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Stunning RKV MKII mod experience - Page 6

post #76 of 81
5/16/09 at 7:13pm
Be careful with low cost 627/637's there are a lot of fakes floating about on eBay and elsewhere.

If you see a pair of 627AU/BPs for 16US it's too good to be true...really...

Peete.
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post #77 of 81
4/2/10 at 8:23am
I'm bumping this old and very useful thread because I've picked up another Head-fiers RKV MKII and Impedenzer. I have to say, it is wonderful with HD-800s with a pair of 627s in. It's also very good for speakers in a near-field set-up. I am considering doing the cap upgrade on it once I work out what is suitable.
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post #78 of 81
4/2/10 at 10:50am
Thread Starter 
Nice score! Please post back if you do the cap upgrade. I'd be interested to see how it works for you.

Dan
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post #79 of 81
1/2/11 at 11:44am

 

Quote:
Be careful with low cost 627/637's there are a lot of fakes floating about on eBay and elsewhere.

If you see a pair of 627AU/BPs for 16US it's too good to be true...really...

I am going to perform this upgrade on my RKV-II as well, and found the OPA627BP on eBay for 15$, but...following your remark I prefer to buy from a reliable source like FARNELL for example: 30€ each, but I am sure of what I get....

 

I will do the upgrade with the OPA637BP , hoping there will be no instability... (I use a HD600).

 

 

Quote:
Nice score! Please post back if you do the cap upgrade. I'd be interested to see how it works for you.

 

I also plan to do the caps upgrade: mine are 220uF / 400V. I do not know if they have 2 or 3 pins. What would your recommandation be for a caps upgrade ? (Nichicon ? something else ?).

 

By the way, if somebody is still using the RKV with the OPA637 upgrade after a few years, please provide us with some additional feedback !

 

Thanks

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post #80 of 81
1/3/11 at 1:47pm
You CANNOT just go for the opa637 and "hope" for no instability. You have to test the output with an oscilloscope. The opa637 is the uncompensated version of the opa627 and might easily be trouble.

Did you bother to read the thread (hint, post #28) ?

Caps upgrade are meaningless, those are already good caps. Unless you go for higher values. Two of the caps are for the PS, two for output coupling.
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post #81 of 81
1/4/11 at 11:49am

I did find the dedicated topic related to the OPA627 / OPA637 installation in the RKV. The people who tried this upgrade confirm that it is necessary to add a 68pF capacitor on the OPA637 to ensure stability, but the sonic improvement seems outstanding ...

 

 

Quote:
Caps upgrade are meaningless, those are already good caps. Unless you go for higher values.

 

I planned to go for higher value. And for lower ESR... I actually have another (sophisticated) device being in the assembly process on my table, so I have to delay this upgrade for a couple of months... Cannot to do too many things in the same time, bt I will follow this topic meantime.

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