Topic: hiss with preamp

[anr]

Agree with Bean.  I have CAFS and various Sound Pro mics and always go Mic In on M10 using an old Sound Pro SPSB-2 Battery Box.  A typical setting for CAFS would be Low Sensitivity and Record Level at 3.5.  Using Line In the same Mics/B Box would barely register.  And I'm very pleased with the results. 

[Church-Audio]

And I ran CA14>SP BB/9100>M10s and ALWAYS ran MIC-IN, so maybe try that over line-in. Or were you using mic-in

I was using mic in and my 9100 has one nob for gain adjustment, though there's a switch inside which I have no idea of the function.  At this point all my recordings have come out better without the 9100 (mostly loud rock shows and some as loud or louder than Metallica), but I think I need to give it another try with a bit more thought put into the settings, since Church said the mics were specd to work better with that 9v power.

When running really loud shows reduce the gain on the 9100 to about 60% to 80% of the full travel of the pot. Also make dame sure you have a quality battery inside. And last but not least make sure you are using the line input for really loud shows.

Chris

[hi and lo]

Agree with Bean.  I have CAFS and various Sound Pro mics and always go Mic In on M10 using an old Sound Pro SPSB-2 Battery Box.  A typical setting for CAFS would be Low Sensitivity and Record Level at 3.5.  Using Line In the same Mics/B Box would barely register.  And I'm very pleased with the results.

A battery box is not a preamp.

How anyone can suggest that someone use an external preamp into a handheld recorder's Mic In, in anything but the most desperate of situations, it beyond me. It might make a decent tape, but it completely defeats the purpose of using an external preamp and makes no theoretical sense.

[kleiner Rainer]

There is another point that irritates me: the obsession with "unity gain". This is only meaningful if you have access to line input AND line output and if you want to use your device in a chain of other devices as a kind of "signal repeater".

For all other purposes, the only relevant level is 0dBFS, the point where hard clipping starts. Whenever I record a sound source, I set the gain control until I have optimum level with enough headroom to 0dBFS to avoid clipping. The *exact* value of gain or attenuation is not relevant for me, because the S/N ratio is specified *at the A/D input*. I use *optimum gain* instead of unity gain, and that concept is also used by all professionals I know.

On my PCM-M10 I set its line input level so that the 0dB test tone from my MixPre D gives a VU meter display of -24dBFS on the M10, this leaves enough headroom for unexpected level excursions even when using the limiter of my MixPre D. I then set the gain on the MixPre D to whatever the situation requires.

Greetings,

Rainer

[hi and lo]

There is another point that irritates me: the obsession with "unity gain". This is only meaningful if you have access to line input AND line output and if you want to use your device in a chain of other devices as a kind of "signal repeater".

For all other purposes, the only relevant level is 0dBFS, the point where hard clipping starts. Whenever I record a sound source, I set the gain control until I have optimum level with enough headroom to 0dBFS to avoid clipping. The *exact* value of gain or attenuation is not relevant for me, because the S/N ratio is specified *at the A/D input*. I use *optimum gain* instead of unity gain, and that concept is also used by all professionals I know.

On my PCM-M10 I set its line input level so that the 0dB test tone from my MixPre D gives a VU meter display of -24dBFS on the M10, this leaves enough headroom for unexpected level excursions even when using the limiter of my MixPre D. I then set the gain on the MixPre D to whatever the situation requires.

Greetings,

Rainer

The reason we care about Unity gain with line inputs is pretty simple. It is believed that when running a recorder at the unity gain level it is most transparent and imparts the least change in the sonic signature. This is debatable to some extent and assumes that a recorder sounds best at its unity gain level because it is neither attenuating nor amplifying the signal.

Do I personally assume that a recorder sounds best at its unity gain level? The answer is no. I would need to carefully evaluate any recorder I use at all gain levels to understand where a recorder truly sounds best, but because that is a rather impractical task and highly subjective, the assumption is made for better or worse.

So, I would encourage anyone to run a few cheap handheld recorders at "Optimum Gain" and tell us that the gain provided by the recorder is cleaner than digital gain that would be applied in post to achieve 0dBFS. So rarely, for what we record, do we struggle to achieve an acceptable S/N ratio, so it doesn't matter at all that we are not shooting for "Optimum Gain."

[kleiner Rainer]

hi and lo,

in engineering "unity gain" means no attenuation or amplification in a circuit block, 0dB gain so to speak. Maybe I do not grasp the tapers concept of "unity gain" because I am more of a design engineer schooled in analog and audio design than an audiophile (and also not a native english speaker). The sweet spot in digital recording as I have experienced it is to set the gain just a few dB below clipping to preserve as much resolution as possible without having to resort to too much (digital) amplification in post. Maybe in the time of 24 bit recording this is less important than back when we had portable DAT recorders with 14 bit effective resolution (yes, I am that old...).

Starting back in my analog cassette tape recording days 30some years ago, I always tried to get best S/N ratio for my recordings, since most of the time it is nature recording that changes to sound pressure levels approaching or surpassing a live rock show when the train goes by. The worst of both worlds, so to speak, without the chance to redo it (and I am not talking about biological and technical noise sources that make "concert talkers" look like a minor problem).

Now back to topic: if you get hiss in the recording when using a preamp, then there is something wrong with your gain distribution (barring mic problems or noisy phantom or plug in power). For a minimum of additional noise, the first stage has to do most of the amplification. Then the noise contribution of the following stages can be neglected. Ask any ham radio operator who does weak signal work on VHF, UHF or SHF. Its physics.

There is one other noise source that a taper friend of mine found: he forgot to turn off the plug in power of his recorder when using a mic with internal battery. The electrolytic caps in the output of the mic were reverse biased and started acting up in the form of white noise and some nasty pops. Maybe this applies here?


Hope this clarifies my last post.

Greetings,

Rainer

[aaronji]

How anyone can suggest that someone use an external preamp into a handheld recorder's Mic In, in anything but the most desperate of situations, it beyond me. It might make a decent tape, but it completely defeats the purpose of using an external preamp and makes no theoretical sense.

I agree, but the 9100 the OP is using only supplies 20 dB of gain and the CA-11s aren't very sensitive so it can be difficult to get good levels line-in for quieter shows...I had the same problem (which I solved by getting more sensitive mics run either mic-in or with a pre that has considerably more gain).

[hi and lo]

hi and lo,

in engineering "unity gain" means no attenuation or amplification in a circuit block, 0dB gain so to speak. Maybe I do not grasp the tapers concept of "unity gain" because I am more of a design engineer schooled in analog and audio design than an audiophile (and also not a native english speaker). The sweet spot in digital recording as I have experienced it is to set the gain just a few dB below clipping to preserve as much resolution as possible without having to resort to too much (digital) amplification in post. Maybe in the time of 24 bit recording this is less important than back when we had portable DAT recorders with 14 bit effective resolution (yes, I am that old...).

You answered your own question and are right on track. With 24 bit recording, it is not as important to preserve as much resolution as possible, so we are afforded an opportunity to use less analog gain from a preamp that may not be of the highest quality. If we were to do a serious listening comparison of the entire gain range of a preamp, we would possibly discover that it has a 'sweet spot' where it subjectively sounds the best. This sweet spot, simply based on the nature of probability, will probably not be the exact gain value that would be needed to hit 0dBFS.

Again, it's purely an assumption that running a recorder at its unity gain is the 'sweet spot.' I don't think it's a bad assumption to make, but is probably not true in all instances as what is sonically pleasing is highly subjective.

[hi and lo]

How anyone can suggest that someone use an external preamp into a handheld recorder's Mic In, in anything but the most desperate of situations, it beyond me. It might make a decent tape, but it completely defeats the purpose of using an external preamp and makes no theoretical sense.

I agree, but the 9100 the OP is using only supplies 20 dB of gain and the CA-11s aren't very sensitive so it can be difficult to get good levels line-in for quieter shows...I had the same problem (which I solved by getting more sensitive mics run either mic-in or with a pre that has considerably more gain).

Makes sense, but because it was suggested to the OP that he should run Mic In rather than simply get a new preamp with more available gain, I raised the issue. The former is a non-ideal workaround while the later is what is truly needed to resolve OP's issue.

[Javier Cinakowski]

Damn, that is an excellent post mshillarious.


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I see the following as sane:
"I am going to plug my preamp into my Sony M10 mic input, to capture the very quiet mating call of the Scaly-Sided Merganser bird from 250 yards away."

This seems insane:
"I am going to plug my preamp into my Sony M10 mic input, at the Megadeath show, FOB."

[Church-Audio]

Makes sense, but because it was suggested to the OP that he should run Mic In rather than simply get a new preamp with more available gain, I raised the issue. The former is a non-ideal workaround while the later is what is truly needed to resolve OP's issue.

There is not necessarily an issue with taking gain at two stages.  Sometimes it is even preferable*, but the basic requirement is that the output noise of the preceding stage exceeds the input noise of the following stage by a reasonable margin, say 6dB.  Then there is no significant loss in system signal-to-noise ratio.  Let's say the preamp has -125dBV input noise and 20dB gain, that yields -105dBV output noise.  So long as the recorder's mic input noise is less than -110dBV or so (and I would hope that it is) then the system works fine and more gain may be taken in the recorder without degrading signal to noise ratio.




* As you increase gain in a single stage, you will consequently reduce bandwidth and sometimes increase distortion.  That is, a given amplifier will usually have less distortion at a given output level with less gain.  Also, if the stage has DC offset then a very high gain in a single stage will reduce headroom, as compared to two stages with the same DC offset that are not DC coupled.  These problems usually don't rear their head until gain exceeds 40dB, and can be tolerable in a good amplifier at 60dB, but eventually as gain increases the system will perform better with two gain stages than one.  This is what you tend to see in very high gain amplifiers.

Exactly right. Most good quality preamps use more than one stage to get gain

[Church-Audio]

Agree with Bean.  I have CAFS and various Sound Pro mics and always go Mic In on M10 using an old Sound Pro SPSB-2 Battery Box.  A typical setting for CAFS would be Low Sensitivity and Record Level at 3.5.  Using Line In the same Mics/B Box would barely register.  And I'm very pleased with the results.

A battery box is not a preamp.

How anyone can suggest that someone use an external preamp into a handheld recorder's Mic In, in anything but the most desperate of situations, it beyond me. It might make a decent tape, but it completely defeats the purpose of using an external preamp and makes no theoretical sense.

Theory is fine. BUT in reality most quality preamps use more than one stage. And there is nothing wrong with using an external preamp into a mic input if need be. If the preamp can handle input and the preamp being connected to it is low noise there is no issue. And nothing wrong with it what so ever. My mics are around -30 db to -25 db at 114 db.. acoustical input. So gain is needed in some cases.