Tube swaps and frequency response

[J M Fahey]

Dear Freefrog, THANKS A LOT.
VERY useful.

First time somebody shows a frequency response curve to back the "different tubes" arguments.

Very interesting:

1) the curves are incredibly alike, over 95% of the frequency range backing the "tubes have flat frequency response, from DC to RF" theory.

At most , the curves have the same shape, and go only slightly above or below, as a whole, less than 1 dB, .
Incredible.

So even overall gain is incredibly uniform. Wow !!!!

2) that said, the only point where the curves show an audible difference is at some 550 Hz ... which perfectly matches the lowest impedance point of the tone control network, and where it clearly it becomes a somewhat difficult load for the driving tube.

Only there you find an around 2 dB variation, in which the deepest notch could be describes as "scooped" or the less deep one could be described as "forward sounding/nasal/smooth/warm" depending on user preferences.

Even so, the largest variation was between two Sovtek tubes, the ones who once acknowledged "up to 3:1 parameter deviations" in standard unselected tubes.

Amazing.

That slight difference in mid response does not warrant the florid sound descriptions often attributed to tubes, except in a very small degree.

Thanks again.

[freefrog]

Dear JM Fahey,

The answer that you read right now was previously another reaction to your reply 46.

A PM and the posts 48 + 50 below make me now EDIT this message.

I just want to say that in my post 42, I wasn't arguing: I was sharing data without much comments in order to let people make their conclusions.

Now, whatever is the reason behind the differences noticed, there was difference and seeing them in the tests that I've published has certainly been useful to me. I might post later some charts showing more precisely the sonic effect of these variations...

[Leo_Gnardo]

Not to be so sensitive froggie! It's true, rare indeed frequency/distortion curves for actual tubes in use instead of the tired old curves that have been copied over & over since Tom Edison was a pup. Now for a real challenge, how about some curves from tubes in combo amps with speakers blaring only a couple inches away. To me, that's a "real world" experiment that may reveal even more what we hear compared to "tubes in the test stand." Looking forward to seeing results of this kind of test.

We have our share of cynics here & I'll admit to being one of them. But I think you're on to something & doing the extra work others 1) don't have the gear to do or 2) just don't care to 'waste their time on', so please don't be discouraged.

Some may be interested to see what's going on at the guitar site you moderate. You can post a link, or if you're worried it will attract trouble send it to me in a PM. Thanks!

[Steve A.]

Frankly I'm tired of the "tubes sound the same" argument.

With some high gain amps I think that the circuitry has a bigger effect on the overall sound than the specific tubes used. While with some low gain amps you can detect very subtle differences between tubes. Just my own opinion and YMMBW (your mileage may be wrong!)

Steve Ahola

[The Dude]

(Quote redacted by request of the "Quotee".)

Am I missing something? Either you or I (either is possible) didn't understand Juan's post. I read that he is thankful to see actual data rather than BS. Either way, I do thank you for taking the time to post the info.

[freefrog]

Leo_Gnardo, g-one & The Dude,

I've took your observations in account and edited out my previous answer to JM Fahey in consequence.

You'll certainly understand that I'm sometimes buzzy / tired and that it can make me touchy/sensitive, as many people.

I still think that it's not easy at all to share peacefully some data without being trapped in arguments (that I personally hate and avoid: I'm only interested in sharing and learning)...

Thx for your understanding.

[The Dude]

I still think that it's not easy at all to share peacefully some data without being trapped in arguments (that I personally hate and avoid: I'm only interested in sharing and learning)...

That is what I appreciated about your post. No conclusions were drawn. It was simply a presentation of data. And, ...... that is how I read Juan's post regarding your data. He was simply making observations about your findings. I saw no malice intended. At any rate, no need to dwell on a misunderstanding. Onward and upward!

[J M Fahey]

Dear JM Fahey,

The answer that you read right now was previously a harsher reaction to your reply 46.

A PM and the posts 48 + 50 below make me now EDIT this message: maybe it was excessive to decipher yours as the proof of a rather destructive irony (?)

I just want you to know that in my post 42, I wasn't arguing: I was sharing data without much comments in order to let people make their conclusions.

Now, whatever is the reason behind the differences noticed, there was difference and seeing them in the tests that I've published has certainly been useful to me. I might post later some charts showing more precisely the sonic effect of these variations...

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What's this all about?

FWIW I'm PRAISING you ..... what would your reaction be if I were dissing you?

You really have a very poor opinion of yourself to react that way to PRAISE.

As of my observations, are fully based in the data YOU provided.

If those curves are not to be believed, why do you care to post them?


EDIT:

I was sharing data without much comments in order to let people make their conclusions.

EXACTLY what I did.

My "conclusions" are simply a verbal description of what is SEEN: way less that 1 dB at the frequency extremes, those curves can be practically superimposed, with only a 2dB difference at the Tone Control notch ... which matches perfectly a notch in impedance seen by the driving stage.

That an impedance notch becomes a response notch is absolutely a consequence of the driving generator impedance being >0 .

[Justin Thomas]

Hi all,

I think the whole "frequency response" thing is settled... but I think maybe the distortion curves aren't nearly as close! I think I'll use the Amperex or JJ tubes because the THD curvers look most like the waveshape I want out of my amp - sharp & pointy! Seriously, though, I think that (as is occasionally brought up) when tubes are driven past the linear operation points into "screaming for holy mercy" land, the distortions ARE different enough to make an audible difference. But as pointed out, not the level of orgiastic floridity used in tube reviews and sales literature... Could we all just say, "hmmm, THAT was different..." and then just shut up and play our guitars, working on MUCH more important points to get the best sound possible? Let's face it - once your "precious" tube is burned out, you'll never get another one just like it. Plug in another one, quitcher bitchin', and PRACTICE! I do cry whrn I break an old "golden age" tube, but not over the sound, because usually it was making some pretty funky noises on its own. No, I cry because I feel like a little bit of history is gone forever...

Justin

[freefrog]

Hi Mr Fahey,

Sorry Sir for the misunderstanding : my body was tired and painful yesterday at night and has influenced my mind/mood in a negative way.

Furthermore, irony is often practiced in my country and most often, it’s not exactly in a gentle way. :-)

Not to mention that my last topic on this forum has attired harsh or ironical answers, giving me the feeling that I wasn’t necessarily “in phase” with the context.

So, yes, I’ve been overly touchy / sensitive - but my derailed humor analyzer is now repaired :-))


Anyway I thank you humbly and sincerely (IOW: not ironically) for your instructive comments.



Before to start a new day of work, I post below another handful of screenshots. They stack the frequencies produced by two miked amps, themselves excited by consistent guitar sounds (=sampled tracks). Same settings and rig in every situation.

The upper line shows how the clean channel of the HRD mentioned above amplifies a sample with 3 different 12AX7’s in V1.

The bottom line shows the response of a "Fender Champ kind of amp" with a single 12AX7 and a 6V6. It's a VHT Special 6 that I’ve heavily modified. This amp hs been played full up in this case, through a generic Celestion 1x12. The same 12AX7’s than above have been tried successively, giving the three plots shown.

Once again, the test has been at least useful to me: I’ve simply selected the tube(s) which was/were the most pleasing to hear for each amp and called it done.

Once again, my readers will build their own conclusions on the basis of these data. :-)

[freefrog]

Hi all,

I think the whole "frequency response" thing is settled... but I think maybe the distortion curves aren't nearly as close! I think I'll use the Amperex or JJ tubes because the THD curvers look most like the waveshape I want out of my amp - sharp & pointy! Seriously, though, I think that (as is occasionally brought up) when tubes are driven past the linear operation points into "screaming for holy mercy" land, the distortions ARE different enough to make an audible difference. But as pointed out, not the level of orgiastic floridity used in tube reviews and sales literature... Could we all just say, "hmmm, THAT was different..." and then just shut up and play our guitars, working on MUCH more important points to get the best sound possible? Let's face it - once your "precious" tube is burned out, you'll never get another one just like it. Plug in another one, quitcher bitchin', and PRACTICE! I do cry whrn I break an old "golden age" tube, but not over the sound, because usually it was making some pretty funky noises on its own. No, I cry because I feel like a little bit of history is gone forever...

Justin

I do agree. I've done some tests because...

a) I'm "unofficial guitar tech" for some friends and I want to be the most objective possible when I recommend them something;
b) Sometimes, life creates situations where we can't practice. I've took advantage of such a situation to do some futile tests allowing me to get better (to have fun innocently being a good way to forget some problems). Sharing some of my results represents a new personal attempt to change the bad in good.

Now, the value and meaning of my "data" are obviously discussible so, feel free to decipher them as you want!

[teemuk]

Interesting test but it would be somewhat more interesting to see results of similar experiment without rest of the circuit affecting it.

Also, the tested tube was in V1 position; most likely to affect overall noise level, less likely to affect any distortion/overdrive characteristics introduced by the tube.