Can Some Genius Explain Vox's "Valve Reactor"?

[Bezmotivnik]

This is a forlorn hope, I'm sure, but I thought I'd ask.

Vox's own explanitory page and diagram made absolutely no sense, even to EEs whom I referred to it. Apparently the copywriter didn't understand it either.

I understand the first part: A straight, solid-state preamp feeding the two triodes in a 12AX7 as if they were a pair of power tubes, which then go to a "virtual" output transformer. Weird, yes, but I follow it. At this point, the technical explanations fall apart. The output is supposedly processed through some "feedback" circuit that magically simulates the interaction between the speaker and output stage at varying volume levels, and then is amplified by a conventional solid-state power amp.

That's as far as I understand it and it doesn't make much sense.

Thanks for any help with this...

 

[ozzynotwood]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

I think its just carefully worded garbage from VOX to try and sell their amp. I've played it, and its probably the best modelling amp I've tried, and if modelling was my thing, I'd get that one, but you'll never say to yourself "Hey, I can really hear the valve reactor doing its thing". Apart from that, no idea LOL

 

[DankStar]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

probably best understood in some kind of digital binary code speak.

 

[JeffB]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

I'd get that one, but you'll never say to yourself "Hey, I can really hear the valve reactor doing its thing"

Just play sans the reactor...i.e. run the line out, or plug in some headphones...you'll hear and feel the difference. Either that or plug into a DA15 and a AD15VT back to back. Same same all around barring the lack of tube in the DA15. The difference *is* there...its not a HUGE GIGANTIC WORLD SHATTERING difference...but the tube DO make a difference in warmth/sparkle/feel. Switching tubes will clearly show there is SOMETHING to it as well...as the voicings markedly change.

IDK how it works but it works...

 

[Artie]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

There's a good chance that they're just using a "simulated inductor". Its a simple opamp circuit that mimics the behaviour of an inductor, (like a speaker coil).

 

[Bezmotivnik]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

There's a good chance that they're just using a "simulated inductor".

In that they have recently dropped the VR series amps, they may put up the schematics in their support archives, at which point I could look at it and see. I had to have the amp apart to repair it when it was brand new (100% -- five for five Vox amps I bought were bad out of the box -- love the look, hate the QC) because of severe reverb feedback, and I didn't see anything that obviously revolutionary going on in the PCB.

Even though the "simulated inductor" is a possibility, it still doesn't really jibe with the verbal explanation of how the Valve Reactor was supposed to work, but that explanation was incoherent to begin with. I don't believe it's still on the reworked site, which still seems to be under construction.

I've never even been able to figure out how to use the effect on the VR-30R. Documentation was weak, to say the least -- consisting mainly of product puffery, obligatory safety warnings and translations.

 

[Top Jimmy]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

It seems it is doing something, though technically who the hell knows. I'm not a tone head, nor do i claim to have a decent working knowledge of the sound path of solid state vs. tube vs. hybrid, etc, but when looking for a nice little practice amp, this was the better of the hybrid/ss I head at GC.

Is it a tube replication, god no. But does it do what it should well at a good price point, heck yes.

I have played through friends tube amps and there is a huge difference and I'm shopping as we speak, but for $200+/- I think it is doing something because I think you can hear it.

Technically what, who knows, but I think it is more then marketing because more then one or two people hear it also.

 

[innerdreamrecords.co]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

product puffery

 

[baritone]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

In the Vox modelers and hybrids, they claim to be using the preamp tubes to function as power amp tubes. I don't know much about electronics, but my guess is that they are using the preamp tubes in the virtual power amp of preamp tone processing. If you are comfortable with the fact that hybrids and modelers sound closer to solid state amps than real tube amps, the sound can be satisfying. It really seems that Vox is trying to use tricky wording to make the products seem like something which they are totally not. It strikes me as a silly marketing gimmick, but the products actually sound good to me.

 

[Bezmotivnik]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

In the Vox modelers and hybrids, they claim to be using the preamp tubes to function as power amp tubes.

That's the easy part, though. That's a fairly simple concept.

It's the speaker/transformer feedback simulation that has me stumped.

Again, this is not in a modeler, nor a modeling amp, but in a straight VR-30R -- though the "Valve Reactor" circuit is supposedly the same in all of them that have this feature.

 

[Sludgenutz]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

There's a good chance that they're just using a "simulated inductor". Its a simple opamp circuit that mimics the behaviour of an inductor, (like a speaker coil).

Artie walks up to the hoop...and drops the basketball in for the score, like the unstoppable giant! "Virtual inductor" is a new one! I have heard of other manufacturers using "artificial inductors" (a DOD analog delay?), before the word "virtual" became part of the English language lexicon.

Great linky, Artie!!!!!!!!

 

[Jeff Seal]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

This is actually simpler than what you might think, whereas most tube amps have transformers to isolate the output signal from the high DC voltage driven signal (decoupling), smaller signal triodes like the 12AX7 can be decoupled with only a small capacitor and a resistor to reference it to ground potential. Negative feedback loops always go to the input of the PI (phase inverter). Eliminating the output section and simulating the response that you would achieve by having an output section that it normally feeds is simple... and thus what the circuit does.

...you asked, I explained...

Jeff Seal

 

[STRATDELUXER97]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

This is actually simpler than what you might think, whereas most tube amps have transformers to isolate the output signal from the high DC voltage driven signal (decoupling), smaller signal triodes like the 12AX7 can be decoupled with only a small capacitor and a resistor to reference it to ground potential. Negative feedback loops always go to the input of the PI (phase inverter). Eliminating the output section and simulating the response that you would achieve by having an output section that it normally feeds is simple... and thus what the circuit does.

...you asked, I explained...

Jeff Seal

Jeff......Ok cool! Now explain it in layman's terms! :laugh2: :laugh2:

 

[JeffB]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

I'm so layman it's not even funny...but what I think Jeff may be saying is...please correct me if I'm wrong

with the 12ax7 and resistor/capacitor...the circuit is fooled into thinking it's hit a power amp..and realistically it HAS...and the circuit tailors itself to have neg feedback or not based on the model of amp simulation. The circuit also takes into account speaker characteristics.

The problem is, because of the extremely low power of 12ax7/resistor/cap power amp "simulation"..there's no (real) volume being produced, so then a SS power amp section is used to give the thing some "clean" volume...like a PA.

A normal modeller, like Line 6...can only digitally emulate the power-amp section of what is being modeled...whereas the Vox actually creates a tube power amp in miniature so there is some tube like warmth/response.


Do I win a prize?

or am I wayyy off? :laugh2:

 

[STRATDELUXER97]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

I'm so layman it's not even funny...but what I think Jeff may be saying is...please correct me if I'm wrong

with the 12ax7 and resistor/capacitor...the circuit is fooled into thinking it's hit a power amp..and realistically it HAS...and the circuit tailors itself to have neg feedback or not based on the model of amp simulation. The circuit also takes into account speaker characteristics.

The problem is, because of the extremely low power of 12ax7/resistor/cap power amp "simulation"..there's no (real) volume being produced, so then a SS power amp section is used to give the thing some "clean" volume...like a PA.

A normal modeller, like Line 6...can only digitally emulate the power-amp section of what is being modeled...whereas the Vox actually creates a tube power amp in miniature so there is some tube like warmth/response.


Do I win a prize?

or am I wayyy off? :laugh2:

I Just plug into my VTH 120 head and play and never think any further about the inner workings of my amp...:laugh2: :laugh2: :laugh2: One thing I do know though,is that it consistently gives me really great tone!

 

[tonelabequa]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

This is a forlorn hope, I'm sure, but I thought I'd ask.

Vox's own explanitory page and diagram made absolutely no sense, even to EEs whom I referred to it. Apparently the copywriter didn't understand it either.

I understand the first part: A straight, solid-state preamp feeding the two triodes in a 12AX7 as if they were a pair of power tubes, which then go to a "virtual" output transformer. Weird, yes, but I follow it. At this point, the technical explanations fall apart. The output is supposedly processed through some "feedback" circuit that magically simulates the interaction between the speaker and output stage at varying volume levels, and then is amplified by a conventional solid-state power amp.

That's as far as I understand it and it doesn't make much sense.

Thanks for any help with this...

No genius around here, but I can give you the basics:

The idea behind the "Valve reactor circuit" is really to emulate the behaviour of a transformer: step down the voltage by a factor, step up the current by the same factor. Or viceversa.

Basically what VOX does here is:

1) take the tube's output voltage, and send it through a voltage amplifier which feeds the load. The load is here the speaker or an analog emulation of a speaker.
2) Take the current flowing into the load, send it through a current amplifier and feed its output current into the tube.

If the gains of the voltage and current amplifiers are equal, this means:

Load voltage = Gain * Tube voltage
Tube Current = Gain * Load Current


...just as a transformer would provide.

The exact circuit (and its variants) is tricky, and a little harder to understand. The explanation involves some math. Suffice it to say that its working principle relies on the exact matching of the gains of voltage and current amplifiers.

It works, and Korg has a few patents covering it.

If you need more in depth, let me know.

 

[GoldenVulture]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

Errr; You joined up to answer a six year old thread ?

 

[Empty Pockets]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

No... he's a time traveler.

 

[DankStar]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

Still doesn't make sense. See you in 2019 for your reply.

 

[Adieu]

Re: Can Some Genius Explain Vox's "Valve Reactor"?

Still doesn't make sense. See you in 2019 for your reply.

Sure it does. That's an employee. A new hire starting to do his job wherever he can find it... which, apparently, is here, six years ago.