On Fri, 8 Dec 2023 07:19:28 -0800 (PST), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>onsdag den 6. december 2023 kl. 16.27.07 UTC+1 skrev Clive Arthur: >>, and if I'd used say a rubber diode to get some quiescent >> current, I think it would be very difficult to control Iq well enough >> over the temperature range. > >tried how bad it is if you bolt bias transistor to TR6 and TR8?Nearly all those ancient audio circuits are barbaric.
Power Amplifier for 100kHz.
Started by ●December 6, 2023
Reply by ●December 8, 20232023-12-08
Reply by ●December 8, 20232023-12-08
On 08/12/2023 15:35, legg wrote:> On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur > <clive@nowaytoday.co.uk> wrote: > >> On 07/12/2023 15:04, legg wrote: >>> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur >>> <clive@nowaytoday.co.uk> wrote: >>> >>>> I'm not an analog design expert, but needs must. >>>> >>>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>>> single supply, and to go up to 100kHz with a working ambient temperature >>>> of -20'C to 180'C. >>> >>> No you haven't. Not using conventional components. >>> >>> RL >> >> Bugger! I could have sworn it was working at 180'C (along with all the >> other parts of the system), but it seems you know better. I must have a >> faulty oven. >> >> I'd better warn all the other downhole instrumentation companies too! >> >> But yes, selected conventional components, analog and digital. And yes, >> I know that if you extrapolate the graphs, most of the parts de-rate to >> negative power dissipation. > > E.M.Cherry's PA circuitry and their clones can form rugged designs, > but they were never intended for data transmission. What's the > format? > > Thermal compensation of quiescent biasing was a good trick, then, but > you'd have to reconsider options over an extended range. Claiming to > have done such a design without doing so is silly. > > You may have to satisfy yourself with something that doesn't work > very well (or at all) at room temperature, if you stick with the > limitations of Self's variation (intended to address inaudible > distortion). > > Self-heating to within the range isn't out of the question, though > inconvenient on the bench. > > RLSo, first of all you tell me that I haven't done what I have done (and what many others could have done), then you tell me that it won't work very well, if at all. Who's going to break the news to the users? They'll be understandably upset that their systems work by some magic other than the electronics they paid for. It performs well enough to pass the acceptance tests without issue. What I'm looking towards is the next iteration - can I tweak what I have or should I start afresh? The latter is always preferable to the designer, the former to their paymasters. High temperature work always takes longer and costs more, mostly because of the testing and the restricted range of components. -- Cheers Clive
Reply by ●December 8, 20232023-12-08
On 08/12/2023 15:44, John Larkin wrote: <snip>> > Setting up a temp chamber is a nuisance. I use a cardboard box with > some padding inside, a heat gun, and freeze spray on my bench, > whenever I can. > > https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1Cardboard is good for a short time, I often use similar with a heat gun blowing in. A proper lab oven for long-term testing of course. First time I did this, I thought I'd inspect after 1000 hours. Too enthusiastic - cooled down, reached in and zap, static, dead board. I often use a fairly wide-mouthed stainless steel Thermos (Dewar) flask (my boards are long and thin) with an aquarium pump on the bench pumping air through an insulated high power resistor (the type with the water cooling tube down the middle) and put the hot silicone pipe to the bottom of the flask with wadding in the top. Cheap Chinese temperature controller and you have something compact and relatively safe using minimal power. -- Cheers Clive
Reply by ●December 8, 20232023-12-08
On Fri, 8 Dec 2023 16:21:08 +0000, Clive Arthur <clive@nowaytoday.co.uk> wrote:>On 08/12/2023 15:44, John Larkin wrote: > ><snip> >> >> Setting up a temp chamber is a nuisance. I use a cardboard box with >> some padding inside, a heat gun, and freeze spray on my bench, >> whenever I can. >> >> https://www.dropbox.com/scl/fi/ncxlgwgyvyoxexzmfqyk3/T660_Temp_Chamber.jpg?rlkey=oud1q89ygu5nafd2i5nym6jii&raw=1 > >Cardboard is good for a short time, I often use similar with a heat gun >blowing in.I almost close the box flaps and shoot in hot air from a heat gun, or freeze spray. The something-vs-temp graphs (frequency, dc offset, whatever) look great.> >A proper lab oven for long-term testing of course. First time I did >this, I thought I'd inspect after 1000 hours. Too enthusiastic - cooled >down, reached in and zap, static, dead board. > >I often use a fairly wide-mouthed stainless steel Thermos (Dewar) flask >(my boards are long and thin) with an aquarium pump on the bench pumping >air through an insulated high power resistor (the type with the water >cooling tube down the middle) and put the hot silicone pipe to the >bottom of the flask with wadding in the top.Nice idea, pumping air through the hole in a wirewound resistor.> >Cheap Chinese temperature controller and you have something compact and >relatively safe using minimal power.I have a cheap peltier six-pack size mini-fridge that has two settings, heat and cool. A small product will fit inside. It's great for tempco testing, but doesn't get hot or cold enough to push failure limits. Our big temp chamber is down in the basement so it's a big deal to set up all our test gear down there, and run cables throught the port. A temp chamber doesn't help find which parts are the sensitive ones. Freeze spray on a q-tip does that.
Reply by ●December 8, 20232023-12-08
On Fri, 8 Dec 2023 16:02:20 +0000, Clive Arthur <clive@nowaytoday.co.uk> wrote:>On 08/12/2023 15:35, legg wrote: >> On Thu, 7 Dec 2023 15:26:52 +0000, Clive Arthur >> <clive@nowaytoday.co.uk> wrote: >> >>> On 07/12/2023 15:04, legg wrote: >>>> On Wed, 6 Dec 2023 15:26:00 +0000, Clive Arthur >>>> <clive@nowaytoday.co.uk> wrote: >>>> >>>>> I'm not an analog design expert, but needs must. >>>>> >>>>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>>>> single supply, and to go up to 100kHz with a working ambient temperature >>>>> of -20'C to 180'C. >>>> >>>> No you haven't. Not using conventional components. >>>> >>>> RL >>> >>> Bugger! I could have sworn it was working at 180'C (along with all the >>> other parts of the system), but it seems you know better. I must have a >>> faulty oven. >>> >>> I'd better warn all the other downhole instrumentation companies too! >>> >>> But yes, selected conventional components, analog and digital. And yes, >>> I know that if you extrapolate the graphs, most of the parts de-rate to >>> negative power dissipation. >> >> E.M.Cherry's PA circuitry and their clones can form rugged designs, >> but they were never intended for data transmission. What's the >> format? >> >> Thermal compensation of quiescent biasing was a good trick, then, but >> you'd have to reconsider options over an extended range. Claiming to >> have done such a design without doing so is silly. >> >> You may have to satisfy yourself with something that doesn't work >> very well (or at all) at room temperature, if you stick with the >> limitations of Self's variation (intended to address inaudible >> distortion). >> >> Self-heating to within the range isn't out of the question, though >> inconvenient on the bench. >> >> RL > >So, first of all you tell me that I haven't done what I have done (and >what many others could have done), then you tell me that it won't work >very well, if at all. > >Who's going to break the news to the users? They'll be understandably >upset that their systems work by some magic other than the electronics >they paid for. > >It performs well enough to pass the acceptance tests without issue. >What I'm looking towards is the next iteration - can I tweak what I have >or should I start afresh? > >The latter is always preferable to the designer, the former to their >paymasters. High temperature work always takes longer and costs more, >mostly because of the testing and the restricted range of components.Right. I take it all back. My reading and comprehension skills seem to be taking a hit today. RL
Reply by ●December 8, 20232023-12-08
On Wednesday, December 6, 2023 at 6:22:34 PM UTC-5, Glen Walpert wrote:> On Wed, 6 Dec 2023 22:49:40 +0000, Clive Arthur wrote: > > > On 06/12/2023 21:19, Phil Hobbs wrote: > >> On 2023-12-06 10:26, Clive Arthur wrote: > >>> I'm not an analog design expert, but needs must. > >>> > >>> I recently adapted a Doug Self audio amplifier design for use on a 60V > >>> single supply, and to go up to 100kHz with a working ambient > >>> temperature of -20'C to 180'C. > >>> > >>> I can't show the circuit, but it was based on Fig 1a here... > >>> http://www.douglas-self.com/ampins/dipa/dipa.htm > >>> > >>> Cdom needs to come down for this higher frequency application, but too > >>> far and you have oscillation. Also, problems occur with slew rate > >>> limiting due to Cdom, the TR5 constant current, and the increase in > >>> hFE of TR4 with temperature. > >>> > >>> So I added an emitter degeneration resistor to TR4 to tame the hFE > >>> variation, removed Cdom and put a smaller C across Rf1 instead. Seems > >>> stable and not slew rate limiting. Took a lot longer to do than that > >>> sentence might imply. > >>> > >>> However. > >>> > >>> The Vbias is a single diode, can't risk 2 diodes as TR6 & TR8 probably > >>> get hotter and their Vbe would drop by more than the diodes, so it's > >>> class B. As it runs at a high temperature, I obviously want to reduce > >>> dissipation, and if I'd used say a rubber diode to get some quiescent > >>> current, I think it would be very difficult to control Iq well enough > >>> over the temperature range. > >>> > >>> So I have a circuit which works well enough, but could be better with > >>> regard to crossover distortion (though it's lower than I would have > >>> thought). In this application, the better the signal quality, the > >>> higher the data rate. > >>> > >>> Any ideas for improving crossover distortion, bearing in mind the > >>> temperature range? The signal is OFDM, so pretty much a load of > >>> 'random' steps, some of which may be small and at a crossover point. > >>> > >> Some local feedback around the output stage would get my vote. The > >> Sziklai pairs have their own local feedback, but that doesn't fix the > >> crossover problem. > >> > >> Another approach would be to turn TR4 into a diff pair. TR3's > >> collector swing is going to waste, and that would let you keep the > >> open-loop gain the same, while stabilizing the tail current. > >> > >> Cheers > >> > >> Phil Hobbs > > > > Thanks, that second one particularly sounds like a good idea. I'll see > > what the sim says. Local feedback on the output stage sounds trickier, > > I'll have to think. > > > > One thing I thought of was to use multiple smaller output pairs in > > parallel, and have a DC offset for each one. Imagine replacing the > > Vbias diode with a string of a few series diodes, and connecting the > > bases of one output pair across D1, the next pair across D2 etc. Would > > need resistors from each pair of emitters to the output. That should > > give lower crossover in more places. Maybe. > Some years ago Jim Thompson posted an audio amplifier design which used > current mirrors to provide bias to the output transistors for the express > purpose of keeping crossover distortion low over a large temperature > range. He claimed it was the bees knees, but a quick search failed to > turn it up. Perhaps someone else saved it or remembers the thread?This circuit looks like what you're talking about, MC34071 : https://www.javanelec.com/CustomAjax/GetAppDocument/9feb1d77-b648-447f-a4ec-f89b60d40589?type=1&inlineName=True But it's a typical OA input and intermediate gain stage so the gain is very large. The discrete Self circuit doesn't come close. Without gain with bw near 10MHz, suppression of large signal output distortion is going to be kinda weak.> > Glen
Reply by ●December 9, 20232023-12-09
Anthony William Sloman wrote: =========================> Clive Arthur wrote: > > I'm not an analog design expert, but needs must. > > > > I recently adapted a Doug Self audio amplifier design for use on a 60V > > single supply, and to go up to 100kHz with a working ambient temperature > > of -20'C to 180'C. > > Few power transistors are specified for operation at 180C and the audio amplifier market doesn't cater to people who want that kind of operating temperature. >** Only time I've seen that sort of temp happen involved an audio power stage employing a small, fan blown heatsink. When the fan failed, output BJTs got so hot the solder connecting them to the PCB melted. Needless to say, collectors were all shorted to emitters by the time I saw it. The OP seems intent on breaking the temperature limits of silicon devices. Maybe he should try vacuum tubes instead, where plates can run a dull red colour for long periods. Likely need a bit more than a 60V supply and not use any electros. .... Phil
Reply by ●December 9, 20232023-12-09
On a sunny day (Wed, 6 Dec 2023 18:54:05 +0000) it happened piglet <erichpwagner@hotmail.com> wrote in <ukqg0e$si84$1@dont-email.me>:>On 06/12/2023 15:26, Clive Arthur wrote: >> I'm not an analog design expert, but needs must. >> >> I recently adapted a Doug Self audio amplifier design for use on a 60V >> single supply, and to go up to 100kHz with a working ambient temperature >> of -20'C to 180'C. >> >> I can't show the circuit, but it was based on Fig 1a here... >> http://www.douglas-self.com/ampins/dipa/dipa.htm >> >> Cdom needs to come down for this higher frequency application, but too >> far and you have oscillation. Also, problems occur with slew rate >> limiting due to Cdom, the TR5 constant current, and the increase in hFE >> of TR4 with temperature. >> >> So I added an emitter degeneration resistor to TR4 to tame the hFE >> variation, removed Cdom and put a smaller C across Rf1 instead. Seems >> stable and not slew rate limiting. Took a lot longer to do than that >> sentence might imply. >> >> However. >> >> The Vbias is a single diode, can't risk 2 diodes as TR6 & TR8 probably >> get hotter and their Vbe would drop by more than the diodes, so it's >> class B. As it runs at a high temperature, I obviously want to reduce >> dissipation, and if I'd used say a rubber diode to get some quiescent >> current, I think it would be very difficult to control Iq well enough >> over the temperature range. >> >> So I have a circuit which works well enough, but could be better with >> regard to crossover distortion (though it's lower than I would have >> thought). In this application, the better the signal quality, the >> higher the data rate. >> >> Any ideas for improving crossover distortion, bearing in mind the >> temperature range? The signal is OFDM, so pretty much a load of >> 'random' steps, some of which may be small and at a crossover point. >> > >Maintaining class AB bias over that temperature range is going to be >difficult. I'd look instead at having no Vbias so the power stage >operates pure class B and then have a fast small class A stage fill in >the cross-over distortion. In other words the Quad feed-forward aka >current dumping idea of the 1970s.I liked that idea.
Reply by ●December 9, 20232023-12-09
On 09/12/2023 6:54 am, Jan Panteltje wrote:> On a sunny day (Wed, 6 Dec 2023 18:54:05 +0000) it happened piglet > <erichpwagner@hotmail.com> wrote in <ukqg0e$si84$1@dont-email.me>: > >> On 06/12/2023 15:26, Clive Arthur wrote: >>> I'm not an analog design expert, but needs must. >>> >>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>> single supply, and to go up to 100kHz with a working ambient temperature >>> of -20'C to 180'C. >>> >>> I can't show the circuit, but it was based on Fig 1a here... >>> http://www.douglas-self.com/ampins/dipa/dipa.htm >>> >>> Cdom needs to come down for this higher frequency application, but too >>> far and you have oscillation. Also, problems occur with slew rate >>> limiting due to Cdom, the TR5 constant current, and the increase in hFE >>> of TR4 with temperature. >>> >>> So I added an emitter degeneration resistor to TR4 to tame the hFE >>> variation, removed Cdom and put a smaller C across Rf1 instead. Seems >>> stable and not slew rate limiting. Took a lot longer to do than that >>> sentence might imply. >>> >>> However. >>> >>> The Vbias is a single diode, can't risk 2 diodes as TR6 & TR8 probably >>> get hotter and their Vbe would drop by more than the diodes, so it's >>> class B. As it runs at a high temperature, I obviously want to reduce >>> dissipation, and if I'd used say a rubber diode to get some quiescent >>> current, I think it would be very difficult to control Iq well enough >>> over the temperature range. >>> >>> So I have a circuit which works well enough, but could be better with >>> regard to crossover distortion (though it's lower than I would have >>> thought). In this application, the better the signal quality, the >>> higher the data rate. >>> >>> Any ideas for improving crossover distortion, bearing in mind the >>> temperature range? The signal is OFDM, so pretty much a load of >>> 'random' steps, some of which may be small and at a crossover point. >>> >> >> Maintaining class AB bias over that temperature range is going to be >> difficult. I'd look instead at having no Vbias so the power stage >> operates pure class B and then have a fast small class A stage fill in >> the cross-over distortion. In other words the Quad feed-forward aka >> current dumping idea of the 1970s. > > I liked that idea. >Yes, the idea appealled to me too. I built the circuit from Quad 405 in: <https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1975-12.pdf> It was very robust amp worked very well for me. piglet
Reply by ●December 9, 20232023-12-09
On a sunny day (Sat, 9 Dec 2023 11:07:44 +0000) it happened piglet <erichpwagner@hotmail.com> wrote in <ul1hq4$26a0k$1@dont-email.me>:>On 09/12/2023 6:54 am, Jan Panteltje wrote: >> On a sunny day (Wed, 6 Dec 2023 18:54:05 +0000) it happened piglet >> <erichpwagner@hotmail.com> wrote in <ukqg0e$si84$1@dont-email.me>: >> >>> On 06/12/2023 15:26, Clive Arthur wrote: >>>> I'm not an analog design expert, but needs must. >>>> >>>> I recently adapted a Doug Self audio amplifier design for use on a 60V >>>> single supply, and to go up to 100kHz with a working ambient temperature >>>> of -20'C to 180'C. >>>> >>>> I can't show the circuit, but it was based on Fig 1a here... >>>> http://www.douglas-self.com/ampins/dipa/dipa.htm >>>> >>>> Cdom needs to come down for this higher frequency application, but too >>>> far and you have oscillation. Also, problems occur with slew rate >>>> limiting due to Cdom, the TR5 constant current, and the increase in hFE >>>> of TR4 with temperature. >>>> >>>> So I added an emitter degeneration resistor to TR4 to tame the hFE >>>> variation, removed Cdom and put a smaller C across Rf1 instead. Seems >>>> stable and not slew rate limiting. Took a lot longer to do than that >>>> sentence might imply. >>>> >>>> However. >>>> >>>> The Vbias is a single diode, can't risk 2 diodes as TR6 & TR8 probably >>>> get hotter and their Vbe would drop by more than the diodes, so it's >>>> class B. As it runs at a high temperature, I obviously want to reduce >>>> dissipation, and if I'd used say a rubber diode to get some quiescent >>>> current, I think it would be very difficult to control Iq well enough >>>> over the temperature range. >>>> >>>> So I have a circuit which works well enough, but could be better with >>>> regard to crossover distortion (though it's lower than I would have >>>> thought). In this application, the better the signal quality, the >>>> higher the data rate. >>>> >>>> Any ideas for improving crossover distortion, bearing in mind the >>>> temperature range? The signal is OFDM, so pretty much a load of >>>> 'random' steps, some of which may be small and at a crossover point. >>>> >>> >>> Maintaining class AB bias over that temperature range is going to be >>> difficult. I'd look instead at having no Vbias so the power stage >>> operates pure class B and then have a fast small class A stage fill in >>> the cross-over distortion. In other words the Quad feed-forward aka >>> current dumping idea of the 1970s. >> >> I liked that idea. >> > >Yes, the idea appealled to me too. I built the circuit from Quad 405 in: > ><https://www.worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1975-12.pdf> > >It was very robust amp worked very well for me.Downloaded it Page 10 Current dumping. Where I worked we had 6 color studios and in each audio room there were 2 Quads as monitor. The first time I ever heard a Quad speaker was when I was invited to a concert for some small music group it was in a church, and they used a Quad speaker... I was totally blown out by that sound, so clear! At that time I was in high school those days and I was building an amplifier for the school band, tubes, EL84 balanced I think it was the guitar player loved the sound (special tube distortion sound) we used whatever speaker we could find, very small budget. Some year ago I was looking for 2 good Quad electrostats, but did not really find a cheap seller that looked reliable. Maybe I will have an other go. As to the current dumping, maybe the OP should give it a try?
