[Pricklely Peete]

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.

 

[Currawong]

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.

 

[Blorton]

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

Dan

 

[Nounours18200]

 
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

 

[00940]

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.

 

[Nounours18200]

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.

 

[rexhu100]

Has anyone tried using Burson V5/V6 op amp on MKII?

 

[rexhu100]

Also, does anyone know the parameters on the original filter capacitors (the 4 big barrels)?

 

[rexhu100]

Also, does anyone know the parameters on the original filter capacitors (the 4 big barrels)?

Never mind, I saw Sugano-san's earlier post

 

[rexhu100]

Why aren't there more people using this amazing amp?

 

[Blorton]

Hi guys! Bringing this one back from the dead to say that the Sparkos 3601 work amazingly well in the final RKV HAA edition. Really makes the HD800S sing. Since the 3601 is unity gain stable, I’m sure it would also work in the earlier generations.

 

[ManiacSmile]

Hi guys! Bringing this one back from the dead to say that the Sparkos 3601 work amazingly well in the final RKV HAA edition. Really makes the HD800S sing. Since the 3601 is unity gain stable, I’m sure it would also work in the earlier generations.

Funny enough your comment came right around the time I dusted off my RKV MKII and K1000 from a 5 year hibernation in a closet. Can you please elaborate on the scope of the changes you made, as I am about to shop for replacement tubes on ebay for this thing.

 

[Blorton]

Tubes don't have the effect in this amp as they do in other designs. You just want a set that work is all.

All I've done is swap opamps. Others have upgraded caps and other parts, and their threads may still be around here.

 

[ManiacSmile]

Tubes don't have the effect in this amp as they do in other designs. You just want a set that work is all.

All I've done is swap opamps. Others have upgraded caps and other parts, and their threads may still be around here.

agree, mine were close to dead, so just getting a new set to start afresh.
Need to dig into the subject, just want to ensure there are no meaningful changes in the circuitry between your version and RKV MKII that would prevent me from just swapping the opamps directly.
Thanks!

 

[Blorton]

agree, mine were close to dead, so just getting a new set to start afresh.
Need to dig into the subject, just want to ensure there are no meaningful changes in the circuitry between your version and RKV MKII that would prevent me from just swapping the opamps directly.
Thanks!

Well, I still have my old one around. I had considered moving these Sparkos to that one to see how that sounds and getting the even fancier ones for this new variation.

However - just as a sanity check, I spent a lot of time looking at the differences between the two boards when I got this new one. You can see it's very similar, just the channels have been moved around.