SM Pro Audio M-Patch 2 - are they all that bad?

[Boris Lau]

Hi there,

i just got that passive monitor controller, and I'm a pretty
disappointed I have to say. The pots feel nice, but the attenuation is
very different from the scale - more like 1-2 dB instead of 5 dB per
scale step in the upper part. Also, when I turn it nearly all the way
down, the sound from the left speaker is gone much earlier than the one
from the right, seems like the stereo pot isn't very accurate.

Does anyone have the same unit? Similar or different experience? Can I
expect better quality for that price, or is it just too cheap (125 EUR)
for my demands?

Boris

--
http://www.borislau.de - computer science, music, photos

[Scott Dorsey]

Boris Lau > wrote:
>i just got that passive monitor controller, and I'm a pretty
>disappointed I have to say. The pots feel nice, but the attenuation is
>very different from the scale - more like 1-2 dB instead of 5 dB per
>scale step in the upper part.

This could be because you aren't loading it right. But it could also be
a difference in scale.

>Also, when I turn it nearly all the way
>down, the sound from the left speaker is gone much earlier than the one
>from the right, seems like the stereo pot isn't very accurate.

This is bad tracking. Send it back and demand a replacement.

>Does anyone have the same unit? Similar or different experience? Can I
>expect better quality for that price, or is it just too cheap (125 EUR)
>for my demands?

Without objective measurements, I can't tell you. But I can say that the
tracking quality and matching to the curve of the $450 Penny and Giles
pot is a lot better than that of the $2 Alps pot. But, if you go through
a bin of $2 Alps pots you can usually find some you are happy with. I
assume that at the $125 price point they went with a fairly cheap pot.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Boris Lau]

Scott Dorsey wrote:
> This could be because you aren't loading it right. But it could also be
> a difference in scale.

My Genelec 8030As are hooked up to it, and the feed is the output of my
audio interface. Should be an ok loading. Also, it's just a passive unit.
I've measured it using the Peak/RMS Meter in my Behringer UltraCurve,
which probably isn't a high precision measuring device but nevertheless.

Feeding it with -1 dB peak yields -1 dB peak, when I crank it all the
way up, fine. When I turn the pot down to -10 on the scale, I get -10.
When I turn it down to -40, I get still get -20.
Up to this point the two channels differ in 0.3dB. Below this actual
20dB of attenuation, they go apart, 15dB difference at -40dB, 30dB
difference at -55dB.
Both pots (Main and Aux In attenuation) show a similar curve, but the
sides are exchanged.


>> Also, when I turn it nearly all the way
>> down, the sound from the left speaker is gone much earlier than the one
>>from the right, seems like the stereo pot isn't very accurate.
>
> This is bad tracking. Send it back and demand a replacement.

Meanwhile I reached a the guy at the store. He said they're all that
bad, and there's a 1-in-100 chance to get a good one. So I'll just
return it.

> Without objective measurements, I can't tell you. But I can say that the
> tracking quality and matching to the curve of the $450 Penny and Giles
> pot is a lot better than that of the $2 Alps pot. But, if you go through
> a bin of $2 Alps pots you can usually find some you are happy with.

Well, even the master volume pot on my other audio interface (Yamaha
i88x) seems to be a lot more accurate. But maybe it's an unbalanced one
with a post-pot balancing circuit...

Thanks for your reply, Scott.

Boris

--
http://www.borislau.de - computer science, music, photos

[Mike Rivers]

On Apr 15, 4:20 am, Boris Lau > wrote:

> When I turn it down to -40, I get still get -20.
> Up to this point the two channels differ in 0.3dB.

I wouldn't pay a lot of attention to the numbers on the faceplate, but
that's not bad tracking.

> Below this actual
> 20dB of attenuation, they go apart, 15dB difference at -40dB, 30dB
> difference at -55dB.

That's pretty bad and certainly would be unacceptable in a device
that's used for mastering or testing, but I suspect that (despite your
expectations) for most people, having a usable volume control range of
20 dB is adequate for turning things down to determine if something
gets lost in a mix at high or low volume, and if you just want to turn
down the volume to talk to someone, it doesn't matter if the channel
balance moves off center - you're not listening for that anyway.

So you need to match the cost with the use. A $500 Coleman unit will
maintain channel balance much closer all the way down to near zero. So
will a $2500 Dangerous Music mastering monitor controller. I haven't
heard this complaint about a $99 Samson, but maybe nobody really
cared.

Something that you're probably not checking, but it's equally as
important (and expensive to do) is accuracy of the output impedance
balance. If the difference between the pin 2 and pin 3 voltages
relative to a common reference (pin 1) wanders as you turn the
control, the amount of common mode rejection will change. This can
also contribute to the wandering channel balance when going into a
differential input.

Some time before everyone discovered that a gadget like this was the
missing link in a computer-based recording setup, I wrote an article
in Recording about how to build one. Well, it wasn't so much intended
as a construction project (I don't know if anyone actually made one
from the article) as an article about figuring out how to design and
build things like this yourself.

In that article, I described a procedure for testing the dollar dual
pots available from Radio Shack so you could buy half a dozen of them,
pick out the one that tracked the best, and throw the rest away (or
return them for a refund). That's reasonable and educational on a one-
off basis but when a company has to build a few thousand units at the
lowest possible cost, they take what they can get off the shelf and
cheerfully accept returns from people who weren't bothered by the lack
of accuracy beyond a certain working range.

> Well, even the master volume pot on my other audio interface (Yamaha
> i88x) seems to be a lot more accurate. But maybe it's an unbalanced one
> with a post-pot balancing circuit...

It probably is. It's easier to get two pots to track than to get four
pots to track. However, this puts another active stage between your
source and your monitor, with its own potential for adding distortion
and noise. At least some of the outputs of the Presonus Central
Station appear to work this way.

Simply stated, the price you paid doesn't support your expectations.
Raise one or lower the other.