Thank you @atmasphere , skimmed the linearaudio link, will delve in later. Looks like it will not be that hard to follow.
In addition to what you write, is not the negative in negative feedback, simple because it is subtracted?
Can a Amp be "timeless" and compete with todays amps?
I’ve been into hi resolution audio for 20+ years, well longer than that but acquired high quality gear about that time. I veered off into other interests for 15 years but still had my system sitting idle in it’s dedicated room. I became interested in it again 6 months ago and began to update it. I still have my Rega Planar 25 table and a Dragon phono stage. I retained my CEC TL1 transport, but replaced my DAC with a Dinafrips Venus II, I also have the Hermes DDC which I feed my CEC into as well as my Cambridge Streamer. I sold my Genesis V speakers because they were having an issue with the left channel bass and since they were out of business I had no way to fix them, it was over my head. I found someone that wanted them and was willing to repair them himself. (he is very happy with them) I replaced them with some Goldenear Triton 1.r’s which I love. So here is the nostalgia part. I still have my VAC Cla 1 Mk II pre amp and my VAC Renaissance 70/70 Mk II amp. I feel they still hold up well sonically, so my thoughts are to send them both to VAC for the Mk III updates this fall of 2022, which includes replacing any necessary parts and "voicing" them back to new as intended when they were first made. I really believe these pieces are worthy of the restoration, are newer pieces today really going to make much headway? I cannot afford to replace these items with "like" items as I am retired and the discretionary income isn’t there anymore. I just feel like they are still really good and offer a very high quality sound. I mean 8- 300 B tubes can’t be all that bad can they? I’ve voiced the pre amp with with Telefunken 12AX7’s and I have a small stash of them. Tube sound is still great right?
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If I get your meaning, probably not. In most amplifiers the feedback is applied to a node that has non-linearities, so often feedback signal itself contains distortion not present at the output! For example in a typical solid state amp, the input circuit is a differential amplifier. One of its inputs (differential amplifiers have two, one inverted and the other non-inverted) takes the signal. The other takes the feedback. But the device (transistor) isn't perfectly linear... Of course, if you applied enough feedback, you could overcome this issue... |
No I meant in a much more simple fashion, i.e. a portion of the output is subtracted from the input. Literally negative. It would technically be out of phase but that is by definition. When @teo_audio writes positive feedback, does he really mean feed forward? |
Yes- we use a resistive divider network to do that in our smaller OTLs (we run 2dB of feedback in the M-60). You either do it that way or thru an active device, such as a tube's cathode while the input signal is applied to the grid. But the feedback network itself can be simple or complex, depending on (...how well its designed...) the expectations for it, such as keeping unwanted frequencies out of the loop. For example in a class D amp that is self-oscillating, the feedback network defines the oscillation frequency (known as the 'oscillation criteria') since so much feedback is applied that the amp goes into oscillation as soon as its turned on; the amp then uses the oscillation as the switching frequency. That network can be a 4th or 5th order loop with 6 or 7 variables; for that you'll need a computer to sort it out. |
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