5532DD op amp replacement?

[ocelot85]

Thanks for that.

The cap is about 1.8CM X 4CM. I'm not sure about the brand, but all the others in the machine are ELNA, ELNA DUOREX II, and NICHICON MUSE.

I was thinking about replacing some of the caps and got a bit confused about the values. But you've cleared that up for me now, thanks.

 

[Mooly]

That sounds very much like a "backup" cap. Many machines use "supercaps" to maintain a 5 volt supply to logic and memory devices. Used in place of rechargeable backup batteries.

Edit... checking it's location and function in the circuit will confirm.

 

[SoNic_real_one]

For sure it is a supercapacitor used to keep the memory values without external power. Back then the EEPROM was expensive and not easy to work with like today. It's value is like it was said above: 47 mili Farad = 47000 Micro Farad.
You don't need to change it unless you loose the stored settings too fast when you unplug the device.

 

[Johnsykes]

I prefer the underestimated AD797. They need some attention in the powersupply rails!

hi , can you explain better ?

 

[phase]

Has been some 8 years since that post, and 6 years since that member has posted on this site.
Maybe do a search for ad797, there are some threads dedicated to that.

 

[Markw4]

hi , can you explain better ?

IME, AD797 can become unstable if there his too much HF capacitance on the power rails, such as if using large value film caps for power bypassing. Shouldn't be a problem if the advice on bypass caps in AD797 data sheet is followed.

 

[Johnsykes]

Thanks Mark

 

[sgrossklass]

IME, AD797 can become unstable if there his too much HF capacitance on the power rails, such as if using large value film caps for power bypassing. Shouldn't be a problem if the advice on bypass caps in AD797 data sheet is followed.

That is highly peculiar. I suspect it's a parasitic (parallel LC) resonance issue of said large film cap with inductance of parallel larger caps and/or traces, which is pretty much what the advice in the datasheet aims to address. A high impedance peak in the wrong frequency range could really ruin your day.

(BTW, isn't the suggested 1-4.7 ohms in series with 4.7-22µF tantalum pretty much the same as a regular lowish-ESR electrolytic? A 10µ/25V or 6.8µ/35V Panasonic FC is spec'd at 2 ohms, for example. You could use a 22-68µ and add an ohm, too, probably still cheaper...)

 

[Markw4]

That is highly peculiar. I suspect it's a parasitic (parallel LC) resonance issue of said large film cap with inductance of parallel larger caps and/or traces, which is pretty much what the advice in the datasheet aims to address.

Maybe. Other op amp data sheets don't give the same warning, and they don't become unstable with 10uf Wima mks4 from power rails to ground at the other end of 1' or 2' of wire. Seems to me there is something about AD797 that requires a bit more care with bypassing and or power rail filtering verses most other op amps. Not necessarily a problem, just something to keep in mind.

 

[s3tup]

Maybe if you use OP07.
110MHz GBW require 110MHz bypass. Especially on non-compensated, knowingly sensitive opamps. Btw, most of the "opamps sound different" beliefs come from a mix of unstable (!!!), misused or plainly fake parts (which, btw, might perform much better than high-performance originals in lacking layout).

110MHz bypass is 0804, 1206 at most, with trace _loop_ no larger than 2x the distance between soic8 most distant pins.

 

[Markw4]

...most of the "opamps sound different" beliefs come from a mix of unstable (!!!), misused or plainly fake parts...

That statement is also a belief.