Question on subwoofer circuit

yzriver · 19th April 2009, 02:41 AM

Could some people explain what is the function of the Operational Transconductance Amplifier LM13700 in the attached circuit? It looks the inputs are rail voltage. Why? Any online reference?

It is a circuit of a subwoofer.

Thank you.

rtarbell · 19th April 2009, 03:55 AM

I can't really see your schematic very clearly - do you have a schematic picture that is larger?

fotios · 19th April 2009, 06:38 AM

I think that, the first OTA of LM13700 (i mean this which of the output is connected to the input of power amplifier) it seems to be modified as a voltage controlled resistor which of the control voltage is produced from the second OTA. If it is so, then the LM13700 in the present circuit serves as a limitter.
From experience, in audio power amplifiers LM13700 usually used as an AGC device, e.g. as compressor or limitter to prevent clipping of power amplifier etc.
Please, take a look in the data sheet of LM13700 from the National Semiconductors site for additional information. Anyway, the whole circuit of this amplifier IMHO it is quite sophisticated.

Regs
Fotios

19th April 2009, 06:38 AM	#3
fotios diyAudio Member Join Date: Feb 2007 Location: ΔΡΑΜΑ - North Greece	I think that, the first OTA of LM13700 (i mean this which of the output is connected to the input of power amplifier) it seems to be modified as a voltage controlled resistor which of the control voltage is produced from the second OTA. If it is so, then the LM13700 in the present circuit serves as a limitter. From experience, in audio power amplifiers LM13700 usually used as an AGC device, e.g. as compressor or limitter to prevent clipping of power amplifier etc. Please, take a look in the data sheet of LM13700 from the National Semiconductors site for additional information. Anyway, the whole circuit of this amplifier IMHO it is quite sophisticated. Regs Fotios __________________ Best Regards FOTIS ANAGNOSTOU Direct Contact: eal@dra.forthnet.gr

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19th April 2009, 03:55 AM	#2
rtarbell diyAudio Member Join Date: Sep 2005	I can't really see your schematic very clearly - do you have a schematic picture that is larger?

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