Tube with Power IC Output Stage - JLTi

[Joe Rasmussen]

Originally posted by planet10


Are you talking about the thingys that Allen said were an upgrade to the bottom of the Vacuum State cascode?

dave

HUSH!

[Nuuk]

Well, at last I have my VBIGC working and there is a big smile on my face

I have only had it running a few hours so please don't take my comments for anything more than initial impressions.

The sound is slightly more open than my OPA627 buffered IGC but in fairness that is using a cheap pot whereas the VBIGC has a stepped attenuator. Then again the VBICG has speaker protection (Velleman 4700).

There is a distinct difference between the two amps which I can best explain as the VBIGC sounding the more airy of the two. Somehow, the OPA627 version sounds a bit 'darker'.

Now also keep in mind that I will have to match the LPF's and put a stepped attenuator into the OPA627 to do a more objective comparison.

Of the two, I think that I prefer the VBIGC but how much that is down to the time and effort that I have put into creating it, I wouldn't like to say.

I will report back later with a hopefully more objective comparison but for now I would like to thank Joe R, Peter M, and Pedja for their help in getting me this far.

BTW, it's ironic that I discovered diyAudio forums while researching for a valve buffer earlier this year. While here I discovered the Gainclone and now, nine months later I have my valve buffer!

[Nuuk]

More details of my VBIGC are now available on Decibel Dungeon.

[agent.5]

Good work Nuuk. I followed the link and read the your article, you mention a time delay of power to the amp because of tube filament warming. Are you taking about a delay to the B+ of the tube -- which I know is quite important, or are you talking about an additional delay to the op-amp (such as the 3875) as well?

[Nuuk]

Are you taking about a delay to the B+ of the tube -- which I know is quite important, or are you talking about an additional delay to the op-amp (such as the 3875) as well?

No, just a delay before the connection to the speakers is made.

It may be better to warm up the valves before the other circuits are powered up and that can be done with a delay circuit. But as I was using the Velleman speaker protection module, I am using that to avoid any squeal' from the speakers while the filaments warm up.

Others like Peter M use the delay circuit to switch on the valve and LM3875 after the valve heaters have warmed up sufficiently. I'm quite new to using valves but have read that it may not be too important to pre-heat the valves and in any case, I usually leave my power amps, powered up all the time.

[fdegrove]

Hi,

Are you taking about a delay to the B+ of the tube -- which I know is quite important,

In this case no delay is necessary whatsoever.
Moreover, at start-up no delay is needed on high voltage tube circuits either...

Most damage is done at turn of where the heater circuits discharge much faster than the B+.

Cheers,

[tbla]

Somehow, the OPA627 version sounds a bit 'darker'.

hi nuuk,

i'm not shure that you reached the potential of the opa627.....did you bias it into class a with a cascoded current source and perhaps the opa627 doesn't like to drive the lpf, perhaps a buffer in the feedback loop will do the trick or best - use a opa637bp with a buf634 in a jung multiloop with inner gain 300 and outer gain 2........?

and the better supply the better sound......

[Nuuk]

Yes, I am not trying to say which buffer is best, rather point out the differences that I have noted. That's why I pointed out that these were just initial reactions.

I'm sure there is much more that can be done to both versions of these buffered IGCs and the advantage of having two great sounding amps is that one can be listened to while the other is modified.

At the moment though, I could do with a little break from more work and just sit back and enjoy the music. It seems like I have been building hi-fi non-stop for most of this year.

[tbla]

a little break from more work and just sit back and enjoy the music

wise words......its really what its all about...!

rock on and enjoy...

[Optical]

So has anybody auditioned the tube buffered 'monster' with the 6 lm3886's?
Im quite interested to hear an opinion on the sound..