Reverb pans...WTF

[Chuck H]

I see a lot of people sneering at Ken Fischer for his "gentleman's agreement" that he would get a cut of the profit from a future amp sale. Indeed to a businessman it seems crazy.

But imagine if he had a multi-year waiting list, so long that he was unknown when he started. Suddenly he gets famous, but he has already taken up-front payments for dozens of amps that he hasn't built yet. He can't raise the price to take advantage of his new status, because he has already sold them.

What would you do in this situation? Trading in boutique amp futures can be merciless.

Ken DID have his own game going. He had a very basic design that worked on many levels and could be tweaked (by his methods) for a specific player. Pretty powerful stuff for the 80's. I've heard all I can stand about his techniques being questionable. They worked for him. And they are now being "discovered" on a more scientific level. So fine... A guy puts in the time to find out what "works" and everyone either loves or hates him. Ken mentioned is several articles that he's tried to train individuals on how to tweak his circuits with poor success. Well... On a purely technical level Kens approach to voicing was bizarre. And history has a way of revealing the brilliance of what even the artisans didn't know about what they were doing. And I think it's telling that this is what's happening with the TrainWreck circuits!!! Whatever he was, or wasn't, Ken made an awful big noise out of a company that only released a hundred amps!!!

[Steve A.]

Well... On a purely technical level Kens approach to voicing was bizarre. And history has a way of revealing the brilliance of what even the artisans didn't know about what they were doing. And I think it's telling that this is what's happening with the TrainWreck circuits!!! Whatever he was, or wasn't, Ken made an awful big noise out of a company that only released a hundred amps!!!

I'm sorry I even brought up what I heard about Ken often getting a cut from very profitable resales- and yes, he would get pissed off if he thought someone should have given him a cut, but didn't. So he could be petty; okay so the guy wasn't Mother Teresa. But he was a genius at designing, building and fine-tuning guitar amps and I think that is how he should be judged.

I think that Dumble might be a better designer (using 5 times as many parts) but people have been able to clone his amps fairly well after reverse-engineering them; I have not heard of anyone doing the same with a Trainwreck amp. BTW there are new TW's being built according to the Trainwreck site. I wonder how they compare with the originals...

Trainwreck Circuits Official Homepage » NEW Trainwrecks

Steve

[Chuck H]

The new "JM TrainWrecks are good!!! A little better than the average clone. And they have a TW logo (FWIW).

But after extensive listening and searching I'm still convinced that Ken had a way of voicing and tweaking the amps that was outside of the "normal" MO. If you look at any gut shots it's clear that there are only a couple of variations to the circuit that were ever used. One was a tiny grid stopper on the second gain stage and the other was the reported use of a plate connected shield for V1. Other than that the circuits looked the same to the average tech (like me). But the sound of the actual KF built amps always stands apart. So WHAT was he doing differently than anyone else?!? He's made mention of filter cap impedance, locating the OT by hand before mounting, edge of stability, checking individual components for the ones that fall exactly where he needs within their tolerance!!! And most confusing, "voicing" the amps (even though there is almost NO difference to the circuit!).

Whatever he was doing, he did it with a bare minimum of parts. I like eloquent circuits. A few times I've studied and considered the TW design I've noticed things that are brilliant, if not obviously so. And with the most basic circuit!

We sort of know what he was doing. But HE was doing it fifteen years ahead of other high gainers!!! And he was apparently a master at it. But until we can quantify it people will beat him up with their learned facts because they're embarrassed that they can't do what he did.

[bob p]

Steve -- I think that it's kind of you to give compliments to Doward Humble.

[bob p]

so who is the JM that's trying to remain nameless? after ken died i remember thunderfunk claiming that he was the only other guy who was authorized to build original TW amps.

i also seem to remember hogy saying something about building TW amps posthumously, with the approval of ken's estate.

wasn't that "edge of stability" stuff with the twisted wires just a way to put pF capacitance across the plate-grid of the triodes to keep them from oscillating? I thought he would add leads to those pins on the sockets, and then form a twisted pair with the wires to create a capacitor, calculating the length of the wires and the number of turns required to make the cap have the right value to stabilize the gain stage. the twisted pair is an old trick that the radio guys used to use.

didn't ken have army radio training?

[Steve Conner]

The twisted wires capacitor gives about 1pF per inch. I've used them when prototyping RF circuits: they're easy to trim by snipping bits off.

KF had a wild, artistic approach to circuit design. It looks very sexy and brilliant to musicians. But from the point of view of being able to manufacture the circuit efficiently, and sell it to paying customers, it must have been a nightmare. What if he tuned it to the "edge of stability" only for his customer to retube it with tubes that had a little more gain?

When you design a circuit, you're supposed to build in enough margins that you can grab parts off the shelf, throw one together and stand a very good chance of it just working. The required margins might conflict with dialing in the last little bit of mojo, in which case, you have to handle that conflict intelligently. Circuit design is all about compromises, and to me a "brilliant" design is one that makes all the right compromises. There's nothing brilliant about falling in love with one aspect of the circuit and tweaking it to the nth degree, at the expense of everything else.

[Leo_Gnardo]

The twisted wires capacitor gives about 1pF per inch. I've used them when prototyping RF circuits: they're easy to trim by snipping bits off.

I've seen this sort of thing referred to as a "gimmick". Can't say I saw any such in the Wreck Express I got to look inside. Also,as Chuck desribes, a bit of shielded cable with shield attached to plate also amounts to a couple of pF, and I've seen that in factory-built late 70's Marshall master-volume amps also early JCM800. "Grid-stopper" resistors can also help control HF oscillation "chirps". Carbon-comp resistors are considered best for stoppers.

From time to time I've also seen a single-wire "gimmick" sticking up from a Mesa PCB, I suppose for a tiny dab of shielding. On those occasions I've found a need for shielding inside an amp, good old copper foil does the trick.

[bob p]

Yes... "Gimmick" cap. Couldn't remember the name.

What if he tuned it to the "edge of stability" only for his customer to retube it with tubes that had a little more gain?

Having that problem is a good thing if you want your customers to be a captive audience. They have to come to you to keep the amp working right, and if they take it anywhere else -- where some guy just plugs in tubes and checks bias -- the amp won't work right and the other tech will look like a turd.

When you design a circuit, you're supposed to build in enough margins that you can grab parts off the shelf, throw one together and stand a very good chance of it just working. ..

Yes, that's what design center values are all about. But I think we're talking about a case where the amp design was purposely eccentric. That made the amp behave in a special way, it made the amp finicky, and it made the customers a captive audience for support work. Trading off design center values in favor of purposeful eccentricity was part of the business model that involved having hte amp come home for service and support.

[Steve A.]

Steve -- I think that it's kind of you to give compliments to Doward Humble.

I respect him as one of the all-time great guitar amp designers- very possibly the most innovative. The various mode switches in his preamps are amazing.

Steve Ahola, the damn thieving pirate

[Steve A.]

When you design a circuit, you're supposed to build in enough margins that you can grab parts off the shelf, throw one together and stand a very good chance of it just working.

I don't think that Ken ever had plans to mass produce his amps, although he was involved in the design of the Kendrick Climax and the original Komet amps which I doubt were as good as the real Trainwrecks.

The required margins might conflict with dialing in the last little bit of mojo, in which case, you have to handle that conflict intelligently. Circuit design is all about compromises, and to me a "brilliant" design is one that makes all the right compromises. There's nothing brilliant about falling in love with one aspect of the circuit and tweaking it to the nth degree, at the expense of everything else.

Production amp designers must "idiot proof" their amps to protect them from jerks who insist on turning all of the gain knobs up to 10 (or 11!) I think of custom amps as being like electronic test equipment which must be set and calibrated properly. I like to design pre/post gain circuits so that you can plenty of volume with the pre gain control set very low. If I run the pre gain control higher then I will turn down the post gain control. (I just did exactly that yesterday on the Drive channel in my SS Fender Princeton 112+ by cutting down on the pre gain circuit while boosting the post gain circuit. With my mods you definitely don't want to turn both gain knobs up to 10! Designers at Fender don't have that freedom!)

I think that Ken did keep his amps off of the cutting edge of instability so his fine-tuning tweaks were not a battle against oscillations but to just get a really good sound and response from the amp.

Steve

[mort]

It's hard for me to imagine a component of the signal path where materials matter more than they do with reverb. Spring reverb is fundamentally a mechanical effect, whose qualities depend on the right balance of rigidity and compliance at the right points. Change the composition of where the springs are anchored, how the springs are joined in the middle, what the springs are made of, the diameter of the wire used to form the springs, the outer diameter of the springs, etc., and you change the sonic properties of the springs every bit as much as hanging tapestries on the wall in the mixing booth or laying down / pulling up carpet in a recording studio. The springs can LOOK the same, and have the same electrical measurements, but behave differently.

So I wonder about not just the folks who make and sell the pans, but about the folks who make the materials that form the springs....that are ultimately used in the pans. I'm fairly confident that whomever makes that steel does not rely on spring reverb as their only client and revenue stream.

Along this same type of thinking, I wonder if using recycled material could be a cause for the diminished sound quality in reverb tanks. Seems plausible...

[bob p]

any news on the pan front, chuck?

[Steve A.]

... the other was the reported use of a plate connected shield for V1...

Besides adding a pinch of capacitance wouldn't the plate connected shield also introduce some negative feedback from the inverted signal at the plate? And you would probably would not want to connect the cable shield to your input jack...

Steve Ahola

[Chuck H]

any news on the pan front, chuck?

Not yet. I modified the $h!tty Belton pan I have. It now sounds tolerable (not good, just not awful). It WILL be replaced. The amp is waiting for a faceplate right now. The artwork went back and forth awhile and the lead time is long. I'll be dealing with the pan when I deliver the amp and consult the customer on what he might want for a decay time. Not that you can accurately predict what you'll get there either IME. The high tolerance for a "medium" decay can be longer than the short tolerance for a "long" decay!?! Check out the specs. Not kidding.

[Chuck H]

Besides adding a pinch of capacitance wouldn't the plate connected shield also introduce some negative feedback from the inverted signal at the plate? And you would probably would not want to connect the cable shield to your input jack...

Steve Ahola

Negative feedback IS the point. I've tried it. too much capacitance. Six inches of shielded lead tested about 10pf IIRC. That's WAY more than I would like because the effect is dynamic. The higher the plate AC the greater the effect. I often use small value caps (like 4.7pf) on the input grid. I like the way it takes off the glassy, brittle highs but leaves all the stuff you need for useful harmonics. And since the more you crank an amp the more the brittle nasties offend, the increasing effect at the input stage seems to smooth things out. Not dark or muted. Just less of that shrill ugliness. But 10pf is too much for my tastes. I started at 10pf (with the shielded lead) and then backed down to 6pf via a cap. That was better but I still thought I was losing useful harmonics on clipped tones. So I backed it down to 4.7pf and that was the happy place I was looking for. You can just barely hear an audible difference on clean tones. So if your into really glassy highs this isn't what you want. But the improvement of the transition zone between clean and overdriven is definitely improved with this cap. FWIW, Glen Kuykendall uses two 20' input cables in series for his Wrecks just for the added input capacitance. Not exactly the same as the cap from plate to grid, but similar.