would there be any advantage in having a pp amp wihtout a traditional phase inverter

[Enzo]

And it is not like there are not tube amps balanced throughout. SOme mic pres are that way. Go over to www.waltzingbear.com and look at the Altec 459 for example. Also note the input and output are transformers, but the circuit is balanced. But that is a different application than the proposal here.

[black_labb]

just to clear a few things up, humbuckers are wired magnetically and electrically out of phase. each of those send the signal out of phase by 180 degrees, bringing the signal back in phase and leaving the him to still be out of phase as the magnet being out of phase doesnt effect the hum signal.

my idea was to wire the 2 coils electrically in phase but they are magnetically out of phase making the signal out of phase (obviously they are coming out of the guitar separately.

when guitars are wired out of phase, it is commonly one of the coils on the neck pup and one on the bridge pup, which is why there is reasonable signal levels coming out. if it were the 2 coils on a single pup then it would be very quiet. wether the little bit of difference between the coils would pose a problem im not sure, and probably wont find out.

again, i am not looking to build this (atleast in the near future), its really just hypothesising about a different design.

if i did do it it would probably be for a bass amp. ive been making my own instruments and pups already so it wouldnt be too big a deal making the instrument side of it. i dont think i will due to the compatibility issues, and its not like id be able to sell the thing either, other than for spare parts.

[Chuck H]

"Chuck, why would you need twice the preamp tubes? A typical 2 channel backface amp (no effects) uses 3x12AX7, why couldn't you do the same with this?"

From what I gathered the post proposes the use of two preamps. One for each half of the signal as seen by an AB1 power amp. That means that if you plan to use two stages of gain (one dual triode, say, a 12ax7), you must now use two stages of gain for each input (two 12ax7s). If you used two different inputs and didn't increase the tube count then you would only have one stage of gain for each preamp. Thats how I see it anyway. Otherwise, at the end of the chain where the two signals are combined in an AB1 power amp, you'll only have half the gain. Afterall, one half the signal is all each preamp in creating due to cutoff and saturation points in the power stage...Right. So if these prospective "halves" are each lower in gain, the whole will be lower in gain. I'm really having trouble wrapping my head around how to explain this. To me it's like trying to tell someone why a steak tastes meaty. I hope I'm clear enough though.

Chuck

[MWJB]

You could still do this with 3x12AX7, 3x triodes per side (input, tone recovery, additional gain stage).

[black_labb]

You could still do this with 3x12AX7, 3x triodes per side (input, tone recovery, additional gain stage).

thats what i was thinking, there are extras from the 2 sides needed, but you dont need a PI.

[Chuck H]

"just to clear a few things up, humbuckers are wired magnetically and electrically out of phase. each of those send the signal out of phase by 180 degrees, bringing the signal back in phase and leaving the him to still be out of phase as the magnet being out of phase doesnt effect the hum signal.

my idea was to wire the 2 coils electrically in phase but they are magnetically out of phase making the signal out of phase (obviously they are coming out of the guitar separately."

Exactly...Same thing. I never assumend you didn't get that. But I have had the experience of moving a pickup a VERY short didtance and hearing the difference.

When considering the preamp tube count I was only pointing out that with a complete preamp for each side of the AB1 output that the tube count would be doubled. Not exactly true. Considering the absence of a phase inverter it really doesn't make much difference in a lower gain topology, true. But if you wanted to do a high gain circuit or add any ammenities (reverb, fx, etc...) you would run into a snag. I actually did mention that problem would depend on preamp design.

Not making waves, I just don't want to be misunderstood. I'm not exactly the great communicator.

Chuck

[black_labb]

"just to clear a few things up, humbuckers are wired magnetically and electrically out of phase. each of those send the signal out of phase by 180 degrees, bringing the signal back in phase and leaving the him to still be out of phase as the magnet being out of phase doesnt effect the hum signal.

my idea was to wire the 2 coils electrically in phase but they are magnetically out of phase making the signal out of phase (obviously they are coming out of the guitar separately."

Exactly...Same thing. I never assumend you didn't get that. But I have had the experience of moving a pickup a VERY short didtance and hearing the difference.

When considering the preamp tube count I was only pointing out that with a complete preamp for each side of the AB1 output that the tube count would be doubled. Not exactly true. Considering the absence of a phase inverter it really doesn't make much difference in a lower gain topology, true. But if you wanted to do a high gain circuit or add any ammenities (reverb, fx, etc...) you would run into a snag. I actually did mention that problem would depend on preamp design.

Not making waves, I just don't want to be misunderstood. I'm not exactly the great communicator.

Chuck

thats perfectly alright, i cant see this design being remotely useful except for a bass amp or somethign similar where very clean levels are wanted.

makes you wonder what amp designers would be doing today if transistors werent around (not that i would want that to happen by anymeans). its always interesting what little changes are made to a design to improve it when the technology is aproaching its max, kinda like combustion engines in cars, how far will some manufacturers go to keep the combustion engines improving when the technology is leveling out.

[Enzo]

Tube amps were a pretty mature technology 50 years ago. We have better parts and closer tolerances in making them, and that yields more consistent, reliable, and predictable products. In the old days when 20% parts were common, two Fender amps of identical model would sound very different. "I like the sound of Joe's Twin a lot better than Fred's."

We now have circuit boards all over instead of hand wiring, and that too leads to more consistent products, and less likely layout errors.

We now have tiny relays that make features more convenient to include. like channel switching, gain boost, and things. And of course we now have the solid state stuff so we can toss it in the handle effects loop drives or direct outs and so on.

But underneath all the eye candy, and extra features, what really is different about the tube amp CIRCUITS now? In the last several decades what new tube circuits have arisen? Not much.

Hifi amps were made that had very good specs 50 years ago. You don't need to invoke balanced-throughout circuits to make a clean bass amp. SIngle sided works just fine. As I read you, the whole point of this exercise was to avoid a phase splitter which you feel adds distortion. A well designed phase splitter does its job adding little or no distortion. And that was well within their capabilities 50 years ago.

I don't think amp designers would be doing a lot different now than they ever did except for adding features. If we never had transistors, we would have continued to develop smaller more efficient tubes like Nuvistors. That would allow smaller, lighter, more portable gear, but the circuits would be about the same. You would have room for four separate preamp channels in one head maybe, but the circuits would be like any four you have now.

We would have developed op amps from tubes - they already did, and it was 50 years ago. But they would now be smaller. On thing abuot opamps is their gain potential. But in guitar amps, as much as we like to yammer about gain, we don't need very much. We start with a quarter of a volt signal and boost it up to several tens of volts by the time it leaves the amp. You want to need gain? Try picking up a radio signal from across the country or around the world, an extremely small signal, and amplifying THAT until it is large enough to strip the audio modulation off of and THEN run it through an audio amp.

They could shrink tubes a lot, and even have developed what I might call array tubes - like a 16 triode in one bulb tube. That would enable logic and computer circuits to take up less space than a house full of rooms. But still a Tube Pentium is out of the question. And that means no Tube CAD. Designs would come slower and be less prolific.

(Edit to add: HEY! This thing deleted several paragraphs from the middle.)

SOmeone patents bringing the NFB into a particular resistor instead of another, but NFB is NFB, you can tweak it, but it is still NFB. Look at all the amps you know. WHat is really new? Take a single ended amp. SOmeone can put TWO power tubes in it in parallel. SO what, that is the same as using a higher power tube. One amp might have local feedback in a stage - that is not common, but not new either. Add a cathode follower before the tone stack... or not... nothing new. Tone stack? Oh there are a few types and we make variations on them, but all of them have been around a long time. Phase inverters? Again, variation on a few types. Push pull, class A,B,C - all been around forever. UL? yep. One HV B+ supply with dropping resistors or two separate higher and lower voltage B+ supplies? Switchable? All old. AHA! Active EQ. Nope, not much different from a regenerative stage - one of the first radio designs.

I am not pickin on any of these things. They all work great, and we can chose from the options, make good music. Just thinking that I can't offhand think of anything in our tube amps that is actually new in the last, oh, 30 years. Anything that is not added by solid state, like digital effects features. What is new is features and marketing. Six channels with emulation, DFX, attenuation, compression.

I can think of one innovation. A high current low voltage tube for transformerless outputs - drive the speaker directly. Current transformerless designs are cobble jobs in my view. But eliminating the heavy expensive OT would be a huge coup for designers.

What do we need in a tube amp that we can't make already? What new ideas do you think we need? I'd genuinely like to hear opposing views.

[Steve Conner]

Hey, there are still plenty of amp designers who act like transistors were never invented!

Enzo, that high current low voltage tube is available now, unfortunately it's a MOSFET, and you won't like the "grid"-to-"cathode" capacitance! Nevertheless, I've seen plenty hybrid designs that use tubes to drive a MOSFET output stage.

If it's got to be glass, the 6C33C has a pretty impressive current capability. But it's still an order of magnitude away from those old Hitachi audio MOSFETs.

If I could have anything, I'd like not a new kind of tube or circuit, but a way of measuring tone. Line 6 probably have it, but they're obviously not telling anyone. I also remember that hobbyist who built an AC30 clone entirely from op-amps. He measured the transfer function of each stage in the AC30 and modelled it with op-amps and zeners. Korg heard about it and bought him out, so you won't find details in the public domain any more.

This kind of painstaking analysis of all the imperfections and different kinds of distortion that give tube amps their tones, with a view to recreating them, is the most interesting and new thing in amp design, IMO.

PS: To the original poster, if you're interested in making a tube amp with low distortion, you ought to try and study a schematic of the McIntosh MC275 stereo amp. And ponder why they still sell for $5k used!

[black_labb]

i wasnt really looking to make a minimal distortion amp, i was just reading a bit about guitar amps, or i was drawing up a circuit for a guitar wiring (cant remember which) and it hit me that a guitar with a humbucker going into a pp amp would have differring phases, then put together and then split again. i thought i should ask to see if there was any use in making an amp to do like that. im not into high gain stuff but i do like vintage style distortion.

regarding technology, im sure there would be a few little things that were found, but as enzo said, the technology was mature and there wasnt too much to be done. its amazing to think that transistors wont be all that much longer before something starts to take over. (i did a subject at uni recently that was split between the nanotech area and innovation engineering (my course) and they were talking about how people are looking at optical processors of some sort. i dont understand how it is supposed to work, but well probably start seeing it in the next 10 years or something. im only 19 atm, and its funny to think that ill probably be using a tube amp and maybe making them still (not that ive done much now). be odd that im using technology thats been "improved" so many times. you could even call digital modelling a "improvement"

this is a bit offtrack i know, but its a bit wierd for me to think about that.

[MWJB]

"and it hit me that a guitar with a humbucker going into a pp amp would have differring phases, then put together and then split again." Absolutely, if you had an instrument that achieved phase inversion before the amp inputs, there is no requirement for a PI in the amp circuitry, if using OOP parallel channels to each end of the OT. Of course, if you're the only person with such an instrument, your market will be a little limited (but that doesn't stop people from building one offs). The character may be a little different to conventional amps but there's no reason to think that it would necessarily sound a world away from current references either. The only way to know for sure is to do it.

We tend to fall into thinking that technology and progess walk hand in hand, it's not always the case. Do you find it weird that your great, great grandfather ate with a knife and fork and that you still do the same today? :-) It's hard to improve on a good design sometimes, no matter how old the technology.

[Enzo]

Unless he ate with chopsticks, and as we all know, chopsticks are important electronic diagnostic tiools.

[black_labb]

"and it hit me that a guitar with a humbucker going into a pp amp would have differring phases, then put together and then split again." Absolutely, if you had an instrument that achieved phase inversion before the amp inputs, there is no requirement for a PI in the amp circuitry, if using OOP parallel channels to each end of the OT. Of course, if you're the only person with such an instrument, your market will be a little limited (but that doesn't stop people from building one offs). The character may be a little different to conventional amps but there's no reason to think that it would necessarily sound a world away from current references either. The only way to know for sure is to do it.

We tend to fall into thinking that technology and progess walk hand in hand, it's not always the case. Do you find it weird that your great, great grandfather ate with a knife and fork and that you still do the same today? :-) It's hard to improve on a good design sometimes, no matter how old the technology.

i wasnt implying that tubes were inferior (it did come across that way looking back), more that there have been quite a few things that are able to perform the same basic function tubes, but they still arent able to replace them completely, due to the advantages of tubes.

[Chuck H]

Enzo:"I don't think amp designers would be doing a lot different now than they ever did except for adding features. If we never had transistors, we would have continued to develop smaller more efficient tubes like Nuvistors. That would allow smaller, lighter, more portable gear, but the circuits would be about the same. You would have room for four separate preamp channels in one head maybe, but the circuits would be like any four you have now."

I agree with your entire post. But wanted to add that just because tube technology has reached it's peak, that doesn't mean that tube amp designs can't still be contemporary and creative. Take music for example. Whats really been new in the last 400 years. I mean, theres only twelve notes. and nothing is different in a significant way ever since the western diatonic scale and the harmonic movemnt into relative minors. Yet we still create perceptibly new musical ideas everyday. Sure it's all been done. But subtle changes in accent, nuance, cadance and harmony allow for very individual expression.

With guitar amps there is still room for the same kind of creativity. Because guitar amps intentionally color the sound of the instrument instead of just recreating it. With infinite combinations of distortion types and levels, not to mention how they are effected by freq. response in prior stages, I think there is lots of room for individual expression. Look at the Trainwreck Express. You can't get simpler than that, but it's fine tuned to a purpose and sounds different from other amps. Sure it's all been done. It's good stuff too. Thats why we use these parameters and circuits to design with. I mean, just because everyone else is using the 12 note diatonic scale doesn't mean nothing new or relevant can be done without changing to a scale of different temperment. If you've ever tried that, you know how awful it can sound.

So even though no one is making tubes do anything different than they ever did...We are able to express ourselves as designers because of the nature of these materials. The same way the 12 note scale has a nature.

Steve Conner:"This kind of painstaking analysis of all the imperfections and different kinds of distortion that give tube amps their tones, with a view to recreating them, is the most interesting and new thing in amp design, IMO."

Even when were able to get transistors to behave like tubes in some regard theres always a rub with a response curve or a distortion characteristic or something. I love to build tube amps, but it will be a pretty good day if technologies in this area improve to where we could actually build a "tube" amp with transistors. The trouble is that designing distortion of a specific charater AND getting the right response curve has to be ALOT harder than distortion avoidance and clean reproduction. But I would love to walk into my local music store and buy a great sounding guitar amp for 250 bucks that I never had to change a tube in.

Chuck

[Enzo]

Yes, I agree we can still be creative, even 12 bar blues in A can sound different when different cats play it. But while it is different, it is nothing new.

So in the spirit of the question what would we have accomplished if transistors never happened, I am thinking most of the innovation would be of that sort - subtle nuances on familiar themes. Van Halen doesn't sound like Cream, but guitar, bass, drums, rock and roll. Differences in style rather than fundamentals.

There are only so many words in the dictionary, yet we still make up new sentences every day. Like that. They still have subjects, verbs, case, tense, etc.