2011/3/5 Giuseppe Zompatori <siliconjoe(a)gmail.com>om>: Fixed this by including the math module "m" in amps.pmf but now it fails at parsing the _amp_wdf macro, probably a cut and paste error :(

Le Sat, 5 Mar 2011 18:55:19 +0100, Giuseppe Zompatori <siliconjoe(a)gmail.com> a écrit : With triodes, the preamp will include at least 2 stages (like the 2 valves of an ECC81). With pentodes, you get higher gain and can make a complete guitar amp with 2 tubes like in the Fender Champ : http://www.drtube.com/schematics/fender/champ-5c1-schem.gif Also, be aware that each manufacturer make compromise between the sound quality and the manufacturing costs. As example, a well-know mark is using cheap power transformers, and when at full volume, the sound will be very bad because half of the distortion you will ear is due to saturation into the power transformer. As a consequence, those amplifiers are widely used by jazz musicians but almost never by rock musicians. The laters will also often blow the power transformers. Another well-know mark is using good but small output transformers, as well than better power transformers than the precedent one. The consequence is than the sound is very good at full volume, but a rock or blues musician will often blow the output transformers. Generally speaking, a common source of non linearities, and often ignored, is due to a non adequate driver stage. Tubes are by design made to work best at high impedance. To get a low output impedance, you need a transformer. But that's expensive hardware, especially in class A. Preamp and driver stages are class A stage, when the output stage is generally a class AB2 push-pull where the grid can become positive in respect to the cathode. Common tubes for such a push-pull are 6L6. According to the datasheets, such tube can take 0.35 watts and the driver output impedance must be lower than 500 ohms: http://www.mif.pg.gda.pl/homepages/frank/sheets/021/6/6L6.pdf It is no one single guitar amp I know on the market with a driver stage that can provide such a power to the output stage, and this is a major source of non linearities when the output stage is driven at high volume. It would be simple to design such a driver : one tube like a triode mounted EL82 in a class A stage with a high quality driver transformer. But it will cost too much money, so no one single manufacturer I know is using such a design. It is too bad because such this sound just terrific, the sound is clean and fully saturated at the same time, and its dynamic is outstanding. :) Be also aware than the valves models used by simulation software like spice are good for consumer audio equipments or sonorisation stages, but than they don't take in account the saturation that a guitar amp will provide. In other words, they are completely out of business in regard to correctly simulate a guitar amp at high volume, or even a simple preamp stage in saturation. For that, a much better approach would be to use models based on the constant current family of curves: http://www.agsrhichome.bnl.gov/AP/ap_notes/ap_note_97.pdf My 2c Ciao, Dominique

> >Well, they say guitarix has improved, yet the last time I was all but > >satisfied with it. You may want to take a look at invada plugins, if > >you haven't already. > > Invada has a simple generic tube drive function AFAIK, I still prefer > the CAPS* amp over it as it's at least based on a real amp. > > >Stammi bene, > > > >Stefano > > Anche tu! > > -Giuseppe

Le Sat, 5 Mar 2011 18:55:19 +0100, Giuseppe Zompatori <siliconjoe(a)gmail.com> a écrit : With triodes, the preamp will include at least 2 stages (like the 2 valves of an ECC81). With pentodes, you get higher gain and can make a complete guitar amp with 2 tubes like in the Fender Champ : http://www.drtube.com/schematics/fender/champ-5c1-schem.gif Also, be aware that each manufacturer make compromise between the sound quality and the manufacturing costs. As example, a well-know mark is using cheap power transformers, and when at full volume, the sound will be very bad because half of the distortion you will ear is due to saturation into the power transformer. As a consequence, those amplifiers are widely used by jazz musicians but almost never by rock musicians. The laters will also often blow the power transformers. Another well-know mark is using good but small output transformers, as well than better power transformers than the precedent one. The consequence is than the sound is very good at full volume, but a rock or blues musician will often blow the output transformers. Generally speaking, a common source of non linearities, and often ignored, is due to a non adequate driver stage. Tubes are by design made to work best at high impedance. To get a low output impedance, you need a transformer. But that's expensive hardware, especially in class A. Preamp and driver stages are class A stage, when the output stage is generally a class AB2 push-pull where the grid can become positive in respect to the cathode. Common tubes for such a push-pull are 6L6. According to the datasheets, such tube can take 0.35 watts and the driver output impedance must be lower than 500 ohms: http://www.mif.pg.gda.pl/homepages/frank/sheets/021/6/6L6.pdf It is no one single guitar amp I know on the market with a driver stage that can provide such a power to the output stage, and this is a major source of non linearities when the output stage is driven at high volume. It would be simple to design such a driver : one tube like a triode mounted EL82 in a class A stage with a high quality driver transformer. But it will cost too much money, so no one single manufacturer I know is using such a design. It is too bad because such this sound just terrific, the sound is clean and fully saturated at the same time, and its dynamic is outstanding. :)

Be also aware than the valves models used by simulation software like spice are good for consumer audio equipments or sonorisation stages, but than they don't take in account the saturation that a guitar amp will provide. In other words, they are completely out of business in regard to correctly simulate a guitar amp at high volume, or even a simple preamp stage in saturation. For that, a much better approach would be to use models based on the constant current family of curves: http://www.agsrhichome.bnl.gov/AP/ap_notes/ap_note_97.pdf

My 2c Ciao, Dominique -- "We have the heroes we deserve." _______________________________________________ Linux-audio-dev mailing list Linux-audio-dev(a)lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev