Discussion in 'Amps and Cabs' started by EADGBE, Apr 14, 2012.
Dr. D explains it best..
...is something totally irrelevant in discussion about generic musical instrument amplifiers, regardless of whether they are tube or solid-state.
One thing to keep in mind is that many of the differences you're talking about are the result of other components in the circuit that are there because of the tubes, not the tubes themselves. The OT is a good example...SS amps don't require them. So if you like the distortion you get from an OT, you may not hear it in an SS amp. (Without some sort of facsimile circuitry.) The point is that the difference in this case isn't coming from the tubes, it's coming from something else that the tubes needed. IOW "tube sound" often doesn't come from the actual tubes.
All that said, I agree with those who've said that some tube amps "sound SS," and some SS "sounds tube," and that the technology doesn't necessarily govern the aesthetic result, esp once it gets past your auditory nerve. I would also agree that it does indeed help to understand a little about how the equipment works when you're trying to use it...so IMHO you may well find that your question is useful and valid.
Bottom line obviously is to try 'em all and play what makes the music work for you. Personally, my stuff runs the gamut...tube, SS, digital, store-bought, homebrew...and regardless of the innards, each bit of it does at least one really cool thing that none of the others can. The trick is to explore each piece and figure out what it likes to do best.
This is a serious question, which should get a serious answer. Back in '88 before the end of the cold war, tubes became scarce and Paul Reed Smith and I started working on a solid state answer. The consequential amp, the PRS Harmonic Generator was not really the answer, but does have a following. The start of Gulf War I (January 1991) effectively put an end to the Harmonic Generator amp before it got started. So I continued on after Paul dropped the project.
I researched the problem extensively between up to 2003, when I decided to set up for production of Pritchard Amps. This research has produced amps that exceed the character of most tube amps. This research examined the following:
1. The nature of triodes. An important feature of triodes, per the Radiotron Designer's Handbook, is that at some input level, the second harmonic is 30 db below the fundamental AND the third harmonic is 50 db below the fundamental. My plate character circuits do that. Their characteristics look like triode tube characteristics when measured on a curve tracer. Crystal lattice effects are not here.
2. What is not important is that they run at high voltages or at high impedances. My preamp circuits run on plus and minus 15 volts, 30 volts total. Since they run at generally 12AX7 current levels, the impedances are a tenth as much. And that helps ignoring the increased capacitances that printed circuits produce. At the same time the lower impedances also ignore radio and television broadcasts better.
3. A distinct problem with solid state circuitry in comparison with tube circuits is the required biasing. Transistors circuits require biasing at a much higher proportion than tubes. So when the tube clips, its biasing is not up set as bad as when transistors clip. The biasing requires some time to straighten out because the bias circuit usually has some sort of capacitor to raise the gain.
4. While junction field effect transistors do have a high impedance like tubes, it is not coordinated with the plate as triodes are. They are more like pentodes, which are routinely not used in guitar amplifier preamplifier sections. However, some high gain amps that use multiple stages, put in resistors in series with the coupling capacitors to reduce the bias shift created by grid conduction. If I remember correctly, Boogie had a patent on that for their output states.
5. My Amp 11 (the 11th chassis design) demonstrated that the bulk of the tube character comes from the output stage. Furthermore, the output stage is not very well described in textbooks. In fact, there is a lot going on.
6. As we know from tube transmitters, the screen grids are often used to modulate the carrier. So signals on the screed grids can effect the output of tube amps as well. These signals are the bias level and ripple. Changes in the bias level produce compression (see a Boogie patent) and the ripple broadens the spectrum of a note, perhaps producing fat.
7. Individually, power tubes have substantial amounts of second harmonics. However, since they are used in push-pull, these second harmonics are either canceled or translated into odd harmonics. A matched pair of output tubes in a true Class A amplifier will cancel since those tubes are conducting all of the time. A matched pair of output tubes in a Class AB amplifier will be translated into odd harmonics because they produce the same character on each half of the cycle. (A mathematical analysis shows that even harmonics produce different waveform shapes for the positive half wave and the negative half wave. But odd harmonics produce positive and negative waves that are mirror images. One output tube does the positive half and the other does the negative half.) Unbalances in output tubes or phase splitters produce even harmonics.
8. There is an interaction between the amplifier output stage and the power supply. This is created by the tube bias current being about 35 milliamps (for 6L6 or EL34) or 70 milliamps for a push-pull pair. However, when driven hard, the power supply must produce about 250 milliamps. This change produces a drop or sag in the power supply voltage. While some of this sag is from the transformer, most is from the power rectifier, such as 5U4. This sag accentuates the attack. It also makes the amp sound like it is continually trying to do more. It provides an element of feel. In a Pritchard amp, the output stage has a bias current of about 70 milliamps also, but when driven hard, the output stage draws an average of about 2,750 milliamps from each of the positive and negative supplies. Consequently, the sag is far greater in spite of lacking a tube rectifier.
Of course, solid state does have a huge advantage over tubes, they are no where near as fragile or microphonic. They are lighter since they don't require as much iron since chokes and output transformers are not needed. For example, my 4-10 using Alnico speakers is 25 pounds lighter than a Super.
The general functional reliability of solid state is greater since after an initial infant mortality the failure rate is very low for about 20 years or so.
The tone reliability, at least of Pritchard amps, is very good. They sound the same day in and day out, inside or outside. Aside from not wearing out, the low impedances are not nearly as subject to humidity.
So, there are many reasons for tube amps to sound better than the usual solid state. However, as Pritchard amps have shown, those considerations can be designed into an amp and can be tweaked to performance beyond tube amps.....
Have a great day, Eric
Sorry to disagree with you, Eric, but all solid state amps, yours included don't do it for my ears. I guess you could argue that my ears are flawed, but you are building a generically "tube" sounding solid state amp. I can appreciate your design philosophy, but for anyone to claim that your solid state device will behave with the true complexities of electrons in a vacuum tube is asinine to me.
You're kidding right?
Deluxe... what model of Pritchard have you worked with, or is your opinion based on sound clips, etc., off the net? Serious question.
Clips mainly. Every clip I've heard pale in comparison to clips of my favorite tube designs. My main problem is most of these designs go for a "tube" sound vs a circuit in particular. The reason they will probably never float my boat is due to even the subjective differences you can hear between individual preamp tubes you can swap in and out of certain designs for different results. Preamp distortion vs PI distortion vs output distortion/compression vs Output transformer saturation, etc. There are so many things you can flexibly do with a simple bassman design to make it do completely different things. I would be intrigued if pritchard went for a hybrid approach of some sort. To me, the limitation of the pritchard designs are the fixed values and fixed "curve" plots. There is something still very solid state/jazz chorus sounding, albeit a very good solid state sound. Some folks probably don't realize they are looking for a solid state sound. For those folks, these amps are probably a REALLY good solution. That's my .02.
There are a couple of factual corrections that need to be understood regarding Eric's amps:
1) They are not simple tube emulators. The design takes the whole circuit into account. The voicings are literally different amplifier topologies.
2) They use real power transformers with real sag. Output saturation is emulated using speaker feedback.
So, there is no "fixed 'curve'" as such.... They are very much dynamic. Moreover, I've had mine modified to suit my personal tastes. The design is quite flexible.
Factual corrections aside, they are still not for everyone.
Here's my main problem. ITs all emulation. I apologize if I offend any owners here, but THINK ABOUT IT!....emulators! Thats like wanting emulated sex or emulated coffee. Need I say more??? Give me the real thing!
I think this "emulation" argument is a straw man. Emulation is just a word, and it's not a perfect word. You can make a semantic argument that has nothing to do with sound. It happens on TGP all the time....
Eric actually tried to understand - I mean really understand - what it is that sounds good to people about tube amplification and then went after that, even to the point of "exaggerating" the characteristics that he studied. I don't know that he got the formula exactly right, but it works for me.
The bottom line is how the thing sounds. Eric's amps nail the sounds in my head, and I will never need to buy another tube amp as long as I live. (Good riddance.) However, there are a few newer non-tube alternatives that may be just as good - including the Axe-II and the Quilter line, as well as PCL-Vintage in Germany. I don't really know, but I do know that no two tube amps are the same, so there is no fixed standard. Eric's amps aren't perfect, but then everybody seems to want something slightly different anyway. It's just another fish in the sea.
BTW, there are NO representative clips of Eric's amps other than those recorded by Andrew Campbell (landru64). Those are not widely distributed, but they are superior to everything else out on the web. Paul Riario's stuff on GW is okay, FWIW, but doesn't show much beyond the basic voicing function.
Both of those clips are pretty darn compressed. That's what high gain does. If you're out to prove that modelers don't compress, play clean and dynamically.
Good riddance? You are more than welcome to purge yourself of all those antiquated amps now that you have your solution. Pm me for my mailing address! Send em over!
I would not have looked into Pritchard based on the clips (but based on the testimonials of working musicians). You can't go by those clips, nor can you form an opinion on it. In fact, I had one person put down one of my songs, saying that it didn't sound very tube-like, and yet his song involved a high-end Marshall, a Les Paul, and some type of pedal, and it sounded more digital and thin than my stuff. Part of the problem is the recording into a format that can be heard properly from cheap computer speakers. Anyone who has heard my amp in person was wowed.
Purged 'em five years ago. Last one was a 6V6-based Reverend Goblin. Nice little amp, but totally redundant....
FWIW, I would still consider tube-based pedals, not because they are more tube-like but because they simply offer a different flavor. Kingsley comes to mind. Eric's amps are versatile, but they don't do everything, e.g. the 'V' voice is more like a Matchless than a vintage Vox.
I say "good riddance" mostly because I suffer no more temptation to play the NOS tube swapping game. Not everybody has that problem.
Yeah thats high gain, and it is perfectly modeled. Now lo/medium gain.
First see post #52.
Great review of the Kemper, A/B comparisons at 2:25
If you have some time watch this:
Note: The AXE FX II now have his own profiling "tone matching". You can tone match any isolated guitar clip and any real amp.
Buttery Broken tones
Mr. Bonamassa's twin amp rig
First part real amp clip, second AxeFx
Here his Marshall Jubilee, first part the real amp.
ORIGINAL --- AXE II --- AXEII PHASED AND DELAYED
Try to get this close with your real amp.
I think that with this post some guys are going to change his mind about what digital can do this days.
For me, it's one word - Punch!
Kinda funny how some tube purists will cite clips as a litmus test of some sort. A clip, sampled by a mic, run thru a myriad of SS and digital gear, and played back on a digital system on 1" speakers.
I feel fortunate i'm not hung up on what circuit I get my tones from.
I have found a great post by Cliff (AxeFx creator) that I think could be interesting on this thread.
I can understand that. I've never spent more time "learning/spending" and less time "playing" than since I got into tube amps.
I still don't really know what I like.....