Class A LM4562 (or OPA2134) preamp layout with groundplane

I´m still chewing on my layout for a 6 channel preamplifier with LM4562 (or OPA2134). Forum member KSTR gave me the hint to use a groundplane instead of star ground(s) for signal and power, I tried to develop my own layout. The schema is buffer -> potentiometer -> gainstage. Biasing into Class A is done like written here: http://www.tangentsoft.net/audio/opamp-bias.html The SMD opamp is on the solder side.
The schematic:

[IMGDEAD]http://img526.imageshack.us/img526/1158/lm4562preschemop9.th.jpg[/IMGDEAD]

Solder side layout per opamp:

[IMGDEAD]http://img526.imageshack.us/img526/9820/lm4562prelaysoldnb5.th.jpg[/IMGDEAD]

And the component side / groundplane layout per opamp:

[IMGDEAD]http://img171.imageshack.us/img171/8444/lm4562prelaytopos4.th.jpg[/IMGDEAD]

This the total solder side layout. There are separte ground traces for any pair of opamps connected to the component / groundplane side. On the vertical space between the opamps a 6 channel stepped attenuator will be fitted.

[IMGDEAD]http://img174.imageshack.us/img174/7496/lm4562prelaysoldcplum9.th.jpg[/IMGDEAD]

An again the component side / groundplane layout:

[IMGDEAD]http://img529.imageshack.us/img529/2615/lm4562prelaytopcplpd2.th.jpg[/IMGDEAD]

Is this the right way of grounding? I´m stuck with this ...? :apathic:
 

KSTR

Member
Paid Member
2007-07-17 2:35 am
Central Berlin, Germany
opamp-bias4.png
 

jcx

Member
2003-02-17 7:38 pm
..
it would be a very strange buffer that didn't have high enough input impedance to leave the op amp output in push-pull Class A with its factory set internal bias

example: BUF634 widebandwith mode Zin = 8 MegaOhm || 8 pF

even 100 uA op amp output stage AB bias current is going to be deep Class A for any V the op amp can swing into such Hi Z

the LM4562 has 5 mA typ per amp to play with and a spec of 13 Ohm open loop Zout - implying lots more than 100 uA output stage bias current already
 
... one single GND plane is IMHO the easiest and best (that is, don't split it, nowhere)
Alright. I tried to imagine current flow in the groundplane and had the thought the particular opamp pairs otherwise would influence each other. Is it right to place the ground point centered?

C3, C4 are not connected to the top poured ground?
They are connected to ground in series with the ground connections of C5 / C6.

even 100 uA op amp output stage AB bias current is going to be deep Class A for any V the op amp can swing into such Hi Z
I absolutely agree with you. If just thought to have the JFET connections as an option and to experiment with different opapms.

Thank you all! :)