Contemplating Tube Pre with my Sunfire Amp
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sleepysurf
Well-known member
Well, I've pulled the trigger and ordered a Modwright SWL 9.0SE. Will report back on it's sonic merits paired with my SS Sunfire Amp.
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Tube60
Well-known member
I could go at great length about this, but in a nutshell, most all tubes, power or small signal, will need a bias. Otherwise they won't conduct. Most tube preamps make do with a simple cathode bias resistor and often a bypass cap to shunt the audio frequencies around the resistor, much like the way a power amp is done. I'd like to do a tube pre-amp, but I'd like to use fixed bias instead, which I think would sound good and be more linear than a fixed cathode bias.Jeff Zaret said:This will be tough one. In my experience and I am by no means an expert you do not bias preamp tubes. This is typically done on tube amps. Of course this may not be an absolute and I am sure I will we told the wrong doing of my ways.
Jeff
As for the errors of your ways, Jeff, next time I'm in Lancaster I'm going to pull your fingernails off for assuming what you did.
Did I say that!? Well, silly me.... Probably simpler to buy you a beer though! 
I'll take the drink anytime.
I assume my pre is a fixed bias since there is no adjustment.
Jeff
I assume my pre is a fixed bias since there is no adjustment.
Jeff
Tube60
Well-known member
Good to hear! I'd love to know how it sounds. Be patient during the burn-in period. Let it run for several hours a day and don't thrash it too much. Also find out what tube the unit has, and buy a few different brands to play with. You'd be surprised at the differences! And I'd like to recommend turning it off when you're done playing. I've tried leaving my equipment running like some people like to do, but I've found no appreciable difference in sound. A typical tube warms up in 11 seconds and the filament and plate structures reach design temps somewhere between 1 to 3 minutes, and the rest of the circuit won't be far behind. Just my .02 of course!sleepysurf said:
HTH!
Tube60
Well-known member
Could be, but my instincts tell me it'll be a simple cathode bias with no adjustment.Jeff Zaret said:I'll take the drink anytime.
I assume my pre is a fixed bias since there is no adjustment.
Jeff
Spike
Well-known member
What's a ModWright SWL 6.0?sleepysurf said:
I think you meant the SWL 9.0 pre. Great unit from Dan Wright. Are you ordering a new unit just in time before the...price increase? If so, get the TungSol 5687 tubes from Dan. The beauty of this SWL preamp is that the 5687 tubes are dirt-cheap for the TungSol NOS tubes!!Spike
sleepysurf
Well-known member
Oops, typo! Thanks for the eads hup! I edited my post, also clarified it's the "SE" version, with upgraded caps, etc. Actually, I don't believe he is offering the "base" model any more.
sleepysurf
Well-known member
Impedance Matching
One thing I hadn't thought about was potential impedance matching issues between the Modwright and my Sunfire. The Modwright has ~600 Ohm output impedance, and my Sunfire Cinema Grand has ~24,000 Ohm input impedance. Not sure if there are any ballpark guidelines for impedance matching, so I'd be much obliged if somebody can educate me!
One thing I hadn't thought about was potential impedance matching issues between the Modwright and my Sunfire. The Modwright has ~600 Ohm output impedance, and my Sunfire Cinema Grand has ~24,000 Ohm input impedance. Not sure if there are any ballpark guidelines for impedance matching, so I'd be much obliged if somebody can educate me!
Spike
Well-known member
No cause for concern
Spike
Not sure about educating, but my AES SixPacs has input impedance of 150k ohms and my Classe' has 75k ohms input impedance. The ModWright works with both of my amplifiers flawlesslysleepysurf said:
Spike
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