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Old 22nd March 2010, 11:14 PM   #51
a.wayne is offline a.wayne  United States
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Originally Posted by analog_sa View Post
In my limited experience - extremely speaker dependent, especially in bass and dynamics. Don't quite see how adding hundreds of db extra open loop gain can really correct for this - there just seems to be insufficient current from single chips.


Offtopic: last week upgraded my old S300 with Rifa main caps, polyprops in place of polyesters in output zobel and feedback decoupling and Vampire binding posts/jacks. The improvement is beyond all my expectations as i've never really liked the S300 before. Can a chip amp sound as powerful @1W? I seriously doubt.
Interesting analog , i too have been tempted to upgrade the s500 PSU caps and diodes and after your comments , I'm leaning that way now more than ever.

When we do the comparison it will be between stock S500 and chip amp
"Bel canto" .
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Old 25th March 2010, 12:46 PM   #52
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I went from all 1950s and 60s Fisher and Scott amps to a Bryston 4B to home built LM3886 amps.

The only thing I can say to people who claim discrete is better is, good luck matching your transistors even remotely as close as those in a chipamp. And to people who claim they can be matched close enough, I guess you can argue any point so use what makes you happy. My fisher and scott amps sounded great, the Bryston 4B sounded great and gave me bragging rights. The LM3886 amps give me great sound and simplicity. And since bragging rights are useless when it comes to getting the job done, I'm sticking to my lm3886's

Build and use what makes YOU happy. Thats what its about.

Last edited by thetube0a3; 25th March 2010 at 12:48 PM.
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Old 25th March 2010, 01:05 PM   #53
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Originally Posted by a.wayne View Post
i too have been tempted to upgrade the s500 PSU caps and diodes

Any suggestions about the diodes? I have no experience with 35A+ diodes. Another thing to do is replace the aluminium heatsink which doubles as a ground bus with copper. Not sure how audible this will be but i'll do it out of principle

And lastly - a separate transformer/rectifier/(regulator?) for the input/driver board.
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Old 25th March 2010, 05:43 PM   #54
Telstar is offline Telstar  Italy
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Originally Posted by tomchr View Post
The LME49810, LME49811, LME49830 support up to +/-100 V rails.
...
Tom, the LME49* are drivers not chipamps - they replace input stage and VAS. I'm sure you know it.
So, I wouldnt exactly compare to the 3886 &C.
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Old 25th March 2010, 05:44 PM   #55
Telstar is offline Telstar  Italy
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Originally Posted by thetube0a3 View Post
The only thing I can say to people who claim discrete is better is, good luck matching your transistors even remotely as close as those in a chipamp.
You are damn right
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Old 26th March 2010, 03:12 AM   #56
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Originally Posted by analog_sa Click the image to open in full size.
"In my limited experience - extremely speaker dependent, especially in bass and dynamics. Don't quite see how adding hundreds of db extra open loop gain can really correct for this - there just seems to be insufficient current from single chips."

Feedback makes an amplifier more linear. More feedback is more linear. Also having the amp stable with that much feedback makes it drive bad loads a lot better. I use no compensation at all on the output like an inductor or RC snubber to calm the amp from oscillation. It is like big rock stable. It also means the dominant pole gets moved out to a very high frequency so out of band signals do not cause foldback distortion of the worst kind. Comparing the very well built straight 3886 to the "high gain composite amp" version on the bench and in listening test was not even fair. One sounds like the typical halfway decent amp the the other sounds like music and forget the amp part.

Also the extra gain means higher damping at all frequencies which translates directly into more control over the transducers. This reduces the effects you mention of the speakers making the difference. This damping also makes the amp run hotter because it is absorbing more back EMF from the voice coil.

As far as current I am not certain what you mean. The 3886 with a good supply will put out 11 amps which translates into an easy 7.5 amps RMS so that is 450 watts into 8 ohms and 225 into 4 if it could swing the voltage. That is plenty of current. So much current that I run 2 3886 balanced output to increase the voltage swing making 160 watt amps out of a pair of them (32 volt supplies) which takes less than 5 amps RMS into 8 ohms.

Further I run the very same amp on 15 volts and drive loads down to half an ohm. Most amps puke at that kind of load but this is the easy way to do it. It will direct drive a ribbon just fine if the power supply voltage is set appropriately.

This explains everything you could not see so I hope now you can "see."
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Old 26th March 2010, 03:14 AM   #57
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Originally Posted by thetube0a3 Click the image to open in full size.
"The only thing I can say to people who claim discrete is better is, good luck matching your transistors even remotely as close as those in a chipamp."

Wait till you see what I have up my sleeve in the way of a discrete amp!
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Old 26th March 2010, 03:35 AM   #58
srinath is offline srinath  United States
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Default What ...

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Originally Posted by Telstar View Post
Tom, the LME49* are drivers not chipamps - they replace input stage and VAS. I'm sure you know it.
So, I wouldnt exactly compare to the 3886 &C.
OK so there were tube amps, which gave way to solid state, which gave way to IC which gave way to chip. Now you're saying there is a different one ... man have mercy on me, I am confused enough.

So FET is also a chip right. MOSFET, JFET etc etc.

Scary.
Cool.
Srinath.
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Old 26th March 2010, 05:48 PM   #59
tomchr is offline tomchr  United States
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Quote:
Originally Posted by Telstar View Post
Tom, the LME49* are drivers not chipamps - they replace input stage and VAS. I'm sure you know it.
So, I wouldnt exactly compare to the 3886 &C.
Depends on exactly how you define "chip amp". I'm sure the discrete crowd would lynch me if I called it a discrete design. But I do agree that the LME498xx family is somewhere in the gray area between discrete and chip amp.

In terms of complexity of design, the LME498xx series is only marginally more complex than the LM3886 -- especially when compared to the complexity of a discrete design. I've done all of them...

~Tom
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Old 26th March 2010, 06:11 PM   #60
tomchr is offline tomchr  United States
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Originally Posted by sumaudioguy View Post
"The only thing I can say to people who claim discrete is better is, good luck matching your transistors even remotely as close as those in a chipamp."

Wait till you see what I have up my sleeve in the way of a discrete amp!
Good luck. Matching discretes on a curve tracer (been there, done that) can yield matching on one parameter to within a few percent if you are patient and have a large sample size to choose from. Resistor matching is the same -- though, one could get within 2 % by buying +/-1 % tolerance resistors. Note, however, that if there is any thermal gradient across the PCB, the tempco of the resistors will throw that matching right out the window unless you have some very clever PCB design (and most designers don't).

Precision analog semiconductors (not to be confused with the run of the mill, tiny feature size CMOS logic chips) fabricated using processes optimized for analog products (National's VIP50 process for example) will yield far better matching between semiconductors than you can ever achieve by manually matching a bag of discrete devices. The resistor matching is just unreal. At the same time, the tempco of precision resistors will be controlled in the process. Typically, there will be at least one resistor type with "zero" tempco. NiCr, TiW, etc.... Great materials. Furthermore, the circuits can be designed to take advantage of the matching, i.e. circuit performance depends on the matching between components not the absolute value of the components (which is much more difficult to control in ICs). By careful chip layout, the matching between parts can be improved. For example a differential pair may be made up of, say, 2x8 devices placed on a common centroid for better matching. The routing to the transistors can be designed to balance the parasitics of each side of the diff pair. Hastings, "Art of Analog Layout" is a good place to start if you are more curious about this topic.

In a discrete circuit, you are usually better off by getting precision components and taking advantage of the precision in their absolute value rather than designing your circuit to be dependent on the matching between parts. Whoever came up with the idea of emitter degeneration resistors deserves a big hug!

Anyway... Back to work. Oh, and good luck with your knock-our-socks-off discrete design...

~Tom
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