Question about touch responsive amplifier design

[pdf64]

Yes, also I think some Mesas had a 'tweed' switch for a spongier response, which worked by switching in more windings on the PT primary, thereby reducing all secondary voltages.

ampdoc1, does the amps overdrive character seem to stay consistent as the power is turned down?

The reason I ask is because I suspect that the mechanism behind the overdrive will change as the heaters run cooler.

At full voltage / temperature, the power amp overdrives when the signal level at the power tube grid is such that Vg-k tries to go above 0V and grid conduction occurs (shorting out the top of the wave to the cathode / ground).
However, with reduced heater temperature the supply of electrons emitted from the cathode may be the limiting mechanism, ie the power tube hits plate current saturation. If so, this must occur at a lower grid signal level than overdrive occurs at full temperature.

So, at full temperature the overdrive mechanism is grid conduction acting to limit the drive signal.
Whereas at reduced temperature, the overdrive mechanism is (plate) current saturation, ie the tube is using all available electrons.

Are you able to monitor the waveforms at the power tube grid and of the plate current to make an assessment of my theory above?

Does anyone have a view on this?
Pete

[ampdoc1]

Re the question about cathode stripping, etc., I really don't know. I've read that this is a problem only affecting transmitting tubes. I don't know how many hours the amp was played over the last 10 years, (I estimate the amp was used about 50 hours during the trial use before I sent it to the owner) but the original tubes are still working fine.


As to the sound, there is no difference that I can hear in the tonality with the the "limiter" at full or minimum states, nor did I expect it to. As I said, I'm not a techie, and don't understand most of the explanation in the last post. But here is my explanation, and I may be way off.

The plate voltage is unchanged so the sound wave "velocity" of the particles is unchanged, but with the heater voltage reduced, less electrons (each with the same relative particle of the sound), are boiled off the cathode to make their way to the plate. My analogy would be shooting BBs at a can. A single BB (electron) will hit the can at a given velocity and make a sound when it hits the can. If you shoot 100 BBs at the same time, they will each still have the same velocity, but will make much more noise.

If this is stupid, don't rip me a new one. I told you I am a self taught tinkerer, but some of my ideas have worked really well despite my ignorance.

Thanks for your interest.


a'doc1

[chromefaceplate]

hi-newb here. this thread seems to epitomize experienced players need in a great tube amp, thus the constant search. am not a tech guy so reading the above is not much help, but i have been asking this question for 45 yikes years, since first trying to get more feel from a new 69 silverface showman head. at least this gets me closer to understanding the difficulty. would like to read MUCH more along these lines. thank you gents.

[talbany]

KISS...Keep it simple stupid.. IMO.. The simpler the design( ie less components in the signal path) the more responsive and dynamic the amp will be..At least from a design stand point..However without all the tone shaping and impedance matching/mismatching the more raw the amp will sound (like a Wreck)..Things like cathode followers and high PF rated cable can also help with smoothing if you know what you are doing!!

Maybe this helps...Maybe it didn't

Don't bore me with caps,pots and resistors..GET ME TO THE TUBES!!

Tony

[sepulchre]

KISS...Keep it simple stupid.. Don't bore me with caps,pots and resistors..GET ME TO THE TUBES!!

Big +1 to that!

[LeftyStrat]

Just to add my two cents. Backing up from touch responsive to just an amp that presents nuances that a guitarist can explore. It becomes another "instrument" that you must learn.

At the end of the day it is "play differently, amp responds differently."

It's an amp I can play three notes; soft, harder, and hardest, and have the first note clean, the second note with a bit of distortion, and the last go into sustain and feedback, and all three notes seem to have the same apparent volume. Maybe with some volume know manipulation.

Ultimately, an amp that does this won't guarantee every player experiences it. It's all about the dynamics of your playing.

It's about realizing that an amp is as much an instrument as your guitar. A wonderful amp will make a Silvertone sound great. A bad amp will make a 59 Les Paul sound like shit.

A hack will still sound like a hack through an original Dumble.

I've watched guitarists take a pedal I hated and find nuances that I wasn't patient enough to discover.

static = suckage (which explains a lot of digital)
dynamic = really good. More chaotic the better.

A great guitar amp is an instrument you must establish a relationship with.

This is probably just me, but I never found the magic in single-ended amps. No sag, too tight.

[talbany]

Just to add my two cents. Backing up from touch responsive to just an amp that presents nuances that a guitarist can explore. It becomes another "instrument" that you must learn.

At the end of the day it is "play differently, amp responds differently."

It's an amp I can play three notes; soft, harder, and hardest, and have the first note clean, the second note with a bit of distortion, and the last go into sustain and feedback, and all three notes seem to have the same apparent volume. Maybe with some volume know manipulation.

Ultimately, an amp that does this won't guarantee every player experiences it. It's all about the dynamics of your playing.

It's about realizing that an amp is as much an instrument as your guitar. A wonderful amp will make a Silvertone sound great. A bad amp will make a 59 Les Paul sound like shit.

A hack will still sound like a hack through an original Dumble.

I've watched guitarists take a pedal I hated and find nuances that I wasn't patient enough to discover.

static = suckage (which explains a lot of digital)
dynamic = really good. More chaotic the better.

A great guitar amp is an instrument you must establish a relationship with.

This is probably just me, but I never found the magic in single-ended amps. No sag, too tight.

This is so true.. I've seen it time and time again when players come in and audition amps..Seems like they are more concerned about impressing you with there chops (if they have any) than actually listening to what the amp is telling them.. Also so many players that have been using amps that are rather flat dynamic wise they don't seem to recognize or respond to what the amp is (instrument) is doing..If they would stop and hold a note long enough to let the note bloom! ..At that point I usually let them take the amp and play it with nobody around they might discover the nuances.. Some players no matter how long they keep it will just never get it!!..They are usually the ones who are most interested in gain than tone/response!!...Some players can do incredible things with a Squire Strat and a Blues Jr..The unbelievable Jack Pearson (Check out 1:00 in it)

http://www.youtube.com/watch?v=QB3abALyCzs

Tony

[sepulchre]

Man, that's beautiful. Whew! I like that little smile after about 30 seconds of pure clean sustain.

[rp]

Also so many players that have been using amps that are rather flat dynamic wise they don't seem to recognize or respond to what the amp is (instrument) is doing..

I've lent amps to amateur friends here, or tried to lend them, most are used to SS or some sort of Valvestate stuff. My amps, all tweed or marshal or matchless clones scare the crap out of them. They can't play them. Its immediately obvious they are too dynamic and sensitive for them, really throws them off. The semi or pro guitarists on the other hand have no problems and give me compliments.

Best gear thing you can do to a kid or amateur to move them to the next level is give them a good 5E3.

+1 KISS and old tweeds (kiss an old tweed?)

[martin manning]

KISS is an axiom of good design, IMO. For the kids I guess it could be updated by reversing the last two S's ;^)

[iknowjohnny]

Also so many players that have been using amps that are rather flat dynamic wise they don't seem to recognize or respond to what the amp is (instrument) is doing..

I've lent amps to amateur friends here, or tried to lend them, most are used to SS or some sort of Valvestate stuff. My amps, all tweed or marshal or matchless clones scare the crap out of them. They can't play them. Its immediately obvious they are too dynamic and sensitive for them, really throws them off. The semi or pro guitarists on the other hand have no problems and give me compliments.

Best gear thing you can do to a kid or amateur to move them to the next level is give them a good 5E3.

+1 KISS and old tweeds (kiss an old tweed?)

Yes ! And while so many people say gear doesn't matter and a great player will sound great with anything, I've always seen it a bit differently. When you learn on a great touch sensitive amp, it changes you as a player and you learn a different way to play. It will make you a much better and more dynamic player. There are dynamics in a great touch sensitive amp that allow you to discover what your hands can do on their own without the aid of excessive controls on the amp and 50 footswitches ! Because of this i have always said gear DOES matter, and a LOT. When a player learns this lesson they then spend all their gear acquisition energy trying to find gear that allows that touch, and those who learn this end up trashing thier fancy modern 3 channel amps and looking at simple vintage or boutique amps or end up here building their own.

[eniam rognab]

dont keep it simple stupid

keep it simple smart

[rp]

BTW the touch thing goes for acoustics too. I've had a great 1960 D18 for 25 years, but my Santa Cruz DPW took me to a new level. The forward bracing moves a lot more air than the postwar D18. The SCGC has a ton of pop you have to control. Totally changed the dynamics of my strumming. I really drive the DPW, and I play in and out of that envelope of air the guitar moves. Good amps make you do that too. Fun.

[talbany]

Also so many players that have been using amps that are rather flat dynamic wise they don't seem to recognize or respond to what the amp is (instrument) is doing..

I've lent amps to amateur friends here, or tried to lend them, most are used to SS or some sort of Valvestate stuff. My amps, all tweed or marshal or matchless clones scare the crap out of them. They can't play them. Its immediately obvious they are too dynamic and sensitive for them, really throws them off. The semi or pro guitarists on the other hand have no problems and give me compliments.

Best gear thing you can do to a kid or amateur to move them to the next level is give them a good 5E3.

+1 KISS and old tweeds (kiss an old tweed?)

Yes ! And while so many people say gear doesn't matter and a great player will sound great with anything, I've always seen it a bit differently. When you learn on a great touch sensitive amp, it changes you as a player and you learn a different way to play. It will make you a much better and more dynamic player. There are dynamics in a great touch sensitive amp that allow you to discover what your hands can do on their own without the aid of excessive controls on the amp and 50 footswitches ! Because of this i have always said gear DOES matter, and a LOT. When a player learns this lesson they then spend all their gear acquisition energy trying to find gear that allows that touch, and those who learn this end up trashing thier fancy modern 3 channel amps and looking at simple vintage or boutique amps or end up here building their own.

I had the unique privilege of sitting down with Jack for a lesson..One of the things that really hit home was how he touched the insturment..He played through an old classical nylon string and was able to get so much volume/sustain out of the guitar with such a light touch ...Later on after the lesson we went to dinner and I asked him how he was able to get such volume and control with such a light touch?.. He said that for so long he had to learn to play on sub par guitars so he had to try and squeeze everything out of them ..Later on when he could afford better guitars and amps it made him that much better at controlling them (he was able to make the turn)..You can actually get better sustain with a light/medium touch..Hit too hard and you can kill it?..BTW.. The other guy there at that dinner was JD Simo...Most will tell you 2 of the best guitar players in Nashville.. That was the highlight of my trip right there!!

Back to Amps!

All The Best..

Tony

[rp]

double post