Current-injected Valve-buffered Gainclone

[tecnofossil]

Perhaps this design offered by John Brosky? The LM3875 or LM3886 *might* work in place of the LM12, but the LM12 is stable at gain levels which are considered to be at the bottom of the range recommended by National Semiconductor.

-Tom

[tecnofossil]

If any is curious about the Tube Cad Journal article the circuit was mentioned in it was here: http://www.tubecad.com/index_files/page0023.htm

-Tom

[ThorstenL]

Konnichiwa,

Originally posted by Gerry
Grid to cathode voltage is ample - approx. 3V depending on age of tube. Grid swing amplitude is typically up to 0.8V.

The output swing of the Lm3875 on the usual 35V rails is around +/-30V. This requires an input swing of around 30/22=1.4V. Doing this with only 3V static Voltage across the LM334 may work but is hardly ideal, refering to FET CCS who also SHOULD saturate with only 1V.

Originally posted by Gerry
Harmonic distortion is entirely a function of current swing. I would be surprised to see a zero current swing on the cathode giving more distortion than a zero current swing on the anode. I might be ignorant, but as far as I am concerned the slew rate of the LM334 virtually guarantees that the swing is indeed zero.

Do you believe there is an inherent relation between harmonic distortion and good sound? Then you made the sound of your Amp better by adding a lot of HD, compared to the previous state.

Originally posted by Gerry
BTW: I am puzzled. The IGC in the DIY community has been mainly your baby. Due to your own experience and various discussions you must have been aware of the excessive harshness/brightness due to the feedback problem of the unbuffered IGC.

I have heard several non-buffered IGC's that did not have the sound you describe.

Originally posted by Gerry
It appears as if the brightness problem caused people to abandon the IGC in droves to head for the NIGC.

I noticed many a fashion. One day the 300B is the best tube, the other the 2A3, then the 45, but no, the 10 is best, no only 845's at low voltage sound good, hey, chipamp's are THE thing, hey, inverted chipamp's are the thing, hey, noninverted chipamps are the thing and so on. In the very rarest of these cases are these opinions formed in "all else being equal" listening tests with a reasonable attemp being made to eliminate bias.

Once you talk different systems, implementations, passive parts etc you cannot any long draw valid comparisons.

If you like an IGC with valve buffer, with LPF or without, inverting or not, if it sounds good to you, have fun and more power to you.

I did not criticise your design, I merely pointed out a few things I feel may make an audible change. Just like I feel that virtually ANY Op-Amp sounds better inverted, all else being equal. You don't HAVE to try it, but you asked opinions. Those I gave where mine.

Originally posted by Gerry
Unfortunately, I couldn't find any posting of you showing one of your tested preferred buffers which adress the problem.

What problem? I do know of one IGC that shortly aquired a buffer and quickly lost it again. All in all system interactions and tastes vary.

Originally posted by Gerry
Surely, ANY of them must have been better than your originally proposed "naked" IGC ?!

Why?

Originally posted by Gerry
As far as I can see the IGC is in principle superior to the NIGC if it is assisted by a proper buffer.

Even without buffer. But as said, much of this is a moot point. I fully suspect someone to try the inverted circuit after a year or so of listening non-inverted, or bypass the buffer and finding the result superior and then many people will re-build their AMp's again. So what (shrug).

Originally posted by Gerry
Anyway, if your favourite constant current buffer doesn't involve diamond-plated nuke-powered batteries I am keen to run it side by side with my circuit and let my wife blindly decide which sounds better.

It doesn't. Simply use a TX-102 as Volume control. Compare to any other setup you like.

Originally posted by Gerry
Regarding your freshly proposed idea to use the tube for the voltage swing and harmonic fingerprint and the opamp purely for the power, I suggest to discuss it on the forum you posted it on. Unfortunately you have been a bit cagey regarding the details lurking behind it.

Hardly cagey. The circuit is straightforward.

Sayonara

[Peter Daniel]

Originally posted by Kuei Yang Wang
I fully suspect someone to try the inverted circuit after a year or so of listening non-inverted, or bypass the buffer and finding the result superior and then many people will re-build their AMp's again. So what (shrug).

Although I converted all the amps to NI config., I still keep one inveritng amp in my basement workshop system, as it seems to me that it sounds so good in there, that changing it wouldn't bring any improvement. I had an NI amp for a short while in that system and was not impressed at all. But when I try the amps in different setups, my prefference is different too. So it is very system dependant. For the record, I never found IGC harsh or bright. After switching to the other amps it seems to me that IGC was actually rather veiled and less detailed, but again it's only my observation.

[Gerry]

Hi there,

I would love to hear whether there have been any further insights/improvements in the last years regarding valve-buffered gainclones with current source ? See my design at the start of this thread.

I see one design published which uses a JFET as a current source, see Option 3 by Maarten here:
Tubeclone 2

It appears to me that many of the gainclone afficionados dont try designs with tubes due to the extra challenges involved. Also the valve/tube guys do in tendency not get involved with opamps. Unfortunately this limits somewhat the further development of such hybrids. Which is a pity IMO because such designs can deliver really great sound for little money.

Cheers

Gerry

[ashok]

I've used tube input stages with some power amps including some chip amps.
The listening tests showed me that I cannot automatically assume that adding a tube front end is going to make the amp sound 'better' or 'nicer'. In some cases it was better sounding but in other systems it did strange things like 'sanitise' the sound. What was VERY dynamic in the bass end was converted to just ordinary sound. By ordinary sound I mean the sound we hear from many average systems which are 'nice sounding'. Component changes didn't improve things.

The only way you can determine how it will sound ' in your system' is to try it out. I'm almost convinced that no one else can give you an answer that would apply exactly for your system. But yes, it "could" make a big difference and unfortunately you will have to try it out yourself to find out !

If it doesn't , don't be disappointed . There will be other combinations which might get you what you want in your system. It would mean that you have just reached a major junction on your long DIY ride ! But there is a LONG way ahead with probably some more great junctions on the way!