Tube vs. Solid State Preamp
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From: Jim Thompson on 1 Apr 2010 13:28 On Thu, 01 Apr 2010 10:26:00 -0700, Joerg <invalid(a)invalid.invalid> wrote: >Tim Williams wrote: >> "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. >> > >The TL598 has dead-time control but it's usually just too weak to drive >really fat MOSFETs. Got to follow it with some real gate drivers, or use >a better chip from LTC. > >But a tantalum? I can already picture it, a sharp popping sound, some >hissing, an orange puff of smoke wafting through the room ... > > >>>> 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. >> > >I have one transformer here where the winding is square copper, wrapped >in lacquer-drenched cloth, then hammered in place around the bobbin. >Lots of amps. I once did a 5V/200A transformer... I used insulated copper foil that was the width of the bobbin, 90� fold at the ends for output :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Joerg on 1 Apr 2010 13:30 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. ... Well, that can most certainly be arranged: http://ixbtlabs.com/articles2/aopentube/ 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 ?:-) > Yup, used them. In fact, one of my RF tools here (a dipmeter) has one in there except they called them acorn tube in them's days. > 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 ;-) > That I don't remember. I'm not _that_ old :-)) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 1 Apr 2010 13:34 John Larkin 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). > > That's impressive. I wonder what the grid current is like. Roughly 100 > nA maybe. Since grid current consists of two mechanisms, which can > sometimes cancel at some negative grid voltage, I'd expect it to have > above, maybe way above, shot noise. But I haven't worried much about > toobs, at least amplifier toobs, in a long time. > Just wanted to show that it is indeed possible. The nuvistor preamps from the olden days where really not inferior in noise figure, even when compared to super low noise FETs. I think at first it was RCA FETs (40673?) and then I believe the first NEC devices came out. The good thing was that the nuvistor preamp wasn't dead if serious weather static hit the input or if you accidentally transmitted into it. FET amps instantly became doorknobs ... tssst ... phut. > I'll probably stick with BF862s for the few low-noise things I'm doing > now. One of those will operate in a vacuum far better than any toob > can maintain! > Tubes are sort of big for that. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jim Thompson on 1 Apr 2010 13:54 On Thu, 01 Apr 2010 10:30:26 -0700, Joerg <invalid(a)invalid.invalid> 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. ... > > >Well, that can most certainly be arranged: > >http://ixbtlabs.com/articles2/aopentube/ That's just plain dumb audiphoollery. > > > I've actually made a very HV transistor by >> using a tube with a grounded grid and an NPN in the cathode path. I needed a 1000V device with characteristic curves much like an ideal CMOS transistor... no ability to get feedback in there. Piece-a-cake with an NPN in the cathode circuit of a pentode (with local feedback). >> >> Size? Ever see a Nuvistor ?:-) >> > >Yup, used them. In fact, one of my RF tools here (a dipmeter) has one in >there except they called them acorn tube in them's days. > > >> 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 ;-) >> > >That I don't remember. I'm not _that_ old :-)) Yeah, You are! You just don't admit it :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Tim Williams on 1 Apr 2010 13:55
"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:4rl9r51487egv6h1svvra86tal2ep4lj0k(a)4ax.com... >>I have one transformer here where the winding is square copper, wrapped >>in lacquer-drenched cloth, then hammered in place around the bobbin. >>Lots of amps. > > I once did a 5V/200A transformer... I used insulated copper foil that > was the width of the bobbin, 90� fold at the ends for output :-) Way ahead of 'ya: http://myweb.msoe.edu/williamstm/Images/Highamp_Chokes.jpg Wound these yesterday. That's 1 x 0.04" copper. Probably overkill for 100A, but I'm going for efficiency. Think I'm going to dip them in epoxy. The windings aren't touching, but there isn't anything to keep them apart. Note that insulated copper strap is useless, because it scratches right through when winding. The core edges are already a bit nicked, and it's got two layers (yellow on white). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |