[Ardour-Users] New tube amps

Will J Godfrey WillGodfrey at musically.me.uk
Sun Dec 24 02:58:59 PST 2017

On Sun, 24 Dec 2017 11:31:39 +0100
David Kastrup <dak at gnu.org> wrote:

>Ralf Mardorf <ralf.mardorf at alice-dsl.net> writes:
>> On Sat, 23 Dec 2017 23:19:19 +0000, Matt Keys wrote:  
>>>>... "but a real guitar tube amp still surpasses even the best
>>>>transistor based guitar gear."  
>>>I picked up my first "tube amp" this month and love it. It's the tiny
>>>(seriously pedal size) Vox MV50 clean. I run a 2x12 cab with it at 4
>>>ohms (50 watts) and it's a monster!  
>> At least this is the reason why Gordonjcp makes a fool out of himself,
>> begin forwarded message:
>> On Fri, 22 Dec 2017 15:35:39 -0500, Al Thompson wrote:  
>>>On 12/22/2017 03:28 PM, Gordonjcp wrote:    
>>>> Valve amps don't sound any different to transistor amps, and anyone
>>>> who says they do quite honestly needs to lay off the cocaine for a
>>>> while and get some perspective.    
>Frankly, if you can only sell a tube amp sound for a reasonable price by
>putting a tube in, then you'll do just that, even if the tube's role in
>the circuit is that of a light bulb.  Then you add Fender-style rotary
>controls and a backlit VU meter, and people expect and pay for tube
>sound and are willing to swear on it.
>Here we are talking about the amp head described at
>Key part of a tube amp sound is the output transformer.  How much of
>that will you see in a "pedal size" amp that has a class D _digital_
>power amp stage?
>The English blurb actually evades lying all too much:
>    The MV50 is equipped an all-analog pre-amp circuit that features
>    Nutube, a revolutionary new vacuum tube that produces authentic tube
>    tone at a fraction of the size. By taking advantage of this
>    incredible new technology, VOX’s engineers were able to design a
>    true, miniature tube amplifier. Beyond the inclusion of Nutube, the
>    pre-amp circuit in the MV50 features a staggering number of analog
>    components that effectively reproduce the dynamic character of a
>    traditional tube amp. Paired with this innovative pre-amp circuit is
>    a reliable and efficient Class D power amp that has been
>    specifically designed for the MV50. From warm, natural cleans to
>    dynamic overdrives, this power amp has been engineered to respond to
>    the nuances of your guitar and, of course, your technique.
>I mean, "staggering number of analog components that effectively
>reproduce the dynamic character of a traditional tube amp"?  The dynamic
>character of a traditional tube amp comes about by a staggeringly
>_small_ number of components.  A typical full-scale tube amp has fewer
>circuits all-in-all than an average Opamp these days.  If you need a
>"staggering number of analog components" then you do it because you need
>to emulate the very few actually _crucial_ but expensive components.
>That's where the tube sound part actually sits.  The tube itself is
>mostly window dressing and possibly noise generator.
>I mean, now you can go whole hog over this and insist on an actual tube
>amp with an actual tube power stage and not "a staggering number of
>analog components that effectively reproduce" a tube amp.
>But you can't pay your marketing department by selling old technology at
>old production costs (or even higher because of economy of scale) and
>likely not meeting modern energy efficiency standards.
>This basically is a transistor amp with digital power stage modelled to
>sound like a tube amp, modeled to _look_ like a tube amp (or a steampunk
>version of one), and designed to _market_ like a tube amp.
>There is nothing wrong with that except that it makes people even
>stupider.  But then that's what marketing is for.
Not qute sure what this is doing on the ARDOUR list...
However, as someone who knows just a little about genuine VALVE amps I'd like
to add some detail.

The pre-amp stage is what gives a valve guitar amp it's characterisitic
'warmth' - othewise known as even order harmonic distortion - mostly 2nd. It
can also supply a small amount of compression - all due to the non-linear
response of a triode valve. HiFi amps of the period used a pentode here to avoid

The output stage gives the much loved overdrive behaviour - 'soft' limiting.
The output valves don't cut off 'hard' like transistor ones, but do so
progressively adding a rich varied amount of mostly odd-order harmonics.
Additional limiting is produced by saturation of the transformer core. The
exact combination is what mostly gives the different brands their specific

Again, in HiFi amps of the time, this was mostly avoided by running the output
stage either in class A or only just into the AB region. Also with a lot of
local negative feedback using screen grid taps on the output transformer, and
some overall feedback (never seen in a guitar amp). Finally, the output
transformer itself was very much larger in an attempt to eliminate saturation.

It wasn't me! (Well actually, it probably was)

... the hard part is not dodging what life throws at you,
but trying to catch the good bits.

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