The peavey transtube thing...

[Doug_H]

Why emulate tubes with transistors? Isn't it the tubes that sound like tubes? Always puzzled me...

That's the same question I've been asking for years... Tube circuits are simple enough...

[zachomega]

The issue isn't simplicity.  It is cost.  A tube amp requires a high voltage power transformer.  Additionally, it may require multiple low voltage AC secondaries for the tube filaments and rectifier supply.  Tube amps also require an output transformer.  Just the power transformer and output transformer costs alone are more than quite a few SS amps. 

Then of course there are all of the high voltage parts inside, the cost of the tubes themselves...It becomes a costly proposition...And as noted previously, tube amps are terribly inconsistent.  Just about everything becomes a variable with them. 

-Zach Omega

Why emulate tubes with transistors? Isn't it the tubes that sound like tubes? Always puzzled me...

That's the same question I've been asking for years... Tube circuits are simple enough...

[Doug_H]

The issue isn't simplicity.  It is cost. 

There's no free lunch...

[Ben N]

I was at a wedding last night, and the guitarist was playing a guitar I did not recognize, but something like a double fat strat with maple neck, through a Zoom mutieffect into a Transtube. The guy had pretty good chops, doing a lot of EVH-like tapping & harmonics, although I personally found the solos to be predictable and sterile.  But that is not the point.  The rhythm section overall was cooking (the guitarist did have great rhythm chops and a really fast right hand), and if the lead tone was kind of one dimensional, almost no one noticed, and no one--including me--cared.  For what this guy needed to do, it was fine.  Next time he gets to jam with Buddy Guy, hopefully he will have something better.
Ben

[PaulC]

There's a lot of circuits here where people are trying to get tube like responce in the pedals.  all those jfet based tube preamps show this.  All the transtube stuff is trying to do is get transister circuits to act a little bit more like tubes.  I think it's great that peavey has been working towards this goal - just like a lot of us here are trying to do (fetzers).

To me the goal is to get tube like sounds in a tiny little bud box.  I'm WAY into tubes myself - my day job is designing tube amps for Heritage.  I could make a tube preamp a lot easier than trying to make transisters sound like them, but I couldn't make it in a phase 90 sized box.

Peavey has some great stuff, and just like everybody else they have some dogs.  The whole reason I posted about this is because it was kind of said that it wan't any big deal - just adding diode clippers.  what they were trying to do is get bias shifts into the circuits - that's pretty cool stuff. 

I do have the schematics for a bunch of these things ( I used to be a service guy for them), but I don't think it would be cool to hand them out.  I'm in the biz myself, and I wouldn't want people passing around the schematics.  Pretty much everything you need to know about what they're trying to do can be found in the online patents.

Later, PaulC
Heritage amps/tim&timmy pedals

[Steben]

Hey guys: of course I'm talking about the tweaking of the voltage of the power amp. I believe it is only found in a distinctive way on the 112 series with T-Dynamics control.
For me the potentials of Transtube have nothing to do with distortion, since we all have plenty of pedals around. It's that power sag thing. My guess is, the TDyn control acts as a compression control.

And in a way, all these amps think in complex circuitry. I don't think it's about making "one" transistor sound like "one" magic tube, but making the amp sound like an amp.  Just like you can easily f..... up any tube design if you only think that tubes are magic. I believe the power amp of these things are IC's and not discrete.

For the fire on the oil: didn't all of The Doors albums were made with a SS amp? What about the VOX pathfinder hype?

[joegagan]

...or Creedence?  Kustom SS
or Albert king?   Acoustic SS ( I heard an old urban legend from someone who heard him live in the Acoustic days that he would disconnect the horn in those cabs)     

[brett]

Not too long ago I saw a patent on a design that used an op-amp to split the signal into positive and negative phases, then applied differential gain and clipping to the two halves.  If I recall correcttly, there were also bias changes with signal volume.  It was filed under "12AX7 emulator" or something like that.  Shouldn't be too hard to find.

I wonder why someone hasn't gone back into production with low voltage tubes?  The 12U7 runs at 12V.  Some say it's a 12AX7 for 12V.  The way I've used it, it sounds like an incredibly soft and  soggy 12AX7  (too much bias shift can be a bad thing too).  But some clever re-design of the tube and placing it in the right circuit could presumably achieve some great results.
cheers

[Steben]

hey brett, looking at it with a nice angle!

Yeah, why not using a push-pull stage with those 12V tubes, even as a preamp... Maybe one could make an effort putting in real sag?
I mean, why wouldn't a small-current device, which a preamp is, pull sag out of a resistor somewhere in the power supply? The only reason I can imagine is that in Tube amps, the power amp draws much more current, thus determing the sag: the poweramp sucks the power down, long before the preamp ever can.
But if there's only a preamp, maybe a large resistor can do the trick? And after that, there is only solid state for example.

[PaulC]

But if there's only a preamp, maybe a large resistor can do the trick?

There's very little change in current with preamps from zero signal to full power.  A large resistor in the power supply would drop the voltage due to the circuit current, but it wouldn't change with operation.  In big tube amps it's not uncommon to see 25% drops in voltage.  With tube rect designs, and low VA rated  trannies you can find 100vdc sags in a bunch of old amps. 

If you wanted to get pwr supply sag out of preamps you'd have to do something like the maven peel thing where you've got a detector circuit on the audio path than can be used to control a regulator in the pwr supply to get the voltage change you'd want. 

Later, PaulC
Heritage amps/Tim & timmy pedals

[Steben]

But if there's only a preamp, maybe a large resistor can do the trick?

There's very little change in current with preamps from zero signal to full power.  A large resistor in the power supply would drop the voltage due to the circuit current, but it wouldn't change with operation.

I'm not so sure; i guess it's true for class A amplifiers, like most preamp stages.
I'm suggesting the use of class B(A) in preamp design.
The permanent drop in the supply is not that harmful. It gives low current, but it's only the drop change that matters.

[PaulC]

I'm not so sure; i guess it's true for class A amplifiers, like most preamp stages.
I'm suggesting the use of class B(A) in preamp design.
The permanent drop in the supply is not that harmful. It gives low current, but it's only the drop change that matters.

Your right - the permanent drop in the supply isn't going to hurt anything.  I think what happened here is I took your sentence about the preamp and the large resistor as standard preamp circuits.  I read it as using a resistor that would just have a constent voltage, and not a change in the % of drop.  If you do like you said, and go with a different direction then you can have circuits that have more of a change in current, and the resistor thing will work fine.

I was still thinking along the lines of the stuff being talked about in this thread.  I was talking about ways of getting sag with circuits that don't have much in the way of current change. 

Later, PaulC
Heritage amps/tim & timmy pedals

[Steben]

Maybe it brings us back to MOSfets as well. If used in the inverter way (like MOS chips-> Llama, TZF,...) I wonder whether it can be used for a sag thing. It depends on the specific way they function. Additionally, they use a lot of current.

[puretube]

they don`t use it!
they transport it... 

[black mariah]

Whether you believe in it philosophically or not, whether you appreciate it aesthetically or not, and whether you have experienced it or not, ever since the beginning of the company, Peavey has made reliability and affordability of their gear a priority.

The thing I like most about Peavey is that none of the Peavey gear I've owned has ever given me a damn bit of trouble... except the Renown, which sounded like ballsack. Other than that, no issues. Ever. Can't say the same for any other manufacturer. I don't THINK my new Valve Junior or Vox Pathfinder will give me hell, but I could be wrong.

[joegagan]

ditto on Peavey reliability. never had a bit of trouble with any peavey gear in 30+ years that wasn't caused by beer going down the wrong port.

[brett]

If you wanted to get pwr supply sag out of preamps you'd have to do something like the maven peel thing where you've got a detector circuit on the audio path than can be used to control a regulator in the pwr supply to get the voltage change you'd want.  

There's already a circuit that does something completely different but uses almost the same circuit:  the Orange Squeezer.
IIRC the OS uses dynamically changes the input resistance seen by an op-amp, thereby changing the gain.  The variable resistor is a JFET.  
I figure that the JFET could also act as a variable resistor in a supply line from a small power supply.  Tho I wonder if the end result would be much different to what you get with the OS circuit?
An even simpler approach would be to use an in-line resistor that would normally make little or no difference (e.g. 1k), and follow it by a MOSFET (e.g. BS170) to ground.  The MOSFET could be controlled by a rectfied, filtered signal (one diode, one cap) so that it diverts power to ground when the signal is large.  (this is how the Ausie/AussieComp/AussieMart compressor worked, except it was grounding the input signal rather than the power supply.

Hmmm....I wonder what types of simple gain stages have their gain proportional to the supply voltage?

[Meanderthal]

 Agreed that Peavey gear is reliable, in that none ever seems to break down. Amazing!

However, in the past(and this is just opinion, but it's shared by many) they have made some REALLY bad sounding stuff! My first mixing board was a really old Peavey with giant Boris Karloff knobs instead of the usual sliders, and a horrible 6 band eq... drove me NUTS! My first bass head was a Mark(something) with the same 6 band EQ. HORRIBLE! I borrowed a TNT bass combo once... just awful(but powerful)! I could never get a satisfactory sound out of any of those pieces. But they all worked. Every time. Someone is probably beating their head on the wall with frustration now over those exact same pieces of gear...
And then there's those column speakers... use em for anything but vocals, and you'll be sorry. But, in those days, everyone made column speakers it seems...

Why did I buy them? (well, not the TNT) They were cheap. It was all I thought I could afford. I was wrong.

However, some of their stuff(like non-column speaker cabs) has always been good. My favorite workhorse power amp of all time is of course the old indestructable CS800. I have a nice Peavey rackmount bass preamp that served me well back when I used a rack rig, late 80s, early 90s. Their tube amps are pretty good.

What's the point of this post? Hey, I never HEARD a Transtube, but I've heard the Valvestate and was horrified that to me it sounded nothing like a Marshall should(sorry, no offence intended). It's not that I think SS dosen't sound good (Kustom, Acoustic, my Behringer bass head, etc...) it's just that sometimes manufacturers can take a good idea on paper and make a mess of it when it hits the physical world. So I have serious doubts as to whether it will be a 'good' one...

[Steben]

In fact, what I realize is that SS has different options in creating tone, going from passive to active, with all funny comparisons included. A Tube amp, the ideal theory set aside, has less.
That's why we spend hours in designing stompboxes. It would be useless if there were no solid states.

And it's true that compressors are damn fine, yet they make the tube story less precious. Sometimes I think people talk about "smooth, compressed tone" not realizing they don't mean any tubes at all. I allready demonized that JCM900 and I do it again: it's the result of lot of mojo without questioning.

[DDD]

Actually it's not a problem to get the power sag in the preamp circuit:
1. Just add a serial resistor\parallel cap into the supply path
2. Add a specific stage that works in a cut-off mode with the low-level signals, but begins to consume current with the higher input levels. Adjusting the cut-off point (or the negative bias in case of npn trannies, for example) and the filter capacitance one can get the desired sag characteristics. Moreover, thus you'll get some "rapid pulsations" on the preamp supply voltage repeating the input signal - just like in the tube rectifiers.
But don't forget of the possibility of the self-oscillation...