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Old 4th November 2012, 09:00 PM   #661
owdeo is offline owdeo  Australia
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Quote:
Originally Posted by ivanlukic View Post

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).
Haha good one. Probably a better way to improve the sound of NS10s is to go into another room. Terrible speakers - popular because if you can make a recording sound good through them it will sound good on anything
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Old 4th November 2012, 09:37 PM   #662
wahab is offline wahab  Algeria
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Quote:
Originally Posted by owdeo View Post
Is that an assumption or have you simulated or measured it in this circuit? You may be right, but it also changes other things such as the amount of feedback.
Only simulations but the results are well beyond the simulators
error margins.

The difference is quite large not to say of orders of magnitude
while the added complexity and cost is negligible.
Attached Images
File Type: gif OWEDO LIN THD1.gif (21.9 KB, 438 views)
File Type: gif OWEDO LIN THD10.gif (25.1 KB, 428 views)
File Type: gif OWEDO LIN.gif (8.3 KB, 428 views)
File Type: gif OWEDO LIN MOD.gif (9.1 KB, 372 views)

Last edited by wahab; 4th November 2012 at 09:42 PM.
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Old 4th November 2012, 09:44 PM   #663
owdeo is offline owdeo  Australia
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Nice work wahab. The cost and complexity of the circuit either way is negligible, so please now build both versions and spend some time listening carefully to both and tell us what you think (if you are that way inclined...)
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Old 5th November 2012, 09:51 PM   #664
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Thank you, Mr. owdeo for sending all of us your favourite pre-amps schematic design and also many thanks to Mr.Doug Self for inventing this design.

Last edited by noddy55; 5th November 2012 at 10:08 PM.
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Old 6th November 2012, 04:18 PM   #665
Struth is offline Struth  Canada
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Hi Guys

There are several articles about the NS-10M Studio, which was an update of the hifi NS10. The original units came with grille cloth but the later Studio version has a very open steel mesh over the tweeter. The response amendment provided by the grille cloth was lost, so some studio personnel placed tissue over the tweeter. This was completely unnecessary as the Studio variant already took the lack of grille cloth into account.

The actual response of the NS-10M Studio is quite amazing! It takes advantage of the boundary presented by the mixing console to help with bass response. The off-axis dispersion is quite low as the near-field intended use places the listener on-axis in most situations.

I use these speakers with some subs in a "2.2" system for listening to music and watching movies. It sounds far better than any surround system in a home - those are optimised for the nonoptimal theatre enviroment.

Regarding preamps: measurable accuracy is a fine thing and an easy objective to attain. Where Doug and others concentrate on THD, you rarely if ever see an IM plot. IM makes or breaks the sound even when an order of magnitude lower than THD. Since it is impossible to have feedback without the loop itself generating new distortion artifacts, the distortion spectrum of the circuit changes with feedback applied. Every circuit actually has some feedback mechanism within it, so distortions of some type are unavoidable but can be minimised and their balance controlled to some extent.

Doug's circuits in particular are designed to use off-the-shelf parts with no matching. Circuit design controls sensitivity to parameter spreads. This is part of why he glosses over complimentary-diff inputs and push-pull VAS. In both cases, matched components are required to assure equal gains for the circuit halves, and matching introduces extra cost. On the other hand, the balanced circuitry greatly reduces even-order distortion and provides a 'potentially' smoother distortion profile provided other facets of the design are cared for. To reduce sensitivity to device matching requires emitter degeneration that adds noise - linearity can be equal with or without degeneration despite the usual graphs you see to the contrary.

Opamps have their appeal and their limitations. Discrete circuitry has the advantage that higher voltages can be used along with asymmetrical supplies. The latter is almost universally over-looked these days, with the influence of opamp-based design.

Have fun
Kevin O'Connor
londonpower.com
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Old 6th November 2012, 11:38 PM   #666
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What are the advantages of asymmetrical supplies and why can't they be used together with opamps?
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Old 6th November 2012, 11:57 PM   #667
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How about a schematic of an asymmetrical power supply? What makes it asymmetric, is there a different voltage on each rail or what?
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Old 7th November 2012, 03:11 AM   #668
Struth is offline Struth  Canada
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Hi guys

Asymmetrical supplies have different voltage values, not symmetrical (identical but opposite polarity) like +/-12V, +/-15V etc. There was a Technics pre that had a +136V rail along with lower but not symmetrical split rails.

If you read the last paragraph more closely, there is no implication that asymmetrical supplies are "beneficial" to a circuit that otherwise would use symmetric supplies, rather, that certain discrete circuits optimally run from asymmetric voltages.

My point was partly that with the ubiquitous symmetric split rails, most hobbyists and designers do not think in any other term than 'symmetrical'.

Have fun
Kevin O'Connor
londonpower.com
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Old 7th November 2012, 08:57 AM   #669
AndrewT is online now AndrewT  Scotland
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An LTP stage can be run with very unequal rail voltages.
Would diamond arrangement drivers similarly suit unequal supply voltages?
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Old 7th November 2012, 03:13 PM   #670
Struth is offline Struth  Canada
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Hi Guys

Most diamond buffers and drivers live within a symmetric circuit that operates best with symmetric supplies.

The LTP is a good example of a circuit that can be operated from asymmetric supplies without detriment.

Another example is the front-end to old-style amps with totem-pole outputs, either BJT or mosfet. Typically, an NPN diff amp with a low negative tail voltage and high positive voltage drives a pair of PNP BJT VASs. The latter might be loaded resistively or with current sources tied to a high negative rail. The PNP collectors drive the base/gate of their respective output device. The output devices will operate from symmetric rails of adequate value to provide the voltage swing to the speaker. Of course, the whole circuit can be turned upside down depending on the device types available for the voltages required.

In the amp example, the output stage might run from, say, +/-40V, and the front end might run off +/-50V, or from +50V and -40V, or from +50V, -40V and -12V. I've seen quite a few with three rails for the front completely unrelated to the output rails.

If you were designing a single-ended preamp and did not want to use current sources or current mirrors, it becomes beneficial to have high supplies to accommodate high R values to control gain while retaining some semblance of linearity. Assuming an NPN input device, the first stage might operate from +40V and -10V. A second stage might have an even higher positive rail and high negative rail. Just an example.

Have fun
Kevin O'Connor
londonpower.com
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