Compressors

[kurtlives]

I want to build a compressor soon but I don't know which one to build. The Orange Squeezers seems simple and good. I hear it is noisy though, is this true? I am not a huge compressor guy so something simple would probbly be good.

What builds would you suggest and why?

Also are the layouts on this site verified? http://www.indyguitarist.com/torchy/

Thanks

[oldrocker]

I have never heard that the OS was noisy.  Hmmm.  Mine is quiet.  How it is used might make it noisy sort of.  If it's used after heavy distortion it might be perceived as noise although it's the gain of the distortion pedals not the OS.  Mine is transparent but very effective.

[kurtlives]

So you like yours? I heard it adds a bit of gain.

[Mark Hammer]

"Daddy, why is the sky blue?"

Okay, for the one zillionth time (and no slight against you; maybe there just ought to be a sticky at the top of the list regarding "Why compressors are so noisy").....

Compressors turn the gain up as far as they "think" they need to.  As the signal gets lower the gain gets turned up more.  As the signal gets stronger, the gain is turned down.  By doing this (more gain for quiet parts, less gain for loud ones), it produces a fairly constant-level signal that sounds like it is sustaining longer because there is less contrast in volume between the initial attack part of the note when you pick it, and the parts that follow later.

The problem with this strategy is that, unless exquisitely designed, the compressor has no native capacity to differentiate between noise and quiet playing.  So, when you stop playing, it treats that like a very very very soft passage, that requires lots and lots and lots of gain to achieve the desired level.  If the circuit is flawlessly designed and you feed it an absolutely dead quiet signal, applying 20db of gain will not increase noise levels appreciably.  If you feed it a signal from a poorly shielded instrument, standing under a fluorescent fixture, beside a television, with single-coil pickups, chances are it will interpret the hum it receives as desparately in need of "help" and will boost that hum.  If you plug your guitar into a fuzzbox that is hissy, and then into a compressor, the moment you stop playing, the compressor will behave as if that hiss desparately needs assistance to be heard and will boost it accordingly.

So, grasshopper, the issue is not the compressor itself.  It is merely following orders.  If you wish it to be quiet and noise free, the lion's share of what you can do to achieve that is simply feed it the cleanest signal you can, and apply only modest amounts of compression unless otherwise required.  There are probably some additional steps you can take, such as op-amp choice, using metal film resistors, shielding input leads, and so on, but those are just icing on the cake, and not the cake itself.

The two most-frequently built compressors are the OS and Dynacomp/Ross.  Both are excellent.  Both are subject to noisiness is misused/misbuilt.  Both can be suitably modified.  The OS is cheaper to build by a factor of maybe $4, but requires some set-up, and sometimes people get the FET orientation wrong.  The Dynacomp has a more "classic" sound, stock, but may require sending away for some parts.  I suppose people can get a bipolar transistor orientation wrong too.  They both have their issues as far as debugging goes, though no more than anything else I suppose.  All in all, though, I think I'd recommend an OS simply because it is a bit easier to modify and experiment with (including adjustment of gain).  Not dramatically so, but enough to matter.

[kurtlives]

Thank you very much.

Do you have a vero layout for the Dynacomp?

[oldrocker]

I use a noise suppressor to cut down on the hiss when I use a compressor after high gain distortion.   But when the hiss is too loud the suppressor threshold has to be set too high and may effect sustained or held chords and notes that you want to ring out.  Like Mark H. stated you have to work with the nature of the beast.  If a compressor is used before other pedals it will work good but may not achieve the heavy compression sound you were trying to get with your distortion.  So a compromise may be in order.  Personally I mostly use a compressor with clean guitar and bass so it's rarely an issue.

[kurtlives]

Ya I would be using it for cleans and it would be at the begining of my chain so I don't think that would be an issue.

Also how do you sheild jacks?

[Zben3129]

I personally own a dynacomp and a boss Compressor. I love both, but  I  think the dynacomp is better.

Its like vanilla ice cream, french vanilla, creamy vanilla, or vanilla bean. There all sick, but some people like french vanilla, some like creamy.

Its all about taste (pun maybe intended

[Electric_Death]

Mark that was about the best explanation to compression I've read yet.
Gave me a great idea for a compressor circuit name..now all I have to do is design one from scratch 

I was thinking though, why not just avoid the conflicts between design and desired results with a compressor and instead just achieve flat frequency response with some clean gain to thicken things up?

[pahurst]

Just a quick note:  No good compressor, with quality parts, is considered noisey!

The Orange Squeezer clone sounds 100 times better if you use the original Raytheon 4558 metal can chip.  It can probably be a newley made one!  Most clone companies use that Tube Screamer plastic chip (4558D), and it just doesn't give it the magic the raytheon metal can does.  That twangy country, or Dire Straits sound!

Alot of people go for the metal film parts, reading that they are the best and quietest, but I think it's a mistake!

Metal film parts are the quietest, but they add a screachy high end to the sound, that hurts my ears.  So, I'd rather have good tone, with maybe a tiny bit of noise,----using old parts (such as Carbon Comp resistors).  The difference in background noise between metal film and carbon whatever, is not enough to bother yea. However, the change in tone is!

[Headshot]

Any idea where you can buy the metal can 4558s?

[Mark Hammer]

Just a quick note:  No good compressor, with quality parts, is considered noisey!

I don't think I would agree with that.  There are concrete limits to what you can do with a simple design such as those found in stompboxes.  The chief problem that makes floor-pedal compressors inherently noisy is not the quality of components used (though better-quality components is usually a preferred choice), but the fact that they do not discriminate the content of the signal, only its level.  I'm fairly confident that a compressor made with consumer-grade 5% resistors and garden-variety op-amps could do an extremely pleasing job in providing quiet compression if it could tell the difference between a low-level input signal that had something of use in it, and a low-level input signal that was made entirely of hiss and hum, and adjusted the gain differentially depending on which of those two scenarios arose.  You're unlikely to get that for under $200 in a floor box, though, especially if you want it analog.  MAYBE digital, but we're not there yet.

The Orange Squeezer clone sounds 100 times better if you use the original Raytheon 4558 metal can chip.  It can probably be a newley made one!  Most clone companies use that Tube Screamer plastic chip (4558D), and it just doesn't give it the magic the raytheon metal can does.  That twangy country, or Dire Straits sound!

Alot of people go for the metal film parts, reading that they are the best and quietest, but I think it's a mistake!

Metal film parts are the quietest, but they add a screachy high end to the sound, that hurts my ears.  So, I'd rather have good tone, with maybe a tiny bit of noise,----using old parts (such as Carbon Comp resistors).  The difference in background noise between metal film and carbon whatever, is not enough to bother yea. However, the change in tone is!

This is also something that I treat skeptically.  I'm not saying your claims are BS.  People hear what they hear and sometimes things provide a very pleasant surprise.  But such claims as you make tend to arise out of circumstances where many things may be subject to change, not just the component in question.  "But I did the A/B comparison, just swapping out that single component!" you say.  Sure, but is the rest of the circuit identical to what *I* would have in my pedal?  After all, those components all have their tolerances, ages, etc.

The question then becomes not whether YOU heard something objectively that was a decidedly audible imporvement, but whether the effect of that specific component change is so robust as to make an easily audible difference all the time for anyone regardless of what else people may have used/done or not used/done.  I mean some people really DID recover from cancer using peach pit extracts, but a whole lot never did and never would.  Many of the recommendations for component changes that people can make may well be based on an empirical observation, but unless what happened in their case happens all the time, it simply turns into more mojo.

I'm not trying to smack your wrists in public here.  Rather, it is one thing to stumble onto a component change that makes a difference in your case, and quite another to make a recommendation that could reliably make a difference for anyone and everyone, unless there is some clear theory-grounded basis for it.  In the case of the OS, there is simply nothing that would permit a single component to single-handedly overcome all the noise challenges such a simple design faces.  If I'm wrong, I'll gladly accept it, but I don't think I'm wrong.

[JDoyle]

..now all I have to do is design one from scratch 

Or seeing as engineers have been trying to do this ever since they realized that the beautiful gain they were getting from their new fangled tube/transistor/magneto/stone amplifier could become significant enough to fry anything following it, which was normally a rather expensive hunk of iron, they then needed needed a way to get the most gain they could without getting too much. Thus was born the limiter to keep it from going over the damage threshold and the compressor to keep it just under the damage threshold.

In other words, look around, someone already sliced the bread, you've just got to make the sandwich...

I was thinking though, why not just avoid the conflicts between design and desired results with a compressor and instead just achieve flat frequency response with some clean gain to thicken things up?

Because that is a boost, not a compressor.

Like Mark said, a compressor makes sure that it's output is always at the same level, independent of the input voltage. So by inference the gain of the compressor has to change proportionally to the input voltage. So in your example, a small signal like the noise on the input, and a large signal like the signal from your guitar, both get the same amount of gain; but in a compressor the small voltage, Vsm, and the large voltage, Vlg, both INDEPENDANTLY get the amount of gain that will put them at the voltage the compressor wants them to be, Vcomp.

So:
(A x Vsm) = Vcomp = (B x Vlg)

Where Vsm<Vlg and A is the small signal voltage gain and B is the large signal voltage gain. Obviously, the gain has to vary from a larger value when the input is Vsm to a smaller value when the input is Vlg.

Generally, upward compressors have a gain that reduces from the maximum for no input signal to 1 when the threshold voltage is met, downward compressors have a gain that reduces from 1 when there is no input signal down to zero when the threshold is met and dual mode comps do both.

Regards,

Jay Doyle

[JDoyle]

Just a quick note:  No good compressor, with quality parts, is considered noisey!

I'm not as diplomatic as Mark. First off here you have four undefined terms:

"Good": does this mean it sounds good? It preforms the compression well? The compression is at a reliable ratio vs. control current? That the conttrol voltage causes minimal offset? Noise? Feedthrough?...

"Compressor": Upward? Downward? Studio? Stompbox? At 9V or 30V? Feedback or parallel? Level dependant attack/decay? Log/Lin ratio of gain/CV???

"quality parts": In relation to all parts in general or parts for the design? Does that mean that the specs are standardized within the part line or that the parts are considered 'optimized' (and by whom?) for guitar effect use? Or audio use? Or high frequency use? Does 'quality' relate to temp co. or some other variable such as offset voltage? (In general the mil. spec. part will be considered higher quality, but the difference is normally temperature range. This matters much more in the dynacomp/ross than in the OS, where offset is going to be more important)

"noisey": Even completely ignoring your qualifier of 'considered' this is still extremely subjective and begs a comparison. Do you mean noisey when compared to the clean signal? Or noisey when compared to a distorted or amplified signal? Or noisey vs. a chorus/flanger/EQ/whatever?

The Orange Squeezer clone sounds 100 times better if you use the original Raytheon 4558 metal can chip.  It can probably be a newley made one! Most clone companies use that Tube Screamer plastic chip (4558D), and it just doesn't give it the magic the raytheon metal can does.  That twangy country, or Dire Straits sound!

Unlike Mark, I've got to call this BS. The chip inside the metal can is the same as the chip inside the plastic DIP. Both were created using the planar process, which is a lot like the way we etch boards. Both have a layer of SiO2 covering their surface and both have the PN junctions buried beneath the oxide never touched by human hands, or any other contaminate for that matter. Can or no can, glass (SiO2) is one of the best insulators known. The ONLY difference is in the fact that the 'can' itself can (and in most cases, should) be grounded, which could lead to a little better shielding for interference... Which is redundant and useless if the circuit is already surrounded by a grounded metal enclusure, which if you put the circuit in a Hammond BB, it is.

This is complete and total mojo and while the opamp in a can may actually sound better to you or anyone else who hears it, it has nothing to do with the can but more to do with the individual device's variables in relation to the plastic chip's variables. I bet you could find a plastic DIP version that sounds exactly like the can version, if you can find one with the same variations...

Alot of people go for the metal film parts, reading that they are the best and quietest, but I think it's a mistake!

Metal film parts are the quietest, but they add a screachy high end to the sound, that hurts my ears.  So, I'd rather have good tone, with maybe a tiny bit of noise,----using old parts (such as Carbon Comp resistors).  The difference in background noise between metal film and carbon whatever, is not enough to bother yea. However, the change in tone is!

Again, you are ascribing differences in physics to differences in tone. Resistors don't have a sound, they have a reaction to the voltage across them and the current through them. Noise is a fact of life in analog electronics. We can reduce it's effect and influence on the signal and the associated functions but we can't eliminate it altogether. But we also have to understand what noise does...

Noise is an error voltage. It is wideband so it can not be reduced with a filter but it primarially occurs below the notes of a guitar but still within audible range and in the upper register of the hearing range. Most importantly it modulates our signal. It adds itself to our signal. Which means the gain of any amplifier that handles our signal will be reduced by the error induced by the noise. Reduce the noise, reduce the error, increase the gain of the signal where the noise was reduced. Our guitar didn't put out any signal where the low frequency noise occured, so that appears to reduce the noise without affecting the signal. But in the upper register, where the harmonics and individual tone of our rig occurs, the reduction of noise has increased the gain with has boosted the high frequency response. Therefore it sounds 'brighter'.

SO: metal films don't make the tone sound brittle/bright/sharp, they reduce the high frequency gain error of the ampilfier thereby increasing the gain of high frequency components and bring the amplifier response closer to ideal.

So that tone you don't like with metal films? That actually IS your tone! Use metal films and drop in some 100 pF caps to ground around the circuit, that should get you where you want to be...

Regards,

Jay Doyle

[Mark Hammer]

Umm, and in case it got missed somewhere in this set of lengthy responses to your SECOND POSTING HERE, welcome! Hope that, if not immediately, you can find this as hospitable and helpful a forum as many have found it to be.

[MartyMart]

I've found that a good all rouder that works well and is simple, is the "Flatline" comp.
It uses an LED/LDR so is an "opto" compressor, they seem to be good to me.
SEARCH forum for the posts/schem and a vero layout
Mine gets used all the time.
MM.

[aloupos]

I built an OS some time ago, and use it in the last position on my peddle board (after my Fuzz Factory and DIY shredmaster).  The noise level is acceptable, in that there's some hiss, but when I'm not playing I lower the volume with a volume peddle.  When the band is playing, it's definitely not perceivable by me, band or audience.  It's doing it's job, making soft sounds louder -- although not as aggressively as I'd like. 

My problem with the OS is that I can't seem to get the compression aggressive enough without adding more gain than I want to -- pushing the 4558 too hard and adding clipping which I don't want from this circuit. 

Is the flatline comp more aggressive?  I was thinking of trying it. 

[d95err]

My OS build was very noisy and distorted way too much at first. Two simple mods fixed this:

1. Added a filter cap (100uF or so) across the power supply. This reduced hum significantly when using a wall wart instead of a battery.

2. Used a 5532 opamp instead of a 4558. This reduced noise and distortion a lot.

The result is great. It has a lot more personality than other compressors. I love the one-knob user interface as well. It adds a little bit of grit, so if you're looking for that ultra-clean compressor-chorus-delay sound, this is NOT it.

[MartyMart]

Is the flatline comp more aggressive?  I was thinking of trying it. 

Yes, has a good range from quite subtle to "squeeze the shit out of the signal"  !!
I don't find it noisy at all and the vol output is big enough to drive a valve amp too ... useful !

[Mark Hammer]

Though there are multiple ways of using them, compressors using FETs generally use them as attenuation (volume reduction) elements.  As such, they have to be able to handle the signal levels fed them.  In some instances, they can distort.  Not like fuzzes, obviously, but enough that one would not get the pristine tone sought after.  In contrast, optical elements (photocells) used to accomplish the same task essentially have no point at which they distort.  Consequently, they can often be cleaner-sounding.    Certainly there is nothing that prevents a FET-based compressor/limiter from sounding fabulous - and there are numerous examples in studio history - but when the design is as simple as a stompbox, photocells tend to win in terms of cleanliness.  Keep in mind that this is entirely separate from the amount of compression or feel provided.  Some folks may be quite willing to trade off "signal hygiene" for feel if it adds to their sound.