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PostPosted: 22 Jun 2011, 11:14 
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HI.
Suncalc wrote:
Remember that this design implements a significant amount of feedback. This allows the input greater swing because the net grid voltage is offset by the feedback from the output. This also allows significantly more linear operation out of the stage.
c-J: Did you look at the distortion numbers from the load line analysis? (0.2% :thumbsup:)

NFB is sorta kinda some sweet poison which kills the music bigtime. It is only a white wash to cover up the original lousy performance of an active stage WITHOUT applying any NFB.
The best amp should be one which delivers lowest distortions without any NFB. :thumbsup: But it is so difficult to design. :worried:

Yes, it can give you apparent 0.0001% THD & the like specular figures on bench test using the sinewaves & square waves like historic static measurement methodology. But such static bench tests do not show the realworld situation of how an amp would perform when handling everchanging dynamic multiple blend of music harmonics.

Our musical ears can detect it. But not any bench tests yet todate.
Any SS amp can deliver sub sub zero THD on bench tests & how come tube amps with tons of THDs can sound so so much better to our ears???? One of the key design features very common in SS amps is the appliction of tons NFB.

That's why I commentd in the first place this 12AU7 linestage's worse design is the huge plate-grid loop NFB which should not be there at all.
Suncalc wrote:
The most extreme example of this principle is the cathode follower with 100% negative feedback

Cathode follower is totally another story of different application.

c-J

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PostPosted: 22 Jun 2011, 16:45 
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I'm only ever about the music and that's what I like about this little preamp. It lets the music through, drives my 3W 6AS7 SET to full volume, where the CD player wouldn't and gives me attenuation where required and source selection. All for a few hundred dollars. Not to mention is looks good too.

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PostPosted: 22 Jun 2011, 19:54 
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Hi.
mwhouston wrote:
All for a few hundred dollars. Not to mention is looks good too.

Amen!

c-J

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PostPosted: 22 Jun 2011, 22:15 
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mwhouston wrote:
Matt Does that mean you like it.
More accurately, I would say that I appreciate it. A much more important question is, do you like it?

As I said, this is not how I would approach a line stage preamp design, but the design itself is a very good one. It delivers some gain (small but useable), has very low harmonic distortion, and probably very low intermodular distortion. The overall performance of this stage on paper is very good. It should be understood however that this stage will (in all probability) be very "tight" because of the level of feedback. This is not necessarily a bad thing, it's just how the stage will sound. Probably almost "transistor like".

I personally have never bought into the "pure music" philosophy of audio design. When I play a bass or listen to my daughter play blues on a trumpet, I am very aware of how the surroundings affect the music. Most of that effect is the result of even order (choral) distortions introduced by the environment. As such, I don't fear the even harmonics in my audio gear. If we have learned nothing else from the dark ages of the mass market transistor amplifiers, we have learned that the lowest distortion almost never produces the most pleasing sound. I'm not ashamed to let my amps color my music, because even though I do truly appreciate all that goes into an artist's musical productions, when I play that recording for me, in my living room, it is MY music and no one else's.

I'll get off my soapbox now. :soapbox:

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PostPosted: 22 Jun 2011, 23:43 
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Yes I do like the sound. Great bass.

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PostPosted: 23 Jun 2011, 03:31 
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I'm accessing this forum over my phone so some answers are a little short. To expand a little on my previous post, the deepest bass is what I notice more. My BoZSE had excellent bass but The 4S appears to go lower and with far more weight. The preamp (The 4S) has this nice little bass bloom at the very lowest notes. It doesn't sound un-natural and with my small 8" doped paper bass drivers it is realy pleasant. Natural or not I like it.

When double basses are bowed you get this belch of thick deep woody bass that lasts and lasts. Matt may have been very close to the Mark by saying it may sound transistor like. Where transistor amps , generally, have good bass extension and weight but not always well articulated bass. This has all the extension, weight and articulation.That's where I feel The 4S shines, big time. Reverb just extends on and on. I think this is another trait of tube gear.

Yes I like it. Really like it. It goes into the case it two days, images to follow.

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PostPosted: 23 Jun 2011, 08:43 
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Hi.
Suncalc wrote:
Most of that effect is the result of even order (choral) distortions introduced by the environment

This is news to me, bud. Want to elaborate?

c-J

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PostPosted: 23 Jun 2011, 16:42 
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I would understand it as room modals. Resonances in the room which react and interact with the music. I have a large listening room only lightly dampend. It's quite lively. The room seems to react within a small bass band. This colours the bass slightly in that region.

A good friend who builds and repairs speakers claims he can pikck it regardless of which speakers I use when he visits he says the same colouration appears to come through.

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PostPosted: 24 Jun 2011, 19:21 
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On second thought it may be room nodals. Not sure. Time to chime in Matt!

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PostPosted: 24 Jun 2011, 20:46 
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Ok. This is hugely off topic so I'll keep it very short. :worried:

In physically constrained spaces (a room) the even harmonics of a tone tend to be reinforced and the odd harmonics tend to die out. (It's a consequence of the physics.) Most of the time you don't notice because the human ear generates even harmonics to allow you to recognize tones (the reason for this is a whole topic in and of itself). This is why I referenced the "choral" harmonics above. These are the even harmonics which reinforce the natural action of the human cochlea. This action always "colors" the sound. What makes a room "dead" or "lively" is the damping of these harmonics. But if you ever put a set of speakers in a truly dead space (like an anechoic chamber) you will be shocked at how wrong everything sounds.

This is why the most famous recordings of classical music are almost all live performances (or at least performances in an orchestra hall). The coloring of the music by the natural environment is expected by the brain and when absent, the brain reacts negatively.

Not a very good explanation, I admit. But I really can't do much better without writing about ten pages.

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