LME49710 Phono Stage

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I've spent a fair bit of time testing and I think I'm dealing with a few problems. On one board servo had failed and shorted the inverted and non-inverted inputs. On the other board the output of the positive rail LME49710 had become shorted to ground although I cannot find any mechanical reason for the short (I've just ordered a 10x loupe). I've started to doubt my power supply now as well.
I tried a 1M resistor between the inverted pin of the servo and ground, that resulted in an 11V offset at the output.

I need to re-stock a few components now so after Christmas I'll be putting together a new PS and making up new amplifier boards and try to work out why the components failed.
 
Following a post mortem on the board that I thought the LME49710 had failed on I found that U3 had developed a short between V- and the output of the unused amp (pin 3). I've got the power supply section of a new board made up and it's measuring as expected, just need to wait now for the rest of the components to arrive before I can go any further.
 
I completed the new board and was still getting 200mV offset at the output so I soldered a 1M leaded carbon resistor from the servo negative input to ground (as suggested by rayma). Now I've got <1mV offset at the output. The offset is jumping about a lot (+-700uV), I don't know if that indicates a problem up-stream. Anyway I'm going to get some more boards made up so I've got a more permanent solution.

I'm thinking about using another LME49710 as the servo... does anyone have an opinion as to whether that might be a better choice than the OPA1652 for that application?
 
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yes, i was going to suggest the same. opamps have inputbias current, and this current charges C6 to some level that you later see as output offset. this resistor should help.

you may want to increase the resistor R14 (from servo output to second signal opamp) to reduce the strength of the servo. this is found to be beneficial for the sound. go up in value until the servo signal before the resistor (at servo opamp output) is around 2V peak-peak. with the “paradise“ phono stage we used OPA134 for the servo, with good result.
 
I'm getting some new boards made up to include the new resistor (and a few other improvements). I'll experiment with the resistor values... I need to make sure I can easily get a soldering iron to both ends of the resistors without accidentally moving/melting other components (I've done both). Is there a trick to experimenting with the resistors or is it just a matter of soldering and desoldering (and hoping the pads can survive the abuse)?
 
New boards arrived, I'm now down to 1-2mV offset so plugged them in and finally listened to them, very happy with the sound. RIAA eq is close enough with the 1% ceramics (worst case 0.13db RIAA deviation @ 20Hz & 0.03dB between channels) and noise and THD measure fine with my uncalibrated test gear.

I'm still thinking that I may be better going with a more suitable op amp for the Servo, will probably try an OPA140.
 
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