[analog97]

Hi: My Cornet2 is working fine, but I have just carefully checked the resistor values and note some discrepencies:

R103-should be 220.........actual is 0
R106- should be 6.8k.......actual is 4.0k
R105- should be 10k........actual is 4.0k

R107,R206L and 206R- should be 330k.....actual is .07 MegaOhm (70k)

I have repeatedly checked these and all others check out fine on the DVM.  Are these worth worrying about?  Do they affect sound quality?  Is this the result of a bad solder joint, i.e. does overheating cause a change in resistance?   Thanks for any advice.

[hagtech]

I'd have to guess you are measuring in circuit, which changes everything.  

R103 is in parallel with the 6.3V secondary and should read less than 1 ohm.  R105 and R106 are in parallel thanks to the tube heaters.  They should read 10k//6.8k = 4.05k.

I'm sure your resistors are fine.  Unless they've turned black and spewed out some smoke or chunks.

jh

[analog97]

Thanks very much.  I have proven that I am a damn novice when it comes to actually understanding.  I thought "in circuit" would change things, but these were the only values that were different from the listed resistor values, prompting my quetion.  6 differences out of 56 resistors, I think.   It is interesting that the vast majority of "in circuit" resistor values do not change.  Thanks for the lesson.  My goal is to be able to learn enough to ask at least one intelligent question.  That will have to wait.  Again, your products really can be built successfully by someone with my limited understanding.  That is a tribute to the design and engineering.  I eagerly await the parts to build the Clarinet I recently received.  I now know that your tube gear is superior to anything I've heard.  I have tried to find out why tubes appear to be superior to solid state.  I am clueless as to this answer......maybe that's my "intelligent" question...why ARE tubes better than solid-state?   Thanks again.    Larry

[hagtech]

tried to find out why tubes appear to be superior to solid state

I think it's feedback.

jh

[bluesky]

Hi Jim

Could you expand on that statement "I think its feedback"?  

Here in Australia we have one major electronics magazine "Silicon Chip", the editor of which has written numerous editorials stating the absolute superiority of modern solid state designs compared to tube designs.  He stated that " on every major parameter of measurement" solid state amps are ahead by the proverbial country mile over tubes and that people who build tube gear are simply on a nostalgia kick.

Recently I read an intersting article by Thorsten Loesch in which he cited some scientific studies that showed that the human ear actually does not hear distortion of the type produced by tubes amps, the SET in particular.  If this is so, then the measurements cited by the editor may not be relevant at all.    

I shall just have to wait and see for myself after completing the Clarinet and Cornet and then doing a direct comparison to Rod Elliott's (ESP) solid state preamp and phono stage.  I have built all the PCB's for all of these projects with premium parts so I think it should be a reasonably effective test for both sides of the fence on this one.

Cheers

Bluesky

[hagtech]

on every major parameter of measurement solid state amps are ahead by the proverbial country mile over tubes

Ok.  So what?  It's the sound that counts, not the numbers.  This debate is so stale.  Nothing like long term A/B listening tests to settle the score.

People have to convince themselves.  Nothing I can say.

jh

[bluesky]

Hi Jim

Obviously I agree with you and am doing the listening bit myself.  I am making the effort to build two lots of stuff just to prove to myself what it is all about.  I have little doubt that your kits will win out.  My good friend Keith Eichmann has already told me that it will be an easy one for your designs and Keith certainly has golden ears and a awful lot of experienece.

However, it was the feedback issue that I was interetsed in.  You use no feedback, as do most tube designs, and I was wondering why the use of no feedback is of such importance.  Feedback is standard issue on all (well most) solid state amps and the opposite is the case with tube designs.  

Does the use of feedback degrade the sound?  

I value your opinion and I am simply trying to learn more.  I am gradually wading my way through a number of books but you have already done all that and I would just like to know what the effect of feedback (or lack of it) does.  

Cheers

Ian

[hagtech]

feedback issue that I was interetsed in. You use no feedback

Yeah, I sometimes get tired of talking about it.  I also use the terms loosely.  Technically, I use feedback.  But local, degenerative type, not global.  It's the global feedback implemented like an opamp which causes the most trouble.  High, uncontrolled nonlinear gain, corrected by feedback.  That's an opamp.  Also a typical pentode amplifier.

Let's look at a CORNET.  The first stage does not use a cathode bypass capacitor.  The cathode resistor applies degenerative feedback, same loop as the input.  So the stage has less gain than in a grounded cathode type stage.  Also higher output impedance.  The cathode follower output also has inherent feedback in a similar fashion.  In both cases, the feedback is also part of the input, so there is little or no phase shift involved.  It is inherent in the circuit.  Like self-bias.

The problem feedback is the global type.  Phase delays push an amplifier towards instability.  It also generates new harmonics.  As the original distortions of the amplifier are fed back to input, these are then amplified and distorted again, causing greater and greater harmonics.  The amplitude of these harmonics can be held low, but the multiplication process generates non-integer and other foul or unmusical relationships.  Some French guy (Jan Didden?) explained this well in a series of article many years ago.  AudioXpress did some reprints.

Now if the forward amplifying stage is clean and linear, the problems are not so bad.  That's why low gain JFET (Borbely) and tube stages can apply feedback sometimes without trouble.  It is the nonlinear, high gain forward stages that have the problem.  Pentodes, transistors, etc.  

Keep in mind that with feedback, it is like a cat that is always chasing its tail.  Always trying to correct itself.  Regulators in the power supply can do this to, adding sonic signature.  Some types of regulators work better than others.  Shunt because they operate pure class A.  

It's a game of tradeoffs.  There are no perfect answers.

Maybe another analogy?  Feedback is like a wife who always slaps her husband every time he gets out of line.  It makes for a well behaved husband.  

jh

[bluesky]

Hi Jim

Thanks for all this information!  It helps me a lot to understand things better.

The more I learn the more I am inclined to the opinion that we have a long way to go with the "science" of measurement. Gross figures only show a partial indication of what is going on in any given design.

I read recently that the human ear drum can oscillate (if that's the right word) in atomic sized distances.  This may go some way in explaining why we prefer the harmonics of tubes as opposed to solid state even though the solid state THD might be incredibly low we can still hear the grating higher order harmonics.

To use a different analogy two violins can play the same C note but the Stradavarius just plain sounds so much better!  Recently I went to a concert where the guest violinist was playing a Stradavarius and was quite amazed at the difference and purity of its sound.  It was a real eye opener for me.  

Ian