Circuit schematic question for Rotel amp.

Alaza · 7th July 2011, 06:06 PM

Hi guys,

I have a Rotel RA-840BX4, and after the Tone switch started being less and less stable I decided to dismount it and short the two channels, forcing it off. My question however is the application of the IC701 in the circuit. The manual is here:

http://www.acousticpsychos.com/Files...BX4-int-sm.pdf

As far as I can see it just gives a gain of approximately 3, but why is it necessary?

Thank you

jaycee · 7th July 2011, 11:46 PM

Just buffering for the passive tone control stage id say. Combined with IC702 it makes a gain of +6 which is pretty usual for a preamp. I'd bypass it and adjust the feedback network of IC702 to make the +6 gain (or less if you dont need so much)

Tekko · 7th July 2011, 11:54 PM

Weird feedback loop, i bet the amp would sound alot better if the feedback was routed to the other LTP input like usually done, than beeing inverted through a opamp and then sent to the signal in together with the input signal.

Alaza · 8th July 2011, 05:22 AM

Since I have forced the Tone switch off, I will never be able to use the Treble and Bass functions again. So couldn't I in practice also just rewire it so I'd bypass IC701 and IC702, or is 702 needed for something I can't see?

Alaza · 8th July 2011, 10:05 PM

I asked a colleague of mine in terms of removing the IC701, and he said it would mess up the system since it's acting as an impedance matcher and buffer, so you would have a voltage division between R711 and R601, which is not desirable.

7th July 2011, 06:06 PM	#1
Alaza diyAudio Member Join Date: May 2011	Circuit schematic question for Rotel amp. Hi guys, I have a Rotel RA-840BX4, and after the Tone switch started being less and less stable I decided to dismount it and short the two channels, forcing it off. My question however is the application of the IC701 in the circuit. The manual is here: http://www.acousticpsychos.com/Files...BX4-int-sm.pdf As far as I can see it just gives a gain of approximately 3, but why is it necessary? Thank you

7th July 2011, 11:54 PM	#3
Tekko diyAudio Member Join Date: Jan 2005	Weird feedback loop, i bet the amp would sound alot better if the feedback was routed to the other LTP input like usually done, than beeing inverted through a opamp and then sent to the signal in together with the input signal. __________________ The point of life is to build atleast one audio amplifier before you die.

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7th July 2011, 11:46 PM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Just buffering for the passive tone control stage id say. Combined with IC702 it makes a gain of +6 which is pretty usual for a preamp. I'd bypass it and adjust the feedback network of IC702 to make the +6 gain (or less if you dont need so much)

8th July 2011, 05:22 AM	#4
Alaza diyAudio Member Join Date: May 2011	Since I have forced the Tone switch off, I will never be able to use the Treble and Bass functions again. So couldn't I in practice also just rewire it so I'd bypass IC701 and IC702, or is 702 needed for something I can't see?

8th July 2011, 10:05 PM	#5
Alaza diyAudio Member Join Date: May 2011	I asked a colleague of mine in terms of removing the IC701, and he said it would mess up the system since it's acting as an impedance matcher and buffer, so you would have a voltage division between R711 and R601, which is not desirable.

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