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PPAS Build Thread. - Page 5

post #61 of 254
Thread Starter 
AD8066 / OPA132 - BUF634 on quiescent, measures 20mA max, 15 typical, 10 minimum into RS-1s at max volume.
post #62 of 254
Try the AD826 if you can find it there. I'm curious about the sound with it.

Edit: ugh...8066 :P
post #63 of 254
Quote:
Originally Posted by Filburt
Try the AD826 if you can find it there. I'm curious about the sound with it.

Edit: ugh...8066 :P
Isn't the AD826 a bipolar input?
post #64 of 254
Thread Starter 
The AD826 is bipolar input.. so special care would be needed to run that in a default gain of 11.. Id probably use it for gains of somewhere around 2.

Filburt - whats wrong with the AD8066?
post #65 of 254
Quote:
Originally Posted by ATAT
The AD826 is bipolar input.. so special care would be needed to run that in a default gain of 11.. Id probably use it for gains of somewhere around 2.
I thought that op-amps get more stable as gain increases.
post #66 of 254
Quote:
Originally Posted by quicksilver96
Isn't the AD826 a bipolar input?
...yes. So are some of the other chips we've been looking at. Bipolar input isn't some sort of unmanageable thing
post #67 of 254
Quote:
Originally Posted by rsabo
I thought that op-amps get more stable as gain increases.
I think the idea behind that is that bi-polars tend to generate DC offset and the more gain the more offset you have to deal with.
post #68 of 254
Quote:
Originally Posted by Filburt
...yes. So are some of the other chips we've been looking at. Bipolar input isn't some sort of unmanageable thing
If I had one more board, I'd definitly try to get the AD8397 to work, just for fun.

neilr: ok, thanks.
post #69 of 254
Quote:
Originally Posted by NeilR
I think the idea behind that is that bi-polars tend to generate DC offset and the more gain the more offset you have to deal with.
*shrug*...I haven't had too much trouble with offset on bipolars either in the PINTs I've made or in my test box (which has, at times, been running at gain 11). So, I think we may be OK
post #70 of 254
Quote:
Originally Posted by Filburt
*shrug*...I haven't had too much trouble with offset on bipolars either in the PINTs I've made or in my test box (which has, at times, been running at gain 11). So, I think we may be OK
I was just referring to the general nature of bi-polars, not specifically any particular circuit. Although you didn't have a lot of trouble with your Pints (nor I with mine) the design of the circuits tends to optimize (minimize) input offsets as opposed to optimizing other things (such as noise) , and I think that is part of the reason why there was so much trouble with the Pint compared to other amps using jfet inputs. other than the fact 8397 likes to oscillate
post #71 of 254
Quote:
Originally Posted by NeilR
I was just referring to the general nature of bi-polars, not specifically any particular circuit. Although you didn't have a lot of trouble with your Pints (nor I with mine) the design of the circuits tends to optimize (minimize) input offsets as opposed to optimizing other things (such as noise) , and I think that is part of the reason why there was so much trouble with the Pint compared to other amps using jfet inputs. other than the fact 8397 likes to oscillate
Well my test box just has a basic local feedback loop in it with not even a resistive divider at the moment. I may stick in a TLE2426 or something at some point. I just use it for testing various ideas. It does have some nice power decoupling in it at the moment, though. Anyhow, I am not having too much trouble with offset in general other than if something else is wrong in the circuit that would foil many other op-amps.
post #72 of 254
Quote:
Originally Posted by Filburt
...yes. So are some of the other chips we've been looking at. Bipolar input isn't some sort of unmanageable thing
I wasn't saying that it was unmanageable, just that the circuit topology so far hasn't been promising with the other bipolar opamp that had been tried (LM617x). I enjoy the sound of the LM617x and once I get around to working on this project, I will try a few things to get that offset down. If I can't, well theres plenty of JFET input chips that I'd stick in there too. I've also got a dual 8397 pint that runs without any problems. :shrug:
post #73 of 254
Quote:
Originally Posted by quicksilver96
I wasn't saying that it was unmanageable, just that the circuit topology so far hasn't been promising with the other bipolar opamp that had been tried (LM617x). I enjoy the sound of the LM617x and once I get around to working on this project, I will try a few things to get that offset down. If I can't, well theres plenty of JFET input chips that I'd stick in there too. I've also got a dual 8397 pint that runs without any problems. :shrug:
Well, the LM617x is also a ridiculously fast bipolar op-amp with a PSRR that may be less-than-friendly in some situations. The AD826 should be easier to stabilise, but I think if we bolster the 6171/72 with some additional power decoupling and maybe some lowpass filtering (ferrites) it may chill out.
post #74 of 254
Thread Starter 
Regarding bipolar inputs -

I believe the problem is not bipolar inputs in an inherent sense, but the current stock configuration.. gain of 11 is pretty damn high for a portable amp.. running it at a lower gain of around 3? would probably minimize offset (1/4th) one could also decrease the input resistor values to good effect. I'd expect one to be able to drop offset values to around 30mV (just dividing right now =p) with the LM6172. I currently dont have the extra resistors to test this theory, so it'll have to go on the backburner.

Also, the AD826 would be easier to implement since the LM6172 is pretty quirky..

Also, unstable opamps are not reccomended on the ground channel (ie lm 6171) since they have a tendency to misbehave.
post #75 of 254
So I was going through some old electronics crap I've got sitting around, and found that I've got a wall wart (probably unregulated?) that puts out 24V @ 100mA, and my PPAS is drawing about 40mA. Will this be ok to use with a pint-style trickle charge circuit (lm317, resistor, diodes) or should I be looking for something with a bit more current avaialble?
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