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Al Krow

Hybrid amps...the best of all worlds?

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Well you should definitely apply for the role of UK rep (or indeed global ambassador) to Handbox!

I've just emailed him. Should I be charging a product design fee? Lol!

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[quote name='wateroftyne' timestamp='1492098954' post='3277966']
I think that's probably a question for the chap who built the amp...?
[/quote]

Plate voltage is just one of dozens of potential design choices that could have a negative or positive effect on some or all of us. I just personally feel that it often gets relegated to being an ad-speak sound bite, but I have plenty of other windmills beckoning...

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[quote name='Passinwind' timestamp='1492102480' post='3278007']
Plate voltage is just one of dozens of potential design choices that could have a negative or positive effect on some or all of us. I just personally feel that it often gets relegated to being an ad-speak sound bite, but I have plenty of other windmills beckoning...
[/quote]

Absolutely - it sounds bloody great, though :-)

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[quote name='wateroftyne' timestamp='1492103338' post='3278018']
Absolutely - it sounds bloody great, though :-)
[/quote]

Cool, In many ways I envy those who actually like their amp rigs. Meanwhile, I'll keep plugging away at my own designs, which are just barely ticking the "adequate" box for my wants and needs. I recently acquired my first fretted bass in over 30 years, which is also my first fiver string one ever. I love to change things up substantially every five years or so, never know which way things might swing this time!

Edited by Passinwind

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[quote name='Passinwind' timestamp='1492104022' post='3278027']
Cool, In many ways I envy those who actually like their amp rigs.
[/quote]

I've been playing for about 30 years myself, and this is first amp I've had that sounds exactly like I want my amp to sound like... and still makes me smile a year later. It's taken a while to get to this point!

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I managed to correspond with Leszek - he has concerns about making a R-400 combo, as he feels he would need to use expensive specialist stands to prevent vibration from damaging the tubes and he doesn't have access to such stands.

Any suggestions to solve? How do Mesa deal with this concern in the WA scout?

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Regarding high voltage and that tube driven mosfets in the WA back end, this is what the
Mesa engineer "agedhorse" answered when I asked those features in a contemporary thread on Talkbass:


"The B+ supply is somewhere around 300V. Power supply voltage is only a small factor as it is entirely possible to design a preamp operating at a lower voltage that sounds virtually identical. There are many other, more important factors involved.

The second tube provides the direct gate drive of the mosfets. It's a combination PI/driver with voltage and current gain. It's a unique application of MOSFET technology."

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Sratas...thanks but I'm not really sure I understood any of what you just said! (But I suspect it was to an earlier Q in the thread and not to mine above) :)

I think the more sensible / obvious solution would be for me to bite the bullet and go for separates. I'm thinking maybe a Barefaced SM to pair up with the R-400 - how does that sound? WoT what are you playing your R-400 through?

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Yeah, it was directed to Passinwind and Wot. Some posts ago we were debating what full voltage tube pre means and the role of the V2 tube in the Walkabout. So I asked the Mesa engineer who gave me that answer. Sorry if I created a bit of confusion by malpositioning my intervention

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My opinion is that the amp and the preamp should not colour the sound.This EQ's work.
Thats why i prefer transistor rig.
But the problem.in most of us is,we dont give enough time to try the eq/compresor/etc of our gear.I have a practice combo 6years,and still discovering things i didnt knew before

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[quote name='sratas' timestamp='1492356608' post='3279631']
Regarding high voltage and that tube driven mosfets in the WA back end, this is what the
Mesa engineer "agedhorse" answered when I asked those features in a contemporary thread on Talkbass:


"The B+ supply is somewhere around 300V. Power supply voltage is only a small factor as it is entirely possible to design a preamp operating at a lower voltage that sounds virtually identical. There are many other, more important factors involved.

The second tube provides the direct gate drive of the mosfets. It's a combination PI/driver with voltage and current gain. It's a unique application of MOSFET technology."
[/quote]

That is interesting, in that the schematic shows the tube in the preamp is basically just a standard Fender style preamp stage, with some fixed resistors for the tone controls (EQ is then handled via an op-amp based stage after the preamp), and it seems to indicate they voiced the driver stage a particular way.

So although "unique" is arguably questionable related to any aspect of amp design, it may well be this is an important and characteristic part of the amp topology, and it is a little different from the more typical approach of a Fender style tube preamp feeding an all solid state power-amp stage.

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I think you may hit a good point. The power stage in the WA reacts like anything else I used. It can impart a considerable color to the tone and, when pushed, it starts to add harmonics and grindy distortion, a pleasant one. Definitely a unique behaviour amongst hybrids

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[quote name='bassman7755' timestamp='1491865241' post='3276052']
Completely pointless IMO. There is solid state circuitry that is indistinguishable from a valve preamp so really there just isn't any point. Valve power amps are harder to emulate because of complex stuff going on in ancillary components like the power supply and transformer.

A solid state preamp, valve power amp hybrid makes much more sense.
[/quote]

I think it depends on your sound. If you're pressing your pre-amp to the point where it's giving you distortion then tubes do that rather nicely. But if you've got a clean sound going on then you're not going to notice much difference.

One of the more noticeable things in tube-amps aside from the power-tube compression already mentioned is also the tube rectifiers. They're much less efficient than solid-state ones and so they power-starve the amp when there are quick changes in the dynamics, which gives a nice sound. I believe amp techs refer to this as 'sag'. If you've got an amp with a solid state rectifier, and a solid state power stage, I doubt you're going to get much from a pair of tubes in the pre-amp.

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I'm a bit confused by that statement. Are you saying e.g. that the tube preamp on a Mesa is a bit pointless and the gorgeous warm sound on a Mesa Carbine M6 is pretty much down to the Mosfet SS power amp?

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If I read it correctly, I guess what he's saying is that in order to take advantage of the dynamic benefits of a tube power amp, you need to run it right in the butter zone of that particular circuit.

Compared to the deeply enjoyable dynamic quirks of a hard driven power amp stage, the effect of tubes in a preamp played cleanly is relatively subtle.

For what it's worth, I've always found power tube compression and sag indispensable for sweetening the middy honk of electric guitars, but for bass I find it much less essential. YMMV, etc. :)

Edited by Danuman

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Ok that makes sense Danuman, thanks.

I've seen quite a bit of love for the Mesa hybrid sound on this thread but pretty much none for the GK MB Fusion 500 or 800 which have a full complement of three 12ax7 tubes in the pre-amp, the lack of a GK fan club for the fusion has taken me a little by surprise? In terms of a lightweight head it was very much on my shortlist.

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Those pre-amp valves in the GK MB Fusion make a lot of difference, in comparison to the regular MB 500. A lot more warmth and depth to the sound, making it able to sound very un-GK-like if desired. Not to say it doesn`t sound like a GK though, it does, just that the pre-amp valves give it a lot more flexibility than the regular MB 500 which is the typical GK sound through and through.

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[quote name='markstuk' timestamp='1492410933' post='3279907']
Interesting that even the mesa engineer suggested there was no real difference with a starved plate design.
[/quote]

I believe the engineer in question is Andy Field, who is a "real life" friend of mine. With all due respect, I think some of you missed his point. I'm quite sure he was referring to using a tube with a curve set that works at the desired voltage in a way that gives the engineer's desired result. Plenty of tubes will work fine with a 12-24 volt plate voltage and sound nothing like a 12AX7 run that way. And then there are also many guitarists who actually love how a 12AX7 sounds in starved plate mode. I know it's very tempting to repeat Interweb folklore, but as someone who has worked on literally thousands of tube amps, the closest thing to wisdom that I can manage is "just depends."

Edited by Passinwind

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It's quite frustrating for me and those like me who aren't unable to understand the deepness and actual complexity of these arguments. I'm completely sure that you and Andy are right, but I can see why you are close friends too and why you do sound alike when explaining.

Sometimes, being able to simplify and communicate a complex item in order to allow comprehension by unexpert people is rewarding and most of all, it can be done, for sure.

This concept, wich is not criticism by any means, reminds me of everyday working moments of mine. My daytime job is medical doctor and research, and just about always I'm asked to explain very complex arguments and implications to the common people, sometimes to those who did not study at all, unable to write etc.
Given the paramount importance to these informations, I simply cannot simply answer " it just depends" even if many times it just depends if we pretend to embrace the full spectrum of unknown possibilities . I know I can do better, and the vast majority of times the patient fully understands what is important fir him. Will I ge chairbound? Will
I die in a month? It just depends is not a proper answer in my world. Maybe they will not comprehend the techy or biological reasons for that, but they understand what he or she needs to know.

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[quote name='sratas' timestamp='1492753277' post='3282847']
It's quite frustrating for me and those like me who aren't unable to understand the deepness and actual complexity of these arguments. I'm completely sure that you and Andy are right, but I can see why you are close friends too and why you do sound alike when explaining.

Sometimes, being able to simplify and communicate a complex item in order to allow comprehension by unexpert people is rewarding and most of all, it can be done, for sure.

This concept, wich is not criticism by any means, reminds me of everyday working moments of mine. My daytime job is medical doctor and research, and just about always I'm asked to explain very complex arguments and implications to the common people, sometimes to those who did not study at all, unable to write etc.
Given the paramount importance to these informations, I simply cannot simply answer " it just depends" even if many times it just depends if we pretend to embrace the full spectrum of unknown possibilities . I know I can do better, and the vast majority of times the patient fully understands what is important fir him. Will I ge chairbound? Will
I die in a month? It just depends is not a proper answer in my world. Maybe they will not comprehend the techy or biological reasons for that, but they understand what he or she needs to know.
[/quote]

Nobody's going to die here and I am just a technician, not an engineer. But I'm certainly willing to point you at some good study material. Do you understand how to derive a tube load line? I'd suggest that we start there, since it's the most basic level of designing a tube preamp.

Edited by Passinwind

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Fwiw my attempt at simplification is that plate voltage doesn't define the sound of a properly designed amp.

Mostly it's about the combined frequency response of each stage of the amp, and in some cases how that response changes when pushed into saturation.

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Thanks passinwind, but I don't want to begin to study the matter. I would like to obtain simple answers. For example: is there a solid reason to have a 300 v tube pre from a listener or player point of view? If the answer is yes, those reasons apply only if the pre is pushed or even if it is used clean? If not, there are examples of starved plate designs in so called all tube monsters, like the SVT, orange AD 200 etc.? Thanks for your attention

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[quote name='sratas' timestamp='1492758276' post='3282881']
Thanks passinwind, but I don't want to begin to study the matter. I would like to obtain simple answers. For example: is there a solid reason to have a 300 v tube pre from a listener or player point of view? If the answer is yes, those reasons apply only if the pre is pushed or even if it is used clean? If not, there are examples of starved plate designs in so called all tube monsters, like the SVT, orange AD 200 etc.? Thanks for your attention
[/quote]

Respectfully, I feel like the whole starved plate thing is/was an unquantifiable tangent, there's a broad range of valid operating voltages for typical tubes, same as with most analog electronic components. And even so many (most?) bass/guitar amps are derived from the same circuits and run the tubes at what I would consider pretty normal voltages (as Passinwind has already alluded to, there are standard techniques to calculate the operating point of the tube, and there is no "full voltage" mode of operation).

In battery powered pedals (and possibly a few amps, but I'm not aware of any) things get a little less clear - folks sometimes run tubes at abnormally low voltages, and IMHO this is mostly a marketing strategy (folks see a glowing tube and are prepared to pay more), but I'm sure there are a few examples of properly designed circuits deliberately using tubes outside of their normal operating range, it's just not a common thing, and none of the classic amps circuits I'm aware of do it.

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