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Mesa Boogie Dual Rectifier backup ss amp

Started by pelanj, March 03, 2009, 07:46:49 PM

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pelanj

Hello all,
since a few years, I use a M/B DR (two channel) as my main amp, having a EL84 equipped .50 Caliber as a backup (both rackmount). I would like to present my view on the "tube sound" with regard to modern metal tones. Then, based on this, I would like to find a currently manufactured (or easy to get in Europe) ss backup amp for the DR, good enough to use at rehearsals where the other guitarist stil uses a DR. And after that, one smaller one for my "bedroom" practice.

My main tone is the Red channel, Orange being cloned to modern set for more "midrangey" sound with a delay. As the speaker box, I use something very similar to M/B vertical half-back 2x12 equipped with EVM12L clones from Eminence, lower chamber is ported in the Thiele style. I also sometimes use one half of ADA SplitStack Vintage (bright position), the other half is in my bedroom for practice. Sometimes a standard 4x12 with V30 Celestions. My main guitar is a Gibson LP Studio. When I am using the Caliber with the same box and guitar at rehearsal volume, I think I can hear the compression (be-it poweramp or not) and the amp is pushed almost to its limit. I do not have this feeling at all with the DR's 6L6 poweramp. So I guess I am not a fan of heavily compressed power amp tones, however that "tube power amp" sound is something I can really distinguish from a ss amp. I wonder what it is.

Before getting the DR, I was experimenting a lot and I have found the following - for my tones/application, a tube preamp is not necessary, a well designed solid state ANALOG (no POD, Digitech RP) preamp (a nice exampe - Rocktron ProGAP)/distortion box (but not for example MT-2) can do it fine. However, I have always found a tube power amp in the signal chain as madatory. Either being a pure 50/50 style rack power amp (properly biased 6L6's slightly preferred in the same amp to EL34's) or a "reamping" system, where a low power all tube head (even any preamp into its FX loop) was run into a load and later amplfied by a 2x12 guitar combo's poweramp (Behringer GMX212 to be specific). Between the tube head and the combo, a splitter was inserted to form a parallel FX loop changeable to a WET-DRY stereo arrangement with this particular combination. A Boss Turbo Distortion with an old Marshall 1959 (not sure about the exact type, maybe even modified) could be tweaked to a very heavy yet articulate sound. A Fender SuperChamp XD, being digital, with it's tube power amp sounded also quite convincing.

I currently own two pedals worth mentioning - a Tech21 GT2 and Digitech Death Metal, both quite usable with a fullrange powered speaker for practice. Both have this thickness and sweetness at low volume, never tried them really loud.

I have read through teemuk's great book to realiye a few things. What I need is probably an ss amp with a convinceable hi-gain sound that cuts through, around 100W (or more to have some headroom) preferably mixed mode feedback power amp and a serial FX loop. The FX loop is needed, because to be as satisfied with the tone/feeling as possible, I would like to implement most probably some kind of a switchable soft limiting device, either tube or not, to substitute the tube poweramp (in a quick experiment, a compressor stompbox could be set to sound quite convincing. In my view,a gain cascading preamp is highy preferable - if a Boss OD was run into a Boss DS, the total sound reminded "tube sound" better than each of them alone.

I would like the amp to be as light and small as possible (Crate PowerBlock does not work). I am looking at the RX or RG series Randalls. I remember once playing an RG150G3 next to a RH50T (all tube). While the RG had a kind of more versatile distortion, it failed in the "tubeyness" at the first few tones. Unfortunately, that is some time ago and it was only a few minutes. I used to have then the RH for some time, so i know the sounds quite well and I have long forgotten how the RG played. Are there any readily available alternatives?

As for the practice amp - basicly there is nothing better as 12" speaker, even at low volumes. Those 8inch speakers sound like c..p with anything but clean sound. I have modified my old MS-2 with an speaker out instead of headphone out (with either 10 or 100 ohm series resistance for attenuation) - and it works quite well with one half of the SplitStack - with everything on full. But I miss post-distorion tone controls. Now, here is the problem. The smaller the amp is, the less controls it has (and no speaker out as well - modifying is easy but voids the warranty). I do not need more than 2 W of power for clean tones and much less for distorted. I need only slightly higher volume than the MS-2 with a 100 ohm series resistor to a 8ohm box - that gives power of around 10 mW. That means any common combo amp could be fine, I would prefer a head instead. One that comes in mind is the MG15 microstack, but it is not sould without the (IMHO) useles speaker boxes. The other possibility is a modified small combo.

So, do any of you have experience of playing such a small amp/combo with a proper speaker? Which could be fine for me?

And, at the end, please select from amps/combos available at www.thomann.de or www.musik-produktiv.de, as any other would be probably hard to get at my place. Thanks for reading my monstrous post and I am open to suggestions and debate:)

phatt

Hi pelanj,

Before you get too far into it all, have a read of this page as I believe it simplifiys what is often made Overly complex.
Yes I agree Power tube stage is hard to copy with Sstate.

http://www.amptone.com/truesecretofamptone.htm

Does sound like you already have most of the gear needed to do the tricks your searching for.
Cheers Phil.



pelanj

Hello Phil,
I have read through amptone many times and I am quite familirar with the concepts. I tried to describe what is my tone and what have I have already done to achieve it. As a summary, I am searching for an amp that could stand next to a DR and not being ashamed or even drowned by it. With a possibility of future installing soft limiting circuit (maybe even a small tube power amp into fx loop). And something smaller for home to power my other 2x12 with less severe requirements.

I would love to build one competely myself, however just adding to and existing and working design is less time consuming and could provide the same results.

phatt

Hi pelanj,  (sorry, i been busy)
          That's great,,then you have some idea of what is possible.
I very much doubt if there is going to be a stand alone SState setup
that will match what you are already using but some here may wish to advise of there setups
as they may have had more luck with tube emulation than myself. :tu:

I quote from your 1st post:
I have always found a tube power amp in the signal chain as madatory.
Either being a pure 50/50 style rack power amp (properly biased 6L6's slightly preferred
in the same amp to EL34's) or a "reamping" system, where a low power all tube head
(even any preamp into its FX loop) was run into a load and later amplfied by a 2x12 guitar combo's poweramp
 
       
Re the difference between 6L6 and EL34. Do you know what Transconductance (TC) means?
If you wish I can give you a general overview of TC and Why it's so important,
might help you define your sound/tone.

Yes even a small tube power amp can be used for "ReAmping". Valve preamps WON'T get you the sound
as you need a push pull power stage to do it. The unbalanced PI along with transformer action is part of the magic,
Teemu's book mentions some of the transformer quirks also.
My personal opinion is that the Transformer can't transfer the high frequency hash that rides on the heavy overdriven square wave.
It's Only present on the primary side but magically disappears on the speaker side. ???
So unless SState can do that It may not sound convincing.
 
I personally use a 10 Watt tube power stage in my ReAmp setup
which is loosly based on the Guytron GT100 concept.

My Signal path goes like this;
Tone box > OD circuit > 10watt PP TubeAmp > Soak/Spk-to-Line > Graphic Eq >
120Watt SState PwrAmp > 15inch speaker (sealed back)
(the first 4 are all home brew gear.)

The result is, Any Tone/Crunch/OD I need At ANY SPL I choose.

Quite obviously there are many ways to do this but as I only have very limited funds
to play with I use whatever I can scrounge from old electronic stuff.

To qualify all this my setup has to compete with a Carvin Legacy,,a Cyber Twin and a couple of F De'villes.
My gear can dial in Exact tones while the others struggle with some of the in between tones. (like Dire Straits)
The Legacy is awesome loud but only with those exotic speakers mine are just no names cheap ones.
But remember I can get the same sound /tone/dynamics at home in my shed,,,, They Can't.
That might appeal to you?  8|

All my stuff is cheap to build,ie, my graphic is an old hifi type cost me $10 at a sale.

Anyway this might give you some food for thought.
Phil.

J M Fahey

Dear Phatt, that´s exactly the relatively no pain but precise way to go.
To summarize it, and compare it what´s available "out there":
the signal chain should be:
1)Active mics/active electronics in guitar/inline clean preamp
Al three amount about to the same end result: powerful, clean guitar signal; sent into:
2)Some GOOD distortion/overdrive that you like; sent into:
3)Good clean preamp, Fenderish or Marshalish or Voxish (your choice) which can be Tube (the classic solution) OR SS which sounds the same *when clean*;  driving:
4) Some *Power* tube, which can be overdriven and Transformer coupled to a real-world speaker , with all its quirks, resonance, impedance and phase shifts, nonlinearity, etc.
Here's where the real Witches Brew cooks, in that complex interaction between those three actors.
I agree with you that a PP amp is best, but even a humble Champ can prove its worth there (I´ve already tested that).
That signal should be suitably padded and re-amplified by
5) A good SS amp driving guitar speakers.
5)Your inclusion of a Graphic between 4) and 5) allows for fine tweaking of the sound, but must be used subtly and carefully to avoid destroying the sound you already have.
I agree that that´s the way to get World Class sound in a very practical way.
Congratulations!!
Please post some MP3s
Bye.
J M Fahey

pelanj

Phatt, transconductance as I understand says, what plate current corresponds to grid voltage, kind of "amplification factor". That is nice setup you have, I am also very slowly heading towards something very similar. I have a 15W higain tube amp to play with, but I have to finish the reamping stuff.

J M Fahey, do you think that speaker load is essential? Could it be something like Weber mass - coneless speaker. Or a speaker completely enclosed in a box not to produce any noise.

My first idea was to get a ss amp with a good distortion tone (Randall, maybe) and use its preamp as tone generator, then "reamping" in the FX loop and use it's poweramp to drive speakers. I think this is a valid approach using the same principles as you both described. Anyway, thanks for helping me with sorting my thoughts:)

J M Fahey

Hi Pelanj. I think that unfortunately today the speaker is still necessary; we should experiment some more until it can be fully emulated. I´ve tested a lot about SS reamping a tube amp. To begin with, with a resistive load it sounds  different (not bad at all, similar to a very good pedal) ; but a real speaker load provides the real thing. Let me define exactly what i´ve found, and which basically agrees with your experiments: if I get a certain voltage waveform (from a tube amp) across the speaker terminals of, say, a Vintage 30 mounted in a certain box, and I reproduce that *same* voltage waveform, across one or many V30s mounted in similar boxes, at *higher or lower* levels, I get the exact same sound with the important advantage that the original tube sound was obtainable at only a fixed volume while this "clone waveform" can be reproduced at any volume, with only two caveats:
1) at lower volumes, *my ear* hears less bass , and
2)The SS final amp must be powerful enough to *NEVER* clip at rehearsal or stage levels.
The Weber mass is 70% of a speaker .... and provides 70% of the sound. Obviously, it´s almost there, but it still lacks emulation of 2 smaller but still important physical aspects of real speakers:
1)the short voice coil of a typical guitar speaker travels outside the gap often, mechanically "clipping" peaks, and that in a frequency dependent way, which I at least coudn´t emulate with diodes. (Well, I could do it at a fixed frequency, say 90 or 100 Hz, but not across a usable range of frequencies). As a by product, the V. Coil leaving the gap loses inductance brutally and in an unsymmetrical way (because magnetic circuits are unsymmetrical), modulating the high frequency response.
2)Reactive load boxes emulate only the main resonance (80/110 Hz) and one or two also emulate the impedance increase above 500 Hz, but none to my knowledge emulates other smaller but audible resonances which are mechanical in nature and are generated by the paper cone itself.
Also a myriad peaks and dips are lost.
That´s why I say that for a perfect response a speaker (even in an isolated box) is still needed, but with patience and hard work that will be emulated too.
As for a Randall, it does NOT sound like a tube amp, it´s very good but on it´s own SS way, which is commendable.
In that case, just hook a Randall preamp to a Big power unit and let it loose.
Bye and keep experimenting (and don´t forget those MP3s)
J M Fahey


phatt

Quote from: pelanj on March 07, 2009, 05:53:33 PM
Phatt, transconductance as I understand says, what plate current corresponds to grid voltage, kind of "amplification factor". That is nice setup you have, I am also very slowly heading towards something very similar. I have a 15W higain tube amp to play with, but I have to finish the reamping stuff.

J M Fahey, do you think that speaker load is essential? Could it be something like Weber mass - coneless speaker. Or a speaker completely enclosed in a box not to produce any noise.

My first idea was to get a ss amp with a good distortion tone (Randall, maybe) and use its preamp as tone generator, then "reamping" in the FX loop and use it's poweramp to drive speakers. I think this is a valid approach using the same principles as you both described. Anyway, thanks for helping me with sorting my thoughts:)


Hi,
Yes Palanj your spot on, it is just a fancy hi-teck way of saying how much signal swing is needed on the input
to attain full output. I do wish those technical book writers would stop all the mumbo jumbo and just write
in plain english, as it took me some years to understand what the hell they where talking about.
Just be aware that "Amplification Factor" is in fact another tube term which is not the TC.

I only metioned the TC because it never gets much mention except in a fleeting commentin mag reviews where they
often say that a particular tube amp being tested has a distinct "British or American" flavour/quality/tone.
When I started out messing with valves I scratched my head and wondered what they meant but
It's all about the TC "Transconductance" or kind of like Gain if you don't want to do hard maths.
6L6 is a Tetrode and EL34 is a Pentode. 6L6 pumps 19 Watts and EL34 is 23 Watts. Ok at a glance they might seem
somewhat similar but what about the TC? To the best of my searching a comparison would look something like this.
Transconductance of some common guitar power valves
TC of Tetrodes
   6V6  = 3,800   umhos
   6L6  = 8,000   "
  5881  = 5,500   "     (I think)

TC of Pentodes
   EL84 = 11,200  umhos
   EL34 = 11,200  "
   ECL86= 10,000  "     (ECL86 also called 6GW8)
Once I understood this It became VERY Clear to me why Fender and Marshall Amps sounded so different.
Even though a 6L6 and a EL34 have similar Power Wattage rating they respond in a very different manner due
to the way they transfer that power, the TC.

An EL84 only needs about 30VAC signal swing on it's input grid to achieve full output wattage, whereas a 6V6 needs
more like 60/70VAC swing. they are very different tubes. Which is why you often see Tetrodes using an 12AT7
Phase Splitter as they have nearly 10 times the current ability over an 12AX7. In simple terms assuming identical
Tube amp circuits, an EL84 powered amp is going to distort LONG before a 6V6 even though the 6V6 has more power.

Now the stuff you are probably wanting to know,
I should add the Amptone link focuses more on Power Attenuators but I have just taken that one step further and
found that ReAmping resolves most of the loss found in resistive load attenuators.
It is still not as liquid as the Guytron amp but I have not spent much on this project.

Fahey has given you other options you may wish to try and you never know you may find something
that I have missed but this will give good results and will get you started, It's simple and works.
I'm posting a basic circuit concept that might help get your head around it if your wondering how to go about it.

As to the soak box,
Make R load about 2 to 3 times bigger than the wattage your tube Amp produces as this will keep it warm but
not overly hot. Aussuming 8 ohms output then 3x27R WW x10Watt resistors will be about 9 ohms and that
is close enough for an 8 ohm system. Exact R is not important if anything a little more may be of some benifit,
try not to go less though. This will handle a pair of EL84 tubes delivering say 17 watts max.
Please make sure Any tube amp you use can actually run full bore without issue as some of the modern tube gear
uses underrated transformers and tend to use excessivly high voltages and things can get very hot.
I have read of horror stories so thought I should add a warning.
The level shift is optional but I find it very useful. If the signal coming from the soak is to big and clips
badly at the EQ or second Amp then reduce the parralel 39k R down to 22k and make level shift pot 10k instead.
The level shift is a recent addition and I'm finding very useful but you may find other ideas more useful.
As shown it will deliver a line level out which should interface to any equipment that has line input.

You could plug into the Effects return of another guitar amp if you wish but it will probably be to strong
for the front input of another guitar Amp.
Have fun with it, Phil.


phatt

 Damn! Could not get both pics to load , so here is the Speaker load to Lineout drawing.
Phil

phatt

Quote from: J M Fahey on March 07, 2009, 12:18:50 PM
Dear Phatt, that´s exactly the relatively no pain but precise way to go.
To summarize it, and compare it what´s available "out there":
the signal chain should be:
1)Active mics/active electronics in guitar/inline clean preamp
Al three amount about to the same end result: powerful, clean guitar signal; sent into:
2)Some GOOD distortion/overdrive that you like; sent into:
3)Good clean preamp, Fenderish or Marshalish or Voxish (your choice) which can be Tube (the classic solution) OR SS which sounds the same *when clean*;  driving:
4) Some *Power* tube, which can be overdriven and Transformer coupled to a real-world speaker , with all its quirks, resonance, impedance and phase shifts, nonlinearity, etc.
Here's where the real Witches Brew cooks, in that complex interaction between those three actors.
I agree with you that a PP amp is best, but even a humble Champ can prove its worth there (I´ve already tested that).
That signal should be suitably padded and re-amplified by
5) A good SS amp driving guitar speakers.
5)Your inclusion of a Graphic between 4) and 5) allows for fine tweaking of the sound, but must be used subtly and carefully to avoid destroying the sound you already have.
I agree that that´s the way to get World Class sound in a very practical way.
Congratulations!!
Please post some MP3s
Bye.
J M Fahey

Fahey,
          Thanks for your words of encouragement, Sounds like your more into the teck side of this stuff than myself :)  I still cringe at the thought of all the maths you need to know to work it out but this is all good as the more options put forward allows people to make well informed decisions.

I look at it this way; I'm 90% there with cheap mostly secondhand or DIY equipment.
Then I look at how much $money$ I have to spend to get the last 10%  yuk
Keep in mind I do this on a strict budget so if budget is no issue then sure try all the options.

All this back EMF / RCL spk equivilants/ Damping stuff is obviously quite real. Fine, No argument from me BUT I would question how much of it you can actually hear?

If I understand you correctly I think you're coming at it from a different view, ie, your trying to capture the tone/dynamics of a said tube amp but that concept is a lot harder to impliment.
It demands the mojo tone already exists inside the tube amp whereas I'm trying to negate all of those complexities.
I'm only using the tube pwramp as a building block, a giant distorion unit if you like. ;D

I have heard enough amps in one lifetime to know that I'm still ahead of the well trodden path where everyone keeps changing Amps/Tubes/PU's/Speakers hoping for some magical mojo to materialise.
Consider EVH, in the early days he likly used resistive loads and some kind of reamping. (probably SState)
The idea may well be flawed but still good enough to make him famous.

Also Randy Bachman used a reamp setup on the famous hit song "American Woman" again technically not ideal but Wow,, what an amazing guitar track that turned out to be. (google Hertzog and Randy B)

BTW, the Guytron GT 100 "IS" based on much the same basic idea, a pair of EL84 driving a resistor then into a big power amp.
The moment I heard that Amp,, I knew it was different and I wanted that sound.

I would simply say this; OK mine is not as refined as the Guytron but in my humble experience,
Any Loss with my setup is far outweighed by the amount of Control I get in return.
Sorry but loading MP3's is out of my ability with computers, I'm still learning how to get around this web thing. OK laugh if you want but some of us older folks struggle and are still trying to catch up.
Cheers, Phil,,, Nambour Australia.

pelanj

That is very nice and informative post, Phil. Your setup is kind of similar to my test setup with non-dedicated
components. I used a small and kind of cheap 15W custom built head with a resistor ("giant distortion pedal"
) and a DI-box (level shifting), then to a ss combo. The tube amp amp I used had a big flaw. It had a great tone but at a too low or too high sound level - this setup allowed me to have any of the nice tones at any volume. Later I moved on to more conventional amps (JCM800 2204, Engl Fireball and now Mesa Boogie Dual Rec.), but I still keep this concept in mind and now I am getting really close to a perfect "bedroom" or recording amp.
I already have the parts for my dummy load and 10-30 W ss power amp but I am still waiting for my low wattage amp being built. I prefer to get all the parts together before I start.

Now I have an idea of a "universal" sound rig. Programmable preamp, a programmable EQ, tube power amp, a relatively small PA amp in a rack, connected with MIDI. There are some amps/preamps close to it, but quite large tube power amps are used, when it is not necessary.

J M Fahey

Dear Phatt, you´ve hit the nail spot-on. What you suggest does indeed sound *very* good; much better (and real) than most DSPs I know (and I say "most" only because somewhere somebody *might* have gotten a little closer). Overdriven push-pull pentodes  are, so far, "state of the art", and you capture just that sound.
No small signal Triode is a Power Pentode (Duh), although all sales managers want us to believe that.
Bye.
J M Fahey

Michael Allen

If you're fine using a solid state preamp and will run a tube power amp from your rack... Check out the Dr. Boogie stompbox. It can and has been used as a standalone preamp. You can find info on it at the diystomboxes.com forums. It's a FET emulation of the Triple Recto (and probably Dual Recto) preamp. This is a great pedal and has really gained a lot of popularity. Incredibly simple solution, and maybe your situation is a little too complex.


pelanj

Just a small point - not only push-pull pentodes, but single ended pentodes/triodes provide the tube feel as well (all the small tube combos out there). I think an ECL86 or ECC81 power amp should be sufficient and hope to try out soon.

The Dr.Boogey pedal looks nice - I might try one later as I have a bunch of distortion pedals with quite nice sound if used with a tube amp.