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sonu 17th April 2004 02:16 PM

Class D am
I just got lm4651/2 , for which I made a good layout of single sided PCB, considering the high frequency operation. But when I connected it after assembling the whole kit and powered the kit with +-13, first I checked it by removing the LM4652 & inductors, there were oscillations on the gate points (150Khz). Then connected the Input, but there was no modulation on the gate, checked on Pin 11, there I am getting audio signals. Then I decided to connect the LM4652 & inductors and check. I
connected an 8ohm sub, but there was no sound. I can just hear a little click click from the sub, when I am very close to it. I don?t know if current limit is getting activated (used Rsckt ?39k). How does the short circuit / current limit work in LM4651, as there is no shunt resistor (for current sense) between the source / drain of LM4652.

Please guide me what may possibly be wrong.

Bharat Sangtani.

li_gangyi 17th April 2004 11:18 PM

did you provide 5V to the standy pin?? which is pin 13 if you didn't know...and maybe the voltage is a tad too low...try in the range of 18-20V...have you checked for any obvious shorts and stuff?? the Cstart might be giving you problems also...I've tried this amp on P2P and works out really well...but I'm kinda stumped with the standby function requiring 5V to the end I just made a potential divider to activate it...

soundNERD 18th April 2004 01:43 AM

sorry that i cant help you, but i would like to play around with those chips. could you post the pcb image here? maybe i could build it and figure it out and help solve the problem



li_gangyi 18th April 2004 06:42 AM

there is a suggested PCB on the PDF (datasheet) itself...but because it uses SMD components...I didn;t use it and went with perfboard and for me...

sonu 19th April 2004 04:06 PM

Class D amp

On checking on standby pin I get a fluctuating voltage between 9V-11V, I have just connected a 4.7uf to -vee as shown in the datasheet. shall I connect it to +6V on chip Ref thru a Resistor.
Can U post me the voltages on pins in normal working Mode.
Will Sided PCB create any problems. One more thing for the clamp diodes I have used BA157, is that OK.

I want to use +-80V to get higher Outputs, can I use a Mosfet driver (IR2110) & 200V Mosfets from the outputs of LM4651, and how will the bootstap cap work in that case.

I am gonna use Likwitz Crossover (@180Hz) to use this for sub amp, should I keep the modulation frequency low to 50/75Khz to get better efficiency, and what all modification in the component is neccesary for getting optimal performance.

Can I use a small toride inductor for L1 for minimum loss in the
inductor. Asking you this cause once I made a Passive crossover with toride, for same reasons, but it generated rattling noise in the sub in moderate power levels, why was it so.

After successful completion of this I wanna make Amp based on HIP4080A, which I have got in stock.
I won't compromise in quality I am gonna check for the best quality and power.


sonu 19th April 2004 05:47 PM

class d amp
Sorry I have grounded standby pin.

li_gangyi 20th April 2004 09:16 AM

Well just bring it up to 5V...and it'll work...then you can figure out if you can use the other parts...hehex...I didn't really mess about with that amp as I was using my friends torroid to power it up and then had to hastily return it...sound was ok on my subs that I tested it with...didn;t try to use "standard" speakers...I figure it wouldn't be that good...I didn't have a scope at that I never had a look at the output waveform....time to try it again I guess...

clemon 22nd June 2004 06:50 PM


Did you build your pcb for sub-woofer application or full-range? I'm looking for an easy pcb layout for full-range use. If your layout is compatible, could I sneak a peek?

sonu 24th June 2004 05:23 PM

I have made a single sided PCB, for Sub's using active crossover,
but it is still not in working yet, I am getting modulation without fitting 4652, but with 4652 there is no output OR modulation even.
Maybe its better to go in with double sided PCB.
I u are thru with ur design then also let me know.


sonu 5th July 2004 04:52 PM

Now I have my Class D Amp ready. And it is a wooopping 650W of real power to drive my 2 HUNGRY Little Subs @ 2Ohms Load. I have powered it at 70V driving P150N Mosfets, and the amp is quite cool even at high power levels. As I have used it for my subs, I have used a active Linkwitz crossover, and it has a real base.
I have not used any feedback but have made shortcircuit & Overload circuit which works perfect.
There is only one problem that i have a 150Kz sine wave of 3V PP showing on my oscilloscope with no input to the amp, is it due to the dead time between the pulses.
I have used a Filter inductor of 550uH with .68uf Caps, which is not a perfect calculation.
Does anybody guide me to get a spread sheet for filter Calculation.


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