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Hello,
I was able to get a few OPA637BP's for dirt cheap. I know that the 627's work well in my Music Hall CD25 (with Brown Dog adapters)and Jolida JD-9 Phono Stage. I was wondering if I could hurt either of these two pieces by trying the 637's in there? Or, if they are not compatible, would I just get hissing and popping noises? I realize that the 637's require a gain of at least 5 across the entire bandwidth, but I have no idea if either of these two units has that much gain. I was also wondering about trying them in my Rogue Stealth. It currently has AD797's in there, but it also has sockets for dual chips as well. I thought about trying them 637's in there in single mode, then trying them in dual channel mode (with the Brown Dog adapters). BUT, I do NOT want to try these experiments if it could damage my equipment. Any help would be greatly appreciated.
Follow Ups:
Depending on its configuration as Riaa or just gain stage. If its a gain block generally the final stage usually used as pretty high gain which unlike a cd player output which generally uses the op amps at unity gain +1..I have found the opa627 to need a gain of atleast 8 to work hitch free with no oscillations,a gain of 10 being ideal.. to determine the gain used you will need to measure the resistor values of the feedback voltage divider and divide the series out to -input resistor by the -input to ground resistor for example 10k series/1.5k=6.66+1=(7.66)..
I tried 637s in my modified Toshiba 3950 using BrownDog adapters. The 637 oscillated. I never installed the 627s for I mucked up the PCB removing the opamp, installing and uninstalling the BD adapter.I would suggest the 627s.
Ignore the comments of trolls and either implement the compensation capacitor on the BD adapter or use 627.
They both have the same gain (> 112dB) , but different frequency compensation:OPA627: Unity-Gain Stable
OPA637: Stable in Gain 5In fact they are identical parts apart from a compensation capacitor on the chip.
Unless you know how to check for oscillations, somewhat difficult unless you have an oscilloscope, it is dangerous to swap op-amps for much faster and decompensated parts.
marchewd, the absolute gain of an amplifier is a function of the feedback network precision, not the open loop gain of the opamp. A unity gain opamp's feedback resistor must be of such a value as to ensure that 1 vote in gives you 1 volt out. The open loop gain may be the same as a higher gain device, but in circuit, unity means 1 in, 1 out and that is the absolute gain. A gain of 5 means that you use a feedback resistor value which gives you an output gain of 5 to 1 in. If you can use an OPA627, you are not going to get ringing with an OPA637, but you would have to change out the feedback resistor and likely make other circuit mods to use it. Do not confuse open loop gain and absolute gain as the responder here has, they are not the same thing at all.
Best Regards,
You can't just up the closed loop gain from 1 to 5 in most practical circuits without all sort of ramifications.Poster was looking for a drop-in, not to re-engineer the amp. Doing this kind of stuff without a 'scope and knowing how to use it IS fraught with danger.
I have fixed quite a few amps where inexperienced tweakers have inserted parts with x20 GBW compared with the original and then wondered why it sounded bad. They could not see or hear the 60Mhz oscillation.
As I stated, Both the 627 and the 637 are the same part and have the same gain but different dominant pole compensation.
Cliff
First monolithic op-amp I used, the Fairchild uA709 in 1972(ish). Prior to that used Philbrick 2 tube and semi hybrid op-amp modules.
"You can't just up the closed loop gain from 1 to 5 in most practical circuits without all sort of ramifications."That was what I was saying. I have a 100MHz scope but don't waste time doing this sort of thing when there are myriads of drop ins. The question was why it was not drop in, the difference is in the closed loop gain, unity verses 5. The open loop gain for what was it, 112db, has nothing to do with why it is not a drop in replacement. One component is all it takes to make all the difference.
Best Regards,
.
Best Regards,
Don't think that is going to fly, I believe that the 637 has too much gain for that application.
Best Regards,
Thanks for the responses. Anybody need some OPA637BP's?
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