Swanky Amp (release 1.4.0)

[prodigal_sounds]

What this all means is: this power sag issue is a beautifully convoluted mess. I think to really nail down a good sound it's important to chase down those side-effects. I realize my current implementation is wrong, and more importantly how it's wrong. And that's the first step to improving it.

It's amazing and wonderful that a wrong implementation can sound so good.

[guitarzan]

Alright, I fully sympathize that it's hard to tune in a good sag sound, and it quickly goes from "that sounds about right" to "that sounds very ... experimental" without ever reaching that coveted Rust depth.

This is related to my implementation: I considered that only the signal up to some effective clip level in the power amp will actually contribute to power draw. That is because signal beyond that level doesn't flow through the plate, hence it is clipped and not in the final waveform in the speaker. And if there's no current in the plate, it's not drawing power. The end result is there's only a limited range of signal that can contribute to the power draw, once it gets too large then the compression is always at the same value since there's no *additional* power being drawn. And to compound this limited range, part of the effect of the sag is to reduce that range. So the amp can (too) quickly get to a state where it's constantly starved of power no matter what you play.

BUT, after careful consideration I realize the signal above the effective clip level will still contribute to power draw, both from leaking in the screen and also just from the pre-amp stages drawing power (but that would be probably much smaller than the power amp power draw).

I don't remember where I got this notion (something I would've read or been told — I won't go near running tube amp innards, just the thought of hundreds of volts DC terrifies me) but doesn't the output transformer trying to saturate (or recover may be a more accurate term, acting as a load) slow down recovery time or something to that effect? Also, the impression I get of the sag currently being in the Fender blackface ballpark makes me think about negative feedback, I don't think tweed deluxes had any, but you've probably already considered that… that's all I got.

EDIT: this is the best I can find right now on the O.T. contribution to sag:
https://www.thegearpage.net/board/index ... is.631087/

Also as volume increases the output transformer saturates acting similarly to a bandpass filter. If really pushed and fully saturated, you will also experience some compression at this stage with a resultant bloom.

EDIT: as Garrin has pointed out, the following actually refers to the power transformer as well as the O.T.
https://www.aikenamps.com/index.php/what-is-sag

The transformers: The resistance of the high-voltage secondary winding also creates sag. From Ohm's Law, the voltage drop across a resistance is equal to the resistance multiplied by the current flowing through it. This means that there is no voltage drop if there is no current, and the amount of voltage drop goes up linearly with increases in current draw. A typical power transformer B+ winding might have a resistance of 50 ohms - 300 ohms, depending upon the current rating and regulation of the transformer. For example, if the current draw in a push-pull class AB output stage at idle is 70mA total, and it increases to 170mA at full power, there is a change of 100mA in the current drawn through the secondary windings. If the winding resistance of the secondary is 200 ohms, there is a voltage drop of 100mA*200 ohms = 20V in the plate voltage to the output tubes. Likewise, the resistance of the primary winding of an output transformer varies as well, typically 80 ohms - 200 ohms plate-to-plate, depending upon the primary inductance, the transformer power rating, and the rated impedance. This resistance also creates a voltage drop, but the amount of sag introduced is minimal in pentode mode, because the plate voltage doesn't have near as much effect on the plate current as does the screen voltage. In triode mode, there is more sag because the plate voltage has more of an effect on plate current in a triode. The supply sag created by the power transformer resistance lowers not only the plate voltage, but the screen voltage as well, since the screen is nearly always a filtered version of the supply going to the plate. The amount of sag induced by the power transformer winding can be offset if there is a large filter capacitor reservoir to hold the voltage constant during current peaks.

[jbraner]

But while I was there, I also found this
http://pvamps.blogspot.com/2015/05/cab-driver.html
which seems to be a "coupler" between a power amp and speaker cab.

Interesting — I've been thinking about different dynamic speaker emulations, and I seem to remember a post by a developer, I think it may have been regarding Mercuriall Cab, but they said they no longer were trying to do dynamic cab modeling because no one was making truly dynamic amp models, and that may have just changed — BUT, does Resonant Amp having the normalized output level limit the dynamic information available to a dynamic cab sim?

NOTE: I'll drop this if anyone thinks it's distracting from talking about the amp

I'm not sure what this plugin is actually doing. I hear it doing *something* but I'm not sure it's making anything "better". I emailed the developer and he seems to be saying it's some kind of saturation plugin. I'm not sure why we need more saturation between the power amp and speaker cab (I know there's *something* interacting between the two - but don't know *what*). Anyway - if someone who knows what they're doing wants to play around with this - help yourself - it's free after all

[guitarzan]

No, I think the idea of a dedicated coupler between the amp-sim and cab-sim is really interesting, anything to help preserve or enhance dynamics!

Regular cab IRs need help, in my opinion. I really want to try a Reflection Free Far Field IR — they attempt to capture the speaker and cab only, minimizing room reflection and microphone contributions. That way it should sound like an amp thru the monitors, not like an amp with wierd ringing early reflections from some other room along with enhanced SM57 honk. I'd rather add room and mic myself.

I think a hybrid cab model using Reflection Free IRs along with some well executed dynamic enhancers would be great.

[jbraner]

Something like this?
https://store.two-notes.com/en/packs/56 ... -pack.html

They sell the cabs separately - I might try one...
(this just came out yesterday)

[guitarzan]

I think it's a different approach altogether, the Reflection Free IRs are captured in as large and wide open a space as possible using a reference mic positioned as a boundry mic (like a pzm). It's a very short sample, like 20ms, all to eliminate early reflections and mic coloring as much as possible. The goal is to get just the cab and speaker, nothing else.

I think regular IRs are meant to be used in a mix, but they always seemed awkward to play to me.

In theory, the Reflection Free IRs and an amp sim should sound just like an amp when heard thru your monitors — no room, no mic, no artificially ringing early reflections. So it would be like an amp right there in the room with you which is what I actually want to play, so more for "tracking" I suppose.

[jbraner]

I'll play around with them. you can "audition" them for free - and they're only €8 per cab to buy

[guitarzan]

I'm not sure what this plugin is actually doing. I hear it doing *something* but I'm not sure it's making anything "better". I emailed the developer and he seems to be saying it's some kind of saturation plugin. I'm not sure why we need more saturation between the power amp and speaker cab (I know there's *something* interacting between the two - but don't know *what*).

I bet the developer is going for Output Transformer saturation. Makes sense… O.T. not modeled in many amp sims… coupler between amp-sim and cab-sim… yep, output tranny saturation.

[jbraner]

Well, I guess it's worth playing around with.
it's free - so I'll put it on my list of things to do...

[acousticglue]

I use WOS but use many free IRs and RedWirez. I also own Ownhammer etc. But Kathellan and God's Cabs are free I do believe and many could be sank into the IR section of Resonant Amp

[DaveClark]

Hi all,

The quote from Aiken Amplification by guitarzan is a significantly simplified explanation of what happens in a real-world transformer in a power amp, done for the purpose of explaining the the basic concepts involved when thinking about how a transformer can produce sag.

In his book Vacuum Tube Circuit Design: Guitar Amplifier Power Amps, author Richard Kuehnel discusses, in the chapter Real-World Output Tranformers, the low-, middle-, and high-frequency responses of an output transformer, using three different equivalent-circuit models. To obtain a detailed picture of sag produced by an output transformer, it would be necessary to consider these differences.

Kuehnel also discusses hysteresis losses and the fact that “The speaker load is also reactive, differing from its nominal impedance value in a highly frequency-dependent manner. These reactances combine to create a frequency-dependent, elliptical load line that differs significantly from the straight load lines commonly used for power-amp design.”

Later: “One possible conclusion we can draw from the previous sections of this chapter is that the design of a power amplifier using realistic transformer characteristics is very complicated.” Indeed! Once an actual power amplifier is designed with a particular physical transformer installed, the amp simulator designer is left to try and divine the physics and math to duplicate the instantiated behavior – arguably an even more arduous task.

Regards,
Dave Clark

Richard Kuehnel. Vacuum Tube Circuit Design: Guitar Amplifier Power Amps. Pentode Press, Seattle, 2008, pages 155-167.

[guitarzan]

The quote from Aiken Amplification by guitarzan is a significantly simplified explanation of what happens in a real-world transformer in a power amp, done for the purpose of explaining the the basic concepts involved when thinking about how a transformer can produce sag.

In his book Vacuum Tube Circuit Design: Guitar Amplifier Power Amps, author Richard Kuehnel discusses, in the chapter Real-World Output Tranformers, the low-, middle-, and high-frequency responses of an output transformer, using three different equivalent-circuit models. To obtain a detailed picture of sag produced by an output transformer, it would be necessary to consider these differences.

Multi-band Compressor set "by ear". Nobody ever wants to go there or even consider it, but damn man, this is just a sim — it'll work in the real world if we want it to. Put a warning label on it "Not Intended for Actual Amplifier Design Work" if that'll help ease your conscience.

Just kidding, I can imagine the math is quite daunting. Seriously though, a 3-band Compressor, Saturation, your ears, and some imagination can go long way.

[jbraner]

In theory, the Reflection Free IRs and an amp sim should sound just like an amp when heard thru your monitors — no room, no mic, no artificially ringing early reflections. So it would be like an amp right there in the room with you which is what I actually want to play, so more for "tracking" I suppose.

Well, I bought the 4x12 V30s in a Mesa cab - recorded in the anechoic room. They sound nice and crisp - and I like V30s (it's amazing how you can have preferences for things like V30s and EL34s even though you know nothing about them in the real world) but nothing earth shattering
I'll use this cab - but I won't be out on the street preaching about the benefits of IRs recorded in anechoic chambers

Garrin - I hope you don't mind these little side discussions. They *are* related to amp sims - but we can take them elsewhere if you prefer

[guitarzan]

Like I said, anechoic chamber is a completely different approach than reflection free IRs. You still have the mic and its phasing issues and artificially ringing early reflections off the cab itself even in an anechoic chamber, at least the way those particular IRs were made.

[kvraudio38]

I tried it out Reaper on Windows 10. The little amount I spent with the settings I had no issues. The interesting thing is its sounds and feeling it gave me. I am so impressed. This is a sound palette that I will cherish. It being open source is also impressing me.

I guess Linux is possible since it is Faust and JUCE or am I wrong? A PayPal account to donate to?