BPA200, replacing LF412ACN with?

[CJ900RR]

Thinking of constructing a pcb based on the BPA200 in Nationals AN1192.

My simple question is, can I replace the LF412ACN with LM4562 straight forward, or do I have to re-calculate the values on other components to?

Best regards, Calle...

[tlmadsen]

HI Calle

Normaly you should be able to replace LF413 with all most any other DUAL op-amp, but why would you. ??
It is part of the DC-servo, so the only real important parameter is its offset. Something like the AD712 (I think it is called) might be better in that respect.

Your DC-servo will not sound "better" by putting a fancy Dual op-amp into it.

I have no problem using a DC-servo (see some of my other replys), but people that don't like them are normally against the hole "topology" more than a single component.

Have fun

[peranders]

The servo opamp will feed back audio signals up to 500 Hz to 1 kHz. So it must be good in those frequenies which most decent opamps are. Over 100 Hz a very small part of the audio signal goes through the servo. As Thomas says almost any opamp will fit. Personally I chosen an AN8620 as a buffer + servo and for the servo part it's massive overkill but it's nice with 80 uV offset! You can see my implementaion of AN-1192 at my homepage.

[peranders]

The servo opamp will feed back audio signals up to 500 Hz to 1 kHz. So it must be good in those frequenies which most decent opamps are. Over 100 Hz a very small part of the audio signal goes through the servo. As Thomas says almost any opamp will fit. Personally I chosen an AD8620 (or OPA2134) as a buffer + servo and for the servo part it's massive overkill but it's nice with 80 uV offset! You can see my implementaion of AN-1192 at my homepage.

[CJ900RR]

Thank you for your answer. That was what I thougt. And today I found some LF411 and LF412 stuffed away at my work. But they where labeled only CN, not ACN. But what I can see from the datasheet its only V-rating that difference from the ACN-version... I will try them first.

But I have a new question. How do I do with the mute-part of the LM886. Do i need mute-resistors and cap's for every LM3886, or do I need only one to mute them all?

Best regards, Calle...

[peranders]

The mute resistor is very important. No resistor = MUTE.

10k is a normal value but I did chose 33k + 100 uF just because I wanted a longer delay _with_ a 100 uF cap. If you don't want the delay, just omit the capacitor but it may be a good idea to have it since you have a DC servo which may create a small startup transient. Please check the datasheet and the diagram over this mute resistor. You should have more than 0.5 mA from that pin.

[BrianDonegan]

Interesting post on the mute resistor:

http://www.diyaudio.com/forums/showt...710#post845710

Try a 4k7.

Also, we are using the LF411CN with great results.

[peranders]

Notice also my comment there about the measurements.