Re: Looking for sensitive audio RMS meter


I'm looking to measure noise, but not THD.

I don't want to use a sound card as those generally cannot be calibrated.

The ones that can be calibrated cost much too much.

I see the points with the excess bandwidth making the measurement less

I'm looking to measure noise at least up to 30 kHz, but 22 kHz might
be fine too.

Perhaps the suggested 3456A or, as Liam suggested, 3457 are a good idea.

If I had money to blow I'd buy an Audio Precision box. My budget is in
the low $xxx for this.

On Tue, May 11, 2021 at 12:35 PM Marian Beermann <> wrote:

I have two 3400A's (with nuvistor frontends), their noise-floor is around
60 ┬ÁVrms, but they do have 20-25 MHz -3 dB bandwidth (so their noise is a
factor ~14 higher due to excess bandwidth). These have tons of gain (like
250-300x) after the input amplifier (which is a nuvistor plate follower
with unity gain on the lowest range, and 1:1000 attenuation at 1 V and
above), which is not conducive for ultra-low-noise performance.

Your best / cheapest bet is a "gain box" and a sound-card as others

Cheers, Marian

Am Di., 11. Mai 2021 um 05:06 Uhr schrieb Kerry Burns <>:

Hello Chris

I have an older 3400A. It works well for most audio measurements ( and
beyond, up to 10 MHz), but the lowest range is 1mV so probably not
sensitive enough for sub 1uV work.


From: <> on behalf of bhome1959 <>
Reply to: <>
Date: Tuesday, 11 May 2021 at 12:41 pm
To: <>
Subject: Re: [TekScopes] Looking for sensitive audio RMS meter

Hi Liam,

I would love a 3457A!

Anyone have a HP 3400A? That would completely suit Bob's requirements.
BTW, I am also looking for one of those that works. I bought one on
fleabay and it has serious problems.


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