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Old 9th June 2005, 06:21 PM   #21
vAD is offline vAD  Russian Federation
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Today, I have seen (have prompted), that the circuit 1 --- 37 times, the circuit very simple 18 times
The big request to all who download circuits, do not collect, read a forum, in circuits it is a lot of discrepancies.
Which I ask to comment on all circuits were collected on breadboard models, and it does not mean that they of 100 % will work for you.
So for example very simple, I today have changed under recommendations ilimzn, many thanks, but all the same is push DC at inclusion and deenergizing
( did not pay attention!!!!!!!!) it is long balanced . Floating feed OPamp provides scope Uout OPamp approximately equal to a Vrail. For this reason it is chosen. I try to result it in 100 % stability.
Very much I ask do not leave(abandon) me, I one am engaged in all it, and there is nobody to communicate nobody understands. Work is far from electronics.
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Old 13th June 2005, 05:35 PM   #22
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All Hi ! I ask the answer to a question, the resistor in base BJT, should transfer(translate) it(him) in a mode of the amplifier of a current
Whether so it?
And how it to be reflected in a sound?


Many thanks deleveld
Many thanks darkfenriz
And many thanks ilimzn
For your comments,
Soon I shall collect final variants of amplifiers. I shall try to provide 100 % stability
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Old 15th June 2005, 05:48 PM   #23
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Please. Two more circuits . Please comment
Attached Files
File Type: zip op_lateral.zip (25.3 KB, 82 views)
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Old 15th June 2005, 05:51 PM   #24
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Two
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File Type: zip 3f_diff.zip (36.4 KB, 75 views)
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Old 15th June 2005, 09:43 PM   #25
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OP lateral
this is interesting topology, pretty uncommon but works nice with fast enough opamps. The only problem is the fact that you cannot fine adjust biasing of the output stage-it depends on opamp biasing which may vary even with the same opamps.
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Old 15th June 2005, 09:54 PM   #26
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3F diff
interesting, you probably don't need R60 & R61
I guess you keep output stage in class A?
It may need freq. compensation also, maybe not..
source resistors are pretty high, damping factor will be less than 30, maybe even less than 20, but some don't bother.
I see your head is full of fresh ideas-keep on.
regards
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Old 15th June 2005, 10:18 PM   #27
ilimzn is offline ilimzn  Croatia
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OP_lateral: used this one myself, and stopped precisely for the reasons Darkfenriz mentioned.
In real life TL071 would be completely inadequate for this as it is not possible to reliably drive 330 ohm loads with sufficient current to open up either output transistor. Keep in mind that you need about 6-7V there, across 33 ohms, which means 212mA - well outside what the TL071 can do. You would need to increase the 33 ohm resistors.
Also, take a look at R21 and R22 - these really do nothing except increase the open loop output impedance of the amp and drop voltage from the rails. Since your driving signal from the OPamp is it's output current, the drop on the 33 ohm resistors remains the same regardless of the voltage on the 0.22 ohm resistors. Therefore, these are not inside the control 'loop', so they do not degenerate the output transistor gain, nor do they thermally stabilise the circuit.
It is possible to adjust idle current by means of applying an adjustable current source between Q1 and Q2 emitters. Depending on what MOSFETs you use, this current source also needs to be thermally compensated.
A possible permutation of this circuit results in the output working in current feedback mode. The feedback is then connected from the output of the whole amp, to the output of the OPamp. The voltage feedback for the OPamp is then connected to the output of the OPamp, and sets amplifier input sensitivity. An arrangement where the DC voltage feedback is connected from the output of the whole amp is also possible to reduce output offset voltage.
It should be noted that in current feedback mode, it is possible to cinfigure the OPamp for effective non-inverting gain less than 1. Some OPamps distinctly dislike this and will become unstable. LF351 would be an example - from experience with a very similar design of my own.

3diff:
What Darkfenriz said, plus the following:
As you are running the amp without global feedback, you will need to run the outputs at a fairly high bias - I'm just now playing with a similar output topology, but in my case I have only one output pair and no source resistors. I still need over 100-250mA of idle current.
One thing that REALLY needs to be changed is this: The 10k pot to set output idle current MUST be a Vgs or degenerated Vbe multiplier. The chosen output transistors will have a positive temperature coefficient of idle current even with 1 ohm source resistors, which means that there will always be a measure of thermal runaway potential. Many people suggest that this is not the problem if the ehatsink is large enough, but I'd rather design it properly and independent of heatsink size for runaway potential. You do not want your idle current wandering all over the place, it needs to be stable, or, considering the gm of the MOSFETs increases with temperature for current below some 12-14A, it may even me beneficial if the idle current decreases slightly with temperature.
Possible improvements:
Replacement of R5 and R6 with current sources. This will prevent bias current for M5 and M6 as well as output stage depending on the front end power supply voltage.
BC547/557 may need to be replaced with something with higher Vcemax in real life. It is good practise to plan on the input pairs to withstand the full supply rail to supply rail voltage - otherwise, if there is ever a failure, the input stage can get damaged in rather nasty ways, as in it works, but the transistors leak. I've fixed too many such amps...
You may also want to investigate merging R61/R40 and R60/R39 into a folded cascode configuration. Look at passdiy.com and find the A75 amplifier, for an example.

One more thing - since you are using a simulator, it is a good idea, once the amp simulates at default environment parameters, to try variations in power supply voltage, and especially temperature, and look at what happens. You may be shocked...
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Old 16th June 2005, 04:58 PM   #28
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thanks darkfenriz
thanks ilimzn
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Old 16th June 2005, 05:14 PM   #29
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Quote:
Originally posted by ilimzn

One more thing - since you are using a simulator, it is a good idea, once the amp simulates at default environment parameters, to try variations in power supply voltage, and especially temperature, and look at what happens. You may be shocked...
Really. Both circuits OP_lateral and 3diff are made only on a simulator, but 3diff was collected and worked 1 year, but with a global feedback,
Yes in real circuits are very far from a simulator, but the simulator gives an approximate picture it works whether or not.
The simulator basically is used for this purpose, and also for drawing circuits (conveniently).
Vgs multiplier - laziness to draw (excuse)
Op_lateral What OPamp is better for using.
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Old 17th June 2005, 09:47 PM   #30
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Quote:
Originally posted by ilimzn
Possible improvements:
Replacement of R5 and R6 with current sources. This will prevent bias current for M5 and M6 as well as output stage depending on the front end power supply voltage.
You may also want to investigate merging R61/R40 and R60/R39 into a folded cascode configuration. Look at passdiy.com and find the A75 amplifier, for an example.

Thank! Looked Pass A 75!!! Superb, anyone similar will be a copy.!!!!!
Replacement R5 R6 with sources of a current in my opinion negatively influences a sound
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