I was looking around on the internet and copied some of the better information I could find about the Power Station. The quotes are from various individuals and just put together.
Here’s an overview of power amp and reactive load characteristics Steve put together to hopefully answer some of your questions. Enjoy!
Two things we see frequently batted around in these discussions are: “Flatness” and “transparency”. Both terms are often used incorrectly and without a clear understanding of the subject.
So, what does “flat” actually mean? In the real world of guitar amp behavior, not a lot really. For the record, we do not claim that the Power Station is “flat”. We do claim that it is “more neutral” than a typical guitar power amp stage. Why do we say that?
First, contrary to a typical guitar power amp stage, the relationship between the power tubes and output transformer in the Power Station is such that the power tubes operate in a very linear region of their ideal operating range. This tends to subdue characteristics that we normally associate with a particular tube, and that in turn, prevents the power amp stage from imposing its sonic personality onto the sound of the amp being attenuated (or boosted).
Secondly, tube power amp source (output) impedance is high relative to a SS power amp whether Class AB or D. Power amps with very low source impedance (usually along with a correspondingly high damping factor), can sound relatively stiff and lifeless as a guitar power amp because they exert a lot of control over the behavior of the speaker. Also, a SS power amp normally requires a much higher output capability in order to prevent the player from crossing over into distortion territory, which in any SS power amp is pretty objectionable. SS power amps that exhibit lower apparent clipping do so either because there is a lot of negative feedback or compression imposed on the design, or the power supply is heavily filtered in order to stay as clean as possible, either of which sounds, and especially feels, artificial. In contrast, a tube power amp is allowed to slip into distortion territory because it sounds musically pleasing when doing so. No surprise there.
A tube power amp, having a significantly higher source impedance allows the speaker to react more - and often more slowly. Greater speaker reactivity means that a small amount of voltage from the speaker reaction reflects back into the power amp, enhancing the feel and responsiveness of the amp. Tube amps also utilize negative feedback to tame some of this reactive interplay between the speaker and amp, but it’s generally less effective at controlling the speaker because of the higher amplifier source impedance. In fact, the Presence and Depth controls on the Power Station vary this feedback at very high frequencies (Presence) and very low frequencies (Depth). This is how the PS is tuned to interact optimally with whatever speaker you may be using it with.
What the player experiences when reamping their amp with the PS is not a coloration of the sound necessarily, but the effect of hearing that sound at a higher or lower volume than you normally would without the PS. For example, when you play the amp by itself, your pick attack is based on the amps volume and how hard you are able to dig in. With the PS connected, you are now allowed all kinds of license with regard to pick attack and playing intensity, which naturally changes how you perceive tone, volume, distortion and frequency response. The thing that changed really is your playing relationship with the amp. Only problem is, once you hit full output, the power amp then imposes it’s own compression and distortion character on the sound of your amp. A higher powered tube amp eliminates that problem, of course at a somewhat higher cost. We originally chose 50W because that seemed to be a good overall compromise between cost, weight and size, and we, I think correctly, assumed that most people would be using the PS to reign in an unruly amp. For those who want both control, and the dynamic snap of a higher powered amp with just a bit of the horns shaved off, we’ve developed the PS-100.
Now, about “transparency”, there is no such thing as a “transparent” reactive load. Its very job is to excite non-linear behavior in your amp, the same way a speaker does. And with regard to frequency response, power output and distortion, the notion that one power amp is more transparent than another is entirely subjective. For example, technically, a SS power amp may be more sonically neutral or flat than a tube power amp, therefore more “transparent” on paper. But do we really want that? When your standalone amp is interacting with its own speaker, there is a lot of give and take between the two that creates the amps personality. Insert a flat, low impedance SS power amp into the stew and a lot of that feel and character goes away.
So…if the reactive load in the PS is supposed to fool the amp into thinking it’s hooked up to a speaker, why should that feel and personality depend on a supposedly “flat” tube power amp? The primary reason for using a tube power amp in the PS is to restore the interactive behavior between the amp and speaker that is lost when the amp itself is no longer driving the speaker you are listening to. And when you are in a room, how the speaker is driven, how the speaker creates reflections in the room you are in, the volume, and how your ears perceive frequency response at different playing volumes (Fletcher-Munson Effect), all weigh on the final result.
Once you attenuate your amp, you’re turning it into a different, more useful and more fun to play instrument. Some things you may like about the behavior about the amp may change, while most of what you gain is beneficial. You don’t lose the things you like. You just put them on the back burner and you can restore them with the flick of the Bypass switch. Now with a 100W amp and two sets of controls, you can get closer to both ideals and keep the FX loop active to boot.
The PS cuts the interaction between your amp and the speaker cabinet. As far as your amp is concerned, the PS is the speaker cabinet. This is important because there is an interaction between the amp and its speaker load. This interaction is 2-fold:
The speaker load actually determines how the amp, itself, sounds. So each cabinet makes the amp sound different.
The speaker moves and reacts to the amp’s power, and the amp reacts to the speaker’s behavior. So there’s a dynamic interaction that changes with volume.
For #1, It’s important to understand that this is more than the tone of the cabinet. If you plug an amp into a 4x12 with Greenbacks, it sounds one way. Plug it into a 2x12 with V30’s, it will sound another way. This isn’t just the tone of the speakers/cabinet. The amp itself actually sounds different depending on the speaker load it’s plugged into.
For #2, it’s important to understand that this is volume dependent.
So here’s what the PS is doing:
The PS cuts the interaction between the speaker load and the amp.
The PS mimics the speaker load. Takes ALL of the power from the amp and soaks it up. It bogs that signal down to line level and sends it to a few places (FX loop, Line out, and its own internal 50W power amp).
The internal 50W power amp in the PS then re-amplifies the sound at the desired volume and that power amp has its own interaction with the speaker load.
Now we get to the settings:
The RL filters (Flat, Fat, Deep and Flat, Brite, Edge) control the reactance of the load the PS is presenting to the amp. I mentioned that every speaker load sounds a bit different. The goal of these controls is to allow the PS to mimic different types of speaker loads. By doing this, it mimics how your amp sounds when connected to those loads.
Though, this is volume dependent. As you turn the PS up, there is more reactance between the cabinet and the Power Station’s tube power amp. As such, you may find you need less reactance from the RL filters. At bedroom volume, it may sound best at Deep and Edge. At higher volume, maybe Flat and Brite.
The Presence and Depth controls apply only to the internal 50W power amp in the PS. That is the last part of the signal path. It’s for fine tuning after you get the RL filters set. Keep them turned off (full CCW) by default and add presence or depth as needed / desired.
Steve chose to offer a broad range of tuneability knowing that it may be a curse and a blessing as is often the case with such things.
We tell players to concentrate less on trying to match and instead adjust to taste, because what you’re really trying to accomplish is a good overall balance for whatever is required at the moment. as that requirement changes, you have the ability to adjust further.
We recommend starting with switches set to flat and knobs to zero. bring up the volume and start with the bottom switch to get the bottom end feel you like. then add the top switch for the sparkle. finally dial in the presence and depth to taste. it may seem backwards, but it’s usually faster and easier to tweak the bottom switch before the top and depth before presence.
the frequency response of the ps-2 power amp shouldn’t be equated with how it interacts with a speaker just as the frequency response of a speaker shouldn’t be equated with it’s impedance behavior. how the power amp behaves with a given speaker determines how the 2 sound together and that’s also determined by how hard the power amp is driven. meaning, that though the ps-2 power amp stage is somewhat more linear than a typical guitar power amp, it’s still a tube amp. once you push it into distortion territory, it starts to lose linearity, and damping factor will decrease. this condition varies with not only load impedance, but speaker type as well. even if you keep the power usage relatively low, power amp behavior will still vary with speaker choice more than would happen with a ss amp. depending on your application, those variables will determine what sounds best to you.
a modeler is not a string of real amps and cabs. they are virtual amps and cabs in which electro-mechanical variables don’t occur the way they do in the real world. with modelers, there are no comparable variables like room size and shape, stage construction, speaker cable type and length, line voltage variations and a host of other environmental variables that govern how real amps and cabs sound and feel.
yes, the ps-2 power stage is more neutral than a typical guitar amp, but you have the presence and depth controls to help “de-linearize” it so to speak, if desired. so i think it’s worth pointing out the pitfalls of assuming that a virtual flat load and a virtual power amp at some arbitrary volume setting will produce a correspondingly “modeled” interactive behavior between them as would occur with real components.
