# MXR dyna comp



## dmm30 (Nov 6, 2011)

I've been looking into getting an MXR dyna comp pedal. 

My problem is, is that the vintage ones are way too over priced, the new reissue ones are only battery powered and over priced, but the regular cheap $80 pedal just doesn't sound as good as the others.

Are their any good clones of this pedal available?


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## sulphur (Jun 2, 2011)

I believe that these are ROSS clones.

I got one off of Jeff here...http://www.maritimeanalog.com/store...mart&page=shop.browse&category_id=27&Itemid=2
Good price, but you'll have to get a hold of him to see what's available.

It'll go from mild to squishy.


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## b-nads (Apr 9, 2010)

Check out a Whirlwind.


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## mhammer (Nov 30, 2007)

The original Dynacomp used a CA3080 transconductance amp chip. AFAIK, production has stopped on those, and supplies are dwindling (much to the chagrin of analog modular synth folks, who tend to use a lot), which results in pricing going up, and also results in manufacturers looking for adequate supply on alternative chips so that they can maintain high-volume production. In a great many instances, manufacturers have switched to the LM13600 or LM13700, or, in Boss's case, THAT chips. The 3080 was never a great chip in the first place; it was simply what they had in 1976.

IMO, the Dynacomp is a decent lower-end compressor. Most people probably wouldn't realize it but the vast majority of compressors made by every Tom, Dick, and Harry use the same basic envelope-detector circuitry as the Dynacomp. That includes the Ross and every Ross wannabe.

The Danelectro Surf & Turf and Behringer DC9 compressors are clones of the Dynacomp....and a whole lot cheaper than Whirlwind.


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## 4345567 (Jun 26, 2008)

__________


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## dmm30 (Nov 6, 2011)

I don't mind the cheaper dyna comps either but when I did a comparison of the reissue and the cheap one, the reissue is just a bit warmer and nicer sounding to my ears. I just think its a tad overpriced, but I guess it beats the $300-$400 price tags of the old ones.


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## mhammer (Nov 30, 2007)

I wouldn't make too much of the comparison between reissue and originals. You'd be surprised how often the 5% tolerance on resistors, and 10-20% tolerance on capacitors, from one pedal to the next, can alter the tone. There _can_ be differences when designs or component-values or part-sources are changed, but often what people attribute to the issue is really coming from unit to unit component-value fluctuation. Given that so very few of us will ever have the experience of sitting down with a dozen originals, and a dozen resissues, trying them all out, and listening for _consistent_ differences, over and above unit-to-unit variation, its no wonder we leap to assumptions about audible differences stemming from the issue.

I owned a late 70's MXR Envelope Filter and a mid-80's MXR Envelope Filter, though not at the same time. I liked one more than the other, or at least thought the one was better-sounding than the other. The design had remained 99% unchanged over time, EXCEPT, as I foud out after tracing the circuit for each, that MXR changed *one* resistor value. It was the resistor that set the resonance of the filter (resonance/Q was preset and not variable). In one model it was 200k and in another it was 240k, the latter giving just a tad more emphasis. So sometimes, there CAN be differences between earlier and later models.

Now, is it "worth it" to spend more time and money on scoring an earlier one? In the case of the filter, the more recent actually sounded better to my ears. But more importantly, replacing a one-cent easily-accessible component is no big deal. So, sometimes the extra time and effort for an original is worth it, and sometimes not.

The LM13600/13700 chips that so many are using instead of the 3080, are actually BETTER chips, that distort less and have lower noise; one of the reasons why the chip manufacturer stopped making the 3080s.


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## dmm30 (Nov 6, 2011)

mhammer said:


> The LM13600/13700 chips that so many are using instead of the 3080, are actually BETTER chips, that distort less and have lower noise; one of the reasons why the chip manufacturer stopped making the 3080s.


Thanks for the heads up


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## Jeff B. (Feb 20, 2010)

Yup, it is a Ross clone. Compressor's aren't something that I usually make very often. The LM1600/1700 are much better chips like Mark said. The Ibanez CP10 is a bit of an under the radar compressor that uses that chip and sounds good, you can usually find them used for about $40-60. I paid $50 for mine about a year ago. The CP-9 also used that chip.


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## mrmatt1972 (Apr 3, 2008)

The Zoom G3/G5 have a dynacomp model that is good sounding. Affordable and you get a boatload of amps and fx.


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## dmm30 (Nov 6, 2011)

I ended up buying the regular dyna comp and I love it! I've only had it a few days but it's never leaving my board.


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## Milkman (Feb 2, 2006)

I picked one up a couple of weeks ago. It works a lot like the Keeley two button.

So far I have no complaints. Certainly I like it more than some much more expensive units I've tried.


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## mhammer (Nov 30, 2007)

The differences between the Dynacomp, Ross, and Keeley 2-knob are minimal, and may really only pertain, or be useful, in certain circumstances. If you play the right style, with the right guitar, there's no reason on earth why a Dynacomp would NOT fulfill your needs admirably.

Congrats on being satisfied with your purchase, bro. Just remember that compressors make terrific clean boosters. Turn the compression down a bit, crank the output, and stomp when you want to give that amp a push.


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## Big_Daddy (Apr 2, 2009)

I have a question. What is the difference between a compressor and a limiter? I sometimes hear the names used interchangeably and often hear the term compressor/limiter. I have an old 80's version MXR Limiter (model 143) that seems to do very much what a compressor would do. Thoughts?


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## mhammer (Nov 30, 2007)

A fair question, and deserving of an answer.

Both devices reduce the dynamic range of the signal, by adjusting gain in a manner corresponding to the level of the input signal. The circuit that detects that input signal level is referred to as the "sidechain".

In the case of a limiter, the gain is adjusted only on signals that are *above* some threshold level; hence the term "peak limiter" (and if "peak" was included with "limiter", more often, maybe we wouldn't be having this conversation). The purpose of such a device has traditionally been to preserve dynamics as much as possible, but without exceeding: a) the clean headroom of the power amp, b) the headroom of the broadcast transmitter, c) the headroom of the speakers. I.E., the intent was to make sure there was never "too much".

The obviousness of limiting will depend on a) where the threshold is set, and b) the ratio of input to output. So, a ratio of 2:1 implis that if the input signal level has doubled, the gain is reduced such that the output is only half of that. If 4:1, then the output is only 25% higher if the input is 4x greater. Infinity:1 means that no matter how hot the peaks and overall input signal get, the output level is staying absolutely pegged at whatever the threshold is. If that threshold is 600mv peak-to-peak, and the input is 1.8v, the output will be 600mv. And so on.

Compression, on the other hand, adjusts gain at both ends. So, if the signal level gets too high, gain is reduced, and if the signal level gets too low, gain is increased. A compressor aims for an average signal level, with only as much deviation from that average as is appropriate in the circumstances. If your compressor has no working status LED and you want to know if it's on or not, if there is no audible difference between picking soft or picking hard, then it's working.

So far so good.

Where the two can easily get confused is when the limiting threshold has been turned way down, and the gain-reduction ratio turned way up (e.g., 8:1 or 10:1), such that the output signal seems to behave like compressor that maintains a single constant output level. When the gain-reduction ratio is turned up, but the threshold is set reasonably high, you get what some folks would call "hard limiting". That is, the input signal is free to have all the dynamics you want, except that it will never ever ever get above the threshold level.

One of the elements that tends to (but does not always) distinguish between compressors and limiters is their use of feed-*back* vs feed-*forward* control via the sidechain.

Let us say we have some gain element (and there are many different kinds, but we won't distinguish here), whose gain is controlled by the sidechain. If the sidechain detects the input signal level, and uses that to adjust the gain element, and there's your output signal, that's feed-forward. The gain has been reduced in response to a peak, but if the signal level remains below threshold for a while, there is no further gain reduction.

But what if the signal level is detected _after_ the gain element? The sidechain now feeds _back_ to the gain element and turns it down. But since the gain element has been turned down, there is now less signal to sense via the sidechain, so the gain gets increased a little. When the signal is low, or when you stop playing, the sidechain senses that the gain-reduction can be relaxed a little, so it turns the gain up. It is the use of feed-back that maintains the same average signal output level. Feed-forward control does not do anythng about low signal levels, only high ones.

I hope that's clear. certainly let me know if there are any bits still not clear.

A half-dozen years ago, I whipped up an expanded version of the Dan Armstrong Orange Squeezer that I affectionately called the Tangerine Peeler. I arranged it to be able to use feedforward OR feedback to achieve limiter or compressor functioning. Somebody else improved upon that and the ensuing discussion can be found here: http://www.diystompboxes.com/smfforum/index.php?topic=70771.0


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## Big_Daddy (Apr 2, 2009)

Great explanation! Many thanks.

Don


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