Single stage line with anode-cathode feedback

[DF96]

Moi, grumpy? No, I am amused. Several of us have tried to explain why it is a bad idea, yet you seem unconvinced. If you don't welcome comments, why post your idea?

[revintage]

Loren 42,

Since when can you get NFB with a resistor from anode to cathode? That makes PFB in my book!

It's like using a framing hammer to nail tacks. Of course it will work, but it is a waste of hammer.

Can´t find those words in my electronic dictionary. Why not explain in electronic terms instead?

[cotdt]

I notice that there is an opamp in the circuit? Yikes!

[revintage]

Moi, grumpy? No, I am amused. Several of us have tried to explain why it is a bad idea, yet you seem unconvinced. If you don't welcome comments, why post your idea?

Not grumpy, hmm? Don´t know where you found your info, but of the above posts there is noone who have even tried to explain. Certainly not you! To say that "an active device in a feedback loop is perverse" is no explanation, neither that a "resistor has lower distortion than an active device".

So why not try again.

[Wavebourn]

Hmmm Interesting! It may be advertised as "Opamp Distortion Compensator". Or "Anti-Distorter" :-)

Edit: add "Anti-Triode" here and call it "Straight Wire Amplifier" :-)

[DF96]

Originally Posted by revintage

Don´t know where you found your info, but of the above posts there is noone who have even tried to explain. Certainly not you! To say that "an active device in a feedback loop is perverse" is no explanation, neither that a "resistor has lower distortion than an active device".

So why not try again.

It might be boring to repeat myself. Re-read the thread, including the pieces you have quoted from me. If you don't recognise any explanation then I don't think we can help you.

[Triodethom]

Originally Posted by DF96

Could someone remind me what the Farnell part number is for an "ideal inverter"?

I check there out of stock and have been discontinued . They however have promised a digital version that is said to be better than ideal and lower noise.

[DF96]

OK, thanks. "Better than ideal" - so it will improve the music, correct for studio errors etc., just like some high-end gear?

[Wavebourn]

Jokes aside.
Nothing is wrong with this topology. With -1 gain opamps work pretty nice, so why not to use such a buffer to add feedback to the single tube stage? However, opamp saturation will cause quite nasty distortions, high peaks instead of flatter tops.

[Simon B]

DF96, for someone with internet access you have a refreshingly innocent idea of "perverse" !

As Wavebourn points out, "with -1 gain opamps work pretty nice".

None of the naysayers are actually coming up with noise figures for this topology versus another that offers high z-in using a single valve, perhaps they might care to do so? Quantification before condemnation might be sensible.

As for distortion, it comes in two flavours, the sound the user likes and the one he doesn't. This doesn't in any case look like it's going to suffer overly from noise or distortion, given a sane implementation, so to dismiss it as 'pointless' seems both arrogant and rude to me - a shame to see that attitude from a moderator, SY.

On a practical note, it might be worth protecting the inputs of the op-amp from their max differential voltage being exceeded as C2 charges at switch on.