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Wel lit helps give an idea what people think is good. There are crap preamps out there...Mike
I was in a similar position a while ago looking for a tube preamp. I was willing to spend for something nice and then the DIY bug bit hard. I looked at several of the kit offerings and then started examining schematics I found online.Finally I settled on Bruce Rozenblit's Line Preamp from Glass Audio. I loved the simplicity of the schematic. It cost less than $90 to build. It is often considered the precursor to the Grounded Grid Preamp. Currently I am listening to a horn concerto and it still amazes me how good it sounds. Several friends have compared it to their more expensive tube preamp offerings (I mean come on, everything is more expensive than $90! ) and been very impressed. The preamp is not a world beater but it certainly causes people to rethink their audio belief system. One friend has insisted that I build him a copy.I am offering you my experience because I think there are no hard and fast rules as to what high quality audio has to cost. It is about results that make you musically content. Too frequently I believe that people want a sense of pride not from the sonics, but from the name that is silk-screened on the faceplate and its sheer cost.Please pardon my proselytizing and thanks for starting such a great thread. Good luck with your decision process.
I am offering you my experience because I think there are no hard and fast rules as to what high quality audio has to cost. It is about results that make you musically content. Too frequently I believe that people want a sense of pride not from the sonics, but from the name that is silk-screened on the faceplate and its sheer cost.
Right, I'm not gonna recommend any make of tube-pre, but a type of tube-pre.Remember this is Imperials take on the cheapo preamp with good sound!!!----------------------------------------------------------------------- Tube rectified (if you can...)- Medium to low gain (the higher gain, the more power supply-self noise... thus really less of a bang for the buck..)- The fewest possible parts in the circuit!- Conductive foil (alps?) or (preferably ..stepped) volume...- Preferably no balance control, or the possibility to take it out of the circuit when not needed.- Fewest inputs possible and outputs as well!- Preferably with a capacitor coupled output! (blocks dc...) (my view of course)- NO REMOTE! Or make sure that the remote circuit does not share any regulators or psu parts with the main psu for the voltage gain stage in the pre...- Tubes... can you fit dampers to them where they are placed? Good!- Sockets... Can you easily replace tubes when needed?- Auto bias is fine, but on this level of price I'm sure that manual bias can sometimes have sonic advantages! (though most pre-amps don't need this to be adjusted... granted)- Can you easily place extra dampening pads or sheets of esr paper in the box? That would be good to!- Does it have a well placed ac cord receptacle? Good!- Does the internal wiring look like its laid out neatly and organized? Good too!And to end this off... a very important thing, I think! - Is there slowstart circuits and mute switch? That would be good too! Really good! - Gainmatching!!!! Don't get a pre with more gain than you need, your amp and speakers willtell you that!!! You want to advance the volume to at least 1 or 2'O clock for maximum output in your system! And then It should not distort either!!! That would be good!Don't get more gain than you absolutely need! You just get higher noise floor! Not more bang for your hard earned buck!- The perceptive one will see that I don't mentions types of tubes or circuit types... Well, It does not matter! Personal choice is for the listener!!! "Anything you want. You got it - Roy Orbison" Well a short list. But this is what I would think about!But then again, I'm sort of careful in my choosing! Make that obsessively so...This is a lot of "options", not all Pre-amps will have them, but as many as you can I think!- Choke power supply is a bonus I think. Gives very fast response in the powersupply. Also serves a smoother for the dc...Imperial
The 12AU7 is a great tube.
Gain ratings for tubes in the 12 series:12AX7: 100% (point of reference, gain - or "MU");5751: 70%;12AT7: 60%;12AY7: 45%; 12AV7: 41%; 12AU7: 19%
What's wrong with a 12AU7?