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Author Topic: CA ST-9100 preamp - some questions  (Read 1896 times)

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Offline LikeASong

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CA ST-9100 preamp - some questions
« on: January 25, 2012, 08:14:49 PM »
I got this fantastic preamp from colargol a few days back and I have two consecutive tapings planned for tomorrow and for Friday. I know taping is -partly- a trial&error job, but I'd like to start with more good trials than errors ;D My gear is as stated below: Church Audio CA-14's (cardioids) > CA ST-9100 > Zoom Q3·HD.

I've read loads of topics about it like these ones:

and I still have doubts about some stuff. I hope you don't bother me asking them.

First of all: when does the amplification/power supply really begin? I've read some stuff saying "at around 11 o'clock" in the preamp's dial... I've tested mine and it does begin some 'hours' before that... Somewhere around half past 9, I don't think there's anything wrong with that but I just wanted to say it. I've attached a graph: the red mark is where my preamp starts to send sound signal to the recorder, and the blue mark is where most people say it does.

If I understand the principles of the preamp, the point where it supplies +0 adittional dBs of gain is the point where it acts basically as a battery box... Did I get that right? So, on an extra-loud show, the knob should be around 10 o'clock, where it supplies just power to the mics and not any -unnecesary- gain... But on a soft recording, the knob should be pumped all the way, giving the maximum gain (+20dB). Right?

Now, the little switch on the battery compartiment... It's used for turning the bass roll-off in and out. Alright. But I'd like to know which frequencies it rolls off and how big is the attenuation applied. Because in some of the topics mentioned above, it is said that it cuts from 10 to 100 Hz at a rate of 6 Hz per octave, but in some other places (for example, Church Audio's ST-9100 eBay page: ) it is said that the roll off ends at 80 Hz, and other contradictory info. Does anyone know the exact specs of the bass roll off? My preamp is V4.0 if it helps.

And last question: I know I won't need the bass roll off in tomorrow's show (semi-acoustic UK folk band in a small theatre), but on Friday I'm taping a LOUD band (Arctic Monkeys!) in a 18.000 people arena and I'm aiming for the first rows. Maybe that is an ocassion for switching on the bass roll-off? This band is known for using loads of bass. And I mean loads. I know most of you will say "do it in postproduction if neccesary", but I don't think that the results are satisfactory if the bass amount is so huge on the master recording that the rest of the freqs become a bit muffled ??? Or am I missing something/doing an illogical reasoning?

Thank you very much :)
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Offline vanark

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Re: CA ST-9100 preamp - some questions
« Reply #1 on: January 26, 2012, 11:12:47 AM »
It appears you know the answers to the questions and as you have noted, they have been asked and answered in the past?

1. 11 o'clock is 0 dB on the preamp.  I generally run at 2-3 o'clock for rock shows, full on (5 o'clock) for acoustic shows but do keep an eye on the levels.
2. I have never used the bass rolloff.  As you have noted, the most popular approach to this is "do it in post production".  You can roll off the bass frequencies at any level and steepness in post.

I'd guess that isn't what you want to hear, but the information you've read previously is correct, in my opinion.
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Offline TimeBandit

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Re: CA ST-9100 preamp - some questions
« Reply #2 on: January 26, 2012, 02:13:34 PM »
maybe you are recording this very loud band in front of stacks it can be an option for switching on the bass roll off. On "softer" situations i would use no roll off on the preamp.
at least almost no one uses zoom gear here (i'm sorry) i don't know what value on the zoom is the setting for "unity gain" .. i used the ca9100 on the Tascam Dr-07 (old model) which was set to "unity" on the dial at around 6, the preamp was around 2 o'clock and that was fine for getting levels at around -12dB.

First things you should learn:
Set your Zoom to "unity" (refer to the manual yours has only 3 settings so you can only do trial and error - maybe the middle seeting is the way for loud shows, soft for acoustic).
Dial in the gain on the Preamp until you reach a decent level for your needs.
Maybe use a band for training where you know that others are taping so it isn't a crime if you mess up your recording.
record in 24 Bit, with the levels set to uncritical -12db and you can raise the gain in post processing with no problems. btw. for that usage the DR-2D from tascam is nice you can use a mode it records simultaneous in 2 different levels, so you can record with -12 and -6 db in a single task for example. it saves both independent on the card and you can choose the better one.

i know unity gain isn't the proper term, but everyone understands what it means for what to set on the recorder, hence the goosefeets
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Offline hi and lo

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Re: CA ST-9100 preamp - some questions
« Reply #3 on: January 26, 2012, 07:54:42 PM »
I believe the only reason to ever use the HFP on a preamp or recording, for our hobby, is if there is not enough headroom at your minimum gain setting to avoid overloading the input stage of any downstream devices. In the 24-bit era, this is pretty much a non-existent problem with most preamp/recorder combinations. Reducing bass before the signal is digitized will free up dynamic range for un-cut frequencies, but otherwise has no real benefit.

If you can capture every frequency without clipping or otherwise overloading downstream compontents, you should. I had to argue this with JFCB before coming to my senses.. he was right, I think.  ;D


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