Tube vs. Solid State Preamp
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From: John Larkin on 31 Mar 2010 22:58 On Wed, 31 Mar 2010 22:40:48 -0400, Bitrex <bitrex(a)de.lete.earthlink.net> wrote: >Jim Thompson wrote: >> On Wed, 31 Mar 2010 18:04:35 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> On Wed, 31 Mar 2010 13:36:54 -0800, Robert Baer >>>> <robertbaer(a)localnet.com> wrote: >>>> >>>>> John Larkin wrote: >>>>>> On Tue, 30 Mar 2010 08:56:08 -0700 (PDT), Chris >>>>>> <christopher.maness(a)gmail.com> wrote: >>>>>> >>>>>>> With today's modern technology, is it possible to make a solid state >>>>>>> preamp that is as quiet as a good tube pre? >>>>>>> >>>>>>> I am thinking about building a preamp. >>>>>>> >>>>>>> Thanks, >>>>>>> Chris >>>>>> Tubes are noisy. >>>>>> >>>>>> John >>>>>> >>>>> Try running a 12AU7 with a plate supply of 45V and grid-to-cathode >>>>> voltage of about -1.5V (tweaked for zero grid current). >>>> What are the voltage and current noise densities? >>>> >>> Don't know about the 12AU7 but the 7788 or in civilian E810F could get >>> to around 1nv/rtHz when rigged as a triode (it wants to be a pentode in >>> normal life). >>> >>> I wish Sovtek, Svetlana or one of those companies would make it. In an >>> environment where a big zap to an input is sort of normal these are >>> really useful. Even a real zinger with a blue flash inside the glass and >>> an audible pop typically leaves a tube unfazed. >> >> We've sort of shot ourselves in the foot with our desire to get >> everything on a single chip... >> >> I'm often puzzled why a hybrid... tubes plus transistors... wouldn't >> be the nicest solution. I've actually made a very HV transistor by >> using a tube with a grounded grid and an NPN in the cathode path. >> >> Size? Ever see a Nuvistor ?:-) >> >> And I can't remember what they were called... a stack of ceramic >> spacers and metal grids... really small. One jokester had the >> "heater" from a blowtorch ;-) >> >> ...Jim Thompson > >It's not real recent, but I wonder if you've seen this: > >http://www.escholarship.org/uc/item/3rd0g181?display=all Cute, but 1 uS isn't going to set the world on fire. Microtips and nanotubes have been used as cold emitters for some time now, but are erratic and have short lifetimes. John
From: Tim Williams on 31 Mar 2010 23:32 "Joerg" <invalid(a)invalid.invalid> wrote in message news:81hoh3Fb4tU1(a)mid.individual.net... > UC3842? How did you get PFC and regulation done with just one chip and one > inductor? Nope, but close, FAN7527. Basically a 3842 with a multiplier after the error amp, with a beefier output and more protection circuitry (over/under voltage, overshoot, etc.). http://myweb.msoe.edu/williamstm/Images/Highamp_PFC.png Pretty much the datasheet circuit. Haven't tested the aux supplies yet though (notice D5 and C13 missing on the board, and only two windings on the inductor). Pretty neat, worked first time, exactly as indicated. Overvoltage protection works too -- kind of unnerving to hear it chatter for the first ~100ms before the error amp pulls in. They really should've built a proper control loop instead of adding that cheap hack. It's a little unstable, you can nudge the line or load with a transient and see it wiggle for about a second (at ~10Hz, so a Q of 5ish?). It's not unstable, the voltage is always 410V give or take ripple, but it's not the perfectly damped response I like. I'll get in there and tweak the feedback loop, maybe add a 'speedup' capacitor for some derivative action. Tonight I tested half the PWM board that it powers... http://myweb.msoe.edu/williamstm/Images/EE409_PWM3.jpg ....I discovered these little bastards sucking over 300mA while the TL598 is running. It seems that, in the ~40ns it takes for the '598 to transition, these things are each drawing a peak of 10A or so (the tantalum is specified as ~2.5 ohms ESR, so most of the current is probably coming from the 0.1uF MLCC over by the '598). Multiply by 4, then 2, then 100kHz, and you get: lots of heat. >> Now I just need to get rid of that masking tape! ;) > > Whoops, did it bake on? No, or not yet... it's kind of ugly though. Need to replace the hookup wire winding with proper litz, too. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Michael A. Terrell on 31 Mar 2010 23:58 Joerg wrote: > > Michael A. Terrell wrote: > > Joerg wrote: > >> Michael A. Terrell wrote: > >>> Joerg wrote: > >>>> The German text in there is rather funny. For "low noise" they use the > >>>> expression "niedriges Geraeusch". That words normally describes a noise > >>>> such as the squeal of a bearing that's about to go bad. > >>> > >>> Or heavy metal. ;-) > >>> > >> If you listen to music from the Scorpions the noise figure does not make > >> one iota of difference :-) > > > > > > I listen to traditional Country music, Bluegrass & Southern Gospel. > > > > Same here. When doing layout checks I listen to these: > > http://www.bluegrass.com/radio/ > http://www.radioparadise.com/content.php?name=Listen > http://bluegrasscountry.org/ > > But when I was young and wild, different story :-) I still listen to http://www.wsmonline.com They have one show that is produced live in a cavern 333 feet below ground. Amazing acoustics for Bluegrass. :) -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: Michael A. Terrell on 31 Mar 2010 23:59 Don Lancaster wrote: > > Michael A. Terrell wrote: > > > > > > I listen to traditional Country music, Bluegrass & Southern Gospel. > > > > > > I think I found your problem. You have no clue. -- Lead free solder is Belgium's version of 'Hold my beer and watch this!'
From: Adrian Tuddenham on 1 Apr 2010 04:33
George Jefferson <George(a)Jefferson.com> wrote: > "Adrian Tuddenham" <adrian(a)poppyrecords.invalid.invalid> wrote in message > news:1jg8ngr.1g7xp3le9s3eyN%adrian(a)poppyrecords.invalid.invalid... > > �Leo� <leo2100(a)gmail.com> wrote: > > > > [...] > >> This happens so because the transistors are more ideal amplifying > >> devices than tubes are...so the signal that comes in is the one that > >> comes out, with as little distortion as possible. Since the tubes are > >> less ideal, they add different components to the original signal... > >> this have turned out to be more pleasant to the human ear. > > > > I would disagree with this statement. The curvature of the transistor > > characteristic is much sharper than many valves and the harmonics > > generated are much nastier-sounding. Valve stages with no feedback are > > quite common and the distortion they generate with moderate signal > > voltages is quite tolerable, but transistor stages with no feedback are > > virtually unusable for audio. > > > > Transistor amplifiers can contain more devices in less space for the > > same price and that allows them to employ much more feedback than valve > > ones, not just overall but within individual stages; this is what gives > > the improvement in overall linearity which you have erroneously > > attributed to the devices themselves. The down side is that when they > > eventually overload, they do so much more sharply and generate higher > > harmonics, which sound vile. > [...] > A tube circuit can never beat a properly designed solid state circuit for > distortion free sound. The big difference is that those valve circuits generally achieve their performance with far fewer active devices and far less feedback, which was the point I was trying to make. Valves are not 'less ideal' as amplifying devices; you can achieve good results with fewer of them than if you tried to achieve the same thing with transistors. If you pile more and more transistors into a circuit with more and more feedback you will get a lower THD figure than with any practical valve amplifier. That is not because of the inherent 'betterness' of the transistors themselves but because they are cheap enough and small enough to allow circuit topologies that wouldn't be worthwhile to produce with valves.. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk |