On Jan 16, 9:34=A0am, 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: > > > =A0> I don 't understand why you don't see it in the sim? > > > =A0> =A0 I see all kinds of problems there. > > > =A0> =A0 THe outputs are current modes and the beta on the outputs are > > most > > =A0> likely are not going to match well. > > > =A0> =A0 =A0On top of that, LTspice shows the upper output (PNP) going =into> > =A0> discontinue state at the cross over. This is going to give you a > > period > > =A0> of what I call a flat liner and 99% sure this is where your cross > > over > > =A0> error is coming from. > > > =A0> =A0 Plot the current on R12. > > > =A0> 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 =3D 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 > > =A0 That op-amp does not pull the reals, the 358 will do that effect on t=he> load side and there by give you more v to bias the transistors. > > =A0 =A0I don't think you have a current demand problem, you may have a ra=il> to rail problem how ever. > > =A0 =A0The 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. > > =A0 =A0 Of course, you really don't want to saturate the amp, so lets ass=ume> you have only 4.5V to work with.. > > =A0 =A0split 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. > > =A0 =A0Now., 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. > > =A0 =A0That configuration you're using in the first place is fighting aga=inst> 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=?> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A08Volts-----------------------------+ > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0==A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 +> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 |<> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+-------------=----+|> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ___ =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0|\> =A0 =A0 =A0 =A0 =A0 =A0+--+|___|-+----------------++ =A0 =A0 =A0 =A0 =A0| > =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 ==A0 | =A0 =A0 =A0 =A0 =A0+> =A0 =A0 =A0 =A0 =A0 =A0+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 ==A0 | =A0 =A0 =A0 =A0 =A0|> =A0 =A0 =A0 || =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 |\+ =A0 =A0 =A0 =A0 | ==A0 =A0 =A0 =A0 =A0| =A0 =A01Ku> =A0 =A0 =A0-||+--++-------------+|-\ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 ==A0| =A0 =A0||> =A0 =A0 =A0 || =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0>+-------+-------=---+---+||+-----+> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+-+-|+/ =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|| =A0 =A0 =A0|> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A04Volts =A0|/+ =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0+> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0|> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 .-.> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 | |> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+ =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0+ =A0 =A0 =A0 =A0 =A0 | |8> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0|/ =A0 =A0 =A0 =A0 =A0 =A0'-'> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+-------------=----+| =A0 =A0 =A0 =A0 =A0 =A0 =A0|> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0GND> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 +> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0=3D=3D=3D> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0GND> > 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.
Audio Amp Crossover Distortion?
Started by ●January 12, 2012
Reply by ●January 16, 20122012-01-16
Reply by ●January 16, 20122012-01-16
On Jan 16, 6:34=A0am, Jamie <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote: > =A0 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. > > =A0 =A0I don't think you have a current demand problem, you may have a rail > to rail problem how ever. > > =A0 =A0The 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. > Why would the op-amp rail to rail limit be a consideration? Imagine the transistors have a large HFE of say 1000. There will be a large voltage gain from the op-amp output to the main output. If the main output is moving rail to rail, the op-amp output will be moving much less, maybe only 1 volt or so. -Bill
Reply by ●January 17, 20122012-01-17
"Bill Bowden" Why would the op-amp rail to rail limit be a consideration? Imagine the transistors have a large HFE of say 1000. There will be a large voltage gain from the op-amp output to the main output. If the main output is moving rail to rail, the op-amp output will be moving much less, maybe only 1 volt or so. ** Stop fucking about and wasting everyone's time. Use a damn ** LM386 *** !!! It will beat the pants off anything using regular op-amps and extra BJTs. With a 9V supply, it delivers almost 0.5 watts at 8 ohms at 0.25% THD. Only 3 or 4 mA idle current too. ... Phil
Reply by ●January 17, 20122012-01-17
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. ...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.
Reply by ●January 17, 20122012-01-17
Jim Thompson wrote:> On Mon, 16 Jan 2012 19:59:06 -0500, Jamie > <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: > > >>Jim Thompson wrote: >> >> >>>On Mon, 16 Jan 2012 19:07:38 -0500, Jamie >>><jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: >>> >>> >>> >>>>Jim Thompson wrote: >>>> >>>> >>>> >>>>>On Mon, 16 Jan 2012 09:34:51 -0500, Jamie >>>>><jamie_ka1lpa_not_valid_after_ka1lpa_@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 >>>>>> >>>>> >>>>> >>>>>What sets the quiescent current thru the PNP-NPN path? >>>>> >>>>> ...Jim Thompson >>>> >>>>The quiescent I of the op-amp and load. >>>> >>>>In Ltspice it was ~ 70 ma with that basic circuit in both >>>>the PNP and NPN. I was using 700..800 ma trannies. >>>> >>>> Putting an R between Vcc and B of the PNP will drop that down >>>>a bit and bring it closer to being symmetrical. Also, you can >>>>use a R on the op output to the collector bridge to lower the >>>>Quies. >>>> >>>>I Didn't save the spice I used but I am sure I can put it together >>>>again and post it if you wish, I just used what was in the stock lib. >>>> >>>> >>>>Jamie >>>> >>> >>> >>>Try it in the real world. Have lots of spare transistors on hand :-) >>> >>> ...Jim Thompson >> >>Actually Jim, I have done that in real world cases. Which is why I >>suggested it.. It does work when you use the correct set of components >>and is a basic of many designs that i've seen over the years. A very >>particle way to having current outputs >> >> Old time 741 with Emitter outputs and related type power amp Ic's >>work very nicely with a config like that. Of course in many cases, you >>need to tailor the bias a little with some bypass R's on the Rail to the >>base of each side if the Qu current is too high. >> >> I had a load of LM380's years ago that I put to some good use making >>little half bridge servos with a circuit of that type. >> >> The only problem with that design is, if the driving op-amp happens >>to circuit for some reason. It will take out the outputs. A current >>limiting R on the op-amp output to the collector node is a good >>practice, something I did not use here in this example. And don't forget >>the bypass bias R's incase the QU Is too high in the chip that is used. >> >> >> I know your an old pro and I am sure you have had your share of >>smoking some silicon. :) >> >>Jamie >> > > > Larkin will bless your work. Me? I do not recommend it... do > yourself a favor and do some Algebra. On a job interview I'd toss > your ass in a blink ;-) > > ...Jim ThompsonJim, I don't need to, I've assembled circuits like that, that are still operating today. You can toss my ass all you want, all it will get you is a bad back.. P.S. I never used a simulator all these years until recently, my math skills have served me well. Jamie
Reply by ●January 17, 20122012-01-17
George Herold 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.That is only a rough lay out, to lower the quiescent current you put by pass R's on the bases of the transistors from the rails. You need to know the quiescent current of the op-amp you're going to use as part of the equation, I used Lpspice on that one and picked a single rail op-amp out of the list. Jamie
Reply by ●January 17, 20122012-01-17
On Tue, 17 Jan 2012 17:57:06 -0500, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:>Jim Thompson wrote: > >> On Mon, 16 Jan 2012 19:59:06 -0500, Jamie >> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: >> >> >>>Jim Thompson wrote: >>> >>> >>>>On Mon, 16 Jan 2012 19:07:38 -0500, Jamie >>>><jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: >>>> >>>> >>>> >>>>>Jim Thompson wrote: >>>>> >>>>> >>>>> >>>>>>On Mon, 16 Jan 2012 09:34:51 -0500, Jamie >>>>>><jamie_ka1lpa_not_valid_after_ka1lpa_@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 >>>>>>> >>>>>> >>>>>> >>>>>>What sets the quiescent current thru the PNP-NPN path? >>>>>> >>>>>> ...Jim Thompson >>>>> >>>>>The quiescent I of the op-amp and load. >>>>> >>>>>In Ltspice it was ~ 70 ma with that basic circuit in both >>>>>the PNP and NPN. I was using 700..800 ma trannies. >>>>> >>>>> Putting an R between Vcc and B of the PNP will drop that down >>>>>a bit and bring it closer to being symmetrical. Also, you can >>>>>use a R on the op output to the collector bridge to lower the >>>>>Quies. >>>>> >>>>>I Didn't save the spice I used but I am sure I can put it together >>>>>again and post it if you wish, I just used what was in the stock lib. >>>>> >>>>> >>>>>Jamie >>>>> >>>> >>>> >>>>Try it in the real world. Have lots of spare transistors on hand :-) >>>> >>>> ...Jim Thompson >>> >>>Actually Jim, I have done that in real world cases. Which is why I >>>suggested it.. It does work when you use the correct set of components >>>and is a basic of many designs that i've seen over the years. A very >>>particle way to having current outputs >>> >>> Old time 741 with Emitter outputs and related type power amp Ic's >>>work very nicely with a config like that. Of course in many cases, you >>>need to tailor the bias a little with some bypass R's on the Rail to the >>>base of each side if the Qu current is too high. >>> >>> I had a load of LM380's years ago that I put to some good use making >>>little half bridge servos with a circuit of that type. >>> >>> The only problem with that design is, if the driving op-amp happens >>>to circuit for some reason. It will take out the outputs. A current >>>limiting R on the op-amp output to the collector node is a good >>>practice, something I did not use here in this example. And don't forget >>>the bypass bias R's incase the QU Is too high in the chip that is used. >>> >>> >>> I know your an old pro and I am sure you have had your share of >>>smoking some silicon. :) >>> >>>Jamie >>> >> >> >> Larkin will bless your work. Me? I do not recommend it... do >> yourself a favor and do some Algebra. On a job interview I'd toss >> your ass in a blink ;-) >> >> ...Jim Thompson > Jim, I don't need to, I've assembled circuits like that, that are still >operating today.OK. Show me your math. What's the quiescent current thru the PNP-NPN path?> > You can toss my ass all you want, all it will get you is a bad back.. > > P.S. > I never used a simulator all these years until recently, my math >skills have served me well. > >Jamie >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 -- | 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.
Reply by ●January 17, 20122012-01-17
On Tue, 17 Jan 2012 18:02:05 -0500, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:>George Herold wrote: >[snip]>> >> 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. >That is only a rough lay out, to lower the quiescent current you put >by pass R's on the bases of the transistors from the rails. You need to >know the quiescent current of the op-amp you're going to use as part of >the equation, I used Lpspice on that one and picked a single rail op-amp >out of the list. > > Jamie >As I pointed out 8 hours ago in... Message-ID: <p15bh7lvalt7s5ug6iqebcaokgbdhu3n5s@4ax.com> ...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.
Reply by ●January 17, 20122012-01-17
On Jan 17, 10:34=A0am, Jim Thompson <To-Email-Use-The-Envelope-I...@On- My-Web-Site.com> wrote:> On Mon, 16 Jan 2012 18:11:03 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Jan 16, 9:34=A0am, 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: > > >> > =A0> I don 't understand why you don't see it in the sim? > > >> > =A0> =A0 I see all kinds of problems there. > > >> > =A0> =A0 THe outputs are current modes and the beta on the outputs a=re> >> > most > >> > =A0> likely are not going to match well. > > >> > =A0> =A0 =A0On top of that, LTspice shows the upper output (PNP) goi=ng into> >> > =A0> discontinue state at the cross over. This is going to give you =a> >> > period > >> > =A0> of what I call a flat liner and 99% sure this is where your cro=ss> >> > over > >> > =A0> error is coming from. > > >> > =A0> =A0 Plot the current on R12. > > >> > =A0> Jamie > > >> > Yes, I did view the current through R12 which looks normal. The thin=g> >> > 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 a=nd> >> > 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 =3D 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 > > >> =A0 That op-amp does not pull the reals, the 358 will do that effect o=n the> >> load side and there by give you more v to bias the transistors. > > >> =A0 =A0I don't think you have a current demand problem, you may have a=rail> >> to rail problem how ever. > > >> =A0 =A0The 1458, as old as it is, still has a lot of usages. The las t=ime I> >> looked, that op-amp (dual) only provides ~ Vcc-1.5 and Vee-1.5. Here y=ou> >> have lost 3 volts to start with. This now gives you 5 volts to play wi=th.> > >> =A0 =A0 Of course, you really don't want to saturate the amp, so lets =assume> >> you have only 4.5V to work with.. > > >> =A0 =A0split 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 volt=s> >> Peak to play with. > > >> =A0 =A0Now., 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 g=et> >> 1.4. Remove that value off the top and you are now getting closer to > >> where the problem is. > > >> =A0 =A0That configuration you're using in the first place is fighting =against> >> you. As one side is conducting the other side is still conducting, jus=t> >> about all the way through. This is going to remove a good chunk of you=r> >> output. > > >> Have you considered a config like the following or something in this l=ine?> > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A08Volts-----------------------------+ > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 + =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |<> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+----------=-------+|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ___ =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0|\> >> =A0 =A0 =A0 =A0 =A0 =A0+--+|___|-+----------------++ =A0 =A0 =A0 =A0 ==A0|> >> =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0==A0 | =A0 =A0 =A0 =A0 =A0+> >> =A0 =A0 =A0 =A0 =A0 =A0+ =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0==A0 | =A0 =A0 =A0 =A0 =A0|> >> =A0 =A0 =A0 || =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 |\+ =A0 =A0 =A0 =A0 |==A0 =A0 =A0 =A0 =A0| =A0 =A01Ku> >> =A0 =A0 =A0-||+--++-------------+|-\ =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0==A0| =A0 =A0||> >> =A0 =A0 =A0 || =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0>+-------+----=------+---+||+-----+> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+-+-|+/ =A0 =A0 =A0 =A0==A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0|| =A0 =A0 =A0|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A04Volts =A0|/+ =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0+> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 .-.> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 | |> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+ =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+ =A0 =A0 =A0 =A0 =A0 | |8> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0|/ =A0 =A0 =A0 =A0 =A0 =A0'-'> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0+----------=-------+| =A0 =A0 =A0 =A0 =A0 =A0 =A0|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 |> =A0 =A0 =A0 =A0 =A0 =A0GND> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=3D=3D=3D> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0GND> > >> Jamie- Hide quoted text - > > >> - Show quoted text - > > >That's weird looking too! =A0There's a JL circuit with tran's in the > >power leads, > >but I think it's push-pull. =A0You can get a lot closer to the supply > >rail that way... > >At least that's my understanding. =A0I'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. =A0You need base-emitter resistors such that the > "crowbar" current is zero. =A0Disconnect 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. =A0It's then a > CLASS-B amplifier. > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 ...Jim Thompson> -- > | James E.Thompson, CTO =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0| =A0 =A0mens =A0 =A0 |> | Analog Innovations, Inc. =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 | =A0 =A0 et =A0 =A0 =A0|> | Analog/Mixed-Signal ASIC's and Discrete Systems =A0| =A0 =A0manus =A0 ==A0|> | Phoenix, Arizona =A085048 =A0 =A0Skype: Contacts Only =A0| =A0 =A0 =A0 ==A0 =A0 =A0 |> | Voice:(480)460-2350 =A0Fax: Available upon request | =A0Brass Rat =A0| > | E-mail Icon athttp://www.analog-innovations.com| =A0 =A01962 =A0 =A0 | > > I love to cook with wine. =A0 =A0 Sometimes I even put it in the food.- H=ide quoted text -> > - Show quoted text -A search of hybrid opamps, brought up this, http://www.electronica.mk/all_articles/Audio_Accessories/40W_Output_Amplifi= er/40W_Amplifier.html Which at least I can understand. The transistors turn on at ~ 1 amp. (Seems like a lot for an opamp...) But that's easy to scale down. (I'd only want an amp total so a 30mA from the opamp should be fine.) I like that the opamp 'handles' the cross over distortion. George H.
Reply by ●January 17, 20122012-01-17
"Jim Thompson"> OK. Show me your math. What's the quiescent current thru the PNP-NPN > path?** That's a trap question. The LM1458 ( a dual 741 really) is not specified for supply rails as low as +/- 4 volts - idle current draw will be low, maybe under 1 mA for both amplifiers. The NPN and PNP transistor types are not specified so may have Hfes of anywhere from 30 to 300 or more - taking the middle ground in both cases, idle current is gonna be around 100mA. But the range is anywhere from 20mA to 500mA. But the big one is how that heck does the schem shown cope with differing Hfes for the two transistors ? The usual topology has the op-amp delivering current into the common or ground via a low value resistor and feedback taken only from the two collectors. This way, the op-amp can have differing rail currents at idle. ... Phil
