Sammas
Well-known member
today i started investigating some guitar amp schematics to try and get a grasp of whats actually happening. Big happening for someone quite unfamiliar with electronics compared to many here.
In the following schematic i can kinda see what is going on now... compared to this morning. Two preamp common cathode (or fully bypassed cathode) gain stages before the output stage. I seem to understand the purpose of the coupling caps, grid resistors, cathode resistors and bypass cap, plate load resistors, load resistor (or grid resistor of the next gain stage)... I've even looked into some of the maths about biasing and the gain of each stage...
Now for the part which confuses me? probably due to a lack of knowledge and an overwhelming large amount of infomation for one day. In the schematic there is 240v supplied to the plate load resistor - The plate voltage supply. I've noticed on several different schematics that they not only vary between designs but between stages as well. For example in one design there are 3 different voltages supplying 4 different gain stages... One (the last one before the output stage) had a plate voltage supply of more than 300v (all were 12AX7's). I don't understand why, and have been searching for sometime trying to figure out what determines the voltage supplied to each stage... i've looked for equations or explainations but can't seem to find an answer. I'd be at the library right now looking for some answers except its almost 10pm.
the coupling caps obviously isolate the grid in the next stage from the high voltage DC... can anyone point me in a direction towards an answer? or more infomation? or anything?
It would also "kill two birds with one stone" if someone could point me to a source of infomation regarding the actual voltage supply in the bottom schem. I can seem to find any answers on the maths (maybe?) behind creating stepped voltages like done in the schematic. For example if i wanted to add 210v supply after the initial 285v & 240v what cap/resistor configuration would get me there...
Im probably in over my head, but its been a productive day and it would be cool if you guys could give me maybe even just a phrase to start the ball rolling again. Tomorrow im off to the library to get me some books on the matter also... but times-a-wasting :wink:
In the following schematic i can kinda see what is going on now... compared to this morning. Two preamp common cathode (or fully bypassed cathode) gain stages before the output stage. I seem to understand the purpose of the coupling caps, grid resistors, cathode resistors and bypass cap, plate load resistors, load resistor (or grid resistor of the next gain stage)... I've even looked into some of the maths about biasing and the gain of each stage...
Now for the part which confuses me? probably due to a lack of knowledge and an overwhelming large amount of infomation for one day. In the schematic there is 240v supplied to the plate load resistor - The plate voltage supply. I've noticed on several different schematics that they not only vary between designs but between stages as well. For example in one design there are 3 different voltages supplying 4 different gain stages... One (the last one before the output stage) had a plate voltage supply of more than 300v (all were 12AX7's). I don't understand why, and have been searching for sometime trying to figure out what determines the voltage supplied to each stage... i've looked for equations or explainations but can't seem to find an answer. I'd be at the library right now looking for some answers except its almost 10pm.
the coupling caps obviously isolate the grid in the next stage from the high voltage DC... can anyone point me in a direction towards an answer? or more infomation? or anything?
It would also "kill two birds with one stone" if someone could point me to a source of infomation regarding the actual voltage supply in the bottom schem. I can seem to find any answers on the maths (maybe?) behind creating stepped voltages like done in the schematic. For example if i wanted to add 210v supply after the initial 285v & 240v what cap/resistor configuration would get me there...
Im probably in over my head, but its been a productive day and it would be cool if you guys could give me maybe even just a phrase to start the ball rolling again. Tomorrow im off to the library to get me some books on the matter also... but times-a-wasting :wink: