Finally got the boards back --
Schematic is here -- R2 is either in as a zero-ohm or out.
http://www.tech-diy.com/Amplifiers/LME49811/Schematic_49811_Sanken.gif
An externally hosted image should be here but it was not working when we last tested it.
Schematic is here -- R2 is either in as a zero-ohm or out.
http://www.tech-diy.com/Amplifiers/LME49811/Schematic_49811_Sanken.gif
Dear jackinnj,
So happy to see someone else is experimenting with the LME chips with Sanken STD03N/P's
Please share your experience about sound quality, and share your bias experience, do you stick to the 40mA adviced by Sanken or you get over it?
One question, why is R12 needed? is it not sufficient enough to bias with only P1?
With best regards,
Bas
So happy to see someone else is experimenting with the LME chips with Sanken STD03N/P's
Please share your experience about sound quality, and share your bias experience, do you stick to the 40mA adviced by Sanken or you get over it?
One question, why is R12 needed? is it not sufficient enough to bias with only P1?
With best regards,
Bas
Hello Bas,
In my experience with those Sankens, I get better performance with at least 60mA bias current (and the 2.5mA diode current as mentioned). The recommended 40mA bias is best for thermal tracking, but at 60mA the xover distortion is much lower in peak amplitude, and thermal tracking is still pretty good - I have had no issues with thermal runaway at all.
Jan Didden
In my experience with those Sankens, I get better performance with at least 60mA bias current (and the 2.5mA diode current as mentioned). The recommended 40mA bias is best for thermal tracking, but at 60mA the xover distortion is much lower in peak amplitude, and thermal tracking is still pretty good - I have had no issues with thermal runaway at all.
Jan Didden
Maybe this is a little clearer -- I've shown with XMM1 to measure the current across the tempco diodes and XMM2 to measure the bias current:
http://www.tech-diy.com/Amplifiers/LME49811/Schematic_49811_Sanken2.gif
There are a couple permutations of the compensation circuitry -- but all the folks who worked on it at national have been laid off!
http://www.tech-diy.com/Amplifiers/LME49811/Schematic_49811_Sanken2.gif
There are a couple permutations of the compensation circuitry -- but all the folks who worked on it at national have been laid off!
janneman said:
Dear Jan,
Yes I am agree. I use Re's of 0,1 ohm. and run the Sanken's on 80mA (which is a voltage of only 8mV between the NPN and NPN Re's).
Douglas Self advice 25mV. over the Re no matter which application. I tired and IMD get twice lower, but then Thermal run away starts to become an issue with the STD03's sadly enough. So that is not really an option in order to benefit the simple thermal compensated bias method of the STD03's
With best regards,
Bas
jackinnj said:
Dear jackinnj,
Either I would try to built a truth (cascode?) current source to bias the STD's (like mr. Evil suggested) Or give it a try with the LME49810 which allow you to set a perfect 2,5mA pre bias for the STD03 diodes.
Ps: If you go for a current source for bias you really should take a look to Jan Didden's Elector article of his PAX amplifier design, where he use current sources as well to bias the Diode string.
With best regards,
Bas
the thermal stability of the output stage is determined by the thermal resistance of the output devices, the supply voltages, the emitter resistors and the transistor gain.Sebastiaan said:
Cordell gave a formula to check this.
High gain transistors and low value emitter resistors can become thermally unstable.
You must raise the value of Re.
Then you can apply the correct Vre.
BTW,
the correct (total) Vre is 26mV at room temperature. This includes the voltage drop across the internal and emitter referenced base resistors as well.
The external Vre will be less than 26mV. It could be considerably less.
I'd suggest 20mV across 0r22 emitter resistors as a starting point.
Mr Evil said:
Yeah, it's raining here in the PRNJ so instead of putting in lillies and hosta I wll be putting in a CCS.
Andew, I apologize publicly for my prior incendiary remark. I am just really t-ee-d off at Nat Semi's management for canning Troy, Mark and Bob and didn't think clearly before I wrote.
Sebastiaan said:
... but the bass response is not determined by the Re, only very remotely so.
I don't think you can measure any difference in Zout between 0.1 or 0.22 ohms, if you figure in all speaker cabling, the output zoble etc. IF there is a difference it will only appear at high frequencies anyway.
Jan Didden
AndrewT said:
janneman said:
Dear Jan and Andrew,
I know both of you are theoretical right about the higher Re.
In my case the amplifier is for an active speaker. And I tried different Re's from 0,1 ohm till 0,5 ohm. in listening sessions. And 3 other people with me prefer the sound of 0,1 Re and believe me, the difference in sound is very noticeable in terms of "speed" and bass tightness in listening experience.
However the system is thermal stabile with 8mV across both Re's, have never thermal runaway or instabilities. Even after listening session on full power for while the bias get stable fast already and back to it's 8mV. point after a couple of minutes of cooldown.
With best regards,
Bas
Yes, reduce the emitter current in the output device and you reduce it's gain. That reduced gain has the consequence of improved thermal stability.
But reducing the emitter current to below optimum for an EF output stage reduces the sound quality of the amplifier (increased crossover distortion).
I do not know what the optimum value of emitter resistor voltage is, but 8mV sounds too low to me.
If the only way to get optimum bias current is to increase the value of the emitter resistor, then that is the solution you should be pursuing.
But reducing the emitter current to below optimum for an EF output stage reduces the sound quality of the amplifier (increased crossover distortion).
I do not know what the optimum value of emitter resistor voltage is, but 8mV sounds too low to me.
If the only way to get optimum bias current is to increase the value of the emitter resistor, then that is the solution you should be pursuing.
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