Tweet
I haven't been building effects for too long. I know some of my problem is just not knowing enough but I've done some research and asked the people I know some questions before I posted here. Most of the folks I talked to are tube amp guys and so they've helped as much as they can. I am experiencing the frustration of designing a circuit from the ground up and I've run into something that I can't figure out.
The design is based on the 5F6-A Bassman preamp circuit. I used J201 Fets as the preamp tube halves. I made all the resistors for drain (100K) and source (5K) variable so I could set the bias just right. The input is a 1M resistor to ground like the bassman, then a 33k in series, then a 220pf to ground before the input of the first stage. Out of the first two J201s I kept all of the same values as the bassman for all the components. They are also running in parallel like a bassman or marshall with the jumper cable, and I have the two volume controls setup the same. The next stage is identical except that it's on it's own and it has no coupling cap or resistor to the gate of the follower stage which is standard with no resistor at the drain and a 100k resistor at the source. It goes to a .1uf output cap and a 100K Log pot for master volume.
The pedal sounds great overall but I am getting a distortion under the main sound that reminds me of a pedal that is not biased correctly. It is a harsher sounding distortion that seems to choke or fade as the strummed chord or single note comes off it's peak. The frustrating part is that the main sound is great. I feel like I'm in the home stretch but I don't know where to go from here. As I was messing with it this evening I found that I could make this underlying distortion last longer by playing with the trimpots at the drains but it still sounded like a squarewave and the overall sound was worse. I'm thinking that I am either missing something simple or I need to learn how to round off and sustain that distortion to make it more musical. I plugged in a lot of other overdrive/distortion boxes this evening and realized they have this sound also but it seems to hang on longer and it's not as harsh. Any suggestions would be much appreciated.
The design is based on the 5F6-A Bassman preamp circuit. I used J201 Fets as the preamp tube halves. I made all the resistors for drain (100K) and source (5K) variable so I could set the bias just right. The input is a 1M resistor to ground like the bassman, then a 33k in series, then a 220pf to ground before the input of the first stage. Out of the first two J201s I kept all of the same values as the bassman for all the components. They are also running in parallel like a bassman or marshall with the jumper cable, and I have the two volume controls setup the same. The next stage is identical except that it's on it's own and it has no coupling cap or resistor to the gate of the follower stage which is standard with no resistor at the drain and a 100k resistor at the source. It goes to a .1uf output cap and a 100K Log pot for master volume.
The pedal sounds great overall but I am getting a distortion under the main sound that reminds me of a pedal that is not biased correctly. It is a harsher sounding distortion that seems to choke or fade as the strummed chord or single note comes off it's peak. The frustrating part is that the main sound is great. I feel like I'm in the home stretch but I don't know where to go from here. As I was messing with it this evening I found that I could make this underlying distortion last longer by playing with the trimpots at the drains but it still sounded like a squarewave and the overall sound was worse. I'm thinking that I am either missing something simple or I need to learn how to round off and sustain that distortion to make it more musical. I plugged in a lot of other overdrive/distortion boxes this evening and realized they have this sound also but it seems to hang on longer and it's not as harsh. Any suggestions would be much appreciated.
Comment