Manley_Variable_Mu®_Limiter

Manley Stereo Variable Mu^® Limiter Compressor

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Variable Mu^® Limiter Compressor Owner's Manual
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READ ME: WHICH LIMITER SHOULD I BUY????????????????

The MANLEY VARIABLE MU^® LIMITER COMPRESSOR has been our best selling product for many years. It is one of the very few compressors that has become a real standard in Mastering studios and contributed to most hit records over the last decade and probably the next. "Mu" is tube-speak for gain, and Variable Mu^® is our registered trademark for this limiter compressor. It works by using the "remote cut-off" or re-biasing of a vacuum tube to achieve compression. The precious vintage Fairchild 670 also uses this technique and is one of few all-tube compressor to do so, that we know of. Even the side-chain has glowing rectifier bottles. How’s it work? The unique 5670 dual triode is at the center of the peak-reducing and compression action constantly being re-biased by the vacuum tube rectified side-chain control voltages which cause this tube to smoothly change its gain. Just like that.

The COMPRESS mode is soft-knee 1.5 to 1 ratio while the sharper knee LIMIT mode starts at 4 to 1 and moves to a more dramatic ratio of 20 to 1 when limiting over 12dB. Interestingly, the knee actually softens as more limiting is used. Distortion can be creatively used by turning up the Input and turning down the Output while using very little or no compression. See the gain reduction curves here!

You might notice that the Variable Mu^® Limiter Compressor has a ganged input control, but do not jump to conclusions that it is mono-unfriendly. Track away! There are separate threshold and output controls to make compensations with plus you can always adjust your individual source levels elsewhere, right? The advantage of the stereo input control becomes dramatically clear when you switch to LINK mode, and that’s what our Variable Mu^® Limiter Compressor does better than anything else: final mix, 2-track, or mastering limiting and compression. Like one reviewer put it: “It’s like pouring a bowl of sweet cream over the mix.” Mmmmmm. Yummy. Give your music a big hug.

Manley Variable Mu® gutz 2004 production:

Click on the picture for a bigger view.

Note 12/2009: The High Pass Side Chain option is now a STANDARD OPTION on all Mastering Versions or Normal Version Variable Mu limiters.

ELOP^® Limiter or Variable Mu^®Limiter Compressor? Which one is for me? Read this.

The Manley Variable Mu^® Limiter Compressor Owner's Manual is available on-line. Go read it at:

Proudly from our beginning, we at MANLEY LABS have been closely involved with numerous mastering facilities around the world. For these most demanding engineers in our industry, we have created specialized products such as our all-tube tape repro head amps, digital converters, high-powered vacuum tube monitor amplifiers, through to custom monitoring consoles, all the way up to complete facility design and installation.

The Mastering Version of our Variable Mu^® Limiter Compressor incorporating detented and logable steps built with 1% metal film resistors on sealed gold-contact Grayhill switches may be custom ordered for an additional $1000 NET added above base cost. NO, we will not mod a "normal" unit to the Mastering Version.

Yes, the newer units use the 5670 tube instead of the 6386. By now the availability of the original USA GE 6386 is poor; we don't have any left at all, and what we do have are not usable due to noise, microphonics, bad side-to-side match, etc.

Does the 5670 sound different? Well, up to about 6db of limiting it's about the same. After that point, the 5670 version tends to sound more "squashed" than the original 6386 version. Some like it better, some don't-- depends on what you're trying to do. To solve all these problems, Paul came up with a really good solution: the T-Bar Mod which uses a pair of 6BA6 pentodes wired as single triodes to replace each dual triode 5670 (or 6386). the 6BA6 TBAR Mod is the preferred system to use in the Manley Variable Mu® for reasons of ability to perfectly match each phase-halve section and each stereo set, ability to select for lo-noise and lo-microphonic sets for a low cost, and because the action of the 6BA6's so closely resemble the smooth 6386 limiting curves.

Read more about Paul's special T-Bar Mod here.

Follow the directions below to convert your 5670-powered Manley Variable Mu® to use the 6386 tubes. It's more work to do this than to install our 6BA6 T-Bar mod kits which we charge $250 for (complete and installed with four 6BA6 tubes selected for quad-perfect matching, lo-noise, and lo-microphonics).

If you want us to convert your unit for you, we can. You'll be supplying the 6386 tubes and we will all pray to the Tube gods that they are quiet and internally matched. Maybe buy extras to be sure. Check out our service page for rates and then fill in the RA form to book the service and you can work with Paul on that.

INSTRUCTIONS FOR CONVERTING 5670 TO 6386

1) Replace 3K57 resistors connected to pins 4 & 6 of 5670 socket with 6K8 1W.

2) Replace 1K resistors connected to pins 2 and 8 with 511 ohms.

3) Replace 10K “balance” trimpot with 500 ohm trimpot.

4) Remove 200 ohm resistor between pins 2 and 8.

5) Replace 33K 1W resistor between wiper of “GR cal” trimpot and the junction of the meter with 22K 1W
(resistor is located near the rear corner of the pcb next to the GR cal trimpot).

6) Repeat procedure for the other channel; re-calibrate as outlined in the owner’s manual.

Question: What is the difference between turning up the INPUT level control to drive
the unit into limiting with more level versus using the THRESHOLD control?

The limiting characteristics shouldn't change much, but the distortion
characteristics will. The input control on these units is located ahead of
the tubes, directly "behind" the input transformer. So as you advance the
input control, you're hitting the input tube (which is the gain-varying
stage) with more and more signal. Gain reduction is done by making the DC
bias on this tube more negative (the threshold control determines how much).
The tube has a limit as to how far it can be biased negative to reduce gain
before it goes non-linear, and since your audio signal is obviously
swinging both positive and negative, the big swings of the audio signal plus
the negative gain control voltage will eventually push the tube into the red
zone. Tubes like the 6386/6BA6/12BA6 can be pushed a lot farther before
the THD builds than tubes like a 5670. Higher signal level also pushes the rest
of the tubes and the output transformer harder, which will change the sound character as well.

You've probably heard someone say, "You've gotta get the Manley compressor." Now you've found out we make two completely different stereo units yet each unit has its own following. (And then there are the fanatics that own both of 'em...) But when you can only get one, the choice really depends on what you need a dynamics processor for. If your requirements include compressing your 2-Buss, drums, or making this your day-to-day compressor, the Variable Mu^® Limiter Compressor is your clear choice. Why? Because when used more than a few dB, the ELOP^®Limiter's fast attack time will want to grab fast transients first (like drums) from a mix and throw them back into the next room behind the speakers. The Variable Mu^®Limiter Compressor has adjustable attack and release which have optimised settings for mixing and mastering but are flexible enough and also go fast enough for most tracking situations. This makes the Variable Mu^®Limiter Compressor one truly versatile machine.

You might think having every control in the world is what you need, but if recording vocals is your main focus or if you're doing live work, your goal is to be ready not to miss 'that moment'. The ELOP^®Limiter is ideal for recording and tracking because it is incredibly easy to use, and hard to get it wrong. It seems to do the right thing at the right time-- no regrets. Peak limiting of individual instruments especially vocals, room mics on drums, and good ol' mega-squashing effects are the daily duties of the ELOP^®Limiter.

The most common mistake most people make when buying a compressor is getting wrapped up in specs and theory. Remember, that the real goal is cool music and great sounds, not knobs and numbers. Time to stop thinking and start listening!

If you are not sure what you have: The incandescent lamps are yellow-ish in color. The LED lamps are blue-ish white in color.

Yes, that is correct. The controls on the Mastering Version are switches instead of smooth pots. Note that the RANGE of operation is less on MASTERING version, and the ATTACK times go slower because it is a dedicated Mastering Unit.

2a. But can I use Variable Mu^® mastering version for recording/tracking voices, drums, guitars, strings, etc.......?

Yes, but note that the RANGE of operation is less on MASTERING version, and the ATTACK times go slower because it is a dedicated Mastering Unit. Therefore it might be advised to stay with the regular version if you expect it to be fully versatile for all jobs tracking, mixing, mastering. Many mastering engineers use regular version anyway.

2b. Question: Do you also put some extra markings around the Mastering Version
knobs in order to make it look more "dense" or is it just more "clicks" with the same markings?

Yes, Extra markings, custom engraved. We generally label each dB step and use a
line for the 1/2 dBs between. It's easy and clear.

Hi,   I am considering purchasing a Variable Mu^®Limiter Compressor
(albeit sometime in the distant future when I've saved the cash).
Anyway, I know that attack times for tube designs tend to be quite slow.
However, the quoted attack times for the Variable Mu^®Limiter Compressor
in your brochure (25ms - 75ms) seem particularly slow. Or
least when compared to the times I've seen quoted for most other compressors
(including optical and variable-gain devices like the EAR 660). Am I right
in thinking that the attack times for the Variable Mu^®Limiter Compressor were
measured for the compressor to achieve a predetermined amount the gain reduction?
Is it likely that some of the other compressors' attack times that I've seen are
based on the time taken for the onset of compression instead of a set amount
of GR.
    I would also like to take this opportunity to ask if you are familiar
with the Cranesong STC-8 Compressor. I am currently using one of these as
my only compressor and am interested to know how/or if the Variable Mu^®Limiter Compressor
will complement it. The STC-8 is a firm favourite of mine for bass and I aslo
like it on vocals. I would mainly like to use another compressor (i.e. the
Variable Mu^®Limiter Compressor) for hip-hop/house/funk style drums, both individually and
sub-mixed. So the range of attack times are of particular interest to me. I
have no real interest in mastering or compressing my finally mixes.
Obviously it would be easiest for me to just listen to one. However, no
local shops have demo units and it wouldn't be fair to ask them to get one
in for me to listen to until I have the cash.
Any info you can give me would be much appreciated.
Cheers,
Ben Williams

Hi Ben

I can try to answer your questions, but there are not really pat answers.
Bottom line, you just have to try it and find out if it works for you.

1) The way the Variable Mu^®Limiter Compressor is designed,
each release setting uses a different capacitor, which means attack is release dependent.
2) Dave Collins, the famous mastering engineer measured the timing many
years ago, without the knowledge of "item 1", and because at the time, he
had an Audio Precision test rig and we didn't. We use his numbers. We are
not sure how he based his measurements, but we assume they are rough at best
and nobody would understand the real numbers anyways.
3) We do not know how other companies base their measurements as there is no
real "standard" to specifions of attack and release times, etc, and it is
not a simple topic except in simple cheesy units. For example both the STC8
and Variable Mu^®Limiter Compressor use multiple attacks and releases
(simultaenously) and ratios tend to be a curve.
4) The STC8 is known as one of the best and fastest dynamics units. You
won't find much faster or more versatile.
5) With designs similar to the Variable Mu^®Limiter Compressor, very fast attacks are related with pops
and thumps, so I would take other attack times in similar units with a grain
o' salt, or understand there has to be non-musical side effects.
6) If you want very fast attack times, the SLAM!^® is shipping and
should be appropriate for your needs. We used drum CDs to develop it.
Again this uses a complex sidechain with at least 4 time constants in use,
so attack and release time ranges won't help you or others come to a conclusion.
7) The Variable Mu^®Limiter Compressor is used on more than 90% of
mastered music, and tends to simply make music sound better.
It is not a generic compressor that can really be
compared to anything else, in use or on paper. If it was, it would not be as
widely used as it is, and other compressors would be a valid substitute.

4. Question: I've heard that you may put some different
(non standard) tubes in to the Variable Mu^® to make
it sound a little thicker in the low end. Tell me about that?

Rumors that the Variable Mu^® is somehow lacking in the lows may be traced
back to some outlandish web posters who originally said it to be
controversial, and it was! If one wants to get attention on the web, a
proven way is to squawk about the most respected stuff or challenge digital
theory. Its that or open heated discussions about politics or religion.

Actually, the problem stemmed from operator error in the hands of a guy who
is just occasionally an engineer. Most of the recognised mastering engineers
use the Variable Mu^® daily, and in all its variations so it can't be that significant
of a problem, right? Any box can be pushed to sound bad which is what the
better engineers avoid. The truth is that the Variable Mu^® adds a special flavor to a
mix that nothing else does, the way that most use it which is just 1 or 2 dB
of compression. It still is the standard for mastering after many years.

5. Question: Can you please let me know if that would be of some benefit for me
in mastering and what tubes exactly these are? Is it at extra cost?

We have used 3 different tubes in the Variable Mu^®, the first one, the 6386, is almost impossible
to get now, the second, 5670, was a reasonable replacement but suffered a bit when
pushed beyond 6 dB of compression, and the third tube type actually uses two tubes to
replace one of the above, but duplicates the original action when pushed
hard. So we designed an adapter called the "T-Bar Mod" so that those two
tubes just plug into the original socket meant for one tube. We can also
select among tubes for best matching. The mod adds $250 to the NET dealer cost.

6. I see an older unit for sale. How do I know which version it is?

Here is the Variable Mu® Identification guide to previous versions.

7. Question: What is the real difference in quality between these and the standard versions?

At normal mastering settings the differences are very subtle, but given that
the T-Bar mod is not expensive, I do recommend it, especially for the
occasional time when some deep compression is demanded from it. The best
advice is to experiment with input and output levels once you get the Variable Mu^®
(including externally) because it is about finding the sweet spot for you.

There is also the "M/S" mod that some mastering guys like and others prefer
to do in digital.

7. My Variable Mu started blowing fuses! Help!
Unplug the unit and remove the top cover. Look for the 22uF 450V axial capacitor at the back on the power supply board as pictured below. The cap might be dark blue or even light blue. Clip one of the legs off with wire cutters and see if you can now power up the unit. Congrats: you have diagnosed a bad shorted-out cap and now you can replace it, paying attention to observe correct polarity when you solder in a new one. Bend it away from those hot resistors so the resistors don't cook up your new cap..