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Author Topic: Aerco MP-2 preamp - Part 2  (Read 79192 times)

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Offline Gutbucket

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Re: Aerco MP-2 preamp - Part 2
« Reply #135 on: September 26, 2012, 10:17:31 PM »
Assuming the center digital trim knob is kept at 12:00, the R-44's input sensitivity is adjustable from +4 to -56dBu.  With the outer knob at 12:00 its -26dBu.

The DR-680 input stage is switchable between Mic & Line sensitivity.  Switched to Line-in mode it's range is +24 to -27.5dBu, and set at 12:00 its +4dBu.  The 680 line-in should be able to take a really hot input, though I haven't tested it with anything super hot.

I dialed the 680 back a bit from 12:00 so I probably had set to ~ +10dBu or so.  That was after setting the Aerco to the dead center of it's gain range, which was higher than Spyder's normal setting (at least what it was set to when he handed it to me) but still well within the comfort zone of the 680.  I probably should have left the Aerco set where Spyder typically uses it into his M10, but the whole idea of borrowing it was to checkout the influence of its output transformers on my Gefells so I figured mid-way on the dial would be safe to get that touch of trafo color.
 
This all leads me to assume it was the Aerco was doing the distorting in my case for whatever reason. [shrug]
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Offline it-goes-to-eleven

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Re: Aerco MP-2 preamp - Part 2
« Reply #136 on: September 27, 2012, 09:26:49 AM »
but the whole idea of borrowing it was to checkout the influence of its output transformers on my Gefells so I figured mid-way on the dial would be safe to get that touch of trafo color.
 
This all leads me to assume it was the Aerco was doing the distorting in my case for whatever reason.

The transformers in the AERCO are input, not output.

Based on experiences recording dino jr, and high signal level bench testing, it is unlikely the aerco distorted. That is not to suggest that it won't if turned up too high, and that may have been what happened.  But I think your recorder would clip way before the aerco.

This is another example of why I prefer stepped pots or switches for gain control.

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Offline Gutbucket

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Re: Aerco MP-2 preamp - Part 2
« Reply #137 on: September 27, 2012, 11:20:13 AM »
I'll have to check the 680 to determine it's real overload point as opposed to the published specs, but I've run other signals line-in at similar input gain settings without issue, so I sort of doubt that the recorder input stage was the culprit but won't rule it out.

Maybe the batteries in the Aerco actually were less charged than suspected, and setting it for more gain than Spyder typically uses, though well within is capability with a full charge, may have pushed it past the available supply rail voltage with a less than fully charged battery.   Just guessing though.
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Offline aaronji

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Re: Aerco MP-2 preamp - Part 2
« Reply #138 on: September 27, 2012, 11:31:11 AM »
Per Jerry, the output of the Aerco can handle 20 V peak-to-peak.  I am not exactly sure what the sensitivity of the Gefells is (maybe 14 mV/Pa), but you'd have to add a lot of gain to a fairly loud signal to clip it.  At 25 dB gain (that's half of the Aerco's range), you'd need SPLs around 124 dB to hit that point (assuming that 14 mV/Pa is correct).  Like it-goes-to-eleven mentioned, I have recorded very loud music (Tortoise) with very sensitive mics (40 mV/Pa) with no problems.  Not much gain on the Aerco there, though.

Also worth bearing in mind that the gain markings on the Aerco sticker are for the switches; those numbers don't relate to the detented variable pots...

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Re: Aerco MP-2 preamp - Part 2
« Reply #139 on: September 27, 2012, 12:34:02 PM »
I am not exactly sure what the sensitivity of the Gefells is (maybe 14 mV/Pa)

The M94s caps have a sensitivity of 12mv/Pa, so even slighlty less than that (no pad or LPF engaged on the MV692s BTW).  The cause of the distortion is mostly speculation on my part at this point really, but thanks to everyone here for the input on figuring it out.  You regular users must be familiar with the Aerco's behavior when it runs low on juice, no?  What's the typical result in that case?

I'll try and post some waveform images if I get the time.  I should be able to also post comparative waveform images of  the same mics going direct into the 680 and through the V3, same band and on-stage setup, different nights.
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Offline acidjack

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Re: Aerco MP-2 preamp - Part 2
« Reply #140 on: September 27, 2012, 01:19:10 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 mine it's marked.... I can't recall exactly, but it's clearly labeled. It's a stepped-gain unit, mine at least.
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 #141 on: September 27, 2012, 02:01:51 PM »
I am not exactly sure what the sensitivity of the Gefells is (maybe 14 mV/Pa)

The M94s caps have a sensitivity of 12mv/Pa, so even slighlty less than that (no pad or LPF engaged on the MV692s BTW).  The cause of the distortion is mostly speculation on my part at this point really, but thanks to everyone here for the input on figuring it out. You regular users must be familiar with the Aerco's behavior when it runs low on juice, no?  What's the typical result in that case?

I'll try and post some waveform images if I get the time.  I should be able to also post comparative waveform images of  the same mics going direct into the 680 and through the V3, same band and on-stage setup, different nights.

my unit has an internal lithium-ion rechargeable battery and i've never been in a situation where it was running low on juice.  if i'm at a festival i power the Aerco with a Tekkeon 3450 set to 7.4v* and i can easily run it all weekend without issue.  if i'm just going to a regular show that is about 3-4 hours in length i just use the internal charge on the battery and i've never come close to running out of juice.  so, in a nutshell, i have no idea how it behaves when the battery is low.... and that's a beautiful thing! 

*i've powered the Aerco with 9v and 7.4v with no audible difference in quality.  Jerry even confirmed that the unit will function just fine with power anywhere betwen 7.4v and 12.v.
         

Offline Myco

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Re: Aerco MP-2 preamp - Part 2
« Reply #142 on: September 27, 2012, 02:03:22 PM »
Per Jerry, the output of the Aerco can handle 20 V peak-to-peak.  I am not exactly sure what the sensitivity of the Gefells is (maybe 14 mV/Pa), but you'd have to add a lot of gain to a fairly loud signal to clip it.  At 25 dB gain (that's half of the Aerco's range), you'd need SPLs around 124 dB to hit that point (assuming that 14 mV/Pa is correct).  Like it-goes-to-eleven mentioned, I have recorded very loud music (Tortoise) with very sensitive mics (40 mV/Pa) with no problems.  Not much gain on the Aerco there, though.

Also worth bearing in mind that the gain markings on the Aerco sticker are for the switches; those numbers don't relate to the detented variable pots...

On a non-scientific note, I have used my same Gefell > Aerco setup going into my DR-680 (using the exact same levels as the R-44) and it did not distort on the 680. On the R-44, I'd have had distortion, so this is what leads me to believe it has something to do with the R-44's inputs, rather than with the Aerco's outputs.
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Offline aaronji

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Re: Aerco MP-2 preamp - Part 2
« Reply #143 on: September 27, 2012, 04:55:28 PM »
On mine it's marked.... I can't recall exactly, but it's clearly labeled. It's a stepped-gain unit, mine at least.

Those labels are for the Aercos with gain switches; the numbers don't match up for the ones with variable pots...

Offline acidjack

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Re: Aerco MP-2 preamp - Part 2
« Reply #144 on: October 01, 2012, 11:06:23 AM »
On mine it's marked.... I can't recall exactly, but it's clearly labeled. It's a stepped-gain unit, mine at least.

Those labels are for the Aercos with gain switches; the numbers don't match up for the ones with variable pots...

Yeah, I gathered that.  It would seem that if you have variable gain, you have to be a bit more careful about how hot you're running it.

That said, I still can't see how people are overloading an R-44 with one unless they're running the Aerco way too hot.  One of my favorite things about the 44 is being able to easily drop the digital input gain with that outer clickwheel on each level control.  Running it at 9 o'clock with the Aerco (which is lower than I do with other analog inputs) I have never had an issue.   With my mics I'm usually running at least one or two positions higher, depending on the mic and situation.
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Offline hi and lo

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Re: Aerco MP-2 preamp - Part 2
« Reply #145 on: October 01, 2012, 03:05:03 PM »
How do the 'clickies' work on the R-44? Is attenuation applied if they're turned to their lowest setting (i.e. no signal is passed)?

Offline acidjack

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Re: Aerco MP-2 preamp - Part 2
« Reply #146 on: October 01, 2012, 03:29:24 PM »
How do the 'clickies' work on the R-44? Is attenuation applied if they're turned to their lowest setting (i.e. no signal is passed)?

It will still register levels if the clickies are all the way down; the clickies, as I understand them, change the sensitivity of the deck's inputs.  You know that I'm completely non-knowledgable about the electrical engineering aspects of this, but when the clicky is all the way down, the sensitivity reads as +4.  As you turn it up, it moves into negative numbers.  I don't know why it goes from positive to negative as you make it more sensitive, but I am sure you do.

The analog in the 680 is the "MIC" versus "LINE" setting on the top of the unit; the -44 just implements it more incrementally.  The clickwheel sensitivity settings are one of the features I like a lot more about the R-44 (and the meters).
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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Offline drewski1986

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Re: Aerco MP-2 preamp - Part 2
« Reply #147 on: January 12, 2013, 07:57:33 AM »
Has anyone used the 3.5mm headphone jack as a line out to a small recorder?  If so, was there any noticeable noise associated with this output jack compared to the rca outs?  Thanks for any information on this.

Offline it-goes-to-eleven

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Re: Aerco MP-2 preamp - Part 2
« Reply #148 on: January 12, 2013, 09:54:47 AM »
I have used it.  It works fine. It connects to the same circuit as the RCA's.  Assuming your plug is not strained, etc, there should be no issue.

I tend to use the RCA's because I consider them more robust, but that is debatable and very dependent on the particular cable used.

For anyone interested who may not have seen it, I have an AERCO for sale in the yard.

Edit: there is a performance consideration.  The RCA outputs allow you to keep both channels more isolated, each in its own shield, potentially reducing crosstalk.  Most 1/8" jack cables don't do that, and the off the shield stuff is often poorly shielded.
« Last Edit: January 12, 2013, 12:10:38 PM by it-goes-to-eleven »

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cashandkerouac

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Re: Aerco MP-2 preamp - Part 2
« Reply #149 on: January 28, 2013, 11:59:27 AM »
I have used it.  It works fine. It connects to the same circuit as the RCA's.  Assuming your plug is not strained, etc, there should be no issue.

I tend to use the RCA's because I consider them more robust, but that is debatable and very dependent on the particular cable used.

For anyone interested who may not have seen it, I have an AERCO for sale in the yard.

Edit: there is a performance consideration.  The RCA outputs allow you to keep both channels more isolated, each in its own shield, potentially reducing crosstalk.  Most 1/8" jack cables don't do that, and the off the shield stuff is often poorly shielded.

i have also used the mini jack with good results, but prefer using the RCA jacks.  the MP-2 rocks!!! and Jerry is awesome do deal with!!!

 

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