Jan,
I believe you are correct; current feedback traditionally refers to feeding back a sample of the current flowing in the load, as opposed to the voltage applied to the load. Some tube amplifiers of long ago used current feedback to achieve adjustable damping factor. I think the Leak was one of them.
Cheers,
Bob
I don't think any LEAK (or QUAD or Radford) amp had adjustable damping factor .. but I was only there on the last of their transistor days.
But I did do some Blind Listening Test experiments when we discovered an old LEAK TL50 sounded better than modern transistor amps and better than a LUXMAN tube amp which was all the rage in the UK at the time. Adding a 1R power resistor in series with the output brought a lot of the 'valve' sound to a big transistor amp.
I think Bob Carver found something similar from his Stereophile Challenge.
It rated only 100w with 8pair of 120W OPS,
It has 2Amp fastblow fuses protection along with kilowatts power supply.
Yes, I was talking about the tube Leaks of the 50's and early 60's. Guess I'm dating myself, but I lusted after that kind of stuff even in the early teens.
Many people have noticed that the addition of a small resistor to the output of a solid state amp makes it sound more tube-like.
Cheers,
Bob
Unfortunately, reality is always the final arbiter. The reputation of this gear completely collapsed in Australia - there were far too many horror stories ...It rated only 100w with 8pair of 120W OPS,
It has 2Amp fastblow fuses protection along with kilowatts power supply.
Because the change in damping factor, or effect on non linear impedance curves of speakers ?
The two are intimately related. There are 2 major effects.
Firstly, 1R output Z is enough to make frequency response wonky cos the impedance of most speakers isn't flat.
But even if you take care to get a flat impedance curve, (like Christophe) moving coil speakers have slightly less LF distortion when driven from a finite Z.
In most cases, the 1st effect is the important one as most speakers are designed assuming zero Zo.
Your speaker may sound better with a valve amp but it wouldn't sound like the designer intended.
BTW, valve amps are dead. Since Mullard & GEC closed their UK factories, only evil tubes are left. 🙂
Is this the case with any SS amp ? I guess we are talking about the Bass or does this affect the amp across it's bandwidth...?
If so it's easy peasey, put a switch on the front panel ... SS or tube sound ...
🙂
Bob Carver did exactly that with some of his later amps.
The effect is across the board. But as most speakers have their biggest change in Z at LF, the most audible result is usual at LF.
I dunno why, but never tried that. On the contrary, spend a lot of money with huge low r coils. Well, it change the Q factor, so the bass reflex tune, so can be a long work to get experience (don't read this word, Wally) of various output impedances.
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I believe you -- but Like I said what is allowed/shown in schematics from them you cant tell what they did and the circuit description in the manual says differential input with CCS etc. And, it is not direct coupled in the feedback path-- it is at the I/O. Etc. It no doubt sounds great. I think we are doing better today and from what I see here at DIYAudio.. a lot better. Save your 4000E and build one of these here.
Thx-RNMarsh
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Possibly.... I think we are all starting to get the picture.
Take a Dynaco PAS2-3 preamp... output fb resistor taken back to the cathode of input tube. CFA? Only if you wish it to be.
Factoid -- the diamond configuration - specifically the diamond buffer was not invented by Panasonic. Though they may have some claim to another diamond variation. The Concept was 'invented' by Baker at MIT in 1963 and published in IEEE papers.... so Panasonic or anyone could use it. Variations et al is the area of patents. My variation/contribution was to take the CFA or compound complimentary push-pull circuit and configure it into a DC/Direct-Coupled configuration and later added ['invented'] the concept of a dc servo. My 5 minutes in the sun. There are many DC variations and many servo variations.... many are better than the original.
Lets get back to the solid state, modern CFA topology and description.
Contrary -- that CFA are harder to compensate?.... they have been shown in my experience to be easier when adding in the HF low distortion at the same time. Can this be elaborated on for everyone's benefit?
Thx-RNMarsh
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For those interested here is the article from Nov.1954 describing E.V. A20 tube amplifier circuit which use variable damping factor , achieved from variable voltage and current feedback amount insertion on input tube cathode .
The first time I saw the original cf was in controlled slew-rate drive amps for gun turrets (yes, I'm even older than you are, hard to imagine 😉) .
Control the current into a cap and you have controlled slew rate.
Jan
No matter. Just the other day I got into a discussion with someone about a 'transparent amp that changed the sound'.
Huh? How can something that is transparent change anything? Transparent is, well, you know, what goes in comes out, like, 'transparent'?
After some to and fro he stated: 'Ohh but I don't use transparent in the usual sense - I separate it from 'accurate'.
He didn't tell me what his use of transparent was, and I didn't ask as I realised at that point that communicating with people who attach their own unique meaning to otherwise uncontroversial words is rather tiring if not pointless...
I understand the use of CFA in the current (no pun intended) context, and use it myself. But as the linked article shows, it is completely different from the original definition. It did frustrate me initially, but hey, I'll go with the flow. Still these things do intrigue me.
Many more examples: 'the new part is shipping'. Huh? Shipping is a verb, a part can be shipped, but it's the manufacturer that does the shipping, NOT the part. And so it goes.
But I may be handicapped in this because speaking a handful of languages you tend to note and compare these things. Being an editor doesn't help either.
Sorry to bore you with it,
Jan
First, not everyone use English in his daily life.
Second, intelligent people can well read between the lines.
Third, what is a word. Think about it. Many high end speakers are "detailed", "resolving", but not "accurate". What is accuracy anyway if one only can think of THD as the only measure of accuracy. African woman is more similar to Chinese woman than African woman to African man.