Super Wreck???

[GainMaster]

A few guys over at the AX84 forum http://www.ax84.com/bbs/index.php have developed a 6 gain stage preamp called the Lead II that can go from clean to modern distortion with a twist of the guitar's volume.

Here is a dirty clip http://www.mediafire.com/?abnzhmdmmo2

Here is a clean to dirty clip http://www.mediafire.com/?2r0amgnzdvm

Here is the schematic http://www.ax84.com/static/corepreamps/ ... ematic.pdf

Since much of the magic of the Wreck is its ability to clean up with a twist of the guitar's volume, I thought some of you might be interested in it.

Brian

[Lonely Raven]

Ouch...I don't mean to be offensive...but that was painful to hear. Dark, dreary, with some odd harmonics. The clipping sounded way wrong. The clean to grind wasn't clean...I could hear some hard clipping somewhere in there that was overlapped with some clean tones. Maybe that was the recording gear distorting?

Maybe it was all just the recording though...do you have some better samples? Different guitar maybe?

[GainMaster]

It was recorded with a Zoom PS02 so it wasn't under the best conditions. Here are some new clips posted by someone else who knows how to play.

http://tinymaninside.net/music/music_lead_II.htm

[Bob-I]

I waited to comment until some more clips came out, the first guy was trying but...

I personally don't like it. It sounds very 80's hi-gain buzzy to me, plus I hear a ton of buzz and hiss in the background before the playing starts.

I think the idea is sound, but it still needs some work.

Thx for posting.

[mlp-mx6]

I just took a second look at the schematic and I really don't understand the purpose for the way the first 2 triodes are wired.

The output is combined, but they're out of phase. What is the purpose of this? Seems an odd way to get a drive/volume control going.

I also listened to the clips, and they're just not my cup of tea.

[CaseyJones]

The idea is sound because Peavey made it work. The downside is that Peavey sold the public on the idea that five or six gain stages is actually a better concept than three or four gain stages. The problem with that many gain stages is that there's obviously much more gain available than you'll ever need. There really is such a thing as too much gain.

[mlp-mx6]

The idea is sound because Peavey made it work.

Was this intended to answer my question?

[GainMaster]

The idea is sound because Peavey made it work. The downside is that Peavey sold the public on the idea that five or six gain stages is actually a better concept than three or four gain stages. The problem with that many gain stages is that there's obviously much more gain available than you'll ever need. There really is such a thing as too much gain.

Actually very little gain is dropped because we used 12au7s instead of 12ax7s for 4 of the gain stages. The feedback setup on the first two stages was to limit the gain on the second 12ax7 stage while allowing full gain on the first stage to get the initial signal up. And yes, Masons clips are fuzzy/buzzy. He still needs to work on his and he knows this. And yes I may have a little dirt creeping through on my clean to mean clip but the gains were on 3/4. Back them down a little and it goes totally clean. Anyway, thanks for the comments and I do appreciate the polite discussion.

Brian

[Fischerman]

I just glanced at it but I don't get how the Preamp stage 3 and 4 work without having a coupling cap between their grid and the plate of the preceeding stage. I can see that the cathode voltage is pretty high (~43vdc in one) and that the current is way high for a 12AX7 (~4.5mA Ik in that same one) so does this positive grid voltage 'partly' bias those stages or what? Just curious how that works. Thanks.

Note: I realize they are 12AU7 triodes and that their dissipation is way higher than a 12AX7...just trying to make sense of it.

[GainMaster]

I just glanced at it but I don't get how the Preamp stage 3 and 4 work without having a coupling cap between their grid and the plate of the preceeding stage. I can see that the cathode voltage is pretty high (~43vdc in one) and that the current is way high for a 12AX7 (~4.5mA Ik in that same one) so does this positive grid voltage 'partly' bias those stages or what? Just curious how that works. Thanks.

Note: I realize they are 12AU7 triodes and that their dissipation is way higher than a 12AX7...just trying to make sense of it.

Those stages are DC coupled. The idea is that you hit the grid with DC v at about 10% of the anode voltage of the stage. The cathode resistor is raised so that the cathode voltage is about 1 to 5v higher than the DC on the grid. In this way the stage is biased normally and sounds like a normal gain stage. Now because the voltage on the cathode is high rather than 1 to 2 v as normal, it is virtually impossible to drive the stage hard enough to cause blocking distortion. The voltage divider is not there to attenuate the stage as it is bypassed by the coupling cap. The voltage divider provides the DC reference for the grid of the following stage. This can be done with 12ax7s as well. Here is a better explination and another amp that uses DC coupling.

Brian

http://vtg-amps.com/Melissa/Mel_Amp_7-21-06.htm

[Bob-I]

It's an interesting design for sure, I'm sorry I can't get my ears around the tone though.

[LeftyStrat]

The real measure of a Trainwreck is not in bar chords or shreddy leads, but how sustained lead notes easily bloom into feedback and higher harmonics. It is also about the definition and note separation even at heavy distortion. A wreck still seems somehow "clean" even at max distortion.

I've only built three clone wrecks so far, each one better than the first, and to my limited understanding of what is going on in the circuit, it is less about massive gain and more about slamming the hell out of a cold biased tube with a signal that has extreme bass rolloff/high frequency emphasis. The tube is cold biased into a nonlinear portion of its curve where it acts like a compressor on lower energy signals and a clipper on higher energy signals. This increases the crispness of the signal which enhances definition. The livelyness of sustained single notes comes from dropping from full on clipping into the compressed range, which varies the harmonic content. The over the top treble is tamed partially by the clipping/compression, which should even out the frequency response.

Of course this is all speculation. My plan was to keep tweaking and building until I got one that blew my socks off and then analyze every stage of that one under a microscope (oscilloscope, spectrum analyzer, signal tracer, current draw at each PS node graphed against signal amplitude, phase of the moon, etc) to figure out what was going on.

My third wreck was the first to blow my socks off, which I just finished, so this weekend I'll be barefoot with a lab coat. I even considered going commando, but with just a lab coat and how good this one sounds, that could end up being dangerous, high voltage and all.

I'll report on my findings. But I'm almost positive massive gain will never duplicate the responsiveness of a Wreck.

[Lonely Raven]

the first guy was trying but...

I'm not exactly sure how to take that....

[GainMaster]

The real measure of a Trainwreck is not in bar chords or shreddy leads, but how sustained lead notes easily bloom into feedback and higher harmonics. It is also about the definition and note separation even at heavy distortion. A wreck still seems somehow "clean" even at max distortion.

I've only built three clone wrecks so far, each one better than the first, and to my limited understanding of what is going on in the circuit, it is less about massive gain and more about slamming the hell out of a cold biased tube with a signal that has extreme bass rolloff/high frequency emphasis. The tube is cold biased into a nonlinear portion of its curve where it acts like a compressor on lower energy signals and a clipper on higher energy signals. This increases the crispness of the signal which enhances definition. The livelyness of sustained single notes comes from dropping from full on clipping into the compressed range, which varies the harmonic content. The over the top treble is tamed partially by the clipping/compression, which should even out the frequency response.

Of course this is all speculation. My plan was to keep tweaking and building until I got one that blew my socks off and then analyze every stage of that one under a microscope (oscilloscope, spectrum analyzer, signal tracer, current draw at each PS node graphed against signal amplitude, phase of the moon, etc) to figure out what was going on.

Here are some scope pics of what is going on in a Wreck. http://home.polstra.com/amps/wreck1/scope/

The original design goal of the Lead II was to produce a preamp capable of modern distortion. The mean to clean thing was an interesting side effect that was enhanced during the design process. One builder who has a Wreck and built the Lead II likes this preamp very much. Anyway, just thought some of you might be interested.

Brian

[Bob-I]

the first guy was trying but...

I'm not exactly sure how to take that....

All I meant was that this isn't the greatist playing. I could hear the tone better in the second clip due to cleaner articulation.