Is the 3.3k/330k the secret sauce for ultimate Engl gain tone?

GlideOn

Member
Was reading up on cathode bias and plate resistance for V1 in Marshall-style amps and the Engl Fireball is frequently mentioned as the amp that takes the distortion channel design to its' Apex.

Supposedly there's a 3.3k/330k value going on that gives it a "fire-breathing" tone.

Well I tried it in my Traynor amp and I was floored, but was a tad soft and compressed.

I have EMI GB128 speakers that perhaps aren't the tightest for that kinda tone.

I definitely want to implement higher gain into another amp - my AX84 SEL which is a bit less critical to having historically-correct Marshall tone. Y'know, having an excellent 15w bedroom level firebreather?
 

glpg80

Well-known member
I’m not a fan of that large of a plate resistor unless the PT is well above stock voltages found in Marshalls. The cathode resistor being that high runs the stage a lot colder too.

Use whatever your years like. That’s all that counts! There’s no right or wrong, just stay within the load lines of typical triode stages and you can do whatever.
 

GlideOn

Member
Yes, I"m sure the PT are beefier than most Marshalls, but isn't getting a relatively high plate resistance key to getting a higher gain tone?

Or deeper 'distorted' tone?
 

shadow

Member
As far as the JCM2000s, the out xfmrs are probably louder, but not the JVMs. Generally, a higher plate resistance in the first couple of stages will produce more compression (220K is popular), but more gain is a balancing act between many components: generally lower value resistors in the signal path, and higher values bleeding to ground, and capacitors that cut off low end to focus the gain in the right areas. A lot of amps have given a nod to Soldano's third gain stage and the Engls seem to be a variant of that, but it's like using the same ingredient for different recipes - still completely different dishes.
 

shadow

Member
What I meant was the Engl output transformers are probably louder than the JCM2000s, but not the JVMs. Increasing the plate resistance will lower the voltage to the plate and increase gain, but increasing the cathode resistor will decrease gain. The exact tonal/gain change will depend on the circuit as a whole. The coupling caps are low values in the early parts of the circuit for the gain channels in Engls, which tightens it up. I see that as their secret sauce.
 

mcstinger

Member
Higher cathode resistor doesn't automatically mean colder running tube. Combination of all components sets the working point. Engl chose for at least few amps one tube stage using quite unusual working point. Regarding to gain of such a stage, it is a bit higher. But distortion shape is different. I have quickly simulated 4 combinations of anode/cathode resistors, including working points.

Screenshot 2022-06-11 00.36.31.jpg
Screenshot 2022-06-11 00.34.09.jpg
 

shadow

Member
Sweet! It seems that the 330/3k3 combo is more squarewavy compared to the other 3, and provides a couple more db of gain. Am I reading this correctly? Very interesting. Makes me want to learn more.
 

mcstinger

Member
Quick FFT analysis shows, that 330k/3k3 combination is a bit richer in harmonics, both even and odd, than other combinations. But that's just a simulation, which is somehow valid for triode model used. In real, things can be different. But if Engl schematics available are reliable to some extent, many amp models share almost the same topology of the first four stages, where higain sound is created. Screamer, Savage 120, Fireball I, Powerball I, E530, Blackmore at least... They are almost carbon copy of the same circuit. It's a small miracle, that they sound different :). So I would say, yes, 330k/3k3 combination in the third stage is probably a part of that Engl signature sound. Of course not alone, but in combination with other stages. I don't know, how is it with Invader, never saw a schematic. Friedman also sounds different, but no schematic and I was too lazy to disassemble it for reverse engineering.
 
Top