Why would you want to? The design you showed is a crude version of the old Texas Instruments output stage, and only needs an op-amp to drive it.
One thing you could do with a 'gainclone' iif you really wanted to make an amp capable of driving lots of current into a low impedance load would be to use the amp as the 'control amplifier' together with a pair of really big output transistors in a 'current dumping' configuration.
One thing you could do with a 'gainclone' iif you really wanted to make an amp capable of driving lots of current into a low impedance load would be to use the amp as the 'control amplifier' together with a pair of really big output transistors in a 'current dumping' configuration.
No! Adding an output stage like that defeats the purpose. The o/p stage shown in the schematic only needs a few mA of drive, so using a 3875 or similar doesn't do anything useful. Now adding a simple PNP and NPN, together with the appropriate passive components to make a 'Quad style' current dumping stage is a much more interesting concept. (My opinion only of course!)
In the circuit do you think there would be any crossover distortion ,I intend to use it only for a sub woofer.I have tried gainclone for sub woofer but dont feel they can supply current,dont get me wrong I think they are great for mid and highs like a sat sub system
If you look at the schematic, you'll see that Q1 and Q2 have no forward bias, so the amp is relying on the global NFB to reduce the crossover distortion. The original Texas app-note design from way back had a proper biasing for this part (I can't find a schematic on the web, but in the UK it was originally publisehed in Practical Wireless magazine in the 1970s). The o/p stage has a gain of x4 (roughly) and that type of o/p stage can have a tendancy to oscillate.
For a low-frequency amp only, the NFB probably operates fast enough to minimise distotion, but crossover distortion is hard to remove by a simple overall NFB loop. Adding a conventional Vbe multiplier between the bases of Q1 and Q2 will help, but quiescent current stability will be hard to manage unless you also add a couple of low-value resistors to the output transistors as well.
For a low-frequency amp only, the NFB probably operates fast enough to minimise distotion, but crossover distortion is hard to remove by a simple overall NFB loop. Adding a conventional Vbe multiplier between the bases of Q1 and Q2 will help, but quiescent current stability will be hard to manage unless you also add a couple of low-value resistors to the output transistors as well.
In my attached circuit
LM3875 provides current alone below +- 2 Ampere output.
At about 2 A output (0.7 Volt across R1/R2) the power transistors start to conduct
and help IC with current.
At 5 Ampere output LM3875 will output 2 A and transistors 3 A.
This is theoretical idea of operation.
To make it work in a real circuit, may need some additional considerations and components.
I have seen a circuit like this published in Elektor long ago.
That circuit used a TDA2030 audio amplifier chip.
LM3875 provides current alone below +- 2 Ampere output.
At about 2 A output (0.7 Volt across R1/R2) the power transistors start to conduct
and help IC with current.
At 5 Ampere output LM3875 will output 2 A and transistors 3 A.
This is theoretical idea of operation.
To make it work in a real circuit, may need some additional considerations and components.
I have seen a circuit like this published in Elektor long ago.
That circuit used a TDA2030 audio amplifier chip.
Attachments
Yeah, that sort of thing can work well. I think usually there's a capacitor between pin 4 of the chip and the output (rather than the direct connection), and a dummy load (perhaps 100 Ohm) from pin 4 to 0v.
The only issue would be to select the value of the sense resistors to bias the output transistors just below the point at which they start to draw current.
The only issue would be to select the value of the sense resistors to bias the output transistors just below the point at which they start to draw current.
Probably you mean this schematic. It uses cheap IC's and transistors.
Power:
2x6V/1x12V = 5W @ 4Ohm, 85mVeff input
2x6V/1x12V = 10W @ 2Ohm, 85mVeff input
2x12V/1x24V = 40W @ 4 Ohm, 211mVeff input
2x12V/1x24V = 80W @ 2 Ohm, 211mVeff input
2x18V/1x36V = 100W @ 4 Ohm, 330mVeff input
Grtz, Joris
Power:
2x6V/1x12V = 5W @ 4Ohm, 85mVeff input
2x6V/1x12V = 10W @ 2Ohm, 85mVeff input
2x12V/1x24V = 40W @ 4 Ohm, 211mVeff input
2x12V/1x24V = 80W @ 2 Ohm, 211mVeff input
2x18V/1x36V = 100W @ 4 Ohm, 330mVeff input
Grtz, Joris
Attachments
I have built very similar schematic(probably even the same) as a DIY kit several years ago.The sound quality was not so good.
That bridge with two TDA2030 uses same technique.
Here is another 120Watt in 2 Ohm using two TDA2030:
http://www.kruetronik.de/info/elektronik/wissen/schaltungen/2030verst.gif
But it was another Elektor project using one TDA2030.
Most of the power is delivered by those transistors.
As the IC does not work very hard, you get lower distortion at high power,
than if IC has to work close to its limits.
The project I think of is more like this circuit I found on the web:
Here is another 120Watt in 2 Ohm using two TDA2030:
http://www.kruetronik.de/info/elektronik/wissen/schaltungen/2030verst.gif
But it was another Elektor project using one TDA2030.
Most of the power is delivered by those transistors.
As the IC does not work very hard, you get lower distortion at high power,
than if IC has to work close to its limits.
The project I think of is more like this circuit I found on the web:
An externally hosted image should be here but it was not working when we last tested it.
Depends on how we adjust the resistors at transistor bases.
As long as the output transistors does not work in class a
then we need not to worry about thermal runaway.
Because they will be both turned off at the crossover level.
As long as the output transistors does not work in class a
then we need not to worry about thermal runaway.
Because they will be both turned off at the crossover level.
Hi there Mr LineUp,
Thankyou,
have you try one of those schematic?
what is the critical point of these amp? THD?
I'm just finish my proto, ptp, something like post no. 9, superbridge but with parts which are i already have lm1875, tip2955/3055.24VDC.
sounds nice, like strong lm1875, only a bit stronger and sounds nicer than my ss amp (MJ15003/15004) without any pre. friendly warm..
just considering, this worth for more improvement ( by changing ICs or Transistors) or just enough..
Thankyou,
have you try one of those schematic?
what is the critical point of these amp? THD?
I'm just finish my proto, ptp, something like post no. 9, superbridge but with parts which are i already have lm1875, tip2955/3055.24VDC.
sounds nice, like strong lm1875, only a bit stronger and sounds nicer than my ss amp (MJ15003/15004) without any pre. friendly warm..
just considering, this worth for more improvement ( by changing ICs or Transistors) or just enough..
I wonder the output buffer circuits in #7, #11 and #12 are faulty ? Can the output of the TDA2040/LM3875 and of the push-pull emitter-followers be "combined" ?
Do these negative feedback output + emitter-followers circuits really work ? Any measurements or SPICE simulation ?
Do these negative feedback output + emitter-followers circuits really work ? Any measurements or SPICE simulation ?
using output device with NS amps , LM387X/388X is possible
with an adequate implementation that would still be simple ,
yet, the added transistors would be protected by the current
limiting circuitry of the IC if the circuit is designed the good way..
it has been done, a few google search should yield some results...
with an adequate implementation that would still be simple ,
yet, the added transistors would be protected by the current
limiting circuitry of the IC if the circuit is designed the good way..
it has been done, a few google search should yield some results...
For a current-hungry application, I would try two or more chipamp-based amplifier circuits in parallel, all inside the feedback loop of an opamp that's driving their paralleled inputs. You would need to also use a very low value resistance in series with the output of each chipamp amplifier circuit; maybe 0.1 Ohm (probably rated at 2 or 3 watts or more, and non-inductive. [Power dissipated = current squared divided by resistance])
With enough paralleled chipamps, you can drive just about anything, really well.
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