A class G amplifier would run off two power supplies. The normal supply and one with higher rails when more and brief power is required.
This could be achieved with this amp module. All you would need to do is track the input signal and when it got too big switch in the higher voltage supply. Sounds easy?
As Telewatt has suggested it is not quite as simple as that and the power supply and the way it feeds the amp would become quite complicated.
Cheers
This could be achieved with this amp module. All you would need to do is track the input signal and when it got too big switch in the higher voltage supply. Sounds easy?
As Telewatt has suggested it is not quite as simple as that and the power supply and the way it feeds the amp would become quite complicated.
Cheers
hello guys,
I think that using a G class amplifier in a place where are no constraints regarding efficiency is not justified. I think that simple things are the best. Why would i complicate my life with a class G amplifier when I can use a simple one in AB class? As long as i have plenty of energy from the wall soket I don't need an efficient amplifier. I need a robust one. If my amplifier is battery powered the things change, in this case I need an efficient one. And in this case a skilled constructor can build an amplifier in class D and that's efficiency!
Anyway I think that a compromise should be made between efficiency and complexity, and this compromise is dictated by the conditions that amplifiers operates in.
I think that using a G class amplifier in a place where are no constraints regarding efficiency is not justified. I think that simple things are the best. Why would i complicate my life with a class G amplifier when I can use a simple one in AB class? As long as i have plenty of energy from the wall soket I don't need an efficient amplifier. I need a robust one. If my amplifier is battery powered the things change, in this case I need an efficient one. And in this case a skilled constructor can build an amplifier in class D and that's efficiency!
Anyway I think that a compromise should be made between efficiency and complexity, and this compromise is dictated by the conditions that amplifiers operates in.
I have a question related to the increased efficiency of a class G amplifier.
How is that amplifier more efficient than a usual AB class amplifier if the devices that handle the supply voltage are working in linear mode?
From my point of view this is more a way to distribute the power disipation than a way to increase efficiency.
As far as I remember this kind of amplifiers where used in car audio sistems where the supply voltage is too low to obtain high level of power, and with some switched capacitors they increase the supply voltage level when the amplifier need it. And here i'm not talking about that power amplifiers with SMPS converters to obtain 35-40 volts per rail.
Again, i'm not so skilled in audio designs, so if i'm wrong please don't hesitate to correct me.
How is that amplifier more efficient than a usual AB class amplifier if the devices that handle the supply voltage are working in linear mode?
From my point of view this is more a way to distribute the power disipation than a way to increase efficiency.
As far as I remember this kind of amplifiers where used in car audio sistems where the supply voltage is too low to obtain high level of power, and with some switched capacitors they increase the supply voltage level when the amplifier need it. And here i'm not talking about that power amplifiers with SMPS converters to obtain 35-40 volts per rail.
Again, i'm not so skilled in audio designs, so if i'm wrong please don't hesitate to correct me.
How is class G more efficient?
The lower the voltage across the output devices the lower the power dissipated for a certain current flow. I.e. if the average voltage across the output devices was 40 volts and the average current was 2 amps then the average power dissipated by the output stage would be 80 watts. If the average voltage was 60 volts then the average power would be 120 watts.
So it's better to run the amp with rails of 40 volts and switch in the 60 volt rail only when required. I.e to handle the very brief higher power signals.
Likewise the devices that handle the extra rails switching are on only for very brief periods and are basically turned fully on or fully off, so the power dissipation is almost zero.
Just can't get away from Ohms law.
Cheers
The lower the voltage across the output devices the lower the power dissipated for a certain current flow. I.e. if the average voltage across the output devices was 40 volts and the average current was 2 amps then the average power dissipated by the output stage would be 80 watts. If the average voltage was 60 volts then the average power would be 120 watts.
So it's better to run the amp with rails of 40 volts and switch in the 60 volt rail only when required. I.e to handle the very brief higher power signals.
Likewise the devices that handle the extra rails switching are on only for very brief periods and are basically turned fully on or fully off, so the power dissipation is almost zero.
Just can't get away from Ohms law.
Cheers
Quasi:
Since we're on class G...
Does a class G amp switch supply rails to follow a high amplitude signal cycle-by-cycle, or to follow it's envelope?
(i.e. would a 50Hz high level tone burst cause the supply to switch 100 times, or just once?)
The way I see it, unless you use an SMPS or a transformer with two secondaries ( and two complete power supplies), a class G amp simply transfers some heat from the output transistors to the power supply pass transistors. No savings in energy or in heat.
You still have to design a full fledged amp for the higher power, since in demanding situations, it may end up having to handle the higher power continuously.
Some amp manufacturers experimented with Class G some years ago, unsuccessfully --they didn't sell. All specs being equal, customers would rather buy a full-time 300W amp, than a sometimes-200-sometimes-300W amp. The public neither understood, nor trusted this power model.
Class G is still the academician's tinker toy. It's most at home on the workbench of an engineering school, demostrating some theoretical principles.
Adrian
Since we're on class G...
Does a class G amp switch supply rails to follow a high amplitude signal cycle-by-cycle, or to follow it's envelope?
(i.e. would a 50Hz high level tone burst cause the supply to switch 100 times, or just once?)
The way I see it, unless you use an SMPS or a transformer with two secondaries ( and two complete power supplies), a class G amp simply transfers some heat from the output transistors to the power supply pass transistors. No savings in energy or in heat.
You still have to design a full fledged amp for the higher power, since in demanding situations, it may end up having to handle the higher power continuously.
Some amp manufacturers experimented with Class G some years ago, unsuccessfully --they didn't sell. All specs being equal, customers would rather buy a full-time 300W amp, than a sometimes-200-sometimes-300W amp. The public neither understood, nor trusted this power model.
Class G is still the academician's tinker toy. It's most at home on the workbench of an engineering school, demostrating some theoretical principles.
Adrian
As we were talking about class G i had an idea yesterday.
Since I intend to use a microcontroler in my amplifier to take care of some functions like protections and some diagnostics and a switching power supply (the one from the a and t labs), I could program that microcontroller to somehow control the output voltage of the power supply as function of the volume. I also intend to use a digital controller for volume and tone control but this depends on the performaces of the audio controller.
All those digital function can be easily integrated in a single microcontroller.
The advantage of using a single microcontroller that has access to volume level and depending on this can control the output voltage of the power supply by changing the division ratio in the control loop of the power supply.
Anyway the necesary supply voltage as a function of the volume level can be computed or even determined experimentally.
This may not be a very elegant idea but I think it works.
Since I intend to use a microcontroler in my amplifier to take care of some functions like protections and some diagnostics and a switching power supply (the one from the a and t labs), I could program that microcontroller to somehow control the output voltage of the power supply as function of the volume. I also intend to use a digital controller for volume and tone control but this depends on the performaces of the audio controller.
All those digital function can be easily integrated in a single microcontroller.
The advantage of using a single microcontroller that has access to volume level and depending on this can control the output voltage of the power supply by changing the division ratio in the control loop of the power supply.
Anyway the necesary supply voltage as a function of the volume level can be computed or even determined experimentally.
This may not be a very elegant idea but I think it works.
the advantage of that power supply is that it's already designed to have multiple output voltage.
Anyway changing the output voltage of that power suply is relatively easy ba changing that division ration in the control loop.
Obviously changing the output voltage thru that division ratio works in certain limits determined by the output power (upwards)
and keeping the continuos conduction mode or CCM (downwards).
Today I ordered the pcb's for the N channel amplifier that quasi recomeneded.
After I finish building the amplifier and modify the schematic for 100 - 120w, I will build that power supply and (the fun part)
play with it to obtain the maximum +/- 55 v as quasi recomended me.
Anyway changing the output voltage of that power suply is relatively easy ba changing that division ration in the control loop.
Obviously changing the output voltage thru that division ratio works in certain limits determined by the output power (upwards)
and keeping the continuos conduction mode or CCM (downwards).
Today I ordered the pcb's for the N channel amplifier that quasi recomeneded.
After I finish building the amplifier and modify the schematic for 100 - 120w, I will build that power supply and (the fun part)
play with it to obtain the maximum +/- 55 v as quasi recomended me.
sometimes I'm speaking nonsenses. I forgot to post the link to that power supply
I'm looking forward to hear some comments about my idea....
I'm looking forward to hear some comments about my idea....
cd-i
I'm starting to build that SMPS from A&T labs now.
I have touched up the foil pattern image quality, and added holes in the center of all pads, since my drill requires this for centering. I've also separated some traces that ran too close together and could possibly short in a photographic exposure process. The pads for the IC's are also larger, to prevent foil lifting during soldering.
I've also gotten a lot of information together on the inductors and other key components.
The "T-QSE1" and "T-QSE2" part numbers are invalid. These are custom wound for A&T labs by QSE, a winding outfit in Chicago, who quoted me some outrageous prices for these parts.
Also, the value on L3, the common-mode choke is wrong; it cannot be 1.8uH, it must be 1,8mH.
If you want, we could start a thread for the construction of the K6 SMPS.
PS.
the updated foil pattern files are .PCX, the smallest lossless file type I could save in. Win Paintbrush may mistakenly think it can open these files, but it can't. You need some other graphic program to view them. I use Thumbs Plus, for viewing and printing.
Adrian
I'm starting to build that SMPS from A&T labs now.
I have touched up the foil pattern image quality, and added holes in the center of all pads, since my drill requires this for centering. I've also separated some traces that ran too close together and could possibly short in a photographic exposure process. The pads for the IC's are also larger, to prevent foil lifting during soldering.
I've also gotten a lot of information together on the inductors and other key components.
The "T-QSE1" and "T-QSE2" part numbers are invalid. These are custom wound for A&T labs by QSE, a winding outfit in Chicago, who quoted me some outrageous prices for these parts.
Also, the value on L3, the common-mode choke is wrong; it cannot be 1.8uH, it must be 1,8mH.
If you want, we could start a thread for the construction of the K6 SMPS.
PS.
the updated foil pattern files are .PCX, the smallest lossless file type I could save in. Win Paintbrush may mistakenly think it can open these files, but it can't. You need some other graphic program to view them. I use Thumbs Plus, for viewing and printing.
Adrian
funberry,
I am interested too in building that power supply but unfortunately this month I'm stuck between my faculty exams and building the power amplifier you gave me. Anyway if all things will go acording to my plans at the end of this month I will start building that power supply too.
You were right about the value of L3, if you take a closer look at the picture of the assembled power supply you can read the value of the L3.
About starting a thread, I think it's a good idea to place the thread in the power supply section of this forum to see others opinion about this power supply.
I am interested too in building that power supply but unfortunately this month I'm stuck between my faculty exams and building the power amplifier you gave me. Anyway if all things will go acording to my plans at the end of this month I will start building that power supply too.
You were right about the value of L3, if you take a closer look at the picture of the assembled power supply you can read the value of the L3.
About starting a thread, I think it's a good idea to place the thread in the power supply section of this forum to see others opinion about this power supply.
The only thing that worries me in that schematic is the current transformer. I did not see written anywhere in the documentation the number of the secondary turns.
But i think I saw the output voltage/ amp. This is enough to calculate the number of secondary turns.
Anyway I have a lot of cores around and I intend to build the inductors and the transformers. An LCR meter is enough to measure the final inductances and in case of the main transformer the leakage inductance.
Another problem for me is the pcb. I tried to make my own pcb's but the results where poor. I prefer to buy the pcb directly from the A&T or to order it to a local supplier, depending on the price.
Daniel
But i think I saw the output voltage/ amp. This is enough to calculate the number of secondary turns.
Anyway I have a lot of cores around and I intend to build the inductors and the transformers. An LCR meter is enough to measure the final inductances and in case of the main transformer the leakage inductance.
Another problem for me is the pcb. I tried to make my own pcb's but the results where poor. I prefer to buy the pcb directly from the A&T or to order it to a local supplier, depending on the price.
Daniel
Class G;
Hey Funberry,
Sorry about the delay (I've been interstate) in commenting on the Class G thing.
Class G amps I looked at many years ago simply switched the voltage supply when the input signal exceeded a pre-set threshold and tracked the power envelope of the signal. I.e. Pre-set delays ensured the power supply did not follow the actual waveform.
I did read recently however that some class G amps use the input signal to modulate the power supply, so I am not sure whether this is done to resemble the waveform. I am not sure whether this modulation is linear or Pulse Witdh Modulation.
Cheers
Hey Funberry,
Sorry about the delay (I've been interstate) in commenting on the Class G thing.
Class G amps I looked at many years ago simply switched the voltage supply when the input signal exceeded a pre-set threshold and tracked the power envelope of the signal. I.e. Pre-set delays ensured the power supply did not follow the actual waveform.
I did read recently however that some class G amps use the input signal to modulate the power supply, so I am not sure whether this is done to resemble the waveform. I am not sure whether this modulation is linear or Pulse Witdh Modulation.
Cheers
Here's the current transformer, D1871.
I use positive photoresist presensitized PCB's and expose them for 5-6 minutes under common fluorescent lamps (6 inches away from the lamp). For the stencils, I print on inkjet transparent sheets (for overhead projectors), using the HP' printer's heaviest ink settings ( a setting for printing t-shirt transfers puts the most ink on the page ).
I wouldn't even try double-sided boards, because they're a nightmare to aligh properly. I etch two complete single-sided boards, then stick them together, copper side out, and voila! double-sided home made goodness. ( I use bits of wire to emulate vias) The double thickness board is especially useful here, since this board is unusually large and carries lots of heavy components. I think a single-layer board would feel wobbly.
Adrian
I use positive photoresist presensitized PCB's and expose them for 5-6 minutes under common fluorescent lamps (6 inches away from the lamp). For the stencils, I print on inkjet transparent sheets (for overhead projectors), using the HP' printer's heaviest ink settings ( a setting for printing t-shirt transfers puts the most ink on the page ).
I wouldn't even try double-sided boards, because they're a nightmare to aligh properly. I etch two complete single-sided boards, then stick them together, copper side out, and voila! double-sided home made goodness. ( I use bits of wire to emulate vias) The double thickness board is especially useful here, since this board is unusually large and carries lots of heavy components. I think a single-layer board would feel wobbly.
Adrian
basically my method of prototyping pcb's is the same.
But for double sided pcb's i align the printed transparent sheets whitout the pcb between them (this is easily done by moving the two sheets until the via and pad holes are mathing). After I aligned the sheets I fasten them with paper clips or staples on three sides. The fastened sheets now look like a plastic bag. You insert the photosensitive pcb in that bag and expose it.
I obtained fairly good alignment precisions in this way. My problems comes from the printer. It does not preserve the exact dimensions so I had to print 3 - 4 times the same drawing and choose the best one. Another problem was that the black colour was not "black enough". A solution to that problem was to use two overlapped sheets on the same side - and that leads me to the first problem (not preserving the exact dimensions of the drawing)...
Thanks for the datasheet of the transformer.
But for double sided pcb's i align the printed transparent sheets whitout the pcb between them (this is easily done by moving the two sheets until the via and pad holes are mathing). After I aligned the sheets I fasten them with paper clips or staples on three sides. The fastened sheets now look like a plastic bag. You insert the photosensitive pcb in that bag and expose it.
I obtained fairly good alignment precisions in this way. My problems comes from the printer. It does not preserve the exact dimensions so I had to print 3 - 4 times the same drawing and choose the best one. Another problem was that the black colour was not "black enough". A solution to that problem was to use two overlapped sheets on the same side - and that leads me to the first problem (not preserving the exact dimensions of the drawing)...
Thanks for the datasheet of the transformer.
I know what you mean.
If the printer skews the image, you can't really use it for such large size work.
Sounds like your best solution may be to take your file to a friend with a good printer.
Or if you have access to a laser printer, those can print on standard (cheap) acetate sheets. Some of them have precise enough paper transport mechanisms that you can print twice on the same sheet, and the images overlap perfectly.
If there are print shops or graphics services companies nearby, they could give you an excellent print of your artwork in notime. And they should not charge much, since doing this is really trivial for them.
BTW, do you think it would matter greatly whether one used a ferrite or a powdered iron toroid for the gate drive transformer?
Adrian
If the printer skews the image, you can't really use it for such large size work.
Sounds like your best solution may be to take your file to a friend with a good printer.
Or if you have access to a laser printer, those can print on standard (cheap) acetate sheets. Some of them have precise enough paper transport mechanisms that you can print twice on the same sheet, and the images overlap perfectly.
If there are print shops or graphics services companies nearby, they could give you an excellent print of your artwork in notime. And they should not charge much, since doing this is really trivial for them.
BTW, do you think it would matter greatly whether one used a ferrite or a powdered iron toroid for the gate drive transformer?
Adrian
hmmm...
ferrite cores are recomended for gate drives transformers...
gate drive transformers are tricky to build.... most of the transformers I built were based on trial and error... built measured....if not worked built again....
below is a link to a very good page about gate drive transformers.....
gate drives transformers
another good link
I built many gate drive transformers based on the informations on those pages.
and related to the pcb's.... i used an HP laser printer...it was an expensive one..... maybe I will make the artworks to a print shop
Daniel
ferrite cores are recomended for gate drives transformers...
gate drive transformers are tricky to build.... most of the transformers I built were based on trial and error... built measured....if not worked built again....
below is a link to a very good page about gate drive transformers.....
gate drives transformers
another good link
I built many gate drive transformers based on the informations on those pages.
and related to the pcb's.... i used an HP laser printer...it was an expensive one..... maybe I will make the artworks to a print shop
Daniel
Gyp5y
As cd-i ponts out in post nr 14, all turns ratios are specified on the schematics.
If you are trying to "build" T1, or are in any way unclear about what it is, I'd strongly reccommend against taking on such a project. Any small mains transformer that puts out +/- 10 to 18 Vac at .2 A will do here.
T3 is a Coilcraft part nr, referenced in post #55.
For T4, the authors give you the nr of turns and core type.
L1 and L2 are common toroid inductors, 8 Amp wire, something between 100uH and 300uH, value is really not critical.
L3, the common mode choke, is again not too critical, since it mainly serves to protect the mains from pollution by the SMPS. It has been referenced in posts #51 and 52. You can probably substitute another common mode choke that has wire thick enough to take 10 Amps, at least for testing purposes.
If you wind your own, noone can tell you how many turns to wind, since they don't know what permeability core you will use. You may need an inductance meter to get the value right.
There is a clear risk of injury in building this, and you really have to know what you're doing.
You need to ask yourself the qustion: Can I put a scope to this thing and troubleshoot it, if it doesn't work the first time?
The manufacturer is under no obligation to provide any support information to individuals not buying their kit. They mentioned on another board that they get many novice questions, which they have to ignore, because they're not in the business of coaching or teaching electronics.
Cheers
As cd-i ponts out in post nr 14, all turns ratios are specified on the schematics.
If you are trying to "build" T1, or are in any way unclear about what it is, I'd strongly reccommend against taking on such a project. Any small mains transformer that puts out +/- 10 to 18 Vac at .2 A will do here.
T3 is a Coilcraft part nr, referenced in post #55.
For T4, the authors give you the nr of turns and core type.
L1 and L2 are common toroid inductors, 8 Amp wire, something between 100uH and 300uH, value is really not critical.
L3, the common mode choke, is again not too critical, since it mainly serves to protect the mains from pollution by the SMPS. It has been referenced in posts #51 and 52. You can probably substitute another common mode choke that has wire thick enough to take 10 Amps, at least for testing purposes.
If you wind your own, noone can tell you how many turns to wind, since they don't know what permeability core you will use. You may need an inductance meter to get the value right.
There is a clear risk of injury in building this, and you really have to know what you're doing.
You need to ask yourself the qustion: Can I put a scope to this thing and troubleshoot it, if it doesn't work the first time?
The manufacturer is under no obligation to provide any support information to individuals not buying their kit. They mentioned on another board that they get many novice questions, which they have to ignore, because they're not in the business of coaching or teaching electronics.
Cheers
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