Tube vs. Solid State Preamp
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From: Joerg on 30 Mar 2010 20:18 Tim Williams wrote: > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:81fcueF1c9U1(a)mid.individual.net... >> Nah, the good old PCC88 can compete when using both triodes in there in >> parallel, around 1.5nv/rtHz at audio. With pentodes configured as triode >> you could supposedly get even lower but I've never tried that. > ... >> Of course, you won't get an energy start rating for an amplifier with one >> of those. > > Why not? They're 100% efficient space heaters. That's as efficient as it > gets, riiiight? > Right, but that's not such a great thing in August around here. > http://www.thevalvepage.com/testeq/tek/545a/545a.htm > Some of those things could constantly blast half a kilowatt of heat into the lab. When I got a 7704 I was thoroughly surprised that it contained a very efficient primary-side switcher. Maybe it was designed during the energy crisis. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Tim Williams on 30 Mar 2010 22:46 "Joerg" <invalid(a)invalid.invalid> wrote in message news:81fimuFsusU1(a)mid.individual.net... >> http://www.thevalvepage.com/testeq/tek/545a/545a.htm > > Some of those things could constantly blast half a kilowatt of heat into > the lab. When I got a 7704 I was thoroughly surprised that it contained a > very efficient primary-side switcher. Maybe it was designed during the > energy crisis. They weren't afraid to use switchers -- HV supply in those is usually a 6AU5 or such blocking oscillator (g2 controlled, of course), with a multiplier hanging off one end for the 2nd anode (~7kV). It's just that the high voltages and massive waste of heater power kind of drowns out everything else in terms of wattage. :) It's pretty funny to think, really, high performance tubes work at the same currents, and nearly the same impedances, as transistors. They just have to be biased with >10 times the voltage, plus heat. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Paul Keinanen on 31 Mar 2010 02:16 On Tue, 30 Mar 2010 23:47:40 +0100, adrian(a)poppyrecords.invalid.invalid (Adrian Tuddenham) wrote: >The circuit design is critically important, especially the method of >matching the input impedance to the source impedance. If you throw away >signal at that point, no first stage valve or transistor, however >exotic, will achieve the best S/N ratio. In some direct conversion receivers with the SBL-1 diode ring mixer, quite interesting audio preamplifiers are used. For best performance, the mixer "IF" (in this case audio) port had to be terminated into a 50 ohm load. Often a common base amplifier stage was used, sometimes consisting of multiple small signal transistors in parallel or using a big power transistor for best noise performance. Perhaps such amplifiers could be used with low impedance microphones as well. The microphone characteristics, such as frequency response is usually specified for some standard load impedance, loading the microphone for power match may alter these characteristics, so some corrections may be needed in the following stages.
From: Robert Baer on 31 Mar 2010 17:36 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).
From: Robert Baer on 31 Mar 2010 17:45
Jim Thompson wrote: > On Tue, 30 Mar 2010 10:41:07 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: >>> On Tue, 30 Mar 2010 09:49:03 -0700, Joerg <invalid(a)invalid.invalid> >>> 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? >>>>>> >>>> Sure, but it will be shunned by tube-freaks :-) >>>> >>>> >>>>>> I am thinking about building a preamp. >>>>>> >>>>>> Thanks, >>>>>> Chris >>>>> Tubes are noisy. >>>>> >>>> Not at all. I remember when I was young and those super low noise RF >>>> FETs came out. Everyone (who had the dough to buy those) jumped on them, >>>> only to find out that the old nuvistor preamp was in about the same >>>> ballpark noisewise but had a dynamic range from here to the Klondike >>>> while them thar newfangled trainsistahs didn't. >>> If you know how to bias BJT's for low noise, you can make phenomenally >>> low audio noise preamp's. >>> >>> Sheeesh! Back when I was a kid I could make a reasonably low noise >>> preamp with Ge devices... low current and low VCE. >>> >> When I was a kid that wasn't needed. The "lowest noise" audio source >> were 45rpm records and even that didn't matter. Because in our time it >> was all rock music. The louder the better. So the race was on who could >> build the biggest honking amplifier. My limit was reached when the >> breaker on a typical European 230V/16A circuit would trip off upon a >> heavy-handed twang on the electric guitar :-) > > You're still a kid :-) > > My record for a solid-state amplifier is 400W (RMS, sustained, fan on > a heat-sink "tunnel" :-) > > ...Jim Thompson A lot better than my record for a tube amp at 100W RMS sustained, with total hum and noise under -60dBmW. Do not remember how far down it was, but cranked up all the way it made no difference open input or shorted input, one could not hear noise and/or hum with ear right at speaker. |