Hi, I'm designing a "minimalist" amp and I need some sort of circuit that will amplify voltage for the input stage without nasty coupling capacitors and operates in class A mode. No current will be flowing out of the circuit.
Tried a simple common emitter circuit but seems like you need the input capacitor for it to work properly.
I know I could use a class AB push-pull configuration but darn it I want it pure class A.
Tried a simple common emitter circuit but seems like you need the input capacitor for it to work properly.
I know I could use a class AB push-pull configuration but darn it I want it pure class A.
You could try using nice coupling capacitors. Or, as it will be running with no output load (so no output current), just don't bother to attach the input signal.
You could use an op-amp with a split supply, and accept any DC offset it produces. That way, at least all those nasty Cs and Ls will be hidden away in the PSU.
You could use an op-amp with a split supply, and accept any DC offset it produces. That way, at least all those nasty Cs and Ls will be hidden away in the PSU.
I don't understand "no current will be flowing out of the circuit" !
So what do you want this amp to drive ?
The CD4069UB looks like it is class B above 0.25µA at 25°C.
http://focus.ti.com/lit/ds/symlink/cd4069ub.pdf
http://focus.ti.com/lit/ds/symlink/cd4069ub.pdf
all internal stages of op amps run Class A
all op amps have some bias current in the output Q, so for small enough load all op amps can operate push-pull Class A
typically this may be as small as 100 uA but a few are known to run "hotter"- the AD797 and LT1x28 both use 500 uA output Q bias which gives +/- 1 mA Class A
then there is always the option of single ended Class A output bias with a current source - or even just a resistor to a rail
just load the op amp with several times the desired output I
you can bias 2 paralleled output op amps with many mA deliberate offset current running through the "current sharing" resistors
if you go for CFA op amps developed for A/DSL service you can get >100 mA Class A output this way
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I believe you can avoid capacitors if you use a bridge design, where the two ends of the speaker are attached to single ended amplifiers both amplifiers consisting of an active element fed from the same supply rail via constant current sources. In this case there is a constant current draw through the supply at a constant voltage and theoretically you can avoid any a.c. flowing through a capacitor.
Take a look at Nelson's Balanced Zen line stage for something close to this (replace load resistors with CCS). Perhaps it might even be a starting point to solve the problem raised at the start of this thread ?
Because it is smoothed due to their size and the PSSR of the amplifier circuit....They are in the signal path as they serve to stabilize GND...I believe that that is a major reason why the PSU caps contribute so much to the performance of the amplifier.
GND stability is vital....It's like bouncing a ball on the floor...it just works better on something solid than on a soft carpet...
GND stability is vital....It's like bouncing a ball on the floor...it just works better on something solid than on a soft carpet...
Make sure you read post #20 and post 27#, #38, and #39
http://www.diyaudio.com/forums/soli...r-subjective-objective-views.html#post2200623
http://www.diyaudio.com/forums/soli...r-subjective-objective-views.html#post2200623
If the PSU capacitors are in the signal path, then at low frequencies the whole national electricity grid is also in the signal path. The problem is that 'signal path' is not always a helpful concept; it seems to lead to misunderstandings.
I'm not sure what is meant by "GND stability". Provided the input, output and feedback are all referred to the same potential (i.e. a single point) it doesn't really matter what that point is doing relative to some other point. Most ground problems are about reference being to different points, when they should be the same point.
I'm not sure what is meant by "GND stability". Provided the input, output and feedback are all referred to the same potential (i.e. a single point) it doesn't really matter what that point is doing relative to some other point. Most ground problems are about reference being to different points, when they should be the same point.
Why do we need PSU caps? To provide a reasonably smooth DC supply voltage. The cap has to be big enough to reduce ripple to below the level required by the amps PSRR, and also to prevent voltage droop between charging pulses dropping the supply too low to accomodate the required signal voltage.
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