Old fashioned simple preamp

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I am thinking about a little bit different approach. What would you think about circuit like this?
 

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I think it's quite clever.

Since you are using gnfb, have you considered replacing R6 with a CCS to improve PSRR and increase fb factor?

I quite like the cap coupling, because my experience is that if you DC bias these caps, the caps sound much better.

The EF output load R7 would tend to add H2; you might consider a CCS here too.

Hugh
 
As far a I can see, this circuit would not be able work properly :( . DC conditions would be OK only if R4 is very large and that would in turn create potential problems with the feedback arrangement and amp bandwith, rendering R10 useless. It won't be very stable with temperature as well.

Did you try to simulate it?

Cheers

Alex

P.S. - Dont get me wrong - I like this kind of topology a lot and used this extencively in the past. For instance all MM/MC preamps I've done for Creek did use very similar arrangement of transistors :) - but with no NFB except local, thought.
 
PMA said:
We are having fun here, aren't we?

Absolutely. Here is a (rather poor quality, sorry) phono stage circuit I've done for Creek in about 1994 . It was released as OBH-8 stand alone MM preamp and also was used in Cambridge Audio A3i amplifier as well as in many Creek integrated amps as a plug-in.

Cheers

Alex
 

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PMA said:
Hi Alex,

excellent!
(somewhat different circuit, as you have said ;) )

P.S.: anyway, your 3rd harm. is higher than mine ... ;)

Pavel, in any case we can not compete to the circuit I attach here, by Michael Kulish from Russia. I made two simulations, one with and one without an output follower, both under the same conditions - 10 kHz, 1 V RMS output, 9dB gain. It is an excellent application of an error-correction way of linearization in a very simple circuit. It works in real life too :) .

Cheers

Alex
 

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x-pro said:

Hi Pavel,

here is a result of my simulation with 3 transistors and local NFB only

Cheers
Alex

Hi Alex,

though it is maybe not apparent, as the component values are missing, the circuit I posted had also local NFB only. Gain is completely defined by R6/R3 (with respect to hFE, off course). R10 is very low in value and can be omitted completely. R4 is just biasing resistor and its value is like 10M. Input impedance is quite high (about 1M) and R4/R10 do not constitute global feedback.

Cheers,
Pavel
 
x-pro said:


, by Michael Kulish from Russia. I made two simulations, one with and one without an output follower, both under the same conditions - 10 kHz, 1 V RMS output, 9dB gain. It is an excellent application of an error-correction way of linearization in a very simple circuit. It works in real life too :) .


Hi Alex,

hereby what I got from the Kulish circuit. No follower and no load. Excellent result, however.

P.S.: I have to add that this is for source impedance of 1k. Distortion very quickly rises with Zout of the signal source. This is very very different from my circuit, which yields quite same distortion even for 100k source impedance.
 

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anatech said:
Hi Alex,
Try to simulate a real world load on your outputs and rerun the sims please. I always find unloaded measurements much more promising than loaded ones. Some circuits are much better than others in this respect.

-Chris

The distortion of this circuit is load-independant without the output buffer, only the gain will change if you connect load (with a coupling capacitor) to the (out2) of the second (unbuffered) circuit.


PMA said:
P.S.: I have to add that this is for source impedance of 1k. Distortion very quickly rises with Zout of the signal source. This is very very different from my circuit, which yields quite same distortion even for 100k source impedance.

I've just copied the values from the original article. Transistors here are run with high currents so the input impedance is fairly low. You may increase the resistor values and reduce that effect thought 10K distortion would rise a bit. Also this is an error-correcting circuit and as such requires balancing of the correction - as you may see I had to adjust one of the values to partially compensate for the buffer distortion. In the same way it is (I think) possible to compensate some of the imbalance due to the source impedance if it is constant.

Cheers

Alex
 
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