INA217 and the DC-Servo

[Ettos]

Hello to everyone!
I was wondering if I can replace the OPA137 (I can't find it!) for the DC output control loop with another FET-input opamp. What do you suggest? Is it good an OPA134? Should I modify the schematic to implement this one?

Thank you very much!
Matteo.

P.S: Sorry for my English...

[evm1024]

Where are you located? TI shows them o their web site. They even have free samples.... What package is used?

--Ethan

[Ettos]

Originally Posted by evm1024

Where are you located? TI shows them o their web site. They even have free samples.... What package is used?

--Ethan

Hi Ethan,
I alredy tried to request free samples from TI but they don't ship them to Italy for some unknown reasons... maybe because there are high taxes and tariffs.
The package I need is the PDIP-8.

Thank you,
Matteo.

[Minion]

In one of My INA217 2Ch preamps i used a TL072 for the DC Servo (half of the TL072 for each channel) and it worked just fine.....

in my later versions I simply used an High quality output cap(470uF 16v Nichicicon Muse or black gate) or a Output Transformer as opposed to a DC servo to block DC...

I haven"t noticed any audible differance useing a Good output cap over the DC servo and it makes the Design much easier to implement and make for a smaller PCB.....

With the INA217 you really only have any DC offset at the High gain settings and the Input of the next piece of equipment in the Chain most likely allready has an Input cap to block DC.....

Good Luck

[Ettos]

Originally Posted by Minion

In one of My INA217 2Ch preamps i used a TL072 for the DC Servo (half of the TL072 for each channel) and it worked just fine.....

in my later versions I simply used an High quality output cap(470uF 16v Nichicicon Muse or black gate) or a Output Transformer as opposed to a DC servo to block DC...

I haven"t noticed any audible differance useing a Good output cap over the DC servo and it makes the Design much easier to implement and make for a smaller PCB.....

With the INA217 you really only have any DC offset at the High gain settings and the Input of the next piece of equipment in the Chain most likely allready has an Input cap to block DC.....

Good Luck

Ok, I think I'll use the TL072... but I'm also interested in the cap solution. Sorry for my ignorance but, how do you wire the cap? The "-" of the cap should go to the "Out" of the ina217 and the + to the jack connector?
Thank you!!
M.

[Minion]

You just put a Cap in series with the output with the + of the cap faceing the Ina217 and the - of the cap connected to the output....A Good quality cap is needed here and possibly even bypass it with a good 0.1uf poly cap....

Capacitors Block DC But Pass AC so putting a cap on the output blocks any DC from entering the next piece of equipment.....

Cheers

PS: if you are only doing one Channel you can use the TL071...

[mshilarious]

Originally Posted by Minion

You just put a Cap in series with the output with the + of the cap faceing the Ina217 and the - of the cap connected to the output....

Given that the DC offset should be a very small figure, often you'd orient the cap the other direction and use a 63V cap to block incoming phantom that was erroneously connected.