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Author Topic: Aerco MP-2 preamp - Part 2  (Read 66418 times)

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Offline drewski1986

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Re: Aerco MP-2 preamp - Part 2
« Reply #120 on: June 21, 2012, 11:55:31 AM »
-8 on the R-44 is at 9:00 (outer knob) I think.

Offline justink

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Re: Aerco MP-2 preamp - Part 2
« Reply #121 on: June 21, 2012, 02:18:01 PM »
I'm running neumann ak 40/50's > aerco > (ocm) R-44.  Last night I ran it at about 25 and still had slight brickwalling.  I have a single variable gain pot on my aerco as well as a balance knob.  It looks to me as if the right channel is worse than the left.  I am thinking that I am overloading the pre since I never saw the overload indicators on the R-44 light up.  Trying to figure out how to post a screen shot of the wav files in audacity but haven't figured it out yet.  Forgot to add that the R-44 was one click up from the bottom (outer knob -2, inner knob at 12:00)

imho, ditch the aerco.  you've got an OCM R-44.  the aerco is an un-needed liability in the chain.

just use it for stealthy shows.
Mics:
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Earthworks TC25 (omnis) 

Pres and a/d's:
Oade ACM Grace Lunatec V3 (FOR SALE - Make Offer)
bm2p+ Edirol UA-5 (FOR SALE - Make Offer)

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Offline Todd R

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Re: Aerco MP-2 preamp - Part 2
« Reply #122 on: June 21, 2012, 03:52:36 PM »
Brickwalling seems to be the term around here for getting unwanted distortion.  Whether that is a correct usage, I don't know.  Also, it is never clear whether the distortion is because the SPLs are too high and the mic distorts, or if the external preamp distorts on it input (mic input too hot), or the preamp distorts on its output (preamp trying to send a louder signal than it is designed for, due to gain levels being set too high), or whether the recorder is distorting on its analog input since the signal coming from the preamp is too high, or if the recorder is distorting since you are trying to go above 0dbFS (db Full Scale -- digital 1's and 0's can only be negative or get up to 0 max, beyond that isn't possible and you have clipping).

If you brickwalled -- ie, ended up with a distorted recording -- it could have come from any of the above. 

Or even one more option: when I had the OCM R44, one thing I didn't like is that the inner variable gain goes from -infinity (no signal) to max signal, and then the outer stepped ring provided the single gain setting, much like the V3.  But if you have the outer gain set too high, and then dial back the inner variable gain, the R44 can distort, but you don't know it since there are no clip meters to tell you it's happening and your levels aren't hitting 0dbFS.

I had this problem once or twice.  I forgot now what the solution is.  I think it's something like you should never go lower than 12:00 on the inner variable gain setting, and if your levels are too hot and you're clipping (trying to go above 0dbFS), then you should dial back the stepped gain.  If you keep the stepped gain where it is and go below a certain point on the variable gain (9:00, 10:00, 11:00?? I don't recall anymore) you can get brickwalling/distortion.
Mics: Microtech Gefell m20/m21 (nbob/pfa actives), Line Audio CM3, Church CA-11 cards
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Recorders:  Sound Devices MixPre-6, Sony PCM-M10, Zoom H4nPro

Offline aaronji

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Re: Aerco MP-2 preamp - Part 2
« Reply #123 on: June 21, 2012, 04:17:15 PM »
^^^ It's kind of hard to overload the Aerco's input, I think.  I recently recorded a deafeningly loud show with quite sensitive (40 mV/Pa) mics and had no problems.  The output can do 20V peak-to-peak; I am pretty sure I could have distorted that if I had added a bunch of gain on the pre.  I would probably have been overloading the recorder input (or been close) with that sort of gain setting, though.

As I mentioned in my previous post, here is what Jerry said about the gain pots in response to my question about how the gain settings correspond to the pot detents and the stickers on the front of the pre:

Quote from: Jerry
It's because the pots have a linear slope which causes uneven gain steps. The markings on the front are for the switches, only 180 degrees of rotation. The gain is different for each step but the steps are closely spaced at the low end and widely spaced at the high end. The other commonly available slope for potentiometers is audio (logarithmic) slope which would be much worse.

Offline twoodruff

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Re: Aerco MP-2 preamp - Part 2
« Reply #124 on: September 25, 2012, 09:08:25 AM »
Anyone know if Jerry will look over a unit and give it a "clean bill of health", I am trading mine to someone who will get more use out of it.
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Offline twoodruff

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Re: Aerco MP-2 preamp - Part 2
« Reply #125 on: September 25, 2012, 09:57:51 AM »
Anyone know if Jerry will look over a unit and give it a "clean bill of health", I am trading mine to someone who will get more use out of it.

Nevermind, i received a response from Jerry. FYI he is asking $25 plus shipping for this service which seems very reasonable to me.
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Offline Myco

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Re: Aerco MP-2 preamp - Part 2
« Reply #126 on: September 26, 2012, 07:46:50 AM »
The Aerco and the R-44 don't play well together, the Aerco overwhelms the R-44's input very easily. I had the same issues when I ran a R-44. Never got it fully worked out.
Microtech Gefell M200: M20/M21/M27 caps> Bumblebee MiAGi-II/Darktrain silver cable's/"Chuck" Belden cables> Aerco MP-2 or Busman modded DR-680 pre-amps> Darktrain cables & interconnects> Tascam DR-680 (Busman mod)
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Online spyder9

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Re: Aerco MP-2 preamp - Part 2
« Reply #127 on: September 26, 2012, 08:59:22 AM »
Same thing happened to Gutbucket a few weeks ago when he used my Aerco with his R44. 

Offline Myco

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Re: Aerco MP-2 preamp - Part 2
« Reply #128 on: September 26, 2012, 10:38:20 AM »
I wonder if it has to do with the fact that R-44 is a negative polarity powered unit, while almost everything else that we typically use is powered using positive polarity?
Microtech Gefell M200: M20/M21/M27 caps> Bumblebee MiAGi-II/Darktrain silver cable's/"Chuck" Belden cables> Aerco MP-2 or Busman modded DR-680 pre-amps> Darktrain cables & interconnects> Tascam DR-680 (Busman mod)
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Re: Aerco MP-2 preamp - Part 2
« Reply #129 on: September 26, 2012, 10:48:18 AM »
I wonder if it has to do with the fact that R-44 is a negative polarity powered unit, while almost everything else that we typically use is powered using positive polarity?

that should only affect sharing a battery.
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Offline Gutbucket

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Re: Aerco MP-2 preamp - Part 2
« Reply #130 on: September 26, 2012, 10:59:54 AM »
Same thing happened to Gutbucket a few weeks ago when he used my Aerco with his R44. 

Thanks for lending me the pre, Dan.

I was running it into the DR-680 actually (MG M94/MV692 > Areco > DR-680 line-in ch5/6).  I suspect the problem was gain staging between the two, but I'm not certain.  It was the only time I've run the Aerco or really taken a good look at one so I'm not that familiar with it.  It was a pretty quick setup and roll situation and I simply set the Aerco gain right in the middle of it's adjustment range and then adjusted line-input gain on the 680 to get decent levels.  I didn't record what that gain setting on the 680 was, but it was somewhere below the middle '0' setting, but not by a lot (DR-680's gain trim adjustment is +/- from 0).  I assumed that would be a safe setting on both devices, but the resulting recording has some not overly severe but audible distortion, and the visual display of the waveform showed uniformly compressed/flattened peaks at a specific level well below 0 DBFS which looked similar to classic brickwall behaviour.  Could be heavy saturation of the Aerco's output transformers I suppose, but I don't own any transformer output preamps so I'm not sure.

[edit- I also wondered about the state of charge of the battery in the Aerco, but Spyder assured me that wasn't the problem.  This was on-stage for an instrumental jazz trio, amplified but no PA, neither overly quiet nor crushingly loud] 
« Last Edit: September 26, 2012, 04:49:08 PM by Gutbucket »
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Offline acidjack

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Re: Aerco MP-2 preamp - Part 2
« Reply #131 on: September 26, 2012, 11:07:57 AM »
I run Aerco>R-44 (ocm) regularly with no issues. Usually set the 44 to 9 o'clock and run the Aerco at 10 or 20dB gain. Most of my stuff is loud.
Mics: Schoeps MK4V, MK41V, MK5, MK22> CMC6, KCY 250/5, KC5, NBob; MBHO MBP603/KA200N, AT 3031, DPA 4061 w/ d:vice, Naiant X-X, AT 853c, shotgun, Nak300
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cashandkerouac

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Re: Aerco MP-2 preamp - Part 2
« Reply #132 on: September 26, 2012, 04:47:35 PM »
i also run my Aerco MP-2 into an R-44 sometimes and have never had a problem.  you have to set the gain on the R-44 first, then set the level on the Aerco.  it may seem counter-intuitive, but it works.  i always start with the outer and inner knobs of the R-44 set to 12 Noon and then will adjust the levels on the Aerco.  configured with the R-44 the levels on the Aerco are always extremely low. 

someone else in this thread recommended not using the Aerco with the R-44 (since it has the Oade OCM), and that is a perfectly viable strategy.  i don't think you sacrifice anything going that route, as the R-44 OCM sounds great without the use of an external pre.  my use of the Aerco with the R-44 is primarily for the "flavor" of the Aerco.  i suppose it's not terribly different from putting grated parmesan cheese on your pasta.  the pasta doesn't necessarily need it to taste good, but you may just prefer it with cheese.  in my opinion Jerry Chamkis makes great cheese!!!   ;D       

Offline Gutbucket

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Re: Aerco MP-2 preamp - Part 2
« Reply #133 on: September 26, 2012, 04:52:39 PM »
I run Aerco>R-44 (ocm) regularly with no issues. Usually set the 44 to 9 o'clock and run the Aerco at 10 or 20dB gain. Most of my stuff is loud.

To aproximately what clock position does the gain knob point for +10-20dB?
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cashandkerouac

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Re: Aerco MP-2 preamp - Part 2
« Reply #134 on: September 26, 2012, 05:36:51 PM »
I run Aerco>R-44 (ocm) regularly with no issues. Usually set the 44 to 9 o'clock and run the Aerco at 10 or 20dB gain. Most of my stuff is loud.

To aproximately what clock position does the gain knob point for +10-20dB?

on my unit i have a continuous gain knob (no steps).  i always set pre-amp gain agianst levels on the recorder.  the "marker" on the gain knob of the Aerco is in a random location (in other words at "0" gain the knob marker does not point to 12 Noon) so i never have any idea how many db of gain are being provided by the Aerco.  however, i do know for sure that I have never opened up the gain on the Aerco past 50%.  and when using it with the R-44 i'm probably only using 10% of available gain from the Aerco.  gain knobs on the R-44 are almost always set to 12 Noon and levels peak at around -6 db on the R-44. 
« Last Edit: September 26, 2012, 05:38:34 PM by bass_ur_face »

 

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