The voltage is too low. I wonder Q1 is off. If Q1 is on, R2 volt drop is about 0.6 V. R3/R1 volt drop will be about 1.8 V/1V, respectively. Q2-Q3 base-to-base voltage will be 2.8 V.
In your test circuit, how do you implement I1, V3 and E1? BTW, can you show me the link of Bob's ThermalTrak thread? Thanks!
Why would you need a buffer at the input?
This chip is an opamp transconductance. It needs a buffer at the output of course.
JP
When you consider the cost of bringing one of these chips to the manufacturing stage I begin to wonder what other changes were implemented in the LME49811 chip to make that big of an investment. Sometimes a large company will start a new chip design if the last part was lacking something or they somehow made a mistake. In that case they will pull the old part. With all of the above to be considered why would national build two monolithic chip structures which resemble each other in so many ways. Or what are the BIG dissimilarities!!
Panson with your rather time consuming and in depth measuring you have not been able to differentiate anything of great consequence it just proves this to be more of a strange choice on National's part.
Have you built the mosfet output for the 30 part and if so is the fet sound any different. From a pair of normal ears not the golden ones. This would be a good place to test that rather heated comparison. Mosfet verses BJT.
Tad
Panson with your rather time consuming and in depth measuring you have not been able to differentiate anything of great consequence it just proves this to be more of a strange choice on National's part.
Have you built the mosfet output for the 30 part and if so is the fet sound any different. From a pair of normal ears not the golden ones. This would be a good place to test that rather heated comparison. Mosfet verses BJT.
Tad
Panson,
I just presumed that I1, V3 and E1 would be supplied by the sink/source from LME49811 - probably a bad asumption.
I'll track down the link.
Ken
http://www.diyaudio.com/forums/showthread.php?t=71534&highlight=thermal+trak
Panson,
I think I've pasted the link correctly. Let me know if it doesn't work.
Ken
Panson, The thread is a bit slow starting, Douglas Self weighs in at post 48 and Bob somewhere after that. The sad part is they don't conclude with the phen-ultimante thermal trak schematic. I wrote Self and asked why not, he said he's put his result in the 5th edition of his book - apparently just published.
Last question for this morning, if I measure between the sink and source of the LME49811 with it disconnected from the output stage what voltage should I see? I get 8.51v and .007A.
Ken
back to front logic.
The buffer is placed after any source that has a medium or high output impedance.
If the source already has a low output impedance AND is also capable of supplying the current demanded by the receiver and the following connecting cables then that source does not need a buffer.
An amplifier (receiver) does not need a buffer at it's input. That is the wrong location for a buffer.
The buffer is for driving the cables and the input impedance.
measure across the VBE multiplier, i.e. from spreadp to spreadn. This voltage will be ~ 6times Vbe of an output transistor.
Each of the output transistors will have a Vbe ~600mV therefore Vmultiplier ~ 3.6V.
1.9V is far too low.
After the predrivers the expected biasing voltage will be ~2.4V
After the drivers the expected biasing voltage will be ~ 1.2V
After the outputs the expected biasing voltage will be ~ 52mV, i.e. 26mV across each Re.
Based on data from other designers I think with Re=0r22 that 26mV is too high . I would expect 20 to 24mV to be about right when the base resistors of all the preceeding transistors is zero.
If each of the base resistors are set to drop ~3mV during quiescent setting up, then expect the Vre to drop ~1mV, i.e. Vre in the range 19mV to 23mV.
Thank you Andrew. My idea is a buffer together with a vol control for an integrated amp configuration. Note that the vol control pot could be a low value one, say, 25 k. If a medium/high output impedance source can not be modified, a buffer (increasing impedance input) is probably a proper choice.
Probably the marketing believed this is a good strategy - minor modifications/short lead time for three parts.
I have tested 49830 with 240/9240. However, I did not spend much time for sonic comparison with 810/811 BJT output.
Using 49830?
Thank you for the link.
I did not measure this open voltage. When Source and Sink open, the chip is not operating properly. The measured value is not meaningful. I think the short-circuit current is more useful.
Hi Panson,
Did you test the short circuit current on the bias pins. My question is:
Can we consider that, with reasonable loading, that these pins are driven by a current source stable in operation and temperature. This is important in the design of thermal drift compensation of the power transistors.
Thanks
JPV
no,
the 25k pot does not need a buffer before it.
The 25k pot could benefit from a buffer after it.
The source that drives the pot should be able to manage 25k//?pF
If it can't then the source will benefit from a buffer fitted at the source end.
The input to an integrated amplifier does not need a buffer.
I did not check that. 
I think it should be not too time consuming. We want to set the diode, say, ThermalTrak, current to match temp coefficient. Right?
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