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Old 30th October 2012, 04:28 AM   #81
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Yipes.


I should perhaps react here in lower case print; there seems to be quite a variation in what members want ... and when that from each is elevated to "should be" status, .....

Everybody has right to his kind of sound, and when it comes to 'warmth', I doubt whether there will be much agreement - OK, to be shure audible 2nd harmonic, and as I understood decades ago, some 3rd harmonic to give string instruments "that edge" - that seems to have been established.

My modest contribution is that I have thought for the past 50 years odd that "high fidelity" means "as close as possible to the original" or some such. Otherwise one is adding another musical signature, and as said, the right of everybody . . . but 'High-end'; 'Hi-Fi'? What exactly is it then that is high?

But regarding my concept of hi-fi, if that was part of the mix here at all, I did not see a circuit of a simple two-triode amplifier with enough negative feedback to give the desired gain, low distortion, output impedance, h.t. independance etc. to at least equal if not surpass several of the tube-rich designs presented here. Perhaps tubes are not as expensive elsewhere as in RSA ......

I had also hoped that the lame idea that "feedback-is-bad" has gone its way by now, plus a few others. And - I also did not read about the requirement of headroom for pre-amplifiers, although admittedly in tube circuits that is not so serious. Perhaps I am behind the times here 'down south', my aim being something like Zout <200 ohms, D<0,05% (with NO interfering high-order harmonics), S/N about -90dB, achievable with a double triode or triode-pentode.

But I see that will not be the horse-for-the-course of some.
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Old 30th October 2012, 05:40 AM   #82
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High Fidelity, Hifi has been determined as you wrote, and that happened a long time ago.
At 60's first european standard (DIN...) was created to specify the minimum performance of Hifi-equipment. All essential feature was specified.

When looking the circuits presented here today It is obvious that very many of these designs do not fulfil even this first Hifi standard. Most of such are different SE-amplifiers and preamplifiers with no feedback. Actually I think that no real Hifi amplifier can be built without any sort of NFB. Now I mean with Hifi such equipment that has good test results done by measurements.

I have also noticed that the first thing that a starting tube hobbyist "knows" is that he does not want to use NFB because it ruins the sound.
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Old 30th October 2012, 05:55 AM   #83
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Quote:
Originally Posted by artosalo View Post
High Fidelity, Hifi has been determined as you wrote, and that happened a long time ago.
At 60's first european standard (DIN...) was created to specify the minimum performance of Hifi-equipment. All essential feature was specified.
That was DIN45500 !
I remember it well because my dad is proud that his little early 70's Telefunken intergrated adheres to that standard!

And I agree about the rest you said. Also, hi-end is not an officially defined term, just a marketing department term to indicate "very expensive"
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Old 30th October 2012, 09:21 AM   #84
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Global Negative feedback is the bogy man here. Listening to an amplifier with and without gNFB and it is obvious that the feedback constrains the sound and robs it of its life. Local feedback can be acceptable if done correctly.
The very reason why most people are here building valve amps is because of their intrinsic linearity the amount of feedback needed is vastly reduced. This is the very essence of why valves win over transistors. Apply lots of gNFB and a valve amps sound moves towards that of a transistor amp.

The FVP amps by Allen Wright are extremely low in distortion without resorting to Global Feedback - and they are still relatively simply, only requiring four triodes.

Shoog
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Old 31st October 2012, 03:04 AM   #85
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Shoog,

You are thus saying that nfb is bad?

There is no reason why local nfb should "sound" or measure any different from global nfb, quantity being the same and stability factors excluded. The basic laws of electronics preclude this.

I respect your right to your opinion, but there seems to be disagreement about "obvious"! I would however strongly agree with "done correctly", in whatever way! Some examples of nfb are high-order harmonic generators; that is not the fault of the nfb per se.

Not to go OT by re-opening that argument here; I believe it has been widely discussed on this site in the past. Only to say that such a stance/experience is shrouded in controversy because of its subjective nature.
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Old 31st October 2012, 10:22 AM   #86
Gost22 is offline Gost22  Bolivia
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Hi,
What do you say to this schematics (tube/valve preamp with ECC88), that give a comment.
thank you!
Attached Images
File Type: jpg ecc-88---preamp-2_1.jpg (62.8 KB, 363 views)
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Old 31st October 2012, 10:38 AM   #87
DF96 is offline DF96  England
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Quote:
Originally Posted by artosalo
I have also noticed that the first thing that a starting tube hobbyist "knows" is that he does not want to use NFB because it ruins the sound.
Yes. I blame postmodern culture and poor science teaching in schools. People enter adult life thinking that truth is just a matter of opinion. Then they discover that NFB and noNFB sound different (as they should), and prefer noNFB because that is what 'free-thinkers' (i.e. non-thinkers, in some cases!) seem to do. Then they get upset when people like me suggest that perhaps they like the sound of low-order distortion and restricted bandwidth. Of course, any amp where you can just 'dial-in' your preferred level of feedback could be poorly designed anyway and almost certainly has the wrong amount of feedback.

Sorry for OT, but Shoog started it!
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Old 31st October 2012, 10:54 AM   #88
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Originally Posted by Gost22 View Post
Hi,
What do you say to this schematics (tube/valve preamp with ECC88), that give a comment.
thank you!
Back to topic.

I think it is OK and you will like the sound! But it is better to keep the 3u3 and 470K on the output if your power amplifier is solid state

Last edited by costis_n; 31st October 2012 at 10:56 AM.
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Old 31st October 2012, 10:56 AM   #89
SY is offline SY  United States
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Quote:
Originally Posted by Gost22 View Post
Hi,
What do you say to this schematics (tube/valve preamp with ECC88), that give a comment.
thank you!
The heavy loading of the two stages will cause the distortion to be higher than it needs to be, but some people may like this effect.
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Old 31st October 2012, 10:57 AM   #90
AJT is offline AJT  Philippines
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Quote:
Originally Posted by Gost22 View Post
Hi,
What do you say to this schematics (tube/valve preamp with ECC88), that give a comment.
thank you!
consider this instead....CCDA: constant-current-draw amplifier
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