Comparing LME49810, 49830 and 49811

[panson_hk]

Originally Posted by tryonziess

Panson,
Have you done any experiments using separate elevated power supply for the frontend and checked the results.
I have read most of this and other threads on these chips but no input on separate power supplies.

Also, have you given any thought to providing a pcb on your website for the power mosfets and a driver for say 3 or 4 pairs. The schematic is vague on the exact parts for the driver part of the output when using mosfets.

Tad

Tad,

Yes, I will make new universal power board for at least four pairs output devices.

I did test for a separate rails for LME. Let me dig them out.

Panson

[panson_hk]

I slightly modified the existing four-pair TT power board to have dual drivers (MJE15030/15031 x 2). Each driver pair drives two TT. Here is THD vs freq for 2.7 R, 4 R and 8 R loads. At 121 W into 2.7 R, THD is only 0.003 %.

[AndrewT]

the extra drivers will allow a slightly increased gain from VAS to Output.
The extra drivers have reduced the current demand from the VAS.

This is proof that a pre-driver stage is required when larger output currents are required.

[JPV]

Originally Posted by AndrewT

the extra drivers will allow a slightly increased gain from VAS to Output.
The extra drivers have reduced the current demand from the VAS.

This is proof that a pre-driver stage is required when larger output currents are required.

Perhaps I don't have a good understanding of this circuit but to me using multiple drivers in // or one driver for the output transistors in // gives the same current requirement for the VAS ( distributivity of multiplication with respect to sum).
It seems to me that the main advantage of multiple drivers is less current in each driver and so less distortion.

JPV

[AndrewT]

the drivers as well as the outputs suffer gain droop at higher currents.
If the drivers only have to drive 2pair instead of 4pair of outputs then the driver gain will be higher and thus the VAS current into the bases of the drivers will be less.
That is equivalent to saying the VAS sees a higher load impedance.

[panson_hk]

Here is a plot for the low-level grounding wire placement. This wire connects power supply 0V and small-level signal section ground. The highest THD curve is obtained by placing that wire ~1 cm from output devices.

The other curves are associated with other wire placements with slight displacement with each other. With the best placement in the test, the THD at 20 kHz for 2.7 Ohm is 0.002 %!

[qusp]

can NJL4302DG/NJL4281DG be dropped straight into your black universal boards given enough heatsink? I was going to grab some of both and try. and also, i'm pretty sure its a yes, but I can use the thermal track only 4 pair board with 2 pair to start and then add more later if needed right?

[panson_hk]

Originally Posted by qusp

can NJL4302DG/NJL4281DG be dropped straight into your black universal boards given enough heatsink?

Yes, they can be used without problem.

[qusp]

thanks, OK I think thats sorted it. will use your amps for my bass channel will send an order in the next few days

[kct]

Originally Posted by Sebastiaan

You actually can use a ground-plane with excellent results. I finally bite the bullet and went for ground-plane topology, after being told many times ground-planes are no good for amplifiers Bruno Putzeys from Hypex finally convinced me, and thought us how to do it.

If you take very good care about placement of components, (start with a empty piece of paper and draw out the ground loops out). Another point, my amplifiers are all feed balanced, so the negative input reference to the output of the driver opamp instead of the ground-plane. That can be the biggest reason why I don't have any ground-loop related hum.

I used the LM4702 in a multichannel amplifier application, with one unbroken total ground-plane, and the THD measurements are below the limits of what I am able to measure (0.0005%). I never achieved this results with star grounding. Noise floor is inaudible low.

Second benefit, I can put my cellphone in front of the circuit and no "buzz" anymore over the speakers.

A ground-plane design does sound different then a star-ground design. The same circuit with ground-plane sound more analytical, and a more airy in the high-end. and it seems subjectively speaking, more resolving details. Most strange was that the bass seemed a factor 10 tighter with the ground-plane. Can't really explain why in technical terms, but it was very noticeable in a listening panel of people.

One other note though, my design is a 4 layer board, and all high current supply lines and loudspeaker lines are all stacked on top of each other and are kept away from the LM4702 and other low current stages. Magnetic influences are minimized.

My opinion is, with careful design and routing, one can make superior results with ground-plane topology, and the LM/LME driver chips can work perfectly with ground-planes.

There is a understandable "fear" fro ground-planes, but we should overwin those, learn from RF experts and papers and give it a try.

With kind regards,
Bas

Sebastiaan,

you have been recently at a EMI Signal Integrity class haven't you ?

I was, and boy what an eye opener it was. I am looking at a circuit board with a different set of eye' s now. Thanks for highlighting this very important yet often overlooked or better said neglected approach.

Keep the loop area as small as possible and things magically fall into the right place


panson_hk,

great job, I am looking forward to the final version.

Thanks for your awesome contribution

DIYAUDIO forever

Cheers