[ppl]

remember the CMRR is going to fall as the imbalance between the Invert and non invert input resistences. Chances are that thay are not matched. and with a Vol Pot on the Input thay sure will not be.

Ripple current of over 1 Amp for a 4,700uF cap is not crazy. I don't have the Os- con data at hand at the moment HoweverLooking at a CDE type 301 a Low ESR, ESL Fast cap I see a rated Max Ripple Current For a 4,700uF/25 Volt Radial lead Electrolytic is 8.5 Amps @ 120 Hz. and 11.4 @ 20KHz. so ripple current is not a problem in your application. BTW other relavent data for this Capacitor is ESR=0.018 Ohms @ 120Hz. & 0.007 Ohms @ 20KHz. ESL=12 nH.. So at least this cap and probaly the one you use are going to technicaly do the Job.

However I still have a Real problem foating the ground Between two capacitors. However it is your Amp and if you are happy with it that is really all that matters.

 

[Tomo]

Hello,

I still don't get it. Does it really make measureable difference?

I mean you do have bypass capacitors in VGD they provide power for the ground drivers as well. Current draw must go to those capacitors which in turn must also recharge. Which, sounds to me, would cause the same problem.

From my point of view, if the caps are good (which gives me low impedance), I could do without ground drivers. But I see you don't believe that. I need to know why. I am sure you have reasons for it. I am interested in them.

Tomo

P.S. I do agree with you about driving Grado cans though. But then I would simply build myself dual PSU. ... Aww ... I am interrogating you ...

 

[ppl]

Hi Tomo. No i do not feal like i am being interrogated, How ever the concept is so simple that my poor comunication skills are not allowing you to understand what i am trying to say. Our old frend from N.Y.C. that has been MIA did a test of this however he uses grado's I use Sony's another low impedance can and the difference is quite noticeable.

anyway the basic concept is you have no direct current source for the ground ether from a VGD, battery or Power transformer to source and sink current on the ground side of the load and are relying upon the stored charge of the capacitors to supply current. so the ability of the load return to sink and source Current will depend upon the charge of the caps.

At the best case under light loads where the caps have not depleated a significant amount of charge the speed is limited by the slow reaction time of the capacitors. http://www.linear-tech.com/pub/docum...n&document=135 While this app note bypasses the purly capacitor aproach and deals insted with resistive networks maybe this will allow an understanding of what is going on in VGD systems.

As stated before your method will work it is done alot of times. most often when cost is a factor.

 

[Tomo]

Thanks,

I will check it out. Thank you also for the schematics you send me.

T