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Argh! Don't you just hate all this marketing hype?

Started by teemuk, February 25, 2007, 12:24:10 PM

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teemuk

In case someone's interested, here's a link to schematics for AD15 & AD30VT.

http://www.westebbe.com/Vox/AD15_30Servicemanual.pdf

It's funny how inconsistent the actual design is with all the "Valve Reactor" hype that Vox website boasts:
http://www.voxamps.co.uk/valvetronix/valvetronixtechnology.asp
http://www.voxamps.co.uk/valvetronix/valvetronixvalvereactor.asp

Being interested on how Vox actually applied the design of "Valve Reactor" circuit I have been hunting a schem for Valvetronix amp for years. Now that I finally see one: Such a dissappointment! My few favourites hype phrases are:

"Our patented Valve Reactor power amp consists of a valve power amp with an output transformer electronically coupled to a solid-state power circuit..."

Hmm... so where is the output transformer then? ...I know, in another information source Korg mentions that the OT is actually simulated. What a dissapointment: they omitted the component that really could have made some difference. And what about driving those 12AX7s on starved plate voltages... Also, I wonder from where the guys at Korg got the idea that running two low power preamp tubes in push-pull configuration would create a "power amp".  :grr

"The output transformer is connected to this new VariAmp Power Circuit which uses Constant Current design and Reactive Feedback technology."

Ok, the "VariAmp" circuit looks suspiciosly like an opamp stage with variable gain, the only difference being that the control varies the amount of feedback as well. Reactive Feedback = mixed-mode feedback. Constant Current design? Where?

"The VariAmp Power Circuit cannot be overdriven, is totally transparent and can be configured to be 1, 15, 30 or 60 Watts. The VariAmp Power Circuit does not color or change the signal in any way and the resulting output tone is pure."

I'd like to see an amp with high output impedance that is "transparent" and "does not colour or change the signal in any way". Funniest thing is that this is actually the sole point in the whole design and the non-flat frequency response may significantly contribute to overdriving the amp at certain frequencies. This is a very good example of the basic marketing hype scheme: With tubes coloring the sound = good, with transistors = bad. Yeah, right.

It should be noted that in the concerned circuit the tubes actually contribute very little and a high amplitude signal from the preamp will likely overdrive the input stage phase splitter resulting into transistor distortion.

And my personal favourite:

"This new technology actually has the ability to switch automatically between Class "A" and Class "AB" depending on the amplifier it's modeling!"

Just because a part of the preamp can do this doesn't mean the class-AB chip amp in the power amp stage could. In practice, the amplifier now exhibits the worst case behaviour on certain settings creating crossover distortion in both tube and solid state class-AB stages. Mentioning that would not be very good marketing though, (unless one can come up with a fancy name for this phenomenon, of course).

What is so frustrating in the whole thing is that a vast amount of people actually believe all these marketing phrases. I hate the fact that these days it's pretty rare to see an amplifier ad that would be technically accurate or even "correct" by its terminology.  :grr

Anyway, enjoy the schematics.
...and to say something good, I really like the conservative power rating of AD30VT. ;)