seifert@ihuxl.UUCP (D.A. Seifert) (06/28/84)
Since we seem to be discussing tubes vs solid state, how about
tubes vs bipolar vs FETs?
power-FETs are supposed to have some of the 'good' qualities
of tubes. One of these is 'soft-clipping'. My theory is get
a big enough amp or more efficient speakers and don't worry
about clipping.
Another spec that came out about the time power-FETs did is
TIM (and its siblings). FETs tend to be fast and have good
bandwidth/low TIM.
Are there any other theories of why FETs sound better than
bipolars? Anyone think bipolars sound better than FETs?
For FET amps, I'm thinking of the Sony 5650 and the Hafler.
(power amp, not pre-amp! Everyone I know who had the Hafler
preamp has replaced it. Something about the bass not being flat.)
--
_____
/_____\ Hey, Woodstock, have you seen my sunscreen?
/_______\
|___| Snoopy
____|___|_____ ihnp4!ihuxl!seifert
fudd@fluke.UUCP (Mark Freeman) (06/29/84)
--- This is a reply to some comments by D.A. Seifert: power-FETs are supposed to have some of the 'good' qualities of tubes. One of these is 'soft-clipping'. Another spec that came out about the time power-FETs did is TIM (and its siblings). FETs tend to be fast and have good bandwidth/low TIM. Are there any other theories of why FETs sound better than bipolars? Anyone think bipolars sound better than FETs? The advantages of FET's over bipolars that I am aware of are: 1) They are positive temperature coefficient devices. This is mainly an aid to designers. 2) They are faster devices. This may help increase slew rate. 3) They are closer to linear devices. This is probably a more important factor in reducing TIM. When slew-rate limiting was "discovered" by the audio industry, high loop gain was identified as the culprit. FET's are square-law devices (and V-FET's are are almost linear devices), and so allow less feedback for the same level of distortion. Some designers have gone to the extreme of "no feedback" (well, each stage has its own feedback), to prevent the evil TIM from appearing. When monolithic op-amps with FET inputs appeared, they were noted for their fast slew rate. But not for the reasons you might expect. They were fast because the FET's had lower gain than the bipolars they replaced. This allowed the miller capacitor in the voltage gain stage to be reduced, and delayed the onset of saturation of the first stage (the cause of slew rate limiting). An excellent article about this subject, from someone at National, I believe, appeared around 1975. I can dig it up, if you really want to get into this subject.
dmmartindale@watcgl.UUCP (Dave Martindale) (06/29/84)
Another theory I've heard claiming that FETs were better than bipolar transistors is that FETs do not have the tendency to "thermal runaway" that bipolar transistors do, and thus no circuitry to compensate for it is necessary, and thus there is one less thing to introduce nonlinearities. I hadn't heard bad comments about the Hafler preamp before - which one is it (Hafler 100 or 110) that "everyone has replaced"?
pmr@drutx.UUCP (Rastocny) (06/30/84)
My reference to teh CJ/Hafler comparison was the "equivalent priced Hafler," that being the DH-110. The Hafler sounds OK out of the box, much better than a lot of products in the same price range, but not as good as others. While we're on the subject, can anyone hear differences between bipolar preamps (let's just confine our discussion to this simple voltage amplifier first) and FETs? Theory says we shouldn't. What does reality say? Has anyone recently "upgraded" their preamp and noticed these differences I reference? Yours for higher fidelity, Phil Rastocny AT&T-ISL ..!drutx!pmr
seifert@ihuxl.UUCP (D.A. Seifert) (07/04/84)
> I hadn't heard bad comments about the Hafler preamp before - which one > is it (Hafler 100 or 110) that "everyone has replaced"? Asked Joe about it yesterday, and he said they were the 101s. (ok, is it 100 or 101? -sigh- ) He said the 110 was supposed to be much better. The problem was that the frequency response in the bass region was not flat. (and perhaps they both had money burning a hole in their pockets? :-) ) Once again, this only applies to the 100/101, not to Hafler products in general. I am quite pleased with my DH 200 power amp. Joe bought two of them and strapped them for mono. (We WILL keep our speaker wires short!) Florescent light hum is cruel and inhuman punishment! -- _____ /_____\ Hey, Woodstock, have you seen the demagnetizer? /_______\ |___| Snoopy ____|___|_____ ihnp4!ihuxl!seifert
rs@hou3c.UUCP (rs) (07/09/84)
Just a peripheral question... What is the "slew rate" of an amplifier. I have seen this spec for amplifiers but have not found a source that defines it. Any pointers to information on sound system engineering would also be appreciated. Thanks, Bob Switzer AT&T Bell Labs ...!houxf!hou3c!rs
fish@ihu1g.UUCP (Bob Fishell) (07/09/84)
(oo) The "slew rate" of an amplifier is a measure of its ability to respond to an instantaneous change in the voltage at it input from one DC value to another, for example, from -3 volts to +3 volts via a hard switch. This will cause the amplifier's output to "slew" from one voltage to another at some rate, given in volts per microsecond, which is dependent on the speed of the internal circuitry. I believe that bipolar transistor amplifiers have the highest slew rate in the pack. -- Bob Fishell ihnp4!ihu1g!fish
ron@brl-tgr.ARPA (Ron Natalie <ron>) (07/11/84)
Slew rate is how fast it can change from one audio signal to another. Very important for square waves which require infinite slew rate. -Ron
ron@brl-tgr.UUCP (07/11/84)
Relay-Version: version B 2.10 5/3/83 based; site houxm.UUCP Posting-Version: version B 2.10.1 6/24/83; site brl-tgr.ARPA Message-ID: <3186@brl-tgr.ARPA> Date: Wed, 11-Jul-84 15:40:19 EDT Date-Received: Fri, 13-Jul-84 10:02:36 EDT hou3c.UUCP> Organization: Ballistics Research Lab Lines: 4 Slew rate is how fast it can change from one audio signal to another. Very important for square waves which require infinite slew rate. -Ron