Question in RDH4

[JoeM]

Well as I just tried to explain at length, they are pretty much useless for guitar amp design...

Did Leo Fender know any of this math?

[Alan0354]

Did Leo Fender know any of this math?

I doubted, but he had the excuse of being the first one and was in the 40s and 50s. What is the excuse in 2012 after 60 years, and people are still copying the circuits from the 50s? Electronics has advanced a few quantum leaps and the guitar amps still pretty much looks the same.

[JoeM]

I doubted, but he had the excuse of being the first one and was in the 40s and 50s. What is the excuse in 2012 after 60 years, and people are still copying the circuits from the 50s? ...

Why? Because they sound good. If you're doing spice modeling I can see the need to understand all the math involved, but I seriously doubt it's necessary to design a guitar amp, especially with so many classic circuits (Fender, Marshall, Vox et al) around.

[J M Fahey]

To put things in perspective, this Math *has* to be understood and use by at least *somebody*, which are the guys who design original equipment.
And I'm not talking about audio only.
I have a couple *thick* "Electronics Encyclopedia" books (4inches thick each), chock full of 50's and 60's electronics schematics pulled from EE World, "Electronics" magazine, service manuals, IIEE presentations, factory datasheets, Army/Navy circuits, etc.
Lots of ultrasonic alarms, plastic soldering machines, thermostats, motor speed regulators, sonars, steel mill equipment, radar, Lasers (gaseous, not diode), high power Flash units, strobes, Lab Instruments, Radio/TV/Audio consumer products, logic blocks, .... etc etc etc.
80% of them tubed.
I read and studied them a lot.
Although most of the stuff can be easily made with Op Amps and such, I found *very* illustrative to understand the basic principle behind each problem solved.
Well, those guys had no "Leo Fender" to guide them along the path, each ane ecvery one of the problems and solutions was new and original.
So, yes, they had to know all those equations and then some.
Do you want to learn them? Congratulations !!

[Alan0354]

I for one think the best is still ahead of us, not behind us. This has nothing to do with belittling the great work Leo and the others did in the 50s, they were the founders of guitar amps. Just like all the advance in MMA do not belittling the contribution of Bruce Lee. BUT things need to move on and there is always room for improvement.

Theory will not make an inventor out of you. It is like being good in English do not make you a good poet. But if you have the gift of writing poem, being good in grammar WILL enhance your poem writing. You don't design with theory and equation alone, inspiration comes from within. But given your ideas, theory and equation will help bringing you up to another level.

I was one of those that don't have a lot of theory and math background and design purely on inspiration and emotion. In fact I was very successful in my career for the first 20 years doing just that, rising from technician to become an engineer in 2 years, then promoted to become senior engineer then promote to become manager of engineering. I gain my knowledge by changing jobs, playing with new technologies. From designing data acquisition system for LeCroy( digital scope), analog IC design for Exar, to Ultra sound medical scanner for Seimens and then Mass Spectrometers, then got into RF for a few years. Kept changing to very different fields to gain common sense knowledge.

But from working in a small company called Charles Evans and Assoc. that about 80% of the technical personnel are PhDs, and particular with a very bright scientist that became the CTO of the company, it change my view. It really open my eyes to a world of knowledge and amazed by the giant brains. I spent the last 11 years studying 3 hours a day 5 to 6 days a week making up all the math and theory and beyond. I am so glad I did it, I still study even I am retired now. There is just so much knowledge out there.

I notice there are quite a few working engineers here, you all have the foundation of EE. Tubes don't seems to be that difficult to learn judging from the days I study the RDH4. Most of the stuff like poles and zeros, miller's effect and basic bias are same as with transistors and op-amps that you supposed to know in side out. Noise is the same as long as you get the model. You can skip 80% of the material and concentrate on the part specific to tubes like the screen, triode curve to name a few. And the formulas are quite simple for the most part. You never know how useful they are until you master it.

[Alan0354]

Why? Because they sound good. If you're doing spice modeling I can see the need to understand all the math involved, but I seriously doubt it's necessary to design a guitar amp, especially with so many classic circuits (Fender, Marshall, Vox et al) around.

I have not done tube simulations yet as I am just studying it. I sure do a lot of simulations for designing everything else including pedals. I no longer spend a lot of time on the bench solder and desolder stuffs. I did 15 years on the bench and I get a very good feel without doing bench work.

[JoeM]

I for one think the best is still ahead of us, not behind us....

Yes, but probably not with tubes. (At least I hope so.)

I don't really have a disagreement with you. But tube amps are not complicated circuits. And even though many years have passed since the original amps came out, they're still popular today. Look how Fender has re-issued so many of the classic BF and Tweed amps.

[Alan0354]

Yes, but probably not with tubes. (At least I hope so.)

I don't really have a disagreement with you. But tube amps are not complicated circuits. And even though many years have passed since the original amps came out, they're still popular today. Look how Fender has re-issued so many of the classic BF and Tweed amps.

I agree, tube amp is just part of my adventure. I never rule out solid state. That's why it is more important to understand what make the tube ticks. There is always a scientific explanation, don't give into "magic" so fast.

From the RDH4, it is not complicated at all, it is very easy, just need to go through the motion of learning it. That's the reason I wrote the screen voltage program and hand plot the load line of triode and pentodes just to get the feel of it. RDH4 gave good ideas how to predict bias, Ebb, Eb in distortion that give different characteristic of the sound. I just re bias and change the RL of the front end stage from what I learned and change the sound.....for the better. I lower the plate voltage to 205V and still get the max swing. It sure improve the sound and it worked out one time through from paper to amp. I know it is child's play for you guys that has been into this, but hey it helps me.

[Alan0354]

Yes, but probably not with tubes. (At least I hope so.)

I don't really have a disagreement with you. But tube amps are not complicated circuits. And even though many years have passed since the original amps came out, they're still popular today. Look how Fender has re-issued so many of the classic BF and Tweed amps.

About people going back to the tweed amps.......It really does not help with the newer generation amp from Mesa. I just can't help but putting down Mesa. I consider them about the worst amp only made famous by Carlos Santana. Their cascade stages sounded so bad, they kept stacking more stages, get the signal high, then divides down before driving the second stage and so on. Then use cap to short out the highs to ground to avoid feedback. If you use the high gain channel, turn the guitar volume down, you'll find it sounds dead, there is no sound quality left. The amp totally sounded dead. I set out to buy a Mesa, I tested and tested, retested different models, I just cannot pull out my credit card. There amps just sound dead to me.

Then they kept patenting stupid designs like simu cast. How stupid just to parallel two different tubes and call it a new name. Anyone tested the Blue Angle that supposed to be all tone, no overdrive? The cheapy Fender Blues Jr can kick it's bud!!! I designed my true channel switching amp in 78 before they even come out with a real channel switching. That was even before I got into electronic field!!! Mark I is only switching extra stage in and out. I am not impressed with any of the channel switching at all.

Then most others follow Mesa right along. No wonder people going back to the tweed amps.

[Steve Conner]

It wouldn't surprise me if Leo Fender had had some edition of the RDH on his bookshelves.

You ask why guitar amp design hasn't progressed beyond the same old circuits. Well one answer is that it has. The Mesa amps were the next step after the Fenders. And you said you don't like them, so one more vote for the old circuits.

Another answer is, you might as well ask why violin or trombone design hasn't progressed since the Victorian era. The tube guitar amp is the same, it's a part of a musical instrument.

[Alan0354]

It wouldn't surprise me if Leo Fender had had some edition of the RDH on his bookshelves.

You ask why guitar amp design hasn't progressed beyond the same old circuits. Well one answer is that it has. The Mesa amps were the next step after the Fenders. And you said you don't like them, so one more vote for the old circuits.

Another answer is, you might as well ask why violin or trombone design hasn't progressed since the Victorian era. The tube guitar amp is the same, it's a part of a musical instrument.

I am sure Leo has a copy of RDH4 and some others like Austin posted. Seen the short documentary of Leo and his work room, the way he put a neck on a plank of wood and nail the pup onto a block of wood where he put under the strings and nail onto the plank of wood with the neck and strings. He then move the pup around to get the sound he want. That is ingenious.

There must be some other ways on the amp, it is electronics, not the physical mechanical instrument. You don't change the structure of the guitar, but you can change the circuit of the amp. I just filed a patent application on guitar electronics and right now passed the first round checking and in the holding pattern for detail searching. I am crossing my finger it can pass. I am doing patent search on another idea on mine that someone already interested in. There is always room for improvement. I am not trying to say I have something great, just keep trying, never settle. I published two papers in scientific journal and own one patent that has nothing to do with music. just keep on trying, you never know what catch and what stick. Leo most likely never imagine he'll be this great when he first started out in his garage of basement.

In fact I just spent 6 months learning how to write a patent application and patent search. This will come in handy as it cost thousands of dollars if not over 10,000 for someone to write it.

[Enzo]

You keep mentioning "improvement". What is improvement in a guitar amp? I don't know that we copy Leo so much as we use the things he discovered that worked. And he "copied" the basic circuits from RCA manuals. Lots of people build clones of old amps like the Fender Deluxe 5E3, because they sound good. What "improvements" does that amp need?

As to merely adding in an extra gain stage and calling it channel switching. OK, so? Channel switching is all about controlling levels of gain. It might be far more interesting from an engineering point of view if they invoked some sort of balanced tube based op amp structure, or maybe some sort of controlled regenerative effect like a regenerative raio receiver. But would it really sound better? Assuming we know what better means?

Tube amps do what we want and do it well and reliably. We could re-engineer all our stuff to some other technology (how do those DSP laden synthesis burdened "modelling" amps sound to you? Not so great to me) just for the sake of doing it, but to what purpose?


I think it is terrific you have the professional opportunity to be surrounded by PHDs and other smart people. I have to admit I was crushed the day I realized I would never have any opportunity to work at the nearby National SUperconducting Cyclotron Lab here at Michigan State. I discovered they want a Masters in EE even for the guys who just solder on circuit boards over there. My lifetime of technical experience is not of value to them. They are like majors and generals, and I am like the lifer master sergeant. SO my hat is off to you.


However, building guitar amps is for the majority of us, not an engineering exercise. If I gave a Fender Hot Rod Deluxe to that crew of world class minds over at the cyclotron, I bet when I got it back it wouldn;t sound much better than it already does. Might have a more reliable 15v supply, but tone? What is the formula for tone?

A friend brought me his old amp he wanted to modify. We worked with the tone stack, we worked with the gain stages, a bunch of stuff. He'd want this, he;d want that, we sdwapped parts aroound. Eventually I realized we were working within a limited area of the amp, so instead of a bunjch of resistors, I installed a handfull of little trimmer pots. He could then twiddle the tone stack slope resistor and the plate load reistor, etc etc. Until he found the combination that sounded good to him. I am not sure how much math it would have taken to come up with those values. We migh after the fact go back and maybe determine what about them made him like what he heard, but predictive value? Limited.

Someone wanting to work on his amp performance can read a bunch of math that explains why lowering the screen voltage does this or raising the screen resistance does that, but if one glosses over the derivation and takes away that changing screen voltage affects gain, he can apply a variable screen supply and determine what he likes with never another drop of math.

I am all for math, and even the laborious derivations of the formulae, but like the ability to read sheet music, a man can learn to play guitar without it, and be quite good at it. Or create amplifiers.

[Alan0354]

There is a lot of improvement I can think of. For one you don't have an amp that sound good at all volume. The closest I get is by using the THD Hot plate. All the other's I tested sounds like crap.

Whole point is I refuse to settle and say we already have the best. I believe there is always a better way, and I am not talking about changing a few resistor, capacitors. This really boils down to believes, if you think the best is behind you, then it's your choice, I don't. Even though I am a Chinese, I am an American, This is the land of innovation and creativity. We never stop yet and I sure not going to start now.

I got all my opportunity because I was aggressive, I don't believe in being the second. I demand excellence on myself, I pushed the upper management to get every single promotion. I was turned down when I want to become the manager. I asked point blank, what do I have to do to get the job. The management told me what they want out of me. I did it, I got promoted. Nothing left for chance. I don't believe in excuse, just work harder.

In 1979, I was looking for my first job, I choose electronics with only experience was modifying my Twin Reverb. I discovered electronics was my passion to the point I quit music all together. I studied so hard and faltered on the job and got fired. I refuse to take unemployment, instead, I studied 18 hours a day for the next 3 months and landed my first real job as a technician where I got promoted to an engineer in 2 years. Just when I got comfortable on the job, I forced myself to change job just to get into a new field. I did this a few times to fulfill my eager of learning and make myself relevant.

I refuse to believe this is the best we or I can do. I just don't. No, the first thing when I see a circuit is to try to understand it, and then ask how can I do differently and do it better.

[Enzo]

The closest I get is by using the THD Hot plate. All the other's I tested sounds like crap.

Fair enough. It sounds to me then that you are going for an overdriven tone, or I maybe don;t know why you need a hot plate. My personal taste is a different direction, and I think there are MANY amps that sound GREAT. I think a Hot Rod DeVille sounds good... as long as you never click the overdrive on. THAt does sound awful. But I LIKE loud and clean.

Refusing to settle is a fine goal or philosophy. IMprove the amp? You bet. But we need to know what we mean by improvement. DIfferent isn't always better. I am open to new things, I'll look at changes. On the other hand, all the advances we have made in the last 50 years, I don't hear anything I think sounds better than a Fender Twin Reverb. Once someone tells me how an amp will sound better than that to me THEN I will seek ways to do it.

[Alan0354]

Fair enough. It sounds to me then that you are going for an overdriven tone, or I maybe don;t know why you need a hot plate. My personal taste is a different direction, and I think there are MANY amps that sound GREAT. I think a Hot Rod DeVille sounds good... as long as you never click the overdrive on. THAt does sound awful. But I LIKE loud and clean.

Refusing to settle is a fine goal or philosophy. IMprove the amp? You bet. But we need to know what we mean by improvement. DIfferent isn't always better. I am open to new things, I'll look at changes. On the other hand, all the advances we have made in the last 50 years, I don't hear anything I think sounds better than a Fender Twin Reverb. Once someone tells me how an amp will sound better than that to me THEN I will seek ways to do it.

I am looking for both clean and overdrive sound. Even clean sound, it change with different volume. Usually it sounds better with moderate volume, not at low volume. THD lower the loudness of the amp whether it is clean or dirty. They did a good job in compensating it. I am impressed.

Sometime, you set out a certain goal, but the result usually are quite different, you hit and miss. You just don't stop if you are into it. Yes, it is a philosophy, but you can put it into practice if you believe in it. Nobody promise it will be fruitful if you try, but you definitely don't get anything if you don't.

Another thing is the Yellow Jacket that fit an EL84 to 6L6GC or other tubes. This get into the Blue Angle, problem is Mesa just cannot design a good clean sounding amp even if they tries. They just cannot help making it complicated. I really look down on Mesa.

Actually I think the over drive sound of the Deville is so much better that Mesa ever get. For clean sound, I like Matchless, I even followed their idea of parallel two triodes and it does sound better.