[some1x]

Can I use AD797 or SE5534 in RKV?

 

[some1x]

I tried asking Helmut at RKV, but couldn't get a clear answer due to the language barrier.

 

[some1x]

Quote:

Originally Posted by zdogg Hmmm, I had some time to do more listening with the opa637 + 68pf cap configuration + K1000. Early on I noticed a little distortion at higher volumes (around 11-12 o'clock with k1000). At first I thought it might be my k1000's (it was a buzzing/ringing sound with certain loud notes...piano was the worst offender). At first only in the right driver, but subsequently in the left as well Distortion seemed absent at lower volumes, but I began to notice a little edginess to the sound as if the notes were ready to distort but didn't quite have enough volume to make it noticable.

I just tried OPA637 + 68pf silver mica cap + K1000. At higher volume, I'm hearing exactly what you described. All the more frustrating because at lower volumes, this setup is clearly better than with stock opamps!

Was the problem permanently fixed when you replaced the tubes?

 

[Blorton]

Some1X,

If I were driving a high-current load like the K1000, I would try the 627s. I actually do have a set waiting to be modded and dropped in, but I've been happy enough with the HD650/silver Dragon combo that I haven't bothered.

Dan

 

[some1x]

Thanks for the advice. I guess I'll order a OPA134 first and see if it is "good enough."

When I emailed Helmut about alternative opamps (AD797 and SE5534), he just told me to use OPA637

Why does OPA637 distort at higher volume, and why wont the OPA627 do the same thing?

edit: According to this link, OPA627 is simply a compensated version of OPA637. Does this mean that I can adjust the compensation cap more until the 637 is fine at higher volume?

 

[Blorton]

Read back earlier in the thread for comments by jcx.

Essentially, when driving a harder load like the K1000, it's likely the 637 is pushed into unfriendly territory. The 627 is more suited for that range and will still yield a nice tubey sound.

I wouldn't even bother with the 134.

Cheers!
Dan

 

[zdogg]

Hey dudes,
I've since sold my RKV, but I would say that with the tube change, the problem with the distortion using the 637's improved quite a bit, but with the 627's it was absent and the beneficial effect on the sound was not much different than the 637. I think I would agree with others and recommend the 627 as the best overall solution.

 

[akwok]

Does anyone still have their LF351s? If so, would you like to sell a pair to me?

I find the OPA627 with K1000s to be waaaay too bright. Any suggestions?

 

[bobcn]

Quote:

Originally Posted by akwok I find the OPA627 with K1000s to be waaaay too bright.

I just did the mod last night (opa627+ceramic caps). I agree that it's brighter with the K1000s. But...

The other cans I use are Grado HP-1s. I didn't like the RKV (+Impedanzer) with the Grados. My Lavry DA10's headphone out sounded better to me.

That's not true anymore. The RKV sounds spectacular with the Grados now. The difference isn't subtle at all. It crushes the Lavry.

I've got an Equinox tail for the K1000s on order and I intend to leave the 627s in until it arrives. Hopefully it will solve the brightness problem. If it doesn't I'm going to have a very difficult decision to make. I really don't want to switch back to the old opamps.

There's one other problem I've run into with the mod: The RKVs clear top means that everyone can see the ham fisted job of soldering the caps to the opamps that I did. It’s embarrassing.

 

[bobcn]

My opa627+ceramic caps modification sounded fantastic for a while. But then it lost the magic I initially heard. I suspected that there was a problem with the ceramic caps I had used, so I went looking for some of the silver/mica caps I had seen mentioned on this thread. I found some in a funky local components store (under a pound of dust). I've replaced the ceramic caps with the silver/mica caps.

The amp has been playing for about five hours now. It sounds spectacular. I'm not a DIY electronics guy so I'm not sure why things have gotten better. I suspect possible reasons are:
o higher voltage capacity (50v versus 300v)
o composition of the caps (ceramic vs silver/mica)
o or, most likely, better heat tolerence -- the caps are only one inch from the tubes.

Anyway, I'm convinced that the type of caps matters a lot.

BTW -- the brightness I complained of previously is no longer a problem.

 

[ppl]

I am glad you guys are still having fun with this circuit. IIRC the RKV is similer in concept to this design on page 9 of AN-272

I see no one has yet tried the AD744 mod it may or may not work if any current is pulled twards the positive supply rail of the opamp it will not work however i belive the Impedence seen at the OPamp output sees a High impedance loaded only by the Tube Bias currents whitch are real small and in this case the AD744 would work great. just my 2c worth

BTW ceramic capacitors have no place in an Audio Amp anyware including the PS IMHO

 

[bobcn]

Quote:

Originally Posted by ppl BTW ceramic capacitors have no place in an Audio Amp anyware including the PS IMHO

My RKV agrees with you.

 

[Sugano-san]

I am happy to read that the RKV opamp mod I originally suggested to Helmut is still popular around here. I might post a longer description with lots of details (ad pics) soon, but at the moment I have other things to do.

I may try the AD744 Class A mod though. I yes, I will post a report.

 

[bobcn]

Quote:

Originally Posted by Sugano-san I am happy to read that the RKV opamp mod I originally suggested to Helmut is still popular around here.

You da man!

 

[Blorton]

Hi Guys!

Bringing this one back from the dead to see if anyone ever got around to trying the AD744's.....

My RKV is still kicking butt with the 637's and I never did get around to upgrading the caps.

Cheers!
Dan