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Old 3rd November 2012, 09:36 AM   #641
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by owdeo View Post
............... if I posted my simulation schematic here given the component values are different? ..............
if you have changed components or component values, then the modified circuit now belongs to you.
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Old 3rd November 2012, 01:32 PM   #642
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Quote:
Originally Posted by owdeo View Post
Would Mr Self object if I posted my simulation schematic here given the component values are different? IIRC he had the circuit free to view on his old website so maybe he won't mind. If he doesn't I will post it.
Post away.

But you're wrong about "darlington and cascode enhancements" they reduce distortion significantly. You won't convince me that the sound of non-linear Cbc is better than not having it.
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Old 3rd November 2012, 02:25 PM   #643
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Quote:
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Post away.

But you're wrong about "darlington and cascode enhancements" they reduce distortion significantly. You won't convince me that the sound of non-linear Cbc is better than not having it.
Doug,

I agree completely.

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Bob
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Old 4th November 2012, 12:10 AM   #644
owdeo is offline owdeo  Australia
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Thank you Mr Self.
Here it is. Please bear in mind that although it might look sub-optimal in some ways from a purely objective analysis, this is what I ended up with after extended testing of various configurations and listening over long periods. There is a relay attenuator up front which expects to see 10k, hence the low input bias resistor. The output offset is high at 0.5V, but since the output is AC coupled and it sounded better without the feedback cap I left it at that, figuring the headroom loss was insignificant.

I never disputed the improvements in objective peformance that VAS enhancements bring, and who am I to argue with you two distinguished gentlemen anyway All I said is that the VAS enhancements sounded worse (to me and in this particular circuit). Pointless arguing about that and I would not expect to convince you Mr Self!

I found the whole process very interesting, having expected that as the THD was improved by increasing gain in the VAS the sound quality would also improve, but this did not seem to be the case in practise. My methods were hardly scientific, but I was only doing it to suit my own ears after all...
The worsening of SQ mostly seemed to be an increase in midrange "forwardness" and "hardness" where eg strings took on a screechy quality. There are some nice audiophile adjectives for you

I did carry out some distortion measurements on the circuit as shown using a friend's Cyril Bateman rig from his capacitor distortion articles. Just looked up the measurements and it seems at 1kHz I was getting:

@ 1V input and 1V output:
2nd harmonic: -110dB, 3rd harmonic -113dB

@ 1V input and 3V output:
2nd harmonic: -106dB, 3rd harmonic -122dB

Not too shabby. In theory the VAS enhancements should have lowered these even further but the levels should already have been inaudible. I thought the overall SQ was audibly worse though.
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Old 4th November 2012, 01:18 AM   #645
Bonsai is offline Bonsai  Taiwan
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It's a pretty conventional Lin topology stage.

Do you think it sounds better than an audio targeted opamp like a 553x or a 4562?

It's clear tha you can probably get more drive out of it than an opamp, since there is no current limit, but at the levels you are talking about (1V out)I'd say this is hardly an issue.
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Old 4th November 2012, 01:37 AM   #646
owdeo is offline owdeo  Australia
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Thank you for that astute observation, the thought had never occurred, hence why I mentioned it a couple of posts ago...

In normal listening or A-B comparisons it sounds much better than the opamp preamps I've compared it to. I also did some single-blind testing of this cct against a single NE5534 configured with the same feedback arrangements and after careful listening to about 60 tracks found that I preferred the discrete circuit about 78% of the time.

My thoughts are that the devil is in the detail, however optimising this topology (or perhaps any) for THD and or noise alone looks nice on the spec sheet but doesn't necessarily equate to subjective improvement of SQ. Perhaps it comes down to the relative levels and distribution of the harmonics, though I guess if anyone really had the answers this would cease to be a topic of discussion and audio reviewers would have to go and get real jobs

On a related subject I've just finished repairing our Sony Trinitron 32" HD CRT TV (the last of the CRTs) and boy am I glad to have it back. Compared to our other recent model Panasonic 50" plasma with 3D processing and much higher resolution, the CRT is much more realistic - natural colours and tones, a picture that seems more 3 dimensional and much faster response time so that there is no delay or jerkiness with fast movement. The plasma has better measured specs in just about every category and yet everyone in our household prefers to watch the smaller CRT. Anyone else see any parallels with audio? And music is tied up with our emotions... I don't understand why many design engineers seem to be happy to just optimise THD when the consensus amoung experienced listeners is that it doesn't correlate well with SQ. Surely it must be possible to pin down the measrements that are actually important for SQ?
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Old 4th November 2012, 03:00 AM   #647
wahab is offline wahab  Algeria
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With a darlington VAS the distorsion of this circuit is reduced
by roughly 20dB while keeping the same harmonics distribution.

Can we conclude that sound quality seems better when adding
tiny amounts of THD + IMD that are measurable yet barely audible ?....
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Old 4th November 2012, 05:49 AM   #648
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It is fascinating how different perception is from specs. There are endless number of examples where less linear circuit gives subjectively better results. One example is old budget NAD 3020 amp. No mirrors, no CCS, yet sound that is subjectively better than more complex circuits. Great linearity is not guarantee for better perception of sound. But most engineers would lose their jobs (which are scarce these days) if they would use simple amateur circuits. They must compete for existence of their jobs. Listener is not priority, because specs look better before you buy something. But Doug (and Bob, and other great engineers...) have sensible approach professionwise, because it is much easier to please scopes and spectrum analyzers than countless personal tastes.
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Old 4th November 2012, 08:49 AM   #649
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Quote:
Originally Posted by owdeo View Post
.... And music is tied up with our emotions... I don't understand why many design engineers seem to be happy to just optimise THD when the consensus amoung experienced listeners is that it doesn't correlate well with SQ. Surely it must be possible to pin down the measrements that are actually important for SQ?
Well, that's what we were hoping you'd get around to. As you have appropriate DIY experience, preamps that fit both criteria, the axe to grind and the formal discipline to tackle the matter, then let's hear it.

It's ironic though, that the usual way now to instill "SQ" into an amplifier is to ensure it generates a specific harmonic distortion "profile". Cynical, innit?
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Old 4th November 2012, 10:30 AM   #650
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High linearity circuits are one way to avoid unpleasant sound, not a guarantee that listener shall actually enjoy the sound. It is safe way for circuit designers. But since everybody has some taste, some coloration he/she prefer, the most successful circuits are those that contain desired coloration inherent in topology. In my experience, for most people, highly linear circuits with tone controls are less successful way in offering listener desired coloration. Therefore, simple circuits with idiosincracies in form of more harmonic distortion, are for many listeners better way of adding the missing sparkle, than treble boost with tone control.

I remember, few years ago, that studio users of Yamaha NS10 mini monitors, used to tape paper tissue (toilet paper) over tweeters, although it only makes response more wavy, due to reflections (not absorption).
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