Tube vs. Solid State Preamp
in [Design]
|
Prev: How do you call
Next: Internet via Cellular
From: Adrian Tuddenham on 1 Apr 2010 15:42 Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: > On Thu, 1 Apr 2010 17:43:19 +0100, adrian(a)poppyrecords.invalid.invalid > (Adrian Tuddenham) wrote: > > >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > > >> On Thu, 1 Apr 2010 09:33:06 +0100, adrian(a)poppyrecords.invalid.invalid > >> (Adrian Tuddenham) wrote: > >> > >> >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.. > >> > >> A good jfet can have noise below 1 nv/rthz and Gm of 40,000 (in tube > >> terms). And very low gate current compared to a tube's grid current. > > > >FETs are the nearest things to superior valves. Interestingly they have > >gently curved characteristics like valves too - and they can be used > >without feedback (if you don't mind the spread of characteristics). > > All that attitude reflects is no knowledge of how to properly design > around BJT's. Admittedly, I've been doing it for 55 years, so _maybe_ > I've acquired some skill at it :-) My disagreement wasn't with the design around the devices, it was with a statement made about the devices themselves, which I believed was inaccurate. I don't advocate designing valve or FET circuits without feedback, but it is often possible to get away without feedback in low end audio applications - however, BJTs could never be used that way*. It is not 'good' design practice seen from the quality viewpoint, but it might be appropriate design practice if space, component count or cost considerations over-rode the desire for quality. * I've just remembered a circuit in which I did use transistors to handle audio without feedback - it amplified the sound of a telephone bell, as picked up by a crystal microphone, and fed it to a loudspeaker to warn a partially-deaf person another room. Everything was biassed off to save battery power and the output from the microphone, which was slightly greater than 0.6 volts, turned it on during the tips of the waveform. The sound was a horrible teeth-grinding squawk, but it served its purpose (except when a visitor with normal hearing dropped a cup of tea in shock). -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
From: Tim Williams on 1 Apr 2010 17:12 "Joerg" <invalid(a)invalid.invalid> wrote in message news:81kab2Fe80U1(a)mid.individual.net... > My experience with tantalums is that they are excellent in terms of > electrical behavior. Until one fine day ... *PHOOMP* My understanding is they only go Chernobyl when overheated. So maybe with a combination of particularly harsh operating conditions in the middle of Indian summer, a few might pop. As long as you keep RMS amps and operating temperature within limits, they'll work. I haven't had one explode on me yet, but I haven't used many, either. I've seen a few pieces of equipment that cooked them, but far more that haven't failed, and haven't had one go off in front of me. I must admit the horror stories have me scared... Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: VWWall on 1 Apr 2010 17:34 Joerg wrote: > Jim Thompson wrote: >> >> 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. > Acorn tubes and Nuvistors were very different things. Acron tubes were used in a direction finder loop pre-amp that I used in the U. S. Army Signal Corps in 1943-1945 in North Africa and Italy. They were 954 and 955, glass envelope tubes with element connections out the side and top. They *were* in the shape of acorns. > >> 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 ;-) >> A Nuvister was a small ceramic vacuum tube. The last one I saw was used in my garage door opener receiver. When it failed, I couldn't find a replacement and had to replace the whole receiver with a transistorized one. > > That I don't remember. I'm not _that_ old :-)) > I was at Bell Labs when transistors were young, and have taught transistor electronics at UCLA Extension, but most of my career has included vacuum tubes from magnetrons to traveling wave tubes. I'm older than either of you! :-( -- Virg Wall, P.E., K6EVE
From: John Larkin on 1 Apr 2010 17:48 On Thu, 01 Apr 2010 14:34:37 -0700, VWWall <vwall(a)large.invalid> wrote: >Joerg wrote: >> Jim Thompson wrote: >>> >>> 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. >> >Acorn tubes and Nuvistors were very different things. Acron tubes were >used in a direction finder loop pre-amp that I used in the U. S. Army >Signal Corps in 1943-1945 in North Africa and Italy. They were 954 and >955, glass envelope tubes with element connections out the side and top. > They *were* in the shape of acorns. Here's one: ftp://jjlarkin.lmi.net/Acorn.JPG I have some nuvistors around here somewhere too. They're not as pretty... metal cans that look a lot like an overgrown TO-5 transistor. John
From: Phil Hobbs on 1 Apr 2010 18:31
On 4/1/2010 5:48 PM, John Larkin wrote: > On Thu, 01 Apr 2010 14:34:37 -0700, VWWall<vwall(a)large.invalid> > wrote: > >> Joerg wrote: >>> Jim Thompson wrote: >>>> >>>> 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. >>> >> Acorn tubes and Nuvistors were very different things. Acron tubes were >> used in a direction finder loop pre-amp that I used in the U. S. Army >> Signal Corps in 1943-1945 in North Africa and Italy. They were 954 and >> 955, glass envelope tubes with element connections out the side and top. >> They *were* in the shape of acorns. > > Here's one: > > ftp://jjlarkin.lmi.net/Acorn.JPG > > I have some nuvistors around here somewhere too. They're not as > pretty... metal cans that look a lot like an overgrown TO-5 > transistor. > > John > > Nuvistors are cool. I remember as a little kid reading the 1966 ARRL handbook that my brother gave me--iirc it had a 432 MHz transverter based on 6CW4 Nuvistors. I've salvaged some from old HP counters too. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net |