I have always tried to steer away from preamps in general because I just can't find one that I think sounds good (meaning is neutral and doesn't suck the life out of the music). At least, with the preamps I've tried in the past---commercial units, kits, and some early attempts at home brew stuff, I have not been satisfied with any of them. The closest I have come to what works for me was a 6DJ8 gain stage coupled to a 6H30 cathode follower, using teflon output caps and oil power supply caps. But still even in that attempt, it just didn't sound as good as no preamp at all.
Especially with larger wattage push-pull type amps (like those using KT88s), it seems like a separate preamp must be necessary to take advantage of the full output power available in the power amp. So If I'm resigning myself to using a preamp, I might as well put my full effort into it.
I've mulled over the idea of using the 300B as a preamp tube for several years. I know this may be trying to pound a square peg into round hole, and wishing for a totally "neutral' 300B preamp may be an oxymoron. And yet going through my list of requirements, the 300B seems to meet these requirements.
Requirements are that I don't want a circuit with a lot of gain--eight to ten dB (2.5x to 3x) is ample. I don't want a circuit with a cathode follower, nor do I want a circuit with more than one stage, but it's still got to have usefully low output impedance. I think by picking the right operating point, putting the plate on a constant current source, and using DC filaments, I could get something that is silent, sounds pretty decent, measures well, and has usefully low output impedance, as well as offering the gain factor I'm looking for.
Is this a crazy idea? I've never used or designed a single thing around the 300B, so this would be a first, and a bit of a challenge for me.
What are the pros and cons of using the 300B this way (other than cost of the tube itself which is clearly stratospheric)? Has anyone undertaken a project like this?
I'd like to hear feedback from anyone who's either thought about a 300B preamp, or has built or used anything similar.
How about the 2A3 instead of the 300B? Other than the filament differences, I'm not sure what is different between these tubes (haven't done any research there yet). I've thought about the 12B4 as I understand is an indirectly heated cousin to the 2A3, but abandoned that idea because it's not available in new production.
I'm not married to the 300B or any particular DHT for that matter. I'm really looking for a solution that will be as neutral as possible and not suck the life out of the music, but will meet the requirements I have stated above. But, since the 300B is popular and well respected, I thought I'd start the discussion there.
Especially with larger wattage push-pull type amps (like those using KT88s), it seems like a separate preamp must be necessary to take advantage of the full output power available in the power amp. So If I'm resigning myself to using a preamp, I might as well put my full effort into it.
I've mulled over the idea of using the 300B as a preamp tube for several years. I know this may be trying to pound a square peg into round hole, and wishing for a totally "neutral' 300B preamp may be an oxymoron. And yet going through my list of requirements, the 300B seems to meet these requirements.
Requirements are that I don't want a circuit with a lot of gain--eight to ten dB (2.5x to 3x) is ample. I don't want a circuit with a cathode follower, nor do I want a circuit with more than one stage, but it's still got to have usefully low output impedance. I think by picking the right operating point, putting the plate on a constant current source, and using DC filaments, I could get something that is silent, sounds pretty decent, measures well, and has usefully low output impedance, as well as offering the gain factor I'm looking for.
Is this a crazy idea? I've never used or designed a single thing around the 300B, so this would be a first, and a bit of a challenge for me.
What are the pros and cons of using the 300B this way (other than cost of the tube itself which is clearly stratospheric)? Has anyone undertaken a project like this?
I'd like to hear feedback from anyone who's either thought about a 300B preamp, or has built or used anything similar.
How about the 2A3 instead of the 300B? Other than the filament differences, I'm not sure what is different between these tubes (haven't done any research there yet). I've thought about the 12B4 as I understand is an indirectly heated cousin to the 2A3, but abandoned that idea because it's not available in new production.
I'm not married to the 300B or any particular DHT for that matter. I'm really looking for a solution that will be as neutral as possible and not suck the life out of the music, but will meet the requirements I have stated above. But, since the 300B is popular and well respected, I thought I'd start the discussion there.