George Herold wrote:> On Jan 15, 2:17 pm, 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 - 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- 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.Your best bet would be to take advantage of your ISP service, that is, if you're using a private one instead of those free Email or economical services. I know times are tough and all the starving chiefs out there are trying their best to profit off the innocent indians. We wouldn't want them to be reminded of what it is like to actually to do something for that money. As far as image hosting sites, I am sure you can find another that isn't so overwhelmed with useless garbage. Your provider should be giving you a small chunk of personal web space. It's an easy thing to do. You simply navigate your browser using the copy and paste to your page or use a FTP program. Then you provide the link to your site plus the name of the image you put there. By the looks of your address, it looks like you should be able to get one that provides you a clean page, not one that is a child form of a business page, which is just as bad! Myself, I have the option of 5 E-mails, each one around 100megs of space the last time I checked. It's been a while. Jamie
Audio Amp Crossover Distortion?
Started by ●January 12, 2012
Reply by ●January 16, 20122012-01-16
Reply by ●January 16, 20122012-01-16
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? > > -BillThat 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
Reply by ●January 16, 20122012-01-16
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 -- | 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 16, 20122012-01-16
On 2012-01-16, George Herold <gherold@teachspin.com> wrote:> I suppose I could try and set up a web page.... Yola?A circuit image should compress extremely well because it contains pixels of a few colors, and most of them are white. Therefore you should be able to post it right to the newsgroup, uuencoded into a single article. (Yes, I can hear it now: ``gasp, a binary to a discussion group?'') Well, if it is small and on-topic, what is the harm? The benefit is that is that the picture permanently stays with the discussion. These URL's people post will be long gone, making much of the archived discussion junk.
Reply by ●January 16, 20122012-01-16
On Mon, 16 Jan 2012 17:54:45 +0000 (UTC), Kaz Kylheku <kaz@kylheku.com> wrote:>On 2012-01-16, George Herold <gherold@teachspin.com> wrote: >> I suppose I could try and set up a web page.... Yola? > >A circuit image should compress extremely well because it contains pixels of a >few colors, and most of them are white. Therefore you should be able to post >it right to the newsgroup, uuencoded into a single article. > >(Yes, I can hear it now: ``gasp, a binary to a discussion group?'') > >Well, if it is small and on-topic, what is the harm?The "harm" is that it sets a bad precedent. It won't propagate anyway, so there is little point.>The benefit is that is that the picture permanently stays with the discussion. > >These URL's people post will be long gone, making much of the archived >discussion junk.
Reply by ●January 16, 20122012-01-16
On Jan 16, 6:54=A0pm, Kaz Kylheku <k...@kylheku.com> wrote:> A circuit image should compress extremely well because it contains pixels=of a> few colors, and most of them are white. =A0Therefore you should be able t=o post> it right to the newsgroup, uuencoded into a single article. >If you choose the right image format and do everything 100% correctly, sure.> Well, if it is small and on-topic, what is the harm? >It sets a precedent. Before you know it people are posting 75MB uncompressed TIFF files and ISPs are banning the newsgroup. Instead of educating the posters after-the-fact why don't we educate the readers beforehand? I didn't see any adverts or popups on that site and neither did some other readers. It's all down to using setting up your web browser properly.
Reply by ●January 16, 20122012-01-16
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 ThompsonThe 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
Reply by ●January 16, 20122012-01-16
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 -- | 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 16, 20122012-01-16
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 ThompsonActually 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
Reply by ●January 16, 20122012-01-16
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 -- | 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.
