 feet away from a piano.

Rob R.

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Scott Dorsey <kludge@panix.com> wrote:
>>
>>I suppose using a 10dB pad will get me less noise than the internal 20dB.
>>But it's still not a good solution. And I suspect I will still be able
>>to overload it with a 10 dB pad, if I have mics 6 feet away from a piano.

> If a 10 dB pad isn't enough loss, and the noise floor is too high with
> a 20 dB pad.... well... what you got are preamps that are way too noisy.
> There's no easy fix for that.
> --scott

It isn't necessarily that they are way to noisy---they are staged in a way
that is not workable for music recording. I believe this device was
tailored more towards ENG, film type work where they might be using
dynamic mics or other low level sources. So they put an aggressive
gain stage right ahead of the attenuation. Too bad. I think if
it is used with a nice external mic pre, the unit becomes very useable.
The other reason is that the gains are not easy to work with. Tiny knobs
that are difficult to set, and matching left and right is almost
impossible.

Rob R.

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In article <d58a4b$tuj$1@news1.chem.utoronto.ca> reedijk@hera.med.utoronto.ca writes:

> I suppose using a 10dB pad will get me less noise than the internal 20dB.
> But it's still not a good solution. And I suspect I will still be able
> to overload it with a 10 dB pad, if I have mics 6 feet away from a piano.

I seem to recall something that I read about this recorder when it
first came out that led me to believe that the preamps were quite
sub-standard. Not that it's the ultimate solution, but do you have an
external mic preamp that you can try with it to see if the preamp is
the only problem?

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

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Mike Rivers <mrivers@d-and-d.com> wrote:

> In article <d58a4b$tuj$1@news1.chem.utoronto.ca> reedijk@hera.med.utoronto.ca writes:

>> I suppose using a 10dB pad will get me less noise than the internal 20dB.
>> But it's still not a good solution. And I suspect I will still be able
>> to overload it with a 10 dB pad, if I have mics 6 feet away from a piano.

> I seem to recall something that I read about this recorder when it
> first came out that led me to believe that the preamps were quite
> sub-standard. Not that it's the ultimate solution, but do you have an
> external mic preamp that you can try with it to see if the preamp is
> the only problem?

It appears to work fine with an external mic preamp.

Rob R.

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Scott Dorsey <kludge@panix.com> wrote:
> Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:
>>Scott Dorsey <kludge@panix.com> wrote:
>>
>>> If you don't like the attenuator in the box, use an outboard one. They
>>> aren't very expensive. Everybody should have a bag of them in the
>>> adaptors drawer.
>>
>>I have some Shure inline fixed bads. What are you describing? Is there
>>some sort of passive attenuator that will pass phantom?

> Yes, the Shure ones should be fine. I like the adjustable ones with the
> switches more, personally, but try starting with the fixed ones. They
> will pass phantom just fine (since the series resistance is much lower
> than the shunt resistance... they are designed for that).

You speak of the A15AS. Looks handy. Only issue is that the choices
are 15, 20, 25 dB---which are good choices for many applications.
Are there any adjustable pads out there that have lower amounts of
attenuation? I ask since the distortion with the CDR300 will go away
with 5 or 10 dB of attenuation most of the time.

The unit I have been trying out belongs to a friend and I am looking
for a user friendly solution. 5 or 10 dB gets him out of the distortion
range without having to add a lot of noise.

Maybe I will be making him a a mic cable insert with 10 dB of attenuation.

Rob R.

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey <kludge@panix.com> wrote:
> Rob Reedijk <reedijk@hera.med.utoronto.ca> wrote:
>>
>>You speak of the A15AS. Looks handy. Only issue is that the choices
>>are 15, 20, 25 dB---which are good choices for many applications.
>>Are there any adjustable pads out there that have lower amounts of
>>attenuation? I ask since the distortion with the CDR300 will go away
>>with 5 or 10 dB of attenuation most of the time.

> Audio-Technica used to make one that went down to 10 dB, but frankly
> 15 dB is a nice number to start with. If the distortion goes away with
> 5 dB, then using a 15 dB pad gives you 10 dB of safety margin and
> headroom.

True, but we fighting noise. With the built in 20dB pad, the noise
in these preamps become unbearable.

>>The unit I have been trying out belongs to a friend and I am looking
>>for a user friendly solution. 5 or 10 dB gets him out of the distortion
>>range without having to add a lot of noise.
>>
>>Maybe I will be making him a a mic cable insert with 10 dB of attenuation.

> Not a bad idea, but try the pads you've got to begin with.

As it turns out he has a 10dB pad built in to his stereo mic, so he
is good shape. He wasn't sure if he should use it. Now we know that
when he is playing his cello with a piano supporting him, he probably will
want to engage it.

Thanks for all the help from anyone.

So does anyone want a mini-review of the unit, even though we now know
that the front-end is terrible?

Rob R.