Zero negative feedback

[smithomo]

Hi Friends,
I'm currently finding a new way to design my new integrate amp with zero negative feedback.
I heard some audio brands were design their amp like this.
What do you think about this kind of amp?
Have you ever listen the sound from this kind of amp.

I'm only afraid the base quality, because of high amplitude signal might not so well in case of without feedback.

Please feel free to share your think here.

[RayCtech]

Originally Posted by smithomo

Hi Friends,
I'm currently finding a new way to design my new integrate amp with zero negative feedback.
I heard some audio brands were design their amp like this.
What do you think about this kind of amp?
Have you ever listen the sound from this kind of amp.

I'm only afraid the base quality, because of high amplitude signal might not so well in case of without feedback.

Please feel free to share your think here.

"Zero negative feedback" have several different implications and does not tell the real truth as a statement without clarifications...

I believe the "zero negative feedback" term normally are referred to a setup without LOOP feedback, but with a lot of local negative feedback.

The local feedback factor are determined by the electrical parameters of the active device (Bipolar, JFET, valve) and the emitter / source impedance in some configurations and you may have a negative feedback factor of 10, 100 or 1000 etc..

The tradeoff with high local negative feedback (and thus low distortion) are noise etc..

[smithomo]

Hi RayCtech,
I mentioned on no loop feedback from output to input.
So there might be some small local feedback within transistor/JFET
Do you have any comment?

[RayCtech]

Originally Posted by smithomo

Hi RayCtech,
I mentioned on no loop feedback from output to input.
So there might be some small local feedback within transistor/JFET
Do you have any comment?

I have since the 70ties been using (my own designs) bipolar and JFET amplifiers with zero loop feedback.
Distortion below 0.005% and so low noise that you cannot hear it
Did a test in the early 80ties at a audio dealer:
Placed two identical Infinity loudspeaker sets side by side.
One set was not connected and one set connected to the amplifier with volume control set to maximum.
No music was played = silence.
All people did believe it was the un-connected speaker set that was connected to the amplifier as the noise level was highest.

The un-connected speaker set picked up room noise due to it was un-connected, but the connected speaker set was "shorted" by the noisefree and low impedant amplifier.

[smithomo]

Originally Posted by RayCtech

I have since the 70ties been using (my own designs) bipolar and JFET amplifiers with zero loop feedback.
Distortion below 0.005% and so low noise that you cannot hear it
Did a test in the early 80ties at a audio dealer:
Placed two identical Infinity loudspeaker sets side by side.
One set was not connected and one set connected to the amplifier with volume control set to maximum.
No music was played = silence.
All people did believe it was the un-connected speaker set that was connected to the amplifier as the noise level was highest.

The un-connected speaker set picked up room noise due to it was un-connected, but the connected speaker set was "shorted" by the noisefree and low impedant amplifier.

Oh Impressive.
Very good designed, interesting.
So what about feeling when you listen the music compare with NF design.
Have you published your designed somewhere?

[VladimirK]

I have built and listened to various GNFB and NoGNFB amps, and can share some observations.

The middle and high frequencies ranges are usually better with NoGNFB designs, especially if they have short signal path.
As for the bottom end, NoGNFB amps are a bit more difficult to match with speakers, irrespective of what output impedance they have. One gets impression of a bit not enough articulated bass. I guess, the reason can be in the preferences of speakers manufacturers, they usually use deep GNFB amps during speaker adjustments. Some kind of speakers will be perfect with NoGNFB amps, but there are not so much of them.

In the designs, having short signal path and low level and carefully arranged GNFB, the last does not make something bad for the sound, while the amp becomes more universal, it is easier matched to almost any speaker.

[homemodder]

I have come to the same conclusions as Vladimirk, for good bass with open loop circuits I find it helps to have a high current, exaggerated (for power Level) multiple output transistor circuit output stage.

[VladimirK]

Originally Posted by homemodder

I have come to the same conclusions as Vladimirk, for good bass with open loop circuits I find it helps to have a high current, exaggerated (for power Level) multiple output transistor circuit output stage.

In this issue, there is something more than simply the output impedance. My last low-level GNFB design, with paralleled jFETs at the output stage, in spite that has a bit higher Zout than NoGNFB disign, gives more articulated bass. It seems that NoGNFB designs, even with mass paralleled power BJTs, have some specific bass signature (I do not say that weak bass, just specific sound signature, a bit less sharply defined), that can be removed only by matching with definite kind of speakers.

[homemodder]

Originally Posted by VladimirK

In this issue, there is something more than simply the output impedance. My last low-level GNFB design, with paralleled jFETs at the output stage, in spite that has a bit higher Zout than NoGNFB disign, gives more articulated bass. It seems that NoGNFB designs, even with mass paralleled power BJTs, have some specific bass signature (I do not say that weak bass, just specific sound signature, a bit less sharply defined), that can be removed only by matching with definite kind of speakers.

Low level circuits are a whole new ball game as they are not driving 8 or 4 ohm speakers.

I tried mass paralleled power BJTs or mosfets as this is the route taken by designers such as Charles Hanson and recommended by John Curl, I ve come to agree with them that it helps.

[Bigun]

Perhaps what would give a good combination is a bi-amping, where the mids+highs are without loop feedback and the bass is with loop feedback. This has been my thinking of late and I am planning a tube amplifier along these lines.

I do feel that the requirements of the mids+highs and bass are different, the speaker drivers are different with respect to their impedance and back emf, and the nature of music transients places some big demands on the bass that are not so common with the highs. Separate amplifiers seems to me a good route for DIY - gives us a reason to build more amplifiers