NOTE Not a discussion for purists, and not talking about an amp with an overall global feedback loop.
Some time back I was pondering people deliberately "sweetening" amplifiers by operating tubes in a manner that would generate a degree (not lots) of second harmonic distortion. The first method that I pondered was picking a load line where the response was not symmetrical. Given that this requires either significantly altering the B+ or the bias current it's not terribly easy to do on the fly (say via a switch).
It occurred to me the other day, that an unbalanced concertina might achieve the same thing (and because it only requires changing the impedance to ground of the cathode connected resistors, would be simple to switch in and out).
Has anyone played around with this type of thing? (I realise that it is anathema to those who want a linear amplifier)
Some time back I was pondering people deliberately "sweetening" amplifiers by operating tubes in a manner that would generate a degree (not lots) of second harmonic distortion. The first method that I pondered was picking a load line where the response was not symmetrical. Given that this requires either significantly altering the B+ or the bias current it's not terribly easy to do on the fly (say via a switch).
It occurred to me the other day, that an unbalanced concertina might achieve the same thing (and because it only requires changing the impedance to ground of the cathode connected resistors, would be simple to switch in and out).
Has anyone played around with this type of thing? (I realise that it is anathema to those who want a linear amplifier)
Yes indeed. I've used unbalanced long tail pairs this way. I've also used unbalanced current mirrors to drive the PP output stage with up to 50%H2.
I do this sometimes to add some spescial character to the tone of my guitar amps. I also do it to test how much H2 I can have before it is noticable, and I'm a bit shocked that I don't hear it till its too high for me to even admit it here
This experiment has led me to almost ignor H2 in measurements of my amps, unless they are skyscraping of course. I only worry about H3 and above.
The first thing I notice with high H2 is a fuller (warmer) bass. I was told by a friend who's an expert in acoustics that a H2 does just that, makes bass seem fuller and even deeper in frequency. The higher frequencies dont seem as affected, though I guess some smearing occurs at some point.
I certainly don't mind the sound of H2...
Please note that I worked on fighter jets in my young age, have many children and a wife, so my hearing isn't very 'golden' anymore
I do this sometimes to add some spescial character to the tone of my guitar amps. I also do it to test how much H2 I can have before it is noticable, and I'm a bit shocked that I don't hear it till its too high for me to even admit it here
This experiment has led me to almost ignor H2 in measurements of my amps, unless they are skyscraping of course. I only worry about H3 and above.
The first thing I notice with high H2 is a fuller (warmer) bass. I was told by a friend who's an expert in acoustics that a H2 does just that, makes bass seem fuller and even deeper in frequency. The higher frequencies dont seem as affected, though I guess some smearing occurs at some point.
I certainly don't mind the sound of H2...
Please note that I worked on fighter jets in my young age, have many children and a wife, so my hearing isn't very 'golden' anymore
Hehe. It is called all kinds. I've called it 'the mystery control' just to get guitarists to use it. Normally I call it 'color'.
There is absolutely no standard nomenclature for anything on guitar amps. Master can be 'growl', gain can be 'exhaust',etc,etc...
Well I guess when you start building amps on a commercial scale somebody will let you name them. I call it the "body" control because that is what it is called on the few commercial amps that have used it on a big production scale.
Also, your example sort of contadicts your point. You pointed out that what is overwhelmingly called the "master" is called "growl" by a boutique amp maker. This would not be notable EXCEPT for the fact that "master" is the most common and therefore standard term.
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Actually I aint contradicting anyone. Just saying you can call it what you want, and there is no industry rule regarding that issue, wether it is a mass produced commercial brand or a one-a-month garage product. The 'industry standard' is 'gain', 'master', 'bass', 'treble', etc. But there is no rule and no regulation about it. Some use the more correct term 'volume' and they are by no means setting the standard or doing anything wrong.
The H2 tweak is not very common at all, some do it, the idea is old, but it is not common, and there is certainly no standard term for that feature.
but hey, at least we all know how to get some 'body' to our tone now
I have used some creative names for some of the knobs on some of my amps, like "bend" and "break" that controlled the balance between positive and negative feedback. I also had a "meltown" knob that did just what it says. The master gain was called "crank". Bass, Treble, and mid....Thump, Scream and Honk.
However, no one can beat Eric Barbours amp and names. Eric used to be an applications engineer for Svetlana and has authored several magazine articles. He now designs and sells vacuum tube based analog music synthesizers and effects boxes. He designed a guitar amp that uses 23 tubes and unveiled it at NAMM a few years back. Lets just say it has some rather creative names for the amp itself and many of the knobs.
The unveiling can be found on you tube and the amp is on his web site.
WARNING !!!!! don't look there if strong language offends you, or small children are looking over your shoulder. WARNING !!!!!
Vacuum Tube Modules for Electronic Music by Metasonix - Home
It was made to draw attention to his other designs and name. Do you know that some now considered as classical group of musicians performed with toilet seats as collars?
The same purpose.
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There are several ways to unbalance a P-P. I have used several including mismatched output tubes. In some cases really mismatched like a 6L6 and a 6V6. This inbalances the DC and AC signals leading to some unusual distortion (assuming this is a guitar amp). Another way is to wire a 1 MEG pot across the output tube grids with the wiper grounded (cathode biased amp). This affects the AC balance only, and is called the "tilt" knob. The effect is not as obvious as other methods. Wire a 100 ohm pot in series with one of the cathode bypass caps in the output stage. This gives a different effect.
Ok, I'll buy that. But it would turn me away. Guess I'm too old school and too conservative.
I happen to have an odd taste in design, so love it when others go off the normal path.
Here is a guitar amp built as a V8 engine. Two 6SL7 preamp, two 6SN7 PI and driver, and four 6AS7 output. It has 'Throttle' as master, 'Exhaust' for gain, and a 'Brake' switch to mellow down the highs.
Here is a guitar amp built as a V8 engine. Two 6SL7 preamp, two 6SN7 PI and driver, and four 6AS7 output. It has 'Throttle' as master, 'Exhaust' for gain, and a 'Brake' switch to mellow down the highs.
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That was my take. The NAMM (North American Music Manufacturers) show is the largest trade show in the music equipment world. It is not open to the general public. How does a little guy on a small budget even get people to walk into his booth when they are there to see names like Fender, Marshall, and Peavey. Word of mouth spreads like fire on the show floor. Regardless of the name, $5000 for an amp? That would buy a mega Marshall stack!
Cool. I built a V8 right after hurricane Wilma nuked the neighboorhood. The corrugated aluminium hurricane panels make for a suitable chassis. They could be found in the streets all over the neighborhood since people didn't mount them properly. Mine used 6SL7's and Chinese 6L6GC's since they are cheap.
The throttle knob is obvious, but I used "timing" (tone) "boost" (master gain) and "launch control" (feedback) but no brake. Since the Fast and Furious movies were a hit here my "engine" was transverse mounted in a painted plywood box made from hurricane leftovers. There was of course a "NOS" pedal that contained a transistor fuzz box. I never photographed it, but I know the current owner, and have visitation rights.
I started on a V12, but never finished it.
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