a few feedback classification schemes have been used over the years - circuit theory PhD have to publish something
"Current Feedback Op Amp" is a "trivial name" - popularized, understood but not strictly fitting a proper classification scheme - like the VAS/TIS "controversy" Trivial name - Wikipedia, the free encyclopedia
http://web.archive.org/web/20070128220917/http://people.ee.ethz.ch/~hps/publications/2000cas.pdf
for compensation there is also lots of literature - since audio power amps mostly use op amp toplogies - and some similar limitations like slower outputs
but I don't know of any universal classification/naming scheme - most options are amp gain stage topology dependent - you can find such awkward things as "Multipath Reverse Nested Miller Commpensation"
Cherry's Nested Feedback Loops do show a fairly "regular" structure for adding gain stages - but still is tied to amp stage topolgy/circuit implementation details
"Current Feedback Op Amp" is a "trivial name" - popularized, understood but not strictly fitting a proper classification scheme - like the VAS/TIS "controversy" Trivial name - Wikipedia, the free encyclopedia
http://web.archive.org/web/20070128220917/http://people.ee.ethz.ch/~hps/publications/2000cas.pdf
from: http://www.diyaudio.com/forums/soli...feedback-not-suitable-audio-6.html#post947696 - thread closed, original reference dead - I give a archive.org link
for compensation there is also lots of literature - since audio power amps mostly use op amp toplogies - and some similar limitations like slower outputs
but I don't know of any universal classification/naming scheme - most options are amp gain stage topology dependent - you can find such awkward things as "Multipath Reverse Nested Miller Commpensation"
Cherry's Nested Feedback Loops do show a fairly "regular" structure for adding gain stages - but still is tied to amp stage topolgy/circuit implementation details
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No: it's the difference (error voltage to use the correct terminology) between the input voltage and the feedback voltage (applied at the input stage's emitter) that drives the forward path of the "current feedback" amplifier.
No: you can affect stablity of a "current feedback" amplifier by adjusting the grounded element of its feedback network because so doing not only affects the amplifier's closed loop gain, but also affects the forward path gain of the amplifier.
Some difinitions for you Bonsai:
http://www.diyaudio.com/forums/soli...ck-how-do-i-see-difference-10.html#post423522
http://www.diyaudio.com/forums/soli...ck-how-do-i-see-difference-10.html#post423522
Hi guys
You asked for it, now you have it: CFB to VFB
Do anybody consider inserting nonlinear BJT part to FB path as an improvement?
Step No. 3. kills the sound!
P.S. Use step No. 1. It plays music.
Regards
I could be sorry to go in technical discussion with you as you just do not support your arguments with any simulations or measurements and you don’t accept others oppinion, but let’s tray.
To argue like this is technically lame.
You can use so called VFB amp in inverted mode and than input signal and error signal are connected to the same BJT base.
Nope, I'm all good with what you have. This is your book after all and it is clear that you can't cater to everyone (from the very serious to the very relaxed in each of the diyaudio.com amplifier disciplines).
I am pretty much appreciative that there exists a relatively clear and single reference that I can look to when I stop mid-solder, scratch my head, and want to try to figure out what is going on in that part of the circuit.
I tend to do that a lot and it slows me down a great deal... (I have most parts for building a KT88 SE, a pair of KT88 PP monoblocks, in the last mine of a Mini-A in it's final stages for chassis and power, have a Chip-Amp halfway there, waiting for the ACA to get back into the store, and a B1 board is waiting in the wings next).
Hi Doug,
When you refer to the Blameless and its performance, can you point us to the specific Blameless design you are referring to, as shown in the Fifth Edition of your book, by Figure number?
Cheers,
Bob
As we speak about power amplifiers, one would hardly explain, according to post #160, why nonlinear part is better than a pure wire. Remember R2, R3 can be a very low resistance. Forget the simulations, use plain logic.
A few minutes after having sent my previous post, I edited it and suppressed the first phrase I wrote :
for a good balance in the input differential pair, voltage across each 4K7 should be equal, at around 2.35 V.
I think the value of the second 4k7, at the right side, is wrong, and should be much lower.
I think that the Mark Alexander CFA qualifies.Obviously the obs. Toshiba IGBT's are not avail, but a thought is to sub the Alfet Lateral MOFETs or use verticals too, as was shown in the old SSM2131 DS.
I have seen the same topology used in the Amber 3501 DA test sets O/P PA ckt, (NE5534, MPQ6842, MPSU07/57 BJT O/P's). It has an offset servo,LF411, as well.
Both implementations measure well. I would hope so, since one is used in a production DA test set that has some nice specs. I always liked this topology for it sheer simplicity.
I wonder how much that you have to change in the MA ckt to not be in breach of the Analog Devices patent? Is the Amber ckt in breach of the MA patent?
Rick
Lazy Cat,
Figure 2, you may move R3 to the left of the interruption, otherwise the amp output shall be almost null as T1 is just cascoding the CCS.
Do anybody consider inserting nonlinear BJT part to FB path as an improvement?
Yes, as its non-linearity compensates the non-linearity of the input BJT.
Refer to "Distortion in Low-Noise Amplifiers" by Eric F. Taylor Aug and Sep 1977, Wireless World.
Figure 2, you may move R3 to the left of the interruption, otherwise the amp output shall be almost null as T1 is just cascoding the CCS.
Do anybody consider inserting nonlinear BJT part to FB path as an improvement?
Yes, as its non-linearity compensates the non-linearity of the input BJT.
Refer to "Distortion in Low-Noise Amplifiers" by Eric F. Taylor Aug and Sep 1977, Wireless World.
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Here you can find a proper op amp model which op amp model the supply currents.Now that I am on to this MA CFA topology, I tried to pspice it and I could never figure out why it would not work. I do not know enough about pspice to figure it out, is it a model issue or is it a limitation of pspice itself or Rick does not know what he is doing
http://www.diyaudio.com/forums/soli...non-switching-need-revival-7.html#post2152844
As we speak about power amplifiers, one would hardly explain, according to post #160, why nonlinear part is better than a pure wire. Remember R2, R3 can be a very low resistance. Forget the simulations, use plain logic.
The transistor that is in the feedback loop can simply be seen as a buffer
wich is at the end of the amplifying chain , the effective summing node
being the other transistor junction , the one connected at the non
inverting input.
As such , it s eventual distorsion benefit from the whole available
feedback , not only the input stage loop gain but also the VAS
contribution to said loop gain , hence its distorsion will be extremely
low , in fact way lower than the one of the input transistor wich
remain by large the main source of non linearity in an inserted
differential.(read inserted in a chain , not in isolation)
I know the theory. The question remains. Do power amps need buffer in the FB path, since R2, R3 are few ohms?
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