Comparing LME49810, 49830 and 49811

[panson_hk]

Originally posted by cuibono
What are the clips on the chips for?

An audio expert shared a secret with me that these clips make sound much better! ..... Just kidding, I use them temporary to hold the heat sink.

[panson_hk]

I just finished a board with 49830 and IRFP240/9240x2. There is not oscillation.

I initially used "incorrect" resistor values for VBE multiplier which can give bias voltage over 20 V! During bias adjustment, I burned the chip and all four MOSFETs.

If driver stage MJE15030/15031 is added, the amp oscillates at 20 MHz. It can be stopped by increasing MOSFET gate resistors from 22 to 100 Ohm.

[smms73]

Hi, Panson

In post 10 the thd level for lme49810 starts to rise at 2.5v with 1kohm.

This is because the output transistors in the chip are poor biasing,
substitute the r1 and r2 for a lower value (5 ohm for example) .
(please can you measure the current in R1).

in the Typical Application for lme49810 in first page of datasheet they use Rsb 2,2kohm withs is a very hight value.
The output transistor of the chip will switch for classb at 2.5ma (very bad) , i think a better value will be 680ohms.

This typical application, i think, was design (adapt) for a fender guitar power amplifier, and as you may know guitar amplifiers dont need to be very linear.

Tchau.

[AndrewT]

Hi Panson,
when using 811 in the driver PCB what value for C8, or should it be left empty?
C8 is the cap across the output bias voltage.

[panson_hk]

Originally posted by smms73

In post 10 the thd level for lme49810 starts to rise at 2.5v with 1kohm.

This is because the output transistors in the chip are poor biasing,
substitute the r1 and r2 for a lower value (5 ohm for example) .
(please can you measure the current in R1).

Tchau.

Hi Tchau,

Thank you for your input. The Test circuit in data sheet uses 10 R as well. But it was not tested for 1kohm load. The problem was solved by using better heat sink. Please see this post http://www.diyaudio.com/forums/showt...87#post1821187

[panson_hk]

Originally posted by AndrewT
Hi Panson,
when using 811 in the driver PCB what value for C8, or should it be left empty?
C8 is the cap across the output bias voltage.

Hi Andrew,

I have data for 49810+21194/93 at the moment. Please see the curves below. The impact of C8 is noticeable in high frequencies. C8 = 0.1 uF || 100 uF gives the best result.

I will post 49811 result when it is ready.

[panson_hk]

Here is 49811 preliminary result (THD vs freq, 18W, 8 Ohm). Output stage is triple-EF (pre-driver, driver and output device). The chip can not provide sufficient driving current for only one driver stage (MJE15030/31).

Without C8, there is a tendency of oscillation after excitation.

[panson_hk]

I should use output triple instead of triple-EF to describe the output stage configuration (pre-driver, driver, output device). After bias adjustment, THD vs freq of LME49811 is shown below. The output power is 18 W at 8 Ohm.

[Shaun]

Originally posted by panson_hk
After bias adjustment, THD vs freq of LME49811 is shown below. The output power is 18 W at 8 Ohm.

Very nice! What criterion did you use to set the bias?

[panson_hk]

Originally posted by Shaun


Very nice! What criterion did you use to set the bias?

The bias is adjusted to eliminate cross-over distortion which can be seen from THD residual.