No global negative feedback

David,

Sorry but my Mac just shows gibberish when I download that from HFC. Now admittedly there are those who say that this par for the course with that particular publication, but would it be possible for you to paraphrase?

 

Sorry, but YOU didnt get it, I got it very well, and answered appropriately...

 

hmm. I knew I shouldnt have bothered.

 

Depends on your intention...

Are you saying that good components allways sound good, regardless of setup...


Are you also saying that a system that doesnt show differences between cables has good resolution...

 

Robbo,

Don't bother-really. Antonio is gifted he just has different priorities.

Antonio, there's nothing wrong with liking some additional harmonics - if that's what you want go ahead. I seem to remember you were using Rel subwoofers which obviously add copious amounts of harmonic distortion as well. Quite possibly a pointer as to your preferred system characteristics.

But I would personally look for a system built to offer a good level of benign distortion rather than trying to modify a competently designed one.

 

Just as an aside, I don't think you will find that I have said all cables sound the same at any point - that's just in your imagination.

I have told you that differences are just that - audiophile cable manufacturers manipulating the sound and relying on marketing to convince the gullible that these slight sonic differences are in fact improvements. A truly high resolution system will show that they are simply tailoring the sound, and a truly high resolution system ruthlessly exposes any component's attempts at tailoring for what it is.

 

Mic,

You know better than me, I hope, the "constrains" of comercial designs, they must cope with a wide range of other components...

You also know that most can be improved, unfortunatelly I dont have the knowledge to do more than some simple mods...

If you think, like I do, that fullrange speakers, without crossover, are usually easier loads for the amplifier, than NFB becomes less needed with such speakers...

Then we get into the discussion wich distortion is worst, if you manage to read the link posted by dcathro, you will see that I didnt invent anything, on the contrary, it has even been proved with blind tests that NFB distortion can be worst than its benefits...

So, we both accept distortion, we both choose what pleases us more, what is the problem...

As for the cables subject, I have the feeling you always align with the ceptics, as for any other tweaks...

 

I do use 2 REL Strata III in Cascais, my "old" system, they integrate well with Sonus Faber EAII / BelCanto eVo 6 bridged...

Now I use one B&W PV1, wich integrates even better, with my fullrange speakers / tubes (no NFB)...

Again, you mention distortion, you must use those Japanese amplifiers with 0,000000 distortion, not for me thanks...

I like the sound of both systems, but the new system, 1/3 cost, sounds better, more accurate, IMHO...

 

antonio, it is easy to stick with what seems to be obvious from someone's words. i think that mike's repeated message in numerous topics on cables, tweaking and similar discipline was: get your cruical components right - speakers, amps, source (in that particular order if i am correct) - and there will not much left to fiddle with, but if you want to fiddle, do it.

the cables' participation to overall sound quality is not to be denied, but it is nowhere near what above do.

i made an effort to understand and experience all the importance of cables, i have rather revealing system by usual audiphile standards, i've heard differences between the cables easily... my simple conclusion is unless you've committed an obvious mistake in coupling something completely wrong in electric terms - like when i plugged a highly resistive vdh cable between my preamp and the speakers, killing HFs - most of the changes are forgettable the next day, in comparison with effect you get if you change your preamp or other critical component for example. i was overwhelmed with chord signature (£450 if i am correct) during 2 weeks in my system. i had no money to buy it, i plugged cheap mogami 2792. i forgot chord the same afternoon.

i've heard and seen very expensive systems using really cheap wires, such as mogami or oechlbach 1017 speaker cable. both costing probable less than 1 screw in the chasis of a MBL amps they were plugged in. you can say it is a show-off, maybe, but is just worked and that's all that matters.

last but not least - the same as with zero feeback or whatever is the topic - this forum is a great place because it lets us - who know less than others about particular practical issues - to learn quick and efficient and avoid wasting time and money on a useless practice.

that's why i beleive it would be great to keep and preserve a relaxed atmosphere on ZG and avoid barking at each other whenever a glitch or disagreement occurs. i feel that the most of communication, opinions and advices here are really friendly and generous in sharing knowledge and experience.

 

Right David, I managed to download that on the PC so I had a good read and there are a number of points.

Firstly Antonio, the so called blind tests you mention were carried out 32 years ago, and do little other than highlight the unreasonable amounts of NFB being employed by early solid state amplifier designers to cover up switching distortion artefacts. Properly implemented NFB is benign, as can be proven by the fact that this "experiment" has not been reapeatable in over thirty years!

Secondly, Martin Colloms is a hifi reviewer. The article is little more than a list of subjective experiences, and as such I cannot take it seriously. After all, this is the same guy who thinks that the latest Naim CD players are groundbreaking. They are not IME, and there is certainly nothing in the way of objectrive data to support his opinion on those players.

Finally, it is entirely feasible that MC did indeed hear differences, but that he fails to recognise the reasons behind them and blames NFB simply because of a lack of understanding. Yes NFB reduces measureable distortion but it also reduces the output impedence of the amplifier and therefore increases the damping.

According to Dave Berning (who I consider to be a pretty clever guy)there is no universally correct amplifier output impedance. This is why Berning and the Cary in the article offer a means to adjust output impedance/damping on some models. Many system designers have known this for years, and damping adjustment controls were found on some amplifiers going back to the 1950s or before. The reason that there is no one correct output impedance is because the speaker is a mechanical system with inertia and its transient response is very much determined by the source impedance driving it. Each speaker design behaves differently, and it is usually desirable to achieve what's called "critical damping". If the mechanical system (speaker) is under damped, the cone will overshoot and ring in response to a step transient. If it is overdamped, it will undershoot and be slow to reach its proper position. Underdamping happens when the output impedance of the amplifier is too high, where as overdamping occurs when the output impedance is too low.

In terms of the bass reproduction, underdamping results in an overly warm resonant reproduction, and overdamping results in a overly dry and heavy presentation. Neither of these are correct. When the amplifier output impedance is optimum, the bass will have its most natural reproduction. A damping/feedback control on the amplifier lets the user best tune the speaker, and yes, the room acoustics enter into it as well.

Or of course that's what Dave Berning says but given that Martin Colloms performed his "test" using a highly overdamped loudspeaker (Wilson), it is highly probable that reducing the amplifier damping by reducing feedback would lead to increased life and better perceived timing. But not for the reasons he summises. Not because feedback in inherently bad for the reporduction of sound. In your case, you have increased the output impedence of your amplifier, introduced some frequency response irregularities, and possibly improved the damping of your single drive unit. But swap loudspeakers and you may well prefer the results with the feedback loop re-inserted.

 

The MC article linked to above is interesting but completely irrelevant to this discussion which concerns the removal of global NFB from an amplifier designed to use global feedback.
I certainly wouldn't argue that low/no feedback amps cannot sound excellent but you'll find, as with the CJ pre amp and Radford power amp mentioned in the article, that these were designed from the outset to be no/low NFB designs.
I also see that the distortion figures for those designs remains fairly low even though it is perhaps a ten fold increase on a typical belt n braces SS amp. Ripping the feedback circuits from an amp using perhaps 20db NFB is likely to produce a huge rise in distortion - far higher than for the examples given in the article and they will certainly be very audible. What you hear will depend on the level of distortion and the type. Odd order distortion is typically unpleasant at low levels but even large amounts second harmonic can be acceptable in that it won't sent you running form the room. What it will do is change tonality, timbre and perhaps the perceived amount of detail heard.

I find it incredible that people will bang on relentlessly about audiophile cables, boutique capacitors and resistors, fancy stepped attenuators etc in the quest for 'fidelity' yet run bodged amplification that perform quite obvious signal manipulation.

 

Hi,

Hmmmm, yet this amplifier is running into very unusual speakers, which may sound much better when driven from a much higher output impedance, also, the removal of negative feedback universally tends to improve recovery from clipping, allowing amplifiers to be driven much harder (what we usually hear when amplifiers clip with music is not the brief clipping of the transient but the recovery from clipping).

Without actually understanding the whole system, the other changes to the Amplifier (like has Antonio wired the output valves as triodes?) it is hard to make any resonable call.

For example, when I originally tested the DIY HiFi Supply "Joplin" amplifier it sounded quite ordinary and did not show much "DHT Magic". Converting the output stage to self bias (from fixed bias) and removing negative feedback, combined with using a lower gain input valve (to reduce the gain back to something that left me some volume control range) transformed the Amplifier and it was this configuration that has become "stock"...

Yet the Amplifier was "designed" around the use of a lot of NFB and fixed bias, still, without it and with self bias the sound quality was majorly better!

Not all is eaten as hot as it's cooked.

Ciao T

 

There is no 'magic' in audio IMO - just good design.

In many ways it boils down to the fact that some people seem to find that certain types of distortion 'enhance' the end result.
That's perfectly ok, but those people need to accept that what they hear is measurable and the effects repeatable - nothing to do with magic.

PS: You missed a good BBQ yesterday.

 

You are the one who speaks of magic, when you cannot measure what is going on...

I dont speak of cables, the cables on my last system are quite average, and I didnt bother trying different, but I do bang on people that try to ridicule those that dont think like them, as much as I can...

This is the typical bullshit when you run out of valid arguments to support your nearsighted views...

As you can see my amplifier hardly needs NFB, in triode mode and with fullrange speakers more so...

 

Hi,

Actually, if we consider the definition of stage magic, the right design is just that.

Here we part ways.

Prior to the mods the Amplifier showed fairly high (for a 2A3 push pull amplifier) output power with low THD, however the distortion had mostly high and odd order components, overload recovery was also pretty bad. The audible results was a harsh, forward gritty sound with some opaqwueness and very obvious "pumping" when overloaded (as even a 13W Amplifier will, if running into normal efficient speakers).

After the mods the power was normal (7W) with a normal level of THD (around 3%), which has no visible components above the 5th and (due to some other design features) a dominant 2nd harmonic, with a quick decay of harmonics. The overload behaviour was also much improved. The audible effect was a detailed, but smooth sound with an overload charateristic that was more akin to a smooth compression.

I would conclude instead that some people object more to the PRESENCE of certain types of distortion, not due to any enhancement. For further reference, i would also recommend the introduction to my Article "Some thoughts about single ended amplifiers"....

Ciao T

 

Ahem, lets try again, though frankly I doub't it will get through, but here goes.

You use an amplifer which by your own admission produces high levels of distortion (compared to 99% of amps in use).

You like the way it sounds.

You've now removed the NFB which will drive distortion even higher.

You think it sounds even better.

In the process, by raising the output impedance of the amp you've also changed the frequency response of the speakers. The severity of the change will depend on the speaker load.

 

I'm not sure that we part ways.

What you are saying is that different types and orders of distortion have different effects on the final sound. I agree with that.

The question is, do you prefer the final sound because the ear 'likes' certain types of distortion in modest amounts, or is the absense of NFB in itself the reason for the preference?

I don't think that the case for saying that NFB is a 'bad thing' is in any way proven. The problems at clipping are of course valid but I'm more concerned with performance within rated output.

 

1,2% without NFB is quite low, 3DSonics has 3%, most tube amps with NFB have at least the same as mine, what makes you say it is worst than 99% of amps...

You are happy with your 0,000000 japanese amplifier, good for you...

 

THD figures mean nothing quoted like that Antonio. It's the make up of the distortion that is far more important, but obviously the less distortion the better.

I'll stick with the increased output impedence making the largest difference, although I disagree with Rob about the effect of high output impedence on speaker frequency response - it's insignificant compared with the affect of the room acoustics and likely to go totally unnoticed in most cases. Interestingly during his experiments, David found that most loudspeakers liked an output impedence of between 2 and 4 ohms, and some were critically damped by an amp with an output impedence of 10.5 ohms.

What's the efficiency of your loudspeakers like?

 

I only mentioned distortion because Rob did it, still 1.2%(10W 1KHz),frequency response is 30Hz-75KHz(10W) and wideband absolute noise is 1.2mV is quite good without NFB...

My speakers are 4 ohm, they say, funny with the Cayin they played bad on 4 ohm tap and well on 8 ohm tap, with the Classic, is the opposite...