ACM & ACMP Reviews by Nuemes

nuemes

Be Here Now
So I'm starting a thread that I'll add to over the next few days as I test the gear.

I've heard there have been noise issues from some people who've gotten ACMP pre's so I've been listening carefully with that in mind.

First up: DI bass on ACMP73

Chain: Hamer American Cruisebass (very similar to Fender Jazz) > pre > Lynx Aurora 8 AD/DA. All gear racked together, on at the same time and going through the same power supply. The exact same cords were used for every single test.

Pre's tested against: Avalon M5, UA 610, Pacifica

#1: Noise/Lack Thereof
I am very happy to report that the DI on the ACMP73 is not at all particularly noisy, in fact it is quiet. With the bass plugged in and no playing, the least noisy to most noisy was as follows: Avalon M5, UA610, Pacifica (no pad), ACMP73, Pacifica (with pad, gain nearly maxed). The difference between these was minor (except w/ the Pacifica pad engaged, gain maxed). DI noise is not an issue for the ACMP73 I received.

#2: DI Sound
The ACMP with or without EQ engaged sounded the most like an amp compared to the other preamps. It has more color - I want to say midrange definition - than the other 3 pre's. It sounds big and frankly has balls. The M5 & UA610 sound refined compared to the ACMP73. The ACMP73 has distortion but still excellent clarity for the purpose of a bass DI, if that makes sense. The closest I could get to the 73 sound was by engaging the pad on the Pacifica but even then the Pacifica wasn't nearly as good as the ACMP73. The ACMP73 does not have the extreme deep lows of the Avalon M5 but that's fine with me for a bass DI; I like the kick to be way down there rather than the bass. I gotta say it: I was expecting to be heavily disappointed and holy Chinese preamps Batman, this is now the best bass DI I own.

So I'm expecting to wake up tomorrow to find out my ears were just bad today, or that some nasty noise will suddenly appear, or that it will break. Considering the ACMP73 cost less than a typical low end bass DI and sounds better than those as well as the ($800+) preamps I own (at least in regards to a bass DI), I am cautiously very, very impressed and damn happy that I've got a tool that will get use on every bass session.

Chance, you've heard it a many times but once more: thank you for making this opportunity available.

Mind you, I'm going to post a lot more tests on this thread. So far so good :)
 
ACMP's on Kick Drum

ACMP73 & ACMP84

Mic: RE20, just outside the kick aimed at beater.

All pre's (ACMP73, ACMP84, Avalon M5, UA160 & Pacifica) sounded good on kick. Each is useable. Without the EQ engaged (and without someone kicking the beater), the order from least noisy to most noisy: Avalon M5, UA610, Pacifica, ACMP's. Very slight difference, not enough to matter.

So here's the deal: once I set the EQ on the ACMP84 (I didn't try the EQ on the ACMP73) I dialed in a kick sound on first try that easily beat out all the other preamps with ease. Likely the best kick sound I've gotten as of yet. As far as kick goes the EQ on the ACMP84 sounds better than any plugs I have.

However, once you engage the EQ a noticeable noise floor appears. It sounds similar to me like the hiss you'd hear with tape. It's not terrible but it's definitely there. And imagine with compression...ugh.

For some perspective I was watching The Charlie Brown Xmas Special with my son for a few minutes tonight. The recordings used on the show have noisy snare brush strokes with a big tape hiss noise floor.

There's clearly a trade to make. If you already have a good outboard EQ then there's no need to use the EQ on the ACMP84. In my case I'll likely take the chance as I've no other hardware EQ. Will require the context of a mix to know for sure.
 
For some perspective I was watching The Charlie Brown Xmas Special with my son for a few minutes tonight. The recordings used on the show have noisy snare brush strokes with a big tape hiss noise floor.

That hiss probably is the snare brush strokes ;) The Vince Guaraldi Christmas album is pretty noisy, but when the snare brush strokes start, that's above the level of the tape hiss. For example, on the first tune, "O Tannenbaum", the tape hiss limits the dynamic range to about 50dB, but the snare strokes are about 10dB louder than that when they come in about a minute into the track.

Either way, the tape hiss is objectionable by modern standards throughout the entire recording. A lot of old jazz records are like that, unfortunately, and modern remasters don't seem interested in removing even some of the noise.
 
I love the old tape hiss on those lazz records. I would hate it if they removed it. :)

Nuemes, did your great kick sound come with EQ engaged or not.

BTW, thanks for the great reviews.
 
I'm on board to follow your tests.
So far I have only the AMCP73s (4 of them) but and have compared them to RNPs, DMP-3s and ART MP(Pro?) On drums I dialed in a really nice Snare sound with a SM57 I could never get equing after the fact, the Kick has Balls for once. I used the 73 on my Neuman TLM-49 and modded T-3 and the voices came out punchier and beefier than my other pres.

I have yet to use the DI but hopefully this weekend.
My pres are as quiet or quieter than the DMP-3s and RNPs.
 
My pres are as quiet or quieter than the DMP-3s and RNPs.

The spec on the AMCP stuff is -120dBu vs. -128dBu for the DMP-3. The noise of a particular mic might cause the preamp noise floor in either case to be inaudible. But I don't think one could conclude the ACMP was as quiet or quieter, at least without taking a comparative measurement.
 
Nuemes, did your great kick sound come with EQ engaged or not.

The kick sound I liked most was the ACMP84 with the EQ engaged. I just dialed in what I typically do with an EQ plugin and the first try sounded excellent - it will get better once I really have time to sit down and get some practice with it.

The caveat though is once you engage the EQ a noise floor becomes clearly evident. Again, not terrible but not so great either. Assuming this gets regular use on kick it will be compressed coming out of the pre and that's going to bring the noise floor even higher.

I've only fiddled with it for a few hours so far though. Will try elec guitar and snare tonight.
 
The spec on the AMCP stuff is -120dBu vs. -128dBu for the DMP-3. The noise of a particular mic might cause the preamp noise floor in either case to be inaudible. But I don't think one could conclude the ACMP was as quiet or quieter, at least without taking a comparative measurement.

I was only making the generalization that using the same mics on the same sources, I could not detect that the acmp 73s were any noisier than the aforementioned pres. I was not attempting to prove or disprove anyones specifications with any exacting measurements.
Since some folks had complained of certain of the group buy units being noisier than others of even the same variety I was simply making the observation that none of the group buy pres I got exhibited an unusual noise problem.

If anyone was going to base their purchasing decision on my statement thinking I was saying the 73s were quieter than a DMP-3... please forgive the error.
 
No need... We can just market the ACMP 84's as having a tape-hiss-simulator function!:rolleyes:

Yeah, but my plugin would be free! And I think I can deliver it later tonight ;)

If you want, I can add a variable hum control, and maybe some second-order harmonic distortion too . . .
 
I was only making the generalization that using the same mics on the same sources, I could not detect that the acmp 73s were any noisier than the aforementioned pres. I was not attempting to prove or disprove anyones specifications with any exacting measurements.
Since some folks had complained of certain of the group buy units being noisier than others of even the same variety I was simply making the observation that none of the group buy pres I got exhibited an unusual noise problem.

If anyone was going to base their purchasing decision on my statement thinking I was saying the 73s were quieter than a DMP-3... please forgive the error.

Well, there is hiss and then there is hum. Hum is usually not part of a noise measurement (even if arguably it should be), because test conditions will generally eliminate induced hum as a noise source. If the hum is internal, I dunno, that would be an unusual thing to test without correcting first.

Anyway, the mic connected is critical. In fact, a noise measurement is done without any mic attached, just a dummy 150 ohm source. This is because condenser mics, for example, have their own noise floor. If that noise floor is much higher than the two preamps under comparison, you won't hear the noise floor of either preamp, no matter how different they are.

Try something like a 57 on a normal vocal, with both pres set to the same output level (if the ACMP pre output level control has a marked unity gain setting, set it there and match gain with the input gain control). That should give a more accurate comparison of noise.
 
Chuck (zmix) mentioned on another board (he is the one who discovered the wrong transisters in the schematic) that after working the pots, the noise clears up. He said that there is a lot of anti-corrosive compound in all the pots
 
Ok, I'll take one! I've already got the Ozone Vinyl freebie, so the Naiant Tapehisserizer would be a cool addition.:D

Yeah, but my plugin would be free! And I think I can deliver it later tonight ;)

If you want, I can add a variable hum control, and maybe some second-order harmonic distortion too . . .
 
I have been able to formulate a plugin that converts your track to total silence. It simulates recording in the 1700s - very vintage (and you can go for even more authenticity by memorizing the track prior to applying the plugin, and later vocalizing what you can remember from the track)

Nuemes - will we get samples?
 
Here y'go:

ACVST

On time and under budget!

Functions:

Buzz: adds 60Hz hum with lots of harmonics! If there is demand, I will do an international version at 50Hz :p

Distort: adds distortion (duh). Mostly second harmonic up to about 1/3 the knob; above that higher order distortion grows rapidly.

Hiss: adds hiss!

Pop: does nothing unless in the midrange, where it will drop out all audio and replace with a constant stream of maximum values. WARNING! This control may cause a nasty pop if operated, and if left in the midrange, will cause illegal output to your converter, potentially destroying headphones, amplifiers, speakers, and your ears! USE AT YOUR OWN RISK!!!
 
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