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Old 5th November 2011, 10:32 PM   #1311
Salas is offline Salas  Greece
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P.S. Had emitter degeneration on my friend's 27dB on the drivers but did not make any significant difference for drift.
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Old 5th November 2011, 10:36 PM   #1312
sonnya is offline sonnya  Denmark
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No, this is not drift... It is more how stable the idle current is in the VAS stage.

This will influence a bias circuit for the output stage. If it is a simple resistor with a bypass cap for driving mosfet's then you are in trouble. If you have a a VBE multiplier you will see a bias current in the output stage that drift a bit more than desired....
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Old 6th November 2011, 12:40 AM   #1313
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Quote:
Originally Posted by Salas View Post
Nice. You had CCSed the input current feed substituting the current feed resistors. Something that Lazy Cat had talked about as an option early in the thread, pointing out the PSRR benefit mainly. But it proves DC conditions stabilizing also. A few patches and this front end will be a true all rounder probably.
Nope, my main intention was exactly the same - feedback bridge DC current injection control. Look to the SSA high performance version and you will see its identical role.

What we can benefit from sonnya's current mirror proposal is that we can symmetrically control both positive and negative injection currents with LM314 current-temp sensor instead of cr500. In that way we can completely eliminate input stage bias thermal dependency.

Last edited by Lazy Cat; 6th November 2011 at 12:43 AM.
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Old 6th November 2011, 01:43 AM   #1314
Jay is offline Jay  Indonesia
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Originally Posted by Bigun View Post
do you really believe bipolar has a 'sound'? I thought that the topology and operating points and power supply are going to have a bigger impact on the sound than choice of FET verses BJT
Each device has their own characteristics (such as Ciss in a mosfet). This will make them "sound" different. You cannot always put them on the same operating condition. For example, make a class-B amp using hexfet (with highish Ciss), you can design a high current drive, but the sound will never be the same.

Of course topology, operating points and power supply are also important. In fact, all are important. Even MJL versus NJL is important. They have to be "designed" as a whole complete system, including the speaker and the source.

If my (ultimate) speaker has 100dB/m sensitivity for example, I will not look at this type of amp design.

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Originally Posted by Bigun View Post
The SSA has it's weaknesses - thermal stability is one of them - in my opinion, and use of zeners (noisy things). And I think it will sound better if it's NOT actually symmetrical - an easy thing to achieve
Do you think 2nd harmonics would be a plus? I'm going to compare with Mooly's amplifier attached where it is asymmetrical. But I have one question before I modified my amp to use the same lateral mosfet and to use negative supply opamp:

The amp attached uses TL071, a JFET input that is wired with negative supply. I have checked the parameters of my opamps, but I couldn't find which feature that allows use of negative supply only. I have some TL061CP which is also JFET-input from the same manufacturer (TI). Do you think I can wire it with negative single supply? Which parameter in the opamp that I should look for to know that the opamp is capable of this negative supply?
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Old 6th November 2011, 02:25 AM   #1315
Salas is offline Salas  Greece
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Quote:
Originally Posted by Lazy Cat View Post
Nope, my main intention was exactly the same - feedback bridge DC current injection control. Look to the SSA high performance version and you will see its identical role.
Sorry If I did not follow those posts, the PSRR thing I remembered from this early one quoted below:

Quote:
Originally Posted by Lazy Cat View Post
Only resistor devider for the bases of the cascodes in Le Monstre really can not provide any isolation from power supply ripple or DC variations, so poor PSSR is quite obvious. In my sch +/- 15 V zener filtered DC potential is substantially more adequate solution. If there would be CSS implemented instead of 1 k input pair current supply resistors, PSSR would be comparable to any CF amp.
As I already mention for such low power amps there is not a big problem to invest a little more in the power supply, which can be for this kind of current consumption even regulated to improve PSSR.
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Old 6th November 2011, 03:35 AM   #1316
Sheldon is offline Sheldon  United States
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Comments welcome. Any compensation required?

Sheldon
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Old 6th November 2011, 04:01 AM   #1317
Salas is offline Salas  Greece
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I think that the diode on the minus rail is reversed. 12V/2k7=4.44mA when 0.6V/100R=6mA. Not enough to turn on well the input transistors?
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Old 6th November 2011, 06:56 AM   #1318
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Sheldon, please try to compare to SSA basic version because you have several mistakes in your sch. Bases of the VAS BJT to 1k, 100uF in the mid bridge, output connection. I don't want you to have some broken trannies.
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Old 6th November 2011, 07:39 AM   #1319
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Hi sheldon, this is the most adequate SSA sch to compare to.
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Old 6th November 2011, 07:49 AM   #1320
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Quote:
Originally Posted by Salas View Post
Sorry If I did not follow those posts, the PSRR thing I remembered from this early one quoted below:
Yes Salas, it was the PSRR debate but later on the topic was mainly concentrated to bias current thermal dependency and its cancellation. Current mirrors with middle current-thermal sensor is a pro-solution. I think LM134 linear response is adequate to maintain the currents in correct range to sustain stable working point conditions of the input pair.
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