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Fast GB: LM4702 high power amp test board ;)

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#103
Here are a couple screen shots of the performance with Veteran's first board with some modifications (nothing major) as mentioned earlier in the thread. The graphs are taken with an Audio Precision 1, 80kHz filter, 8 ohm load, both channels driven and in phase (there is some Ch-Ch interaction that causes THD to be higher when both driven). The output power plot is with 1kHz and the frequency plot is with 25W/Ch. Not too bad performance and it sounds really good to me but I must admit I am not a critical listener. But I heard things in songs I had never heard before and these were very familiar songs to me. Excellent definition in the music now, so clear.

-SL
 

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#105
SCHEMATIC

Hi Veteran,
Can I see your schmatic again. I have problems connecting to the link in your post. I'm planning a CF output stage with BJTs. Probably parallelled output transistors with MLJ3281/1302 since I have quite a few gathering dusts. Any comments.
Cheers,
K K
 
#110
This is my final design of LM4702 with MOSFET transistors. I don't need more power and any other modifications, because two of this boards will work in symmetrical mode. I can put you on the list for 5 boards - I will have them Monday 🙂

Measurements made by SpittinLLama shows that this is very good amplifier even when assembled with standard components:

An externally hosted image should be here but it was not working when we last tested it.
 
#112
Veteran,
Why didn't you mount the LM4702 to the heatsink like the MOSFET's? I've seen the pins bent up so they can be loaded through the bottom. I figured this was required. Do you heat sink the LM4702 at all? Any pics of the current config to show this?
 
#115
alexcd,

heat sinking of the opamp is not required, but in my experience the chip has gotten a little bit warmer than I would have liked when running past +/-50V. I do NOT, however, recommend using the output stage heatsink for the chip since there is a greater chance for that sink to get hotter than you would like the opamp to be. I like the idea of putting a TO-220 heatsink on it since that is about the right size/heat dissipation and it keeps the opamp off of the output stage heatsink.

Interrestingly, the National application note has an un-sinked chip, and those guys have reported no problems. In fact, there is a specific FAQ respons over e to whether to sink the LM4702. Do a quick search on National's pages and you will see what I mean.

David
 
#116
alexcd said:
Veteran,
Why didn't you mount the LM4702 to the heatsink like the MOSFET's? I've seen the pins bent up so they can be loaded through the bottom. I figured this was required. Do you heat sink the LM4702 at all? Any pics of the current config to show this?
Click to expand...

Depending from supply voltage. A little heatsink is needed - PCB is designed to mount all of the devices on one heatsink.
 
#117
Companion to LM4702 - the LM4562 dual op-amp 😉

schematic
 

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