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While we are at it, a selection of output transformers, a way to adjust the bias of each output tube individually the ability to use preamp tubes as output tubes (12ax7 for AB push pull and EF86 for Class A single ended, etc) and the ability to create mismatched output pairs for AB push pull (EL84 with 6V6, EL34 with 6L6).
That would be fun.

We need something besides Celestion speakers (not a fan). Personal favorites are JBL G1245-8, a well broken in EVM SRO (early version of the 12L), Peavey Scorpion Plus 12" and Peavey Scorpion 10". Plus some vintage field coil speakers that suck enough current from the power supply to make it sag.

Of course, a way to save presets with actual typed names and a nameable "Bank" arrangement so you can categorize your creations to your personal needs. No "faux" names referring to existing amps unless you create one.


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I used to have a vintage Champ "clone" (RCA Tube manual from the 50's) that had a 6sj7 in V1. Could have been a 6sn7, I don't remember perfectly. I do remember it had it's own sound even though those tubes tend to be microphone.

So we need a model of a perfect one and of a somewhat microphonic one with a way to model the speaker exciting the tube. Sometimes wrong is right.


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Originally Posted by Mike Rivers
Originally Posted by The Real MC
Other things that matter...

. . . tone recovery stage or not . . .

What the heck is that? A guitar amp term like "tone stack?" (I've been trained by what that means)

A triode after the tone stack. It isolates the tone stack from the phase inverter (or output tube in class A) to prevent loading. Some amp designs do not have them, usually the "student models"

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"Tone recovery stage" must be one of those terms that people who work with instrument amplifiers invented. There are probably more.

I'd call it a buffer.

Is there a glossary of those "amp" terms somewhere?

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Ya learn something new every day...

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Originally Posted by Anderton
Ya learn something new every day...

Vacuum tube amp design is interesting. I've been reading on that stuff out of curiosity. The only time I monkeyed with a tube circuit was my Hammond organ. I picked up a module with power applied and felt 250VDC on my fingers. OK, time to quit for the day...

Originally Posted by Mike Rivers
"Tone recovery stage" must be one of those terms that people who work with instrument amplifiers invented. There are probably more.

I'd call it a buffer.

Sort of... Buffers are near infinite input impedance and near zero output impedance. Triodes aren't that ideal.

Quote
Is there a glossary of those "amp" terms somewhere?

Haven't seen one. I picked up those terms from reading amp design books by Dave Hunter, Gerald Weber, Groove Tubes, others.

Not finding any such glossary in the old Radiotron 1952 manual, which is online. Never saw the RCA Receiving Manual, where many guitar amp circuits have originated - maybe there...?

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Originally Posted by Anderton
I the ability to tweak the schematic was super-innovative, and been half-heartedly copied by others. What was interesting was how Peavey was all in on modeling so many of its amps. It's almost like they didn't want to sell hardware any more smile


I was disappointed in how limited the choices were. I was expecting something much more akin to what Positive Grid did. I did like that it "felt" like I was actually tweaking a variable in the software chain, but it seemed a little dubious as to whether it had a 1:1 correspondence. The schematic menuing was a bit clunky. I think the biggest problem with it was the preset/saving process was very peculiar, it was confusing as to whether you had actually saved something as a preset, or if you were getting it back when selecting what seemed to be a preset.

I would have liked to have seen a totally modular component level approach.


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I view the whole thing as something of a fool's errand, in that a "guitar amp" is actually a series of stages that can be replicated in any DAW with vsts substituting for each one. Kuruprions is so worried about being "innovative" - forget ersatz amp models and make your own plugin chain that duplicates the "amplifier" process. That's the same difference as having one company put all of the functions into one program. It works better IMO, more dynamic and realistically non-linear.

It's actually kind of amusing to realize just how much a "tube amplifier" is really a couple of distortion stages with a tone stack in there. And if you're brave enough to listen to a d.i.'ed amp sound sans speaker sim, it's remarkable how primitive and basic a signal it is *until it hits the speaker*. Doing cascaded eq curves with compression stages+asymetric distortion makes a bigger difference than the modeled amp circuit that's adding harmonics scaled to level through eq.

I've got track templates that go like

Pultec (input impedance) > LA2 (V1) into Scheps Omni Channel (tone stack) > LA2 (V2) > Reaper asymmetric distortion (phase inverter/crossover distortion) > Scheps Omni Channel (saturation/transformer) > Melda dynamic eq (impedance curve/damping effects) > "speaker sim dujour".


One should try that, it works better than you might think if you keep in mind realistic limitations for eq, gain. I tried to mimic a presence circuit wiith Reaper's feedback capabilities, but it was too finicky ( and not likely to yield a fantastically worthwhile result). Although it's a rabbit hole of untold proportions, I've got probably... 20+ templates I spend hours on tweaking. Not advised. Faking transfer curves into distortion with compressors and dynamic eq is more accurate for chasing existing amp tones than the hybrid-faux approach above, though. It's funny how close you can get to a plexi if you just mimic the tone stack and gain stages.



So Kuroprions, why are you still using digital models of existing amp designs, why are you so stodgy and against progress? <g>


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At the end of the day, my only questions are:

* Did I like the sound enough to have fun playing the guitar part?
* Does the track sound good in a mix?

These days, it's amazingly easy to satisfy those two requirements. At least for me smile

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Originally Posted by Chip McDonald
So Kuroprions, why are you still using digital models of existing amp designs, why are you so stodgy and against progress? <g>


Not sure where you read that and I don't remember saying it. Above we have a brief discussion of an amplifier plugin with more versatility, not just more tubes but transformers, phase inverter circuits, negative feedback, bias, etc.
Nobody makes it and I don't write code. It would be a fun rabbit hole to go down but not a be-all-end-all for me. I might try it once and forget about it, like I have with most of my amp sims most of the time.

I did say that in general I don't like the interfaces and it isn't just amp sim plugins, it's most plugins. There is a prevailing aesthetic that I interpret as "musicians are dumb shits, let's make everything look like analog gear but with cool words by all the knobs" and I don't like it. Eventide gets it, they make beautiful plugin interfaces that are easy to use and each one looks different enough to tell them apart visually. So far, they don't make amp plugins but I'd like to see it if they ever do.

Not all plugins have terrible interfaces, Fishman Triple Play is very straightforward but it's kneecapped by some of the hideous interfaces for the synths it hosts. Kontakt Player and SampleTank are easy to use if you just want to select sounds to goof around on but some of the sound banks aren't fun to tweak. I end up being a preset surfer more often than not, that's wanting to play more than fiddle about - the never ending battle between the Artist and the Engineer. If the Engineer wins, you got nothing. I try to keep the Engineer away until tracking is done. It's impossible but the more Artist time I get tracking the better.

Tracktion/Waveform set an example for "clutter control" years ago - when you click on something up in the tracking section of the DAW, it automatically brings up menu items for that specific area in the good sized box at the bottom center of the screen. Click in another place and that set of options disappears and is instantly replaced by the one you just hit. It cleans up it's own mess as you go. Coming to that from MOTU Digital Performer 4, which was "kitchen sink meets Swiss Army Knife" except cluttered and apparently designed by hippies, it was a huge relief to start using Tracktion.

I'd like to see more of that concept on plugins, you are only going to be tweaking one parameter at a time - put a list at the top big enough to read and a box underneath it that offers options for whatever you're going to adjust. That would require conceding that Creatives would prefer simple function over pseudo-realistic 2d images of a 3d device that is at it's best when one can grasp the knobs with fingers and thumbs.

We don't have effective thumbs on the screen. So, give me a slider - it's that simple.

If and when I have used amp sims recently it is only in parallel and after the take is tracked. I'll go straight into the DI almost every time, duplicate the track (9 total tracks recently for one experiment) and start tossing plugins in the individual tracks. In 9 tracks I may have 2 or 3 different amp sims, 2 different settings on pitch shifters (detuning-both flat and sharp), tracks that are entirely and only delay and/or reverb, EQ, etc. Then I can automate those tracks so things can build and shrink and tones can transition from one sound to another. I usually keep the original clean track in the mix at some level for clarity and fade in one or both amp sims, or saturation plugins or whatever. The Artist is still watching and suggesting but I need my Engineer cap at that point. I'm done tracking, which is largely non-verbal "in the Zone" time for me.

There is never a thought in my head like "Oh, this sounds just like a 1959 Fender Tweed Deluxe." I have a couple of vintage Fender sims, they sound cool on vocals and xylophone.

I can be subtle or make it into a scary monster if that's what the song calls for. For me, amp sims are just another tool for changing sounds. I don't think of them as being representative of using an amp because they just are not that (yet). If and when I hear an amp sim that I LOVE with an interface that it easy and fun to work with, I'll like that. Doesn't mean I'll use it for all or any of my guitar parts. Maybe it will be good on a snare drum. I won't care if it says Vox or Good Humor Ice Cream on it either.

If I want something to sound like a guitar amp, I can mic one. I am buying a condo in a multi unit building, I have neighbors one wall and one ceiling away. There is freeway noise, vacuum cleaners, all sorts of fun interruptions in the real world that mics can pick up. So some of my freedoms regarding recording are limited but there is a universe of sound in the box. With headphones on I can work on things whenever I want. As with many musicians, I am a bit of a night owl.

I have zero commitment to guitar even sounding like a guitar when it comes down to it. It (and bass) are simply the tools I am most comfortable with using to express music. I suck at keyboards and am not motivated to improve.
We are often defined more by our limitations than our ability to sound like everything. I think in terms of tension and release. If I can create tension, release is easy. I lose interest when my art flatlines.

What I love about working in the box is that reality is completely out the window, gone and good riddance. Make sense? Cheers, Kuru


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Originally Posted by The Real MC
... Buffers are near infinite input impedance and near zero output impedance. Triodes aren't that ideal.

Triodes (and, in general, vacuum tubes) aren't characterized by an input or output impedance, it's the circuit configuration around the tube that determines those characteristics. The input impedance is pretty much determined by what resistance determines the grid bias, and the output impedance is determined by the resistor across which the output voltage is dropped. A tube in a conventional amplifier circuit (with voltage gain) with a 47 kΩ plate resistor and AC-byapssed cathode resistor will have an output impedance of around 47 kΩ. A cathode follower circuit, which is generally used as a buffer, with a 100 Ω cathode resistor will have an output impedance of about 100 Ω.

At least that's how it usually works, but guitar amplifiers are designed for a special purpose.

Originally Posted by Chip McDonald
I've got track templates that go like

Pultec (input impedance) > LA2 (V1) into Scheps Omni Channel (tone stack) > LA2 (V2) > Reaper asymmetric distortion (phase inverter/crossover distortion) > Scheps Omni Channel (saturation/transformer) > Melda dynamic eq (impedance curve/damping effects) > "speaker sim dujour".

I was once looking for a crossover distortion generator and made one out of two back-to-back diodes. Where can I find the Reaper asymmetric distortion plug-in? Is it part of the standard Reaper installation? I haven't been keeping up with my Reaper versions but that sounds like something I'd like to play with - not to simulate the sound of an instrument amplifier, but to illustrate the different sound of two different kinds of distortion that measure the same THD. One with crossover distortion sounds more unpleasant than one with pure harmonic distortion. I used this in an article about specifications.

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Originally Posted by Mike Rivers
Originally Posted by The Real MC
... Buffers are near infinite input impedance and near zero output impedance. Triodes aren't that ideal.

...the output impedance is determined by the resistor across which the output voltage is dropped. A tube in a conventional amplifier circuit (with voltage gain) with a 47 kΩ plate resistor and AC-byapssed cathode resistor will have an output impedance of around 47 kΩ. A cathode follower circuit, which is generally used as a buffer, with a 100 Ω cathode resistor will have an output impedance of about 100 Ω.

At least that's how it usually works, but guitar amplifiers are designed for a special purpose.

You forgot the INTERNAL impedances of the tube elements.

ALL active devices have internal impedances which must be accounted for with external components. Even the grid if it is attached to a tuned circuit. If the internal output impedance of the plate of one triode is 50000ohms (GE 12AX7), a triode amplifier buffer with 47 kΩ plate resistor with AC-bypassed cathode resistor will have an output impedance that is the SUM of internal and external impedances - actually 97 kΩ. That's enough of a difference to impact a tone stack (tuned circuit). You can't direct couple output tubes to a speaker because the output impedance of the push-pull tube pairs is almost three orders of a magnitude higher than the speaker impedance. That's why a tube power stage uses an output transformer to couple the tubes to the speakers.

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I just had my detailed reply eaten by the software so maybe it doesn't like this discussion.

You said that the tone recovery thingamajig goes between the tone stack and the phase inverter (or a single-ended output stage) so how does the output (source) impedance of the tube affect the tone stack? Is that impedance, or the load on the tone recovery tube reflected back to its grid significantly? Does the capacitance of the grid, or any capacitors connected to the grid affect the tone stack? That's not inconceivable since the pots in a typical tone stack circuit are 250 kΩ or so.

What I know about tube circuitry is mostly from my ham radio days in the 1950s and '60s. Stray capacitance is important in RF circuits because it can become a resonant circuit with the inductance of a piece of wire and cause an unwanted oscillation. But I don't figure that a guitar amplifier is going to oscillate at 20 MHz or so.

There actually are some transformerless tube output circuits, but they're tweaky. An output transformer is the way to go. Not only is it to match the impedance of the speaker with that of the tube, but it also keeps DC off the speaker.

So what were we originally talking about in this thread? What circuit designs within an amplifier should be modeled and what's not to bother with?

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Originally Posted by Mike Rivers
You said that the tone recovery thingamajig goes between the tone stack and the phase inverter (or a single-ended output stage) so how does the output (source) impedance of the tube affect the tone stack? Is that impedance, or the load on the tone recovery tube reflected back to its grid significantly? Does the capacitance of the grid, or any capacitors connected to the grid affect the tone stack? That's not inconceivable since the pots in a typical tone stack circuit are 250 kΩ or so.

Biggest impact is loading of the tuned circuit (tone stack), changing its design frequency(s) and/or its system gain. The tone stack is basically a passive filter. which is vulnerable to impedances at its input and output. Since the triode is not an ideal buffer, the impedance of its elements has to be factored in the design of the tone stack.

Most student tube guitar amps omitted the tone recovery tube for economy. The amp will still work, but the phase splitter following the tone stack is not as good a buffer. So tone controls in such an applications are a bit more limited due to adverse loading. Top models like 1950s Fender Super, Twin, and Bassman with treble/mid/bass tone controls did not have tone recovery triodes, instead they placed a high gain stage consisting of both triodes of a 12AX7 BEFORE the tone stack. Tone recovery triodes following the tone stack became the standard by the 1960s, which was an economy move to reduce tubes.

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Originally Posted by The Real MC
Biggest impact is loading of the tuned circuit (tone stack), changing its design frequency(s) and/or its system gain. The tone stack is basically a passive filter. which is vulnerable to impedances at its input and output. Since the triode is not an ideal buffer, the impedance of its elements has to be factored in the design of the tone stack.

OK, maybe you need to better translate "tone stack" for me. Is it a specific circuit with specific component values common to all amplifiers of a certain category, that will produce a specific set of frequency response curves (to what tolerance?) for a given setting of the controls? I thought it was simply the tone control portion of an amplifier circuit, and that part of the characteristics of that particular amplifier is how the sound responds to setting of the tone controls. Seems to me that whether or not the output of the tone stack is buffered, it can be designed to have a workable range of control.

Is there something dynamic going on? Will an un-buffered tone stack operate differently when playing loudly or softly?

And what's a better buffer than a triode (if it's the right triode)? Maybe a pentode with a little help to the electrons getting across the vacuum by a push from another grid?

Quote
Most student tube guitar amps omitted the tone recovery tube for economy. The amp will still work, but the phase splitter following the tone stack is not as good a buffer. So tone controls in such an applications are a bit more limited due to adverse loading.

Can you be more specific? In what way are they "a big more limited?" And how might this affect the playing of someone who knows he's playing through an inexpensive or 'student grade' amplifier?

Quote
Top models like 1950s Fender Super, Twin, and Bassman with treble/mid/bass tone controls did not have tone recovery triodes, instead they placed a high gain stage consisting of both triodes of a 12AX7 BEFORE the tone stack. Tone recovery triodes following the tone stack became the standard by the 1960s, which was an economy move to reduce tubes.

I can understand putting more gain ahead of the passive tone stack, hence driving it at a higher level will improve signal-to-noise ratio, but so will driving it from a low impedance source. Is the 12AX7 used as an amplifier followed by a cathode follower to drive the tone stack?

OK, I looked for a schematic of one of those amplifiers and lo and behold, the Bassman 5F6 (the second Bassman schematic I looked at), sure enough, has the tone stack fed from the cathode of the second half of a 12AX7, though the cathode resistor is 100 kΩ, which seems to be rather high if the purpose is to provide a low impedance source for the tone stack.

I could be out to lunch here. Make me smarter.

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I think amp sim companies should hire the Real MC as a consultant.

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Originally Posted by Mike Rivers
[
I was once looking for a crossover distortion generator and made one out of two back-to-back diodes. Where can I find the Reaper asymmetric distortion plug-in? Is it part of the standard Reaper installation?

It used to be, but I just looked and see that it isn't anymore; it was a graphical "diode clipping" JS script, which I think is now mutated into the "loser saturation" JS. Ashcat had it in his "Tilt" script, the closest stock script I think is the "Bad Bus Mojo" script with separate +/- thresholds.
Chris from Airwindows does a lot of asymmetrical stuff IIRC, I don't know if you're familiar with his plugins....?

Quote
with pure harmonic distortion. I used this in an article about specifications.

Look at the "saturation" js in Reaper, I think it's a deprecated version of what I was referencing - I'm not sure where it went, the guy that made ("LOSER"<-- his moniker) it had a lot of plugins that were stock scripts in Reaper, but I think he had a falling out with the devs and took his ball and went home, so to speak. It might be in a in a 5.x version.


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