On Tue, 17 Jan 2012 21:52:48 -0500, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:>Jim Thompson wrote: >[snip]>> >> Those Youtube videos Bitrex found of IIT lectures are based on chips I >> designed 50 years ago... all math... no simulator existed until about >> 25 years into my career. Also have some of my chips used as class >> examples at Rochester Institute of Technology. >> >> Calculate that quiescent current and get back to me with the result. >> (Show all your work :-) >> >> ...Jim Thompson >I suppose I could, but I don't know where that would lead me to?Might lead to understanding rather than groping.> > In any case, the LT part# I used in the sim was a low quiescent type >to start with. I am sure as simple as that circuit is, the sim can't be >that far off. I suppose if you select an opamp that has more than one >diode drop from the rails it could cause the outputs to have a high >Qu level. But why would you want to use a op-amp that bad? Infact I >can't think of one that has more than 1 diode drop on the rails at the >moment. > > And Like I said, proven circuits that are still operating today tells >me alot..Naaaah! It tell me the great disaster is about to befall you.> > Back in the old days my HP calculator, slide rule and lots of paper >was my friend. With Polaroid's of scope shots stuffed in scrap books. > > Btw > > It just came to me, this type of circuit is used to drive a optics >focus coil current mode amplifier on a 2 Mev irradiation unit. The lower > NPN is used to suppress the reactive energy when throttling back >instead of using a snubber or diode, this keeps it symmetrical when we >turn off the mag field to avoid unexpected beam steering. That uses a >large power >IC audio amplifier with the base of the transistors in the rails of the > IC with some by pass R to set the Qu I. > >JamieStay awake tonight... your end is near ;-) ...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 | I love to cook with wine. Sometimes I even put it in the food.
Audio Amp Crossover Distortion?
Started by ●January 12, 2012
Reply by ●January 17, 20122012-01-17
Reply by ●January 17, 20122012-01-17
On Tue, 17 Jan 2012 22:23:55 -0500, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:>krw@att.bizzzzzzzzzzzz wrote: > >> On Tue, 17 Jan 2012 22:00:36 -0500, Jamie >> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: >> >> >>>krw@att.bizzzzzzzzzzzz wrote: >>> >>> >>>>On Wed, 18 Jan 2012 01:18:41 +0000 (UTC), Kaz Kylheku <kaz@kylheku.com> wrote: >>>> >>>> >>>> >>>>>On 2012-01-18, krw@att.bizzzzzzzzzzzz <krw@att.bizzzzzzzzzzzz> wrote: >>>>> >>>>> >>>>>>On Tue, 17 Jan 2012 16:23:22 -0700, Jim Thompson >>>>>> >>>>>> >>>>>>>Those Youtube videos Bitrex found of IIT lectures are based on chips I >>>>>>>designed 50 years ago... all math... no simulator existed until about >>>>>>>25 years into my career. Also have some of my chips used as class >>>>>>>examples at Rochester Institute of Technology. >>>>>> >>>>>>25 years? Circuit simulators existed more than 40 years ago. >>>>> >>>>>You're assuming Jim's career launched 50 years ago, when upon walking into a >>>>>firm off the street without a clue, he got a job designing integrated circuits. >>>>>Then, 25 years later, simulators appeared. >>>> >>>> >>>>Well, he's just about to turn 19 (76 in human years). >>>> >>>> >>>> >>>>>Indeed, it is quite obvious that a little math around here wouldn't be such a >>>>>bad thing. >>>> >>>> >>>>You might try it. Unless he started his career before age 11 (76-40-25), I >>>>doubt his statement. Note that this assumes I used the very first circuit >>>>simulators, which I highly doubt. >>> >>>The only thing I ever did was tried out Verilog and I absolutely hated it.. >> >> >> Huh? In English, please. >> >> >>> It may have been greatly improved since then but it just didn't turn >>>me on. >> >> >> I don't like C, so have never bothered with Verilog. VHDL (and likewise, >> PL/I) are much more my style. >> >> >>> Being that I also do C, Pascal, Asm etc, you would think that would >>>just fit in but it didn't. >> >> >> I still don't understand the relevance. > > Ok, if you say so.Yeah, you got me. What does Verilog have to do with circuit simulators? ...or C, or Pascal, or Asm, or...
Reply by ●January 19, 20122012-01-19
Jim Thompson wrote:> > On Mon, 16 Jan 2012 18:11:03 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > > >On Jan 16, 9:34 am, Jamie > ><jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote: > >> Bill Bowden wrote: > >> > On Jan 15, 11:40 am, Jamie > >> > >> > <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote: > >> > >> > > I don 't understand why you don't see it in the sim? > >> > >> > > I see all kinds of problems there. > >> > >> > > THe outputs are current modes and the beta on the outputs are > >> > most > >> > > likely are not going to match well. > >> > >> > > On top of that, LTspice shows the upper output (PNP) going into > >> > > discontinue state at the cross over. This is going to give you a > >> > period > >> > > of what I call a flat liner and 99% sure this is where your cross > >> > over > >> > > error is coming from. > >> > >> > > Plot the current on R12. > >> > >> > > Jamie > >> > >> > Yes, I did view the current through R12 which looks normal. The thing > >> > operates class AB, so only one transistor is on at a time, so a 50% > >> > discontinuous current is normal. I did improve the distortion using a > >> > 1458 op-amp in place of the 358. Looks much better now. The problem > >> > now is I only get 1.5 volts peak into 8 ohms with an 8 volt supply and > >> > I was trying for 3 volts or more. The HFE figure for the 2N2219A is > >> > minimum 40 at 500mA or 7.5mA at 300mA. The 120 ohm resistor draws . > >> > 7/120 = about 6 mA so the op-amp must deliver 13.5 mA and the spec > >> > sheet says only 10 mA short circuit. So, apparently, it needs higher > >> > gain transistors or an op-amp with lower output impedance, or both. > >> > Any ideas? > >> > >> > -Bill > >> > >> That op-amp does not pull the reals, the 358 will do that effect on the > >> load side and there by give you more v to bias the transistors. > >> > >> I don't think you have a current demand problem, you may have a rail > >> to rail problem how ever. > >> > >> The 1458, as old as it is, still has a lot of usages. The las time I > >> looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here you > >> have lost 3 volts to start with. This now gives you 5 volts to play with. > >> > >> Of course, you really don't want to saturate the amp, so lets assume > >> you have only 4.5V to work with.. > >> > >> split that in half, since you looks apparrent you are operating in > >> Class A state on the output side of the op-amp and you get ~ 2.25 volts > >> Peak to play with. > >> > >> Now., let us not forget, the minimum required for each of those > >> transistors to start working. ~ 0.7 and then times this by 2 and you get > >> 1.4. Remove that value off the top and you are now getting closer to > >> where the problem is. > >> > >> That configuration you're using in the first place is fighting against > >> you. As one side is conducting the other side is still conducting, just > >> about all the way through. This is going to remove a good chunk of your > >> output. > >> > >> Have you considered a config like the following or something in this line? > >> > >> 8Volts-----------------------------+ > >> + | > >> | > >> | > >> + > >> |< > >> +-----------------+| > >> ___ | |\ > >> +--+|___|-+----------------++ | > >> | | | + > >> + | | | > >> || | |\+ | | 1Ku > >> -||+--++-------------+|-\ | | || > >> || | >+-------+----------+---+||+-----+ > >> +-+-|+/ | || | > >> 4Volts |/+ | + > >> | | | > >> | | .-. > >> | | | | > >> + + | |8 > >> | |/ '-' > >> +-----------------+| | > >> |> GND > >> + > >> | > >> | > >> === > >> GND > >> > >> Jamie- Hide quoted text - > >> > >> - Show quoted text - > > > >That's weird looking too! There's a JL circuit with tran's in the > >power leads, > >but I think it's push-pull. You can get a lot closer to the supply > >rail that way... > >At least that's my understanding. I've yet to try a circuit with > >power gain in the supply leads. > > > >George H. > > I did that sort of thing as an LDO, ~1970... it's in a hybrid I made > for the TOW missile. You need base-emitter resistors such that the > "crowbar" current is zero. Disconnect OpAmp output from as shown, > then connect it via a resistive divider between rails (it'd be a > single resistor to ground if split supplies were used. It's then a > CLASS-B amplifier. >Connecting the op amp output to the circuit's output via a suitably-chosen small resistance gives you a nice combination of feedforward at small signals and output-stage feedback at large signals. Frequency compensation can be a bit squirrelly. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
