On Fri, 13 Jan 2012 19:53:58 -0500, Bitrex <bitrex@de.lete.earthlink.net> wrote:>On 1/13/2012 7:13 PM, Jim Thompson wrote: >> On Fri, 13 Jan 2012 23:54:46 +0000 (UTC), Kaz Kylheku >> <kaz@kylheku.com> wrote: >> >>> On 2012-01-13, Phil Allison <phil_a@tpg.com.au> wrote: >>>> ** FFS - class A push-pull output stages are very common and technically >>>> elegant. >>> >>> Indeed, that looks like what the circuit is shooting for. >>> >>> I found a this schematic which has a similar configuration of transistors >>> as the OP's circuit, also single supply, but seems better: >>> >>> http://www.circuitstoday.com/wp-content/uploads/2011/03/class-A-headphone-amplifier-circuit.png >>> >>> Here, a pair of diodes and resistor R5 are used to set up the collector current >>> through the transistors, instead of a resistive voltage divider bias. Since >>> diodes are used, there is independence from fluctuations in the rails. R5 at >>> 39 ohms is much larger than the 0.2 ohm emitter resistors in the circuit >>> discussed in this thread, so the quiescent current is kept to about 18 mA. >>> (Approximation: 1.4V diode stack minus 0.7 forward voltage, divided by 39 >>> ohms). >>> >>> The OP's circuit could be improved by adopting some of these ideas, and also >>> with the addition of some bypass caps on those voltage dividers around the op >>> amp. >> >> While you are amusing yourself, what is it that determines the output >> Q-point... quiescent voltage at the + node of C3 ?:-) >> >> ...Jim Thompson > >Looks like R3 should go to the output node. It doesn't make any sense >being where it is now. Then DC feedback would make the output sit at >about 5 volts, which would be about right for a symmetric swing given >the compliance of the upper current source. I also don't know why R3 is >connected where it is, it would make more sense connected to the top of >R1. I think you'd then have a pretty conventional, but workable amplifier.Too many parts ;-) What kind of gain is needed? Likewise, what impedance are the headphones? ...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 13, 20122012-01-13
Reply by ●January 13, 20122012-01-13
On Jan 13, 7:05=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My- Web-Site.com> wrote:> On Fri, 13 Jan 2012 15:36:20 -0800 (PST), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Jan 12, 9:47=A0pm, George Herold <gher...@teachspin.com> wrote: > >> On Jan 12, 9:30=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-=My-> > >> Web-Site.com> wrote: > >> > On Thu, 12 Jan 2012 18:12:59 -0800 (PST), George Herold > > >> > <gher...@teachspin.com> wrote: > >> > >On Jan 12, 7:27=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...@=On-My-> >> > >Web-Site.com> wrote: > >> > >> On Thu, 12 Jan 2012 08:45:44 -0800 (PST), George Herold > > >> > >> <gher...@teachspin.com> wrote: > >> > >> >On Jan 11, 11:55=A0pm, "Phil Allison" <phi...@tpg.com.au> wrote: > >> > >> >> "Bill Bowden" > > >> > >> >> I see excessive crossover distortion with this audio amp not s=hown> >> > >> >> with LTspice. It simulates ok, but the wired circuit produces =about a> >> > >> >> 50uS dead time step as the signal crosses the mid point. I tri=ed> >> > >> >> increasing the bias with no help. Both inputs to the op-amp lo=ok good> >> > >> >> with no distortion. Any idea what is going on? > > >> > >> >> ** You need to post a schematic =A0- =A0dickhead. > > >> > >> >> Totally =A0SMARTARSE of you to post only a Spice list on SEB. > > >> > >> >> ... =A0Phil > > >> > >> >I was going to say it's a push-pull.... but it's flipped about. > > >> > >> >Here's a pic > >> > >> >http://imageshack.us/photo/my-images/708/crossover.jpg/ > > >> > >> >Does this output have a name? > > >> > >> >George H. > > >> > >> Unstable ?:-) > > >> > > What's the 10k to the noninverting input about? =A0There's an inve=rsion> >> > >somehwere else in the circuit? > > >> > >Bill, Since it's a single sided power supply a class A would be > >> > >easy... And less parts. > > >> > >George H. > > >> > I like "sliding" class-A... 1/2 the normal standby power. > > >> Hmm, never heard of sliding class-A, a JT invention? > > >> So I'll guess some outer control loop that senses the voltage and > >> adjusts the bias. =A0A second pass element? > > >> But it's gotta be fast. =A0Is it load specific? > > >> George H. > > >OK that was a silly idea. =A0(Two pass elements is not going to save any > >power.) > > >(It isn't any fun to google before posting... :^) > >So a sliding class A is also called class H? =A0A variable (switch mode) > >power supply rail run a volt or two above the linear pass element. > > >That's a pretty cool! > > >So how fast can you oscillate a SMPS and how fast can you swing it's > >output voltage? > > >George H. > > [snip] > > Google or Wiki are not always reliable sources of information. > > Check out... > > http://www.analog-innovations.com/SED/HearingAidSlidingClassA.pdfWoah... Some reading material! great.> > as one way I've done it. > > Normal class-A has one active signal device loaded with resistance or > a fixed current mirror of value I. =A0Say your supplies are +V and -V, > load to ground. =A0So the peak power that can be driven into the load is > I*V. =A0Quiescent power 2*I*V.Yeah I've done plenty of class A.... brute force. Add more voltage and resistance and I can drive that coil faster.> > Now imagine a current mirror load whose value decreases when the > active signal device increases its current (and vice versa). =A0Say the > quiescent condition is the same as above. =A0But now you can drive peak > power of 2*I*V, twice what the normal class-A can do.Dang, I've only done one current mirror... doing circuits out of AoE. just a few transitors, stuck into white proto board. That's OK I'll never run out of circuits to try, or novels to read. Now I've got some nice hearing aid app note to read... Grin George H.> > =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 -
Reply by ●January 14, 20122012-01-14
"Kaz Kylheku" Phil Allison> >> ** FFS - class A push-pull output stages are very common and >> technically >> elegant. > > Indeed, that looks like what the circuit is shooting for. > > I found a this schematic which has a similar configuration of transistors > as the OP's circuit,** Like hell - that has a CCS as half the output stage. The OP's schem is like a donkey with a dog's head. ... Phil
Reply by ●January 15, 20122012-01-15
On Jan 13, 4:03=A0pm, George Herold <gher...@teachspin.com> wrote: > On Jan 13, 12:16=A0pm, Phil Hobbs > > > You could call it "Output stage that oscillates fiercely with no load, > > and melts transistors rapidly" ;) > > > Cheers > > > Phil Hobbs > > > Grin... maybe a good heater then. > > Bill, I hope you'll take this as good natured kidding. =A0We all make > mistakes. > I only made one mistake. That was the time I thought I made a mistake. -Bill
Reply by ●January 15, 20122012-01-15
George Herold wrote:> On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote: > >>"Bill Bowden" >> >>I see excessive crossover distortion with this audio amp not shown >>with LTspice. It simulates ok, but the wired circuit produces about a >>50uS dead time step as the signal crosses the mid point. I tried >>increasing the bias with no help. Both inputs to the op-amp look good >>with no distortion. Any idea what is going on? >> >>** You need to post a schematic - dickhead. >> >>Totally SMARTARSE of you to post only a Spice list on SEB. >> >>... Phil > > > I was going to say it's a push-pull.... but it's flipped about. > > Here's a pic > http://imageshack.us/photo/my-images/708/crossover.jpg/ > > Does this output have a name? > > George H.I would love nothing more than to view that jpg however, It seems that site is so loaded with Flash content and scam ads that It just wants to cover all of my screen with pop up forms all over the place. You see, I need to click on the actual image to see it properly because it is not sized correctly for view and they know this. You click on it, which normally brings up the image in fall details but, it also starts a whole crap load of other scams, ads and forms to pop up all over. These free sites in my opinion, are worthless if you really want some one to see the content. They are just lures to get more people to see their useless ads, take advantage of poeple and in many cases makes your PC useless when you're trying to shut down the forms as they keep starting as they attempt to install shopping tool bars and all the other crap. Just my opinion. These Free sites are nothing but bone yard traps. You know, most providers of services (ISP)'s provide their customers with a personal webpage or webspace of more than enough with a clean slab to start with. Jamie
Reply by ●January 15, 20122012-01-15
On Wed, 11 Jan 2012 20:14:05 -0800 (PST), Bill Bowden <bperryb@bowdenshobbycircuits.info> wrote:>I see excessive crossover distortion with this audio amp not shown >with LTspice. It simulates ok, but the wired circuit produces about a >50uS dead time step as the signal crosses the mid point. I tried >increasing the bias with no help. Both inputs to the op-amp look good >with no distortion. Any idea what is going on? > >Version 4 >SHEET 1 880 1108 >WIRE -128 80 -128 48 >WIRE -128 80 -352 80 >WIRE 80 80 -128 80 >WIRE 208 80 80 80 >WIRE -352 96 -352 80 >WIRE 80 128 80 80 >WIRE 208 176 208 160 >WIRE -416 208 -432 208 >WIRE -352 208 -352 176 >WIRE -144 208 -352 208 >WIRE -512 224 -512 208 >WIRE 80 224 80 208 >WIRE 144 224 80 224 >WIRE 80 240 80 224 >WIRE -352 256 -352 208 >WIRE -144 304 -144 208 >WIRE -112 304 -144 304 >WIRE 80 320 -48 320 >WIRE 208 320 208 272 >WIRE 320 320 208 320 >WIRE 336 320 320 320 >WIRE 432 320 400 320 >WIRE -112 336 -144 336 >WIRE 80 336 80 320 >WIRE -208 352 -208 336 >WIRE 208 368 208 320 >WIRE -80 384 -80 352 >WIRE 144 416 80 416 >WIRE -480 432 -480 416 >WIRE 80 432 80 416 >WIRE -208 448 -208 432 >WIRE -144 448 -144 336 >WIRE -144 448 -208 448 >WIRE -96 448 -144 448 >WIRE 16 448 -16 448 >WIRE -208 464 -208 448 >WIRE -480 528 -480 512 >WIRE 80 544 80 512 >WIRE -208 560 -208 544 >WIRE 16 608 16 448 >WIRE 320 608 320 320 >WIRE 320 608 16 608 >FLAG -80 288 +V >FLAG -480 416 +V >FLAG -480 528 0 >FLAG -80 384 0 >FLAG 432 400 0 >FLAG -512 224 0 >FLAG -352 336 0 >FLAG 208 544 0 >FLAG -208 336 +V >FLAG 80 544 0 >FLAG -208 560 0 >FLAG -128 48 +V >SYMBOL voltage -480 416 R0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >WINDOW 0 44 23 Left 0 >WINDOW 3 51 56 Left 0 >SYMATTR InstName V1 >SYMATTR Value 8 >SYMBOL pnp 144 272 M180 >SYMATTR InstName Q1 >SYMATTR Value 2N2905A >SYMBOL npn 144 368 R0 >SYMATTR InstName Q2 >SYMATTR Value 2N2219A >SYMBOL res 64 112 R0 >SYMATTR InstName R1 >SYMATTR Value 120 >SYMBOL res 64 224 R0 >SYMATTR InstName R2 >SYMATTR Value 560 >SYMBOL res 64 320 R0 >SYMATTR InstName R3 >SYMATTR Value 560 >SYMBOL res 64 416 R0 >SYMATTR InstName R4 >SYMATTR Value 120 >SYMBOL res 416 304 R0 >SYMATTR InstName R5 >SYMATTR Value 8 >SYMBOL cap 400 304 R90 >WINDOW 0 0 32 VBottom 0 >WINDOW 3 32 32 VTop 0 >SYMATTR InstName C2 >SYMATTR Value 470� >SYMBOL voltage -416 208 R90 >WINDOW 0 -32 56 VBottom 0 >WINDOW 3 57 63 VTop 0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V2 >SYMATTR Value SINE(0 .25 1000) >SYMBOL res 0 432 R90 >WINDOW 0 0 56 VBottom 0 >WINDOW 3 32 56 VTop 0 >SYMATTR InstName R6 >SYMATTR Value 10k >SYMBOL res -368 240 R0 >WINDOW 0 54 44 Left 0 >WINDOW 3 52 76 Left 0 >SYMATTR InstName R9 >SYMATTR Value 20k >SYMBOL cap -352 192 R90 >WINDOW 0 0 32 VBottom 0 >WINDOW 3 32 32 VTop 0 >SYMATTR InstName C4 >SYMATTR Value 1� >SYMBOL res -224 336 R0 >WINDOW 0 -38 44 Left 0 >WINDOW 3 -38 74 Left 0 >SYMATTR InstName R7 >SYMATTR Value 2k >SYMBOL res -368 80 R0 >WINDOW 0 50 43 Left 0 >WINDOW 3 49 76 Left 0 >SYMATTR InstName R10 >SYMATTR Value 20k >SYMBOL res 192 448 R0 >SYMATTR InstName R11 >SYMATTR Value .2 >SYMBOL res -224 448 R0 >WINDOW 0 -37 42 Left 0 >WINDOW 3 -35 76 Left 0 >SYMATTR InstName R8 >SYMATTR Value 2k >SYMBOL Opamps\\UniversalOpamp2 -80 320 R0 >SYMATTR InstName U2 >SYMBOL res 192 64 R0 >SYMATTR InstName R12 >SYMATTR Value .2 >TEXT -504 600 Left 0 !.tran 0 100m 0 startupDo this... http://www.analog-innovations.com/SED/TLV246HeadphoneAmplifier.pdf ...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 15, 20122012-01-15
Bill Bowden wrote:> I see excessive crossover distortion with this audio amp not shown > with LTspice. It simulates ok, but the wired circuit produces about a > 50uS dead time step as the signal crosses the mid point. I tried > increasing the bias with no help. Both inputs to the op-amp look good > with no distortion. Any idea what is going on? > > Version 4 > SHEET 1 880 1108 > WIRE -128 80 -128 48 > WIRE -128 80 -352 80 > WIRE 80 80 -128 80 > WIRE 208 80 80 80 > WIRE -352 96 -352 80 > WIRE 80 128 80 80 > WIRE 208 176 208 160 > WIRE -416 208 -432 208 > WIRE -352 208 -352 176 > WIRE -144 208 -352 208 > WIRE -512 224 -512 208 > WIRE 80 224 80 208 > WIRE 144 224 80 224 > WIRE 80 240 80 224 > WIRE -352 256 -352 208 > WIRE -144 304 -144 208 > WIRE -112 304 -144 304 > WIRE 80 320 -48 320 > WIRE 208 320 208 272 > WIRE 320 320 208 320 > WIRE 336 320 320 320 > WIRE 432 320 400 320 > WIRE -112 336 -144 336 > WIRE 80 336 80 320 > WIRE -208 352 -208 336 > WIRE 208 368 208 320 > WIRE -80 384 -80 352 > WIRE 144 416 80 416 > WIRE -480 432 -480 416 > WIRE 80 432 80 416 > WIRE -208 448 -208 432 > WIRE -144 448 -144 336 > WIRE -144 448 -208 448 > WIRE -96 448 -144 448 > WIRE 16 448 -16 448 > WIRE -208 464 -208 448 > WIRE -480 528 -480 512 > WIRE 80 544 80 512 > WIRE -208 560 -208 544 > WIRE 16 608 16 448 > WIRE 320 608 320 320 > WIRE 320 608 16 608 > FLAG -80 288 +V > FLAG -480 416 +V > FLAG -480 528 0 > FLAG -80 384 0 > FLAG 432 400 0 > FLAG -512 224 0 > FLAG -352 336 0 > FLAG 208 544 0 > FLAG -208 336 +V > FLAG 80 544 0 > FLAG -208 560 0 > FLAG -128 48 +V > SYMBOL voltage -480 416 R0 > WINDOW 123 0 0 Left 0 > WINDOW 39 0 0 Left 0 > WINDOW 0 44 23 Left 0 > WINDOW 3 51 56 Left 0 > SYMATTR InstName V1 > SYMATTR Value 8 > SYMBOL pnp 144 272 M180 > SYMATTR InstName Q1 > SYMATTR Value 2N2905A > SYMBOL npn 144 368 R0 > SYMATTR InstName Q2 > SYMATTR Value 2N2219A > SYMBOL res 64 112 R0 > SYMATTR InstName R1 > SYMATTR Value 120 > SYMBOL res 64 224 R0 > SYMATTR InstName R2 > SYMATTR Value 560 > SYMBOL res 64 320 R0 > SYMATTR InstName R3 > SYMATTR Value 560 > SYMBOL res 64 416 R0 > SYMATTR InstName R4 > SYMATTR Value 120 > SYMBOL res 416 304 R0 > SYMATTR InstName R5 > SYMATTR Value 8 > SYMBOL cap 400 304 R90 > WINDOW 0 0 32 VBottom 0 > WINDOW 3 32 32 VTop 0 > SYMATTR InstName C2 > SYMATTR Value 470� > SYMBOL voltage -416 208 R90 > WINDOW 0 -32 56 VBottom 0 > WINDOW 3 57 63 VTop 0 > WINDOW 123 0 0 Left 0 > WINDOW 39 0 0 Left 0 > SYMATTR InstName V2 > SYMATTR Value SINE(0 .25 1000) > SYMBOL res 0 432 R90 > WINDOW 0 0 56 VBottom 0 > WINDOW 3 32 56 VTop 0 > SYMATTR InstName R6 > SYMATTR Value 10k > SYMBOL res -368 240 R0 > WINDOW 0 54 44 Left 0 > WINDOW 3 52 76 Left 0 > SYMATTR InstName R9 > SYMATTR Value 20k > SYMBOL cap -352 192 R90 > WINDOW 0 0 32 VBottom 0 > WINDOW 3 32 32 VTop 0 > SYMATTR InstName C4 > SYMATTR Value 1� > SYMBOL res -224 336 R0 > WINDOW 0 -38 44 Left 0 > WINDOW 3 -38 74 Left 0 > SYMATTR InstName R7 > SYMATTR Value 2k > SYMBOL res -368 80 R0 > WINDOW 0 50 43 Left 0 > WINDOW 3 49 76 Left 0 > SYMATTR InstName R10 > SYMATTR Value 20k > SYMBOL res 192 448 R0 > SYMATTR InstName R11 > SYMATTR Value .2 > SYMBOL res -224 448 R0 > WINDOW 0 -37 42 Left 0 > WINDOW 3 -35 76 Left 0 > SYMATTR InstName R8 > SYMATTR Value 2k > SYMBOL Opamps\\UniversalOpamp2 -80 320 R0 > SYMATTR InstName U2 > SYMBOL res 192 64 R0 > SYMATTR InstName R12 > SYMATTR Value .2 > TEXT -504 600 Left 0 !.tran 0 100m 0 startupI 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
Reply by ●January 15, 20122012-01-15
On Jan 15, 2:17=A0pm, Jamie <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:> George Herold wrote: > > On Jan 11, 11:55 pm, "Phil Allison" <phi...@tpg.com.au> wrote: > > >>"Bill Bowden" > > >>I see excessive crossover distortion with this audio amp not shown > >>with LTspice. It simulates ok, but the wired circuit produces about a > >>50uS dead time step as the signal crosses the mid point. I tried > >>increasing the bias with no help. Both inputs to the op-amp look good > >>with no distortion. Any idea what is going on? > > >>** You need to post a schematic =A0- =A0dickhead. > > >>Totally =A0SMARTARSE of you to post only a Spice list on SEB. > > >>... =A0Phil > > > I was going to say it's a push-pull.... but it's flipped about. > > > Here's a pic > >http://imageshack.us/photo/my-images/708/crossover.jpg/ > > > Does this output have a name? > > > George H. > > I would love nothing more than to view that jpg however, It seems that > site is so loaded with Flash content and scam ads that It just wants to > cover all of my screen with pop up forms all over the place. > > =A0 =A0You see, I need to click on the actual image to see it properly > because it is not sized correctly for view and they know this. You click > on it, which normally brings up the image in fall details but, it also > starts a whole crap load of other scams, ads and forms to pop up all over=.> > =A0 =A0These free sites in my opinion, are worthless if you really want s=ome> one to see the content. They are just lures to get more people to see > their useless ads, take advantage of poeple and in =A0many cases makes > your PC useless when you're trying to shut down the forms as they keep > starting as they attempt to install shopping tool bars and all the other > crap. > > =A0 Just my opinion. These Free sites are nothing but bone yard traps. > > =A0 You know, most providers of services (ISP)'s provide their customers > with a personal webpage or webspace of more than enough with a clean > slab to start with. > > Jamie- Hide quoted text - > > - Show quoted text -Yeah sorry, It seems to have gotten much worse. Got a better image hosting site? I tries this tinyurl one. But it wanted me to enter a security code for each image. I suppose I could try and set up a web page.... Yola? George H.
Reply by ●January 15, 20122012-01-15
On 2012-01-15, Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:>> http://imageshack.us/photo/my-images/708/crossover.jpg/ >> >> Does this output have a name? >> >> George H. > I would love nothing more than to view that jpg however, It seems that > site is so loaded with Flash content and scam ads that It just wants to > cover all of my screen with pop up forms all over the place.I didn't notice. Ah that's right, I run the NoScript blocker available for Firefox. NoScript identifies all the sites which, for the given page, are being used as sources of JavaScript code. You can individually add them to the good list.> These free sites in my opinion, are worthless if you really want some > one to see the content. They are just lures to get more people to see > their useless ads, take advantage of poeple and in many cases makesWhat ads? Adblock! I absolutely do not see a single ad or popup on this site. Just text, a few buttons like "Sign Up" (That one is scripted: clicking on it works) and the image. Your fault for not getting a clue about what browsers can do for you.
Reply by ●January 16, 20122012-01-16
On Jan 15, 11:40=A0am, Jamie <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:>> I don 't understand why you don't see it in the sim? > > =A0 I see all kinds of problems there. > > =A0 THe outputs are current modes and the beta on the outputs are most > likely are not going to match well. > > =A0 =A0On 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. > > =A0 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 =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
