Originally Posted by EngAtRes
I am on the engineering team at Resonessence labs and wanted to post a link to our FAQ where we have addressed the AD797 JFET input issue. Please feel free to check it out, we tried to go into some detail to show that it really is a JFET input.
Also, we are very appreciative of any feedback / opinions / suggestions on our products.
Resonessence Labs Engineering Team.
Thanks for pointing me with more information.
Im in no position to argue with you and have no in tentions to do so.
You have explained in link that the circuit of the AD797 clearly shows bipolar devices for Q1 and Q2, this does not qualify it to be placed in the categry of a Jfet device as you have specified in your specification. You can designed basic circuits and conditioned the AD 797 to give you results that reach outcomes close to that of a Jfet but this doesn't give you the justification to class this as a Jfet device. Only the designer or AD can do this. Why? because all the other opamps that have this semmetrical differential bipolar device like the one used in AD 797 and it is a commom circuit that most manufacturers such as AD BB and LT uses places this typical circuit as bipolar and not Jfet. If you do continue to document the AD 797 as a Jfet then that means all the other manufacturers must do the same, If that is the case then what do you call a differential circuit with real Jfets instead of bipolar? Do you see the can of worms you are opening up!
I like to explaned that the AD797 is not a Jfet or fet input device to all involved in Head Fi with no electronics background.
Feedback is commonly used in most opamps to control non lineararities. It provide stability under normal operating conditions and most amplifiers will have some feedback. The AD797 requires feedback to be stable. Q1 an Q2 are place in a differential arrangement for better noise rejection than a normal single stage. Q1 and Q2 of an AD797 are normal transistors with a base, collector and emitter. the Base and emitter will have a 0.6-0.7 volts drop across it when it is correctly powered up, therefore require bias current to control the emitter/collector. therefore AD do not class this as a jfet device
A fet device is differently drawn in circuits and has a gate, drain and source compared to a bipolar; base, collector and emitter. The gate requires no current for the device to switch on/off at the drain/source therefore it behaves like a valve. Yes you can say that a fet is a SS valve!
Devices such as AD 825, AD 8627-1/8637-1.AD 8065, OPA 2134, OPA 627/637/827. are all Jfet devices, why because the are outlined and classed as jfets according to there data sheets and there electrical characteristics are typical of a jfet.
Devices such as AD797, 827/826 , OPA 1611 are not classified as jfets because there electrical characteristics are typical of a bipolar device. Infact the OPA 1611 says it is a bipolar!!!
I dont care if you classified the AD797 as a jfet because I dont give a rats. I know that the AD 797 is a bipolar device and not a Jfet. What team invicta has to worry about is the legality of quoting and placing the AD 797 as a jfet because your competitors and curtain parts of the world will be scrutinising it like I have!