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Is there any point to "valve" (tube) Compressors....?
Old 30th October 2014
  #1
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Lorenzop's Avatar
 

Is there any point to "valve" (tube) Compressors....?

....which are NOT vari-mu by design (i.e. with valves actually doing the gain reduction)?

Let me explain my question/theory:
It seems most valve-compressors are basically opto or vca with a valve make up stage on the output, at best also on the input.

Well, I am therefore wondering: if I where to take a normal vca\opto compressor, and stick a valve preamp after it or a valve processor such as a Thermionic Culture Vulture, would I basically achieve the same thing?
Would it be the same as an integrated valve compressor, infact with even better controllability of all the valve gain stages stages (at least as flavour of distortion\make up goes?)

As far as I am aware the only difference would be the extra impedance conversion and circutry in interfacing a compressor with a valve processor in chain, but other than that I dont really understand\see any difference.

Would appreciate your thoughts on this!
Old 30th October 2014
  #2
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frans's Avatar
In short: no. Look here: Types of Compressors
and short as it is the page doesn't mention all compression topologies. Just as an overview.
Old 30th October 2014
  #3
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....so you do concord I'd be equally well served sticking a good valve processor after a good compressor for the "make up gain" ?
Old 30th October 2014
  #4
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Quote:
Originally Posted by Lorenzop View Post
As far as I am aware the only difference would be the extra impedance conversion and circutry in interfacing a compressor with a valve processor in chain, but other than that I dont really understand\see any difference.
Why are you discounting this difference as insignificant?

A given compressor with a solid state make up amp will still have a tone, which may or may not be complementary to the tone imparted by the tube stage you're placing after it. If these are vintage style units chances are you will be introducing not only the tube stage but another input and output transformer to the signal path. Maybe that creates magic, maybe it creates mud.

Just because there are tubes somewhere in the signal path does not necessarily mean that the end result will be better for having gone through that stage. If I plug a C414 into a UA610 the source doesn't necessarily come out the other end sounding as if it were a C12 into a API512.
Old 30th October 2014
  #5
"tube" is not a sound feature. It's an electronic component, a small gear in a large and complex network. Not more, not less. It's the network that matters, the idea as a whole. The problem is, most people aren't willling or able to understand the complexities of engineering.

Instead, they purely focus on the few "flashy" terms they can remember and draw the wildest conclusions. The fattest, warmest, silkiest compressors I've heard to date are something ppl would classify as solid state devices.
Old 30th October 2014
  #6
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Precisely as to avoid false conclusions, I am asking this question, to understand better how these "magic circuits" actually work.

I get the point that a circuit should be taken as a whole, however, as far as I can tell, a make up stage is a make up stage. Just like input stages/preamps fall into several categories of circuit types. Or am I wrong? In other words, I really don't think that putting a valve inside the compressor circuit as opposed chained after it for make-up gain is going to drastically alter the overall sonic grand scheme of things.

If I am wrong, please be explicit as to why - explain to me the workings of the circuit- rather than saying generally things like "its the network that counts". Fair enough -but why exactly?
Old 30th October 2014
  #7
I certainly agree to your notion in the general sense.

But sometimes it could be a PR relevant aspect (you know, such gear is made to be sold ), up to a part of a puristic technical concept. There are countless way to amplify, and it's not uncommon for compressors to use the same element for both gain reduction and makeup amplification. It's thinkable that designers correct a nonlinearity within the detection circuit with an inverse nonlinearity in the "makeup", or millions of other scenarios. "It depends". The really cool thing about tube circuits is their physical simplicity. They can greatly reduce the amount of components if used wisely, it's not all about the tubes' "main nonlinearity". In fact, most circuits try to drive tubes in their most linear region.

Last edited by FabienTDR; 30th October 2014 at 07:33 PM.. Reason: fixed some typos
Old 30th October 2014
  #8
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Thanks.

I think I see what your getting at. Said briefly, IN THEORY (a rather broad theory) it would be almost the same, but IN PRACTICE because the designers use the make up stage tube in a certain way, replacing it with another chain would achieve something different -sound included. Better or worse, thats up for opinion
Old 30th October 2014
  #9
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Hi
Pretty much yes.
A LA2A has a valve make up amplifier after the opto element. Part of the 'wonder' of this unit is the fact that the headroom of this valve stage is quite limited which will start to impact on the overall sound. A design using an amplifier that was not so 'limited' and stayed clean to beyond +24dBu output at all frequencies would not have the same 'mojo' even if it has the same input transformer and sidechain.
Vari Mu circuits tend to have a pretty 'wild' amont of control 'feedthrough' (thump) compared to most other technologies and distortion when attenuating (compressing) more than say 20dB gets pretty bad too.
A VCA design by comparison can have very little 'feedthrough' and the distortion only increases a very small amount. Opto has practically no feedthrough and distortion is pretty low. FET designs have a little feedthrough and distortion is 'medium' but can be noisy. The overall performance of all these technologies will be affected br preceeding and following circuitry.
Matt S
Old 30th October 2014
  #10
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kafka's Avatar
Well, no, but yes, depending on what you want. You could say the same thing about transformers, FETs, fancy-pants capacitors, or any other component.

No circuit exists in a vacuum (although some vacuums exist in circuits sorry, I had to do it!). They're all descended from some some circuit in a 'how to use this component' manual, somewhere. Those circuits have different characteristics that determine how they sound i.e. slew rate, gain, harmonic distortion, etc. They can't all operate exactly as you want through the entire power spectrum. So, that will give them all some unique sound. Whether that's a tube, or a FET, or a VCA, is just one of the elements contributing to that sound.

In other words, given that there aren't any two transistor amplifiers that sound the same, there's nothing radical, per se, about opting to use tubes instead.
Old 30th October 2014
  #11
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Every unit sound different regardless the topology,
so when you say "would it be the same", yeah maybe
on paper the signal path of some units could be that,
but it won't sound the same, or nobody would need anything
more than 1 model for each type of compressor topology,
or better, no brand would produce anything but 1 model
of each topology

Plus, as fabien said, tube is a component,
tube doesn't equal A given type of sound,
different tube units and circuits (despite having the common component)
sound, behave and have wildly different character
Old 30th October 2014
  #12
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Slug1's Avatar
One does have to wonder though if things (sonically) are or are not impacted by how these components are connected within a given path. Simply placing a tube processor before, after, or within the path of a solid state compressor may not necessarily recapitulate the sonic character of a specific opto compressor design. And the valves are used for different things in different setups as was mentioned by Matt Syson, not just to add distortion and harmonics to the signal, but in some cases to actually participate in the compression process. And different types of valves have better or worse uses given how they will be used in the process. So to the OP, I don't think that valve compressors (I understand they are not Vari Mu) are just something that can be replaced by sticking a valve processor after a solid state compressor. But I'd bet in some cases sticking a culture vulture after a transparent Dangerous Compressor might be just what the doctor ordered for a particular project or track. But it may not do the same thing as an LA2A on a bass guitar track. Painting brown patches on a white horse doesn't make it an Appaloosa.
Old 31st October 2014
  #13
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kafka's Avatar
Well, it's a given that amplifiers are constant gain devices, and changing the gain will change the performance. Since that's what a compresssor does, you're going to change the sound as it compresses, and not just the volume. That change in tone is probably half of what people are looking for when they chose one unit over another, whether it's tube, transistor, or VCA.

If you want a compressor that just changes the gain without affecting the tone, use the stock one in your DAW.
Old 31st October 2014
  #14
Gear Nut
I have two different, slightly-opposed but also slightly-complementary thoughts on the subject. First, *theoretically* there should be no difference between 10db of makeup gain applied inside the compressor post-gain reduction and 10db of makeup gain applied post-compression with another unit entirely. Second however, nothing is perfectly linear, and in proper circuit design you use one stage to balance another's nonlinearities. Furthermore, good circuit designers will design a makeup gain stage - or any gain stage really - to not only compensate for any nonlinearities in the gain reduction element but also to synergistically work with the gain-reduction element, creating something that's more than the sum of its parts.

On the other hand, that's for good circuit designers with the best circuit topologies. I'm sure there are many pieces on the market where there isn't a lot of thought given to how the two stages interact, and therefor no synergy derives from using both together.

As a result, I would suggest that the best way to answer this question would be to take the various potential pieces of gear and chain them, listening to the result, and then print that to A/B with a volume-matched bit of audio using the comp's internal makeup gain. The answer to this question will vary with the gear involved, so the only way to know for sure with two given pieces of gear will be to test them and find out for yourself.

As an aside, I have long wanted to take a Bluestripe 1176 schematic and replace the gain elements with tubes for the hell of it to see how it sounds. Alas, my circuit-design-fu is not strong enough yet; I can hang tough with the best DIY'ers out there, but my theoretical understanding of *designing* circuits is still lacking. Some day, though!
Old 31st October 2014
  #15
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Quote:
Originally Posted by JonHollister View Post
I have two different, slightly-opposed but also slightly-complementary thoughts on the subject. First, *theoretically* there should be no difference between 10db of makeup gain applied inside the compressor post-gain reduction and 10db of makeup gain applied post-compression with another unit entirely. Second however, nothing is perfectly linear, and in proper circuit design you use one stage to balance another's nonlinearities. Furthermore, good circuit designers will design a makeup gain stage - or any gain stage really - to not only compensate for any nonlinearities in the gain reduction element but also to synergistically work with the gain-reduction element, creating something that's more than the sum of its parts.

On the other hand, that's for good circuit designers with the best circuit topologies. I'm sure there are many pieces on the market where there isn't a lot of thought given to how the two stages interact, and therefor no synergy derives from using both together.

As a result, I would suggest that the best way to answer this question would be to take the various potential pieces of gear and chain them, listening to the result, and then print that to A/B with a volume-matched bit of audio using the comp's internal makeup gain. The answer to this question will vary with the gear involved, so the only way to know for sure with two given pieces of gear will be to test them and find out for yourself.

As an aside, I have long wanted to take a Bluestripe 1176 schematic and replace the gain elements with tubes for the hell of it to see how it sounds. Alas, my circuit-design-fu is not strong enough yet; I can hang tough with the best DIY'ers out there, but my theoretical understanding of *designing* circuits is still lacking. Some day, though!
Thanks Jon this pretty much sums it up for me!
Old 31st October 2014
  #16
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IUnknown's Avatar
Hi,

without sticking to deep into the discussion:
I put my Culture Vulture always before my MPressor (VCA comp), and i am so happy with the results that this is my to-go setup.

In the next project i will try to put the CV after the MPressor and see what is coming out.
Old 31st October 2014
  #17
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Hi
One major 'problem' with comparing any compressors is the transfer function of the sidechain.
Below threshold where there is NO compression going on, you have essentially a 'fixed' amplifier with given frequency response, distortion etc. In some cases the distortion is mainly 'constant' up until it 'clips' and others will gradually (with luck) increase with distortion as level increases. These latter units are those which seem to add 'analog mojo' even when not doing their intended purpose of compressing (reputedly).
Now consider the sidechain. At the level where it starts to compress, what is the ratio, over a certain transition period? If set at say 2:1, does this 'law' stay true for ALL increase in level or does it 'fold back' or other strange activity?
Is the rectifier frequency response limited, giving more or less compression related to frequency?
As I mentioned previously, some designs may 'thump' when compression really kicks in, this could add the equivalent of a bass 'kick' depending on settings of attack/release.
All of these latter effects are likely to have far greater impact on the 'sound' than the simple choice of devices used.
Matt S
Old 31st October 2014
  #18
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you really need to have zero experience to come up with some of these topics. am i the only one who actually use these devices?

have a listen, educate your ear, chime back in.
Old 31st October 2014
  #19
All of this is exact example dependant, Some tube circuits designed as pre/line amplifiers are capable of driving their output transformers into saturation while still having no discernible clipping on the driving tubes.
You could design a solid state pre to do this naturally to a lesser extent.:-)
Ergo! Compression can come from all sorts of circuits not described as compressors.
Back in the good old days some of our best compressors where called tape machines.:-)
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