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I have seen that the AD711 and the AD797 have been used to upgrade the the opamp in Wright's Super Regulator. Has anyone else tried any other opamps that worked and are stable? How do they sound compared to the LF351's or the IC's mentioned about? Any info would be great.
Follow Ups:
info, I reall appreciate it.
I did a bunch of experimenting on Allens superregs a little while ago, and found the AD797 to sound great, but what makes an even bigger difference in my experience is replacing the 0.47uF 400V cap (thats in parallel with the 1M resistor, not the one thats in parallel with the 22uF output cap).I originally replaced it with an auricap and thought it sounded quite brittle, and experimented a bit more until I found a solution that I like a little better than the cap thats supplied with the superreg.
Oh also, replacing the 22uF electrolytic with an ansar supersound was a nice tweak, but not as drastic as the 0.47uF cap mentioned above.
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I've tried several different Opamps in them including high end parts from LT and Burr Brown and I agree that the AD797 sounds the best. Sounds the best in Camille's shunt regulators as well. Thanks Allen, since I tried the AD797 at your suggestion.
Charlie,
Thank You for the reply and info, I will give the AD797 a try.
But It does need a large (2uF is good) SMD ceramic bypass cap directly across the + & - pins to be stable.We have used other opamps that are unity gain stable with good results - but the 797 is the best.
I had tried the AD797, but it oscillated heavily, so I went back to the LF351. I didn't know about the bypass cap directly across the + & - pins - I thought that the on board capacitor would suffice.Did you say 2uF SMD CERAMIC cap? Is this readily available? Is it easily soldered on the pcb?
... so I went back to the LF351. I didn't know about the bypass cap directly across the + & - pins - I thought that the on board capacitor would suffice <Nope - in fact there is no "on board" cpacitance as such supplied in the SReg kit - there are holes for one but the pcb layout guy (not me) made them too far away to work effectively.
> Did you say 2uF SMD CERAMIC cap? Is this readily available? <
Yes, and they are in 63V rating and big enough that even I can fit them on the SReg, and even (most times) on SACD player boards. Now you can even get 4u7 ceramics but I don't know if they are up at the 40V+ rating one might need for a SReg fitting.. Farnell in a good place to look fir such things for us non Bush boys - but Farnell have a US network as well - associated with Newark I believe.
There is another oscillation fix for the SReg that sometimes solves things - but othertimes it makes it worse:
Add a capacitor across the 10k R that goes from the output of the opamp to the gate of the shunt MOSFET - this cap is actually shown in the map of the FVP2 on page 12 of that chapter in the "Tube Preamp CookBook" - but depending on the actual layout you use - it is normally better off without it, which is why it's not shown in the kit schematic.
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But if the SReg oscilates even with the SMD bypass right on the opamp pins - then try adding it until the oscillation stops. It will be somewhere in the region of 100pF up to around 1nF - and you'll need a decent scope hung on the (regulated) B+ rail to see it.
Thanks, Allen, for the tips.I will look at Farnell's and oder a series of needed values.
What I forgot to mention in my previous message is that with the AD797 fitted on the SuperReg, I found that I liked the sound of my FVP5 better. But, after I saw the result on the scope, I took it off.
The crazything about the SReg is that it still works wonderfully well as a regulator even when oscillating.But if you liked the sound with oscillation - you'll love it when it's stable!
Apparenly you guys have needle tipped soldering irons, a huge magnifying glass, and you never drink caffeine...
I would start by using Tacpak or some adhesive especially for SMDs to fasten the cap to the top of the IC so it doesn't move when you solder it or loosen when heated. Once dry then solder the jumper wires first to the IC's +/- power pins then solder each wire to each side of the cap. The only things you need are a small tip temperature controlled iron and some sort of magifying glass that has its own stand. Sometime you can find these Mag/stand at electronic liqidators for cheap. I will take some practice but you should able do this. Please make sure you are grounded and have adeqate ESD control where you're soldering so you don't damage your IC/s, remember you don't have to feel the zap to know its happening. When you feel the zap volage discharge is around 3500 volts, IC's don't take much to damage them or to create walking wounded that will still work now but fail later or do funny things when temperature or stress on the part is just right. I hope this helps.
...but the SReg circuit board makes it a little easier, as you can put a correctly sized SMD cap right across the boattom of the pcb and connect directlty to pins 4 & 7 of the chip where they come through the board.And you don't have to use a SMD cap - a wired cap will work just as well as long as the leads are just long enough to reach the opamp pins.
I know what you mean....honest I do. But the larger sized SMD can be done with a regular soldering iron. You need a temp controlled one....and you need to be quick. What is really essential is a good way to hold the part in place....ideally with something that acts like a heat sink.
Hi Alan,
Thank You for the reply and info. I will try the AD797 and the 2uf cap across the +/- pins of the IC.
Hi Steve,I am knowing you have brought the super reg kit from Allen, I am interested it too. Do you mind share me some information like circuit diagram or what active component it will use.
my email: raychow830@yahoo.com.hk
Thanks,
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