ACM & ACMP Reviews by Nuemes

[kidvybes]

...so hopefully everyone who purchased one or more of these pres will recognize their value and put them to good use, but what I'm wondering is, if 797Audio built these:
http://www.gearslutz.com/board/new-product-alert/201095-cheap-neve-clones-beijing-palm-expo.html
...then who's building these for Golden Age?:
http://www.worldstudios.se/IMG_0009.jpg
(that look very familiar...copy of the Chameleon Labs copy of the Chandler...a Chinese clone of a Chinese clone?)...

 

[ausrock]

Uh oh........

I'm ducking for cover now........

Don't worry Doc, there'll be nothing posted from me to worry about.............and even if I did, I'm sure you wouldn't believe me anyways

 

[Junior!]

I didn't hear of that. Do you have quotes/dates from anyone regarding an EQ issue with the 727 units prior to the Group Buy units going out?

Yeah, I remember that from the massive GS thread. Turns out it's in post #468. I think some of that info gets lost because it's spread across multiple threads.

 

[ausrock]

Yeah, I remember that from the massive GS thread. Turns out it's in post #468. I think some of that info gets lost because it's spread across multiple threads.

Ahha........that's it. I suspect, and I repeat SUSPECT, that 797 were already committed to their pcb designs and chose to proceed without implimenting the mods suggested by PMI's people.

 

[P. Glaser]

Ahha........that's it. I suspect, and I repeat SUSPECT, that 797 were already committed to their pcb designs and chose to proceed without implimenting the mods suggested by PMI's people.

I'm not so sure they didn't do the same with Chance's tech's design as well.

 

[ausrock]

Hmmmmm...........yeah, OK



BTW...........Merry Christmas to y'all.

 

[nuemes]

The John Ma/Hyatt/Chance pre soap opera is an xmas gift that keeps giving.

Speaking of which, happy baby jesus saves the world eve! Don't forget to eat jesus' body and drink his blood tommorow lest ye burn in hell for all eternity - oh, unless you repent right at the last minute(!)

 

[Junior!]

The John Ma/Hyatt/Chance pre soap opera is an xmas gift that keeps giving.

Sorry, didn't mean to dredge up any of that old drama. I only posted it because you asked and I had a spare moment to do a google search.

Carry on and Merry Christmas everyone...

 

[tarnationsauce2]

I don't think we are narrowing in on high frequencies, I think it's a bit more involved than that--there is a commonality among the sources people like, and also between the sources that people don't like.

Here, try this instead of testing hats on the ART again:

test_file.wav

Run that out of your converter, and first directly back into your converter, and record the result. That's just a baseline to determine how your converter performs.

Next, run the file out of your converter into the ACMP, with the input gain on its minimum setting, and the output gain on max. If that results in clipping, either the ACMP or your converters, turn down the test file in your DAW until the output doesn't clip the ACMP input. Shoot for the same -6dBFS level as you did with the hi-hat test.

Hey MSH, I performed your test for the heck of it.
I did a direct patch of the converter In to Out (DAW at 0dB).
With all the preamps I did have to vary the DAW output a little bit within a couple dB of eachother. They were all around -24dB out of the converter biggest difference was the SCA A12 needing about 6dB more than the N72 and ACMP.

In all cases I used MIC input, High impedance used, input gain all the way down, output all the way up. And on the ACMP the EQ button was out.

I realized after the fact I recorded all these in 32-bit float. Hopefully you can support that format. I didn't want to downsample because I didn't want aliasing or anti-aliasing to throw off the noise floor. I did no sort of post digital gain matching (normalizing etc.), it was all done while recording. These are the raw untouched files, don't want to contaminate the test!

Using an FFT, the ACMP proved to be pretty good in these tests. Better than equal to the N72 in all cases. Noise, harmonics, 60Hz hum, frequency response, and intermodulation look good to me.

Converter
ACMP-84
SCA N72
SCA A12

 

[mshilarious]

I can do 32 bit, but not until I'm back home on Sat. Unless you want to plot the FFT for me . . .

 

[mshilarious]

Notice: anyone who doesn't believe that science has anything to do with the design of electronic circuits, please skip this post.


OK, here are my observations: overall, the performance of the ACMP on hi-hat remains a puzzle. Clearly, it is not a favored preamp for this source given the samples above and Dr. Bill's concurrent experience. My leading hypothesis was the ACMP was generating an excessive amount of intermodulation distortion. I also suspected it had a reasonable amount of harmonic distortion, based upon zmix's early observation, although I didn't expect the harmonic distortion to be the source of trouble on hi-hat, since most of the distortion products would be too high to be troublesome.

Indeed, the ACMP did show more intermod than the other preamps, and than the converter loop. The 1kHz peak is significant. But there is no prominent 17kHz peak, as I would have guessed--the 1kHz peak isn't quite high enough to generate its own intermod products.

So the performance of the ACMP on hi-hat remains unexplained. A very clear difference in frequency response in the hi-hat test can be noted. There was the possibility that was from extreme distortion, harmonic and/or intermod, or from some other source. But I think that now must be set aside.

Really, the difference was so large that it would have been difficult to explain as a function of distortion. It seems more likely that variations between the two microphones or the placement of the microphones must account for most of the observed difference--which as I always say, can obviate the need for a variety of preamps in the first place. Indeed, many if not most condenser microphones will show more distortion (of all types) than these preamps.

I went back to the ART hi-hat sample, and using an algorithm I generated a rather large amount of intermod distortion, about 40dB more than the ACMP. While it did sound trashier, there was not as large of a difference in frequency response of the resulting file as the ACMP. So again, it leads me to suspect microphones or placement as the source of the difference.

Another possibility is that there was some feature of the hi-hat test, perhaps such as input level, that was not replicated with the test signal. Or a test signal with more high-frequency sine wave components at different intervals, with sharp transients, could be used in a retest. I consider the former to be more likely to be conclusive than the latter, though.

Finally, there is the possibility that something wacky was going on with respect to the mic/preamp input transformer reactance. That could be eliminated from consideration with the use of a suitably low-output impedance transformerless microphone.

In any subsequent tests on live sources, it would be helpful to repeat the test twice, swapping microphones and placements between the two units under test, to avoid that as a potential source of error.

I could not make any conclusion about harmonic distortion, other than the units don't seem to have much. However, the converter loop in this case showed more distortion than the preamps, except for second-order. That's an odd result; possibly the preamps provided a lower impedance source to the converter input than the converter itself, although most if not all converters have their own buffers to avoid such woes . . . no conclusion here.

My last overall observation is the 60Hz hum picked up in all tests--were all the connections balanced?

 

[antichef]

In any subsequent tests on live sources, it would be helpful to repeat the test twice, swapping microphones and placements between the two units under test, to avoid that as a potential source of error.

My last overall observation is the 60Hz hum picked up in all tests--were all the connections balanced?

I did swap mics between the first (discarded, due to the 0db peaks) and the second tests. Those two mics almost completely cancel out on a pink noise phase cancellation test, but that's all the matching I've done with them. For placement, I measured the distance from the edge of the hihat and made sure each was pointing at the center of the hihat and that each was level, etc.. The sound from the hat itself could be asymmetrical, and the room isn't exactly well controlled, but everything was close to the center. All my connections were balanced, but I think I maybe I have a ground loop problem - would that explain the hum?

Anyway, as you know, science requires controlled laboratories -- not what you got from me , but if I get a chance, I'll try again, this time in a more controlled way.

 

[drBill]

So the performance of the ACMP on hi-hat remains unexplained.

Maybe it didn't like the mic he was using. Just to clarify, I would use the ACMP on HH if needed, it just wouldn't be my first (or even second) choice. I tend to form unscientific opinions about various pieces of gear and go with my gut instinct when recording, as I generally do not have hours to experiment with swapping out different pieces.

 

[mshilarious]

I did swap mics between the first (discarded, due to the 0db peaks) and the second tests. Those two mics almost completely cancel out on a pink noise phase cancellation test, but that's all the matching I've done with them. For placement, I measured the distance from the edge of the hihat and made sure each was pointing at the center of the hihat and that each was level, etc.. The sound from the hat itself could be asymmetrical, and the room isn't exactly well controlled, but everything was close to the center. All my connections were balanced, but I think I maybe I have a ground loop problem - would that explain the hum?

Anyway, as you know, science requires controlled laboratories -- not what you got from me , but if I get a chance, I'll try again, this time in a more controlled way.

Well, I do think you did a fairly well controlled test, but without a smoking gun, I needed to keep looking for explanations . . .

Ground loops shouldn't affect balanced audio lines; that's one big point of balanced design. But a lot of people assume 60Hz hum is from ground loops, when much of it is really from induced interference. Anyway, the converter loop should be unaffected. I live in EMI hell myself (I did my work on balanced guitar designs because I had to), but I can generally get a lower 60Hz hum in a converter loop test. And my converter didn't test notably better than yours in other respects.

To me, as I said, this is a fairly good illustration of why preamps don't matter all that much, especially if operated well within their linear range. Yes, the ACMP does show some intermod. But the ART on low plate is much worse, and will show much more harmonic distortion too (this is why I never turn mine off high plate). That just shows what happens when a preamp design gets too extreme, which none of the units under test seem to be.

On the other hand, what happens to a preamp near or past its limit? That will vary quite a lot. I would strive to avoid that, unless I knew I wanted that specific characteristic. And a lot of people do for certain preamps. I always feel like I can screw up a signal as much as I want later, but that's just me.

 

[nuemes]

ACM-1200 & ACM-6802T review w/ acou guitar

ACM-1200 & ACM-6802T with AKG C414uls review for Gibson J45 steel string acoustic.

All mics recorded in omni about 3 feet in front of the sound hole. Pre was Digi 002 (sorry, only pre I have more than 2 of).

Noise floor not a problem for any of the mics nor was ouptput level.

ACM-1200: Medium output between the 3 mics. Barely higher noise floor than C414. Least bass of the 3 mics. Sounds a bit muddy in the mids, makes it somewhat dull sounding. Crispy highs (not in a bad way). With the low filter engaged the 1200 ends up sounding better then the other two mics for strumming within a dense mix where bass isn't needed on the acoustic. The 1200 seems to sit back a bit, which I like, especially compared to the C414uls (I find the C414uls very upfront and thus good for acoustic fingerpicking/lead but not for rhythm strumming).

ACM-6802T: Highest Output level of the 3 mics. Just slightly higher noise floor than the 1200. Bass is clearly the deepest of the 3 mics. Highs a bit too crispy in a slightly biting way. Sounds sort of out of control; too much bass and too many highs. The ACM-6802T sounds more in common with the C414 than the 1200, but it sounds like an exaggerated C414 with a V EQ curve. Might be good for sources that have too much mid-range(?)

AKG C414uls: Lowest output level of the 3 mics. Most quiet noise floor but not by much. Bass is not as low as the 6802. Has a more low-mid bass sound rather than deep lows. Much more controlled (balanced) than the other 2 mics - almost sounds like it's been compressed (in a good way). Bass is full but not out of control-ish like the 6802. Highs are crisp (as opposed to crispy), nicer than the other 2. Had the most clarity and is the most musical of the 3 for fingerpicking.

Overall, I'm not particularly pleased with any of these 3 mics for acoustic guitar. If I had to choose between the three I'd use the ACM-1200 for strumming within a dense mix and the C414uls for fingerpicking.

 

[Weasel9992]

That's a great breakdown. It's pretty much exactly the way I would put it...kinda goes the same for vocals on the 1200 as well...great in a busy mix where a vocal has to sit a little higher, but not right for the close, intimate stuff. I have an MA-200 that's killer for that.

Frank

 

[dgatwood]

Overall, I'm not particularly pleased with any of these 3 mics for acoustic guitar. If I had to choose between the three I'd use the ACM-1200 for strumming within a dense mix and the C414uls for fingerpicking.

You might dislike the sound because they're all LDCs. Most folks tend to pick SDCs for acoustic (e.g. the ACM-310) unless they're specifically going for the effect of an LDC for some reason.

 

[nuemes]

great in a busy mix where a vocal has to sit a little higher, but not right for the close, intimate stuff. I have an MA-200 that's killer for that.

Ah - I didn't think about that, yeah the ACM1200 might be just right for back-round vocals for that reason. Sounds like you're pleased with the MA-200. I've been curious about it. Where else is it getting use for you besides vocals?

 

[nuemes]

You might dislike the sound because they're all LDCs. Most folks tend to pick SDCs for acoustic (e.g. the ACM-310) unless they're specifically going for the effect of an LDC for some reason.

SM81 comparison is next!

 

[nuemes]

ACM-1200, Shure SM81 & Neumann TLM49 on Acou Gtr

ACM-1200 & Shure SM81, cardioid with roll-off engaged recording Gibson J45. Preamp is Pacifica into Lynx Aurora. Also compared with Neumann TLM49 (no roll-off).

Noise floor: most quiet on the TLM49. 1200 & SM81 shared a louder but fine noise floor.

Strumming:
ACM1200 sounds like it doesn't have as much individual clarity of strings within a chord as the SM81 & TLM49 - but in a good way (forgive me here, I lack the words to describe it appropriately). It smears the individual notes more (if that makes any sense) making for a more pleasant strumming sound compared to the SM81 & TLM49, which sound like they're trying to define each note. Really like the top end on the ACM1200 for strumming; it's not nasty or biting, in fact it's a suprisingly smooth top end for this application which I gather is not very typical within it's price range. Of the three mics the ACM1200 is the clear winner for strumming within a dense mix. It would require the least EQ and sits back farther than the SM81 & TLM49. I have been trying to find that sound for a long time. Really digging the 1200 in cardioid with low roll-off for this.

Fingerpicking:
TLM49 wins here. The most intimate, smoother than the SM81 or 1200. The SM81 also has a more intimate sound with more bass and individual note clarity than the 1200. The TLM49 & SM81 easily beat the ACM1200 in this application.

Pretty amazing. I had very low expectations - so low I waited over a month to even bother trying the mic. All the sudden the ACM1200 is my go-to for strumming on the J45. How awesome is that?

Has anyone tried two 1200's on overheads? It seems like it might be a good fit, setting the kit back from the kick & snare and handling cymbals nicely I'd guess(??)