The only project I know is follow:
http://www.audiodesignguide.com/my/Follower_99c.gif
Commercial amp devices I haven't see until know
I am looking both class A and class A/B.
Thank you for sending more examples of unity gain amplifier models and diy projects.
It would be also very interesting a circlotron topology with mosfet's, i. e. a two transistor push pull unity gain power amplifier without complements, particularly as commercially available part.
http://www.audiodesignguide.com/my/Follower_99c.gif
Commercial amp devices I haven't see until know
I am looking both class A and class A/B.
Thank you for sending more examples of unity gain amplifier models and diy projects.
It would be also very interesting a circlotron topology with mosfet's, i. e. a two transistor push pull unity gain power amplifier without complements, particularly as commercially available part.
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This forum list 2 amps using the IXTH20n50d one is a circlotron the other is a simple single ended follower.
Two simple Current Amplifiers for low impedance loads
Two simple Current Amplifiers for low impedance loads
And have these been actually built and tested? (DC offset?????)
Don't believe everything you see on the internet.
Most manufacturers with reasonable design portfolios (Analog, Linear, TI, etc.) have op amp current boosters in an app note or two someplace. TI picked up AN-272 from National, for example. Years ago, with a bunch of help from tomchr, I got an improved variation of figure 1 there laid out with the Sanken STD03s as output devices. Never built it and probably the STD01s would be a better choice for loop gain. Similar op amp with BJT big shoes kind of schematics aren't terribly hard to find; ON has a few interesting fast BJTs in their audio portfolio and Sanken a few fast darlingtons. There's also a number of DIY Audio threads about how to follow an op amp with a VAS. I'm not sure anyone's ever followed through with a build, though for unity gain implementations it's probably not a concern.
Probably you're aware of parallel LME49600 implementations like the LPUHP and MPUHP projects here on DIY Audio. There aren't many higher current parts but the ADA4870 and LT1210 are starting points for similar designs with more consolidation of the output devices. The LT1210 doesn't come up much but there's a couple threads about the ADA4870.
I think an op amp MOSFET push pull, either circlotron or complementary, would be very interesting. Fast, high current, +-15V tolerant, linear op amps are around. So the potential for pushing FET gates seems good. Busy with some class D stuff and haven't had time to look much into transistor selection. Exicon, maybe.
Probably you're aware of parallel LME49600 implementations like the LPUHP and MPUHP projects here on DIY Audio. There aren't many higher current parts but the ADA4870 and LT1210 are starting points for similar designs with more consolidation of the output devices. The LT1210 doesn't come up much but there's a couple threads about the ADA4870.
I think an op amp MOSFET push pull, either circlotron or complementary, would be very interesting. Fast, high current, +-15V tolerant, linear op amps are around. So the potential for pushing FET gates seems good. Busy with some class D stuff and haven't had time to look much into transistor selection. Exicon, maybe.
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Have a look at
"The Class i output stage"
by Castor-Perry Kendalll
Linear Audio Volume 2
https://linearaudio.net/volumes/783
Note that it needs to be driven at low impedance,
an active volume control could do that.
"The Class i output stage"
by Castor-Perry Kendalll
Linear Audio Volume 2
https://linearaudio.net/volumes/783
Note that it needs to be driven at low impedance,
an active volume control could do that.
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Interesting approach - thank you for this advice.
Designing a low-distortion audio output stage - Part 1: Introduction, the problem with push-pull
The Class i low-distortion audio output stage (Part 2) | EDN
The Class i low-distortion audio output stage (Part 3) | EDN
The Class i low-distortion audio output stage (Part 4) | EDN
I am looking for commercial available amplifiers, where is in use only an unity-gain (resp. buffer-) stage (both preamp- resp. line-stage-units and power amplifier units, actually current amp resp. power follower units).
Unfortunately I haven't find such devices in serial manufacturing until this day (only as DIY project like Andrea Ciuffoli's power follower I know).
Thank you for your advices.
It's unlikely you'll find any; despite 75+% of the market not needing more than unity gain the manufacturers I've discussed the idea with have been pretty confident there's no market for such an amp.
Similar to class I is Doug Self's class XD. Arguably a more elegant approach in BJT space is John Curl's high bias class AB. That gets the output device fT up and allows more gain to be applied from the input pair, which has the advantage of both reducing crossover distortion and THD/IMD. The approaches are not exclusive but class I and XD mainly help with the former. Whereas if you get the loop gain high enough for negligible IMD often crossover distortion also becomes negligible with no extra effort. Such increased feedback is one of the reasons Bob Cordell argues for FETs over BJTs---more about that in his articles and power amp book---and is part of why I mentioned the parts I did a few posts above.
Unity gain amps do have the advantage that, if one's doing a discrete BJT output stage, one can select smaller and therefore faster parts since output currents and rail voltages are lower and less thermal handling is needed. Means a higher fT for a given bias and correspondingly more potential for loop gain. Also means lower thermal requirements for higher Curl-style biases.
Similar to class I is Doug Self's class XD. Arguably a more elegant approach in BJT space is John Curl's high bias class AB. That gets the output device fT up and allows more gain to be applied from the input pair, which has the advantage of both reducing crossover distortion and THD/IMD. The approaches are not exclusive but class I and XD mainly help with the former. Whereas if you get the loop gain high enough for negligible IMD often crossover distortion also becomes negligible with no extra effort. Such increased feedback is one of the reasons Bob Cordell argues for FETs over BJTs---more about that in his articles and power amp book---and is part of why I mentioned the parts I did a few posts above.
Unity gain amps do have the advantage that, if one's doing a discrete BJT output stage, one can select smaller and therefore faster parts since output currents and rail voltages are lower and less thermal handling is needed. Means a higher fT for a given bias and correspondingly more potential for loop gain. Also means lower thermal requirements for higher Curl-style biases.
that sounds like a lot of commercial amp components are on the marked.
Please let me know the most populare models (both pure class and class-AB) - thank you very much.
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I think Nelson meant: there's no known market for UNITY-gain power amps. (I doubt theaters do what was proposed.) However if tiefbassuebertr will contract to buy 10,000 unity-gain amplifiers at reasonable price, Nelson would consider the proposal.
Functionally you can make a unity-gain power amp out of a gain-20 power amp and a 20:1 attenuator in front. _IF_ I was stuck in a theater using unity-gain power amps, that is what I would replace them with.
Unity-gain presents some design challenges. We would really like the input to work with "small" signals, not be flying around +/-45V. And while I can't see any Natural Law to force it, NFB stability tends to work out easiest with closed-loop gain of 10 or 100; conventional unity-gain applications have to slug the life out of the amplifier for NFB stability, sacrificing slew-rate. (Can you spell "741"?) (OTOH LM310 Voltage Follower got good slew for the time by being unit-gain-only.)
Functionally you can make a unity-gain power amp out of a gain-20 power amp and a 20:1 attenuator in front. _IF_ I was stuck in a theater using unity-gain power amps, that is what I would replace them with.
Unity-gain presents some design challenges. We would really like the input to work with "small" signals, not be flying around +/-45V. And while I can't see any Natural Law to force it, NFB stability tends to work out easiest with closed-loop gain of 10 or 100; conventional unity-gain applications have to slug the life out of the amplifier for NFB stability, sacrificing slew-rate. (Can you spell "741"?) (OTOH LM310 Voltage Follower got good slew for the time by being unit-gain-only.)
Ok, this is DIYA and a lot of folks love their Rube Goldberg sound systems, especially if they are retired and have nothing else to do. I should be there but I'm not. After working with real electronics for decades, I'm just to frugal. I know that modular system cost a fortune and die a bankrupt death. So, the only "commercial" unity gain buffers you will find are "audiophile" projects because normal amps cost no more and you can distribute a line level bus easier than say +20dBm. I have invented a lot of things like "class-I" in bread board years ago and in spice today, but in the end it comes down to what is useful vs what can be done.
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