ECC82/12AU7 Line Preamp

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Hi jmilledoc
I understand your point, we never talk about music here.
For these things in history, the musical notes in the Western system, are as 2 ^ n, in terms of its frequency, that is the reason why the second harmonic is pleasant, it falls into the previous/next octave with the same musical note.
Triode physics tells us that his main distortion is the second harmonic, even harmonics in general, otherwise the transistor distorts the odd harmonics, it falls into the previous/next octave with a different musical note, which is unpleasant.
Do the experiment with a piano or other keyboard and see, (hear)
Best regards
Johann
 
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And not to be facetious but, yes, if you're designing a hifi amp (as opposed to a guitar amp), you actually would do better selling the 12AU7s and getting another tube which can be used in a simpler circuit and give higher performance. Your circuit does extract better performance than usual for that tube type, but the 12AU7 is not a very linear tube to start with.

SY, I suppose you suggest other than ecc types

according to this spec sheet. the ecc82/12AU7 have the lowest distortion of the commonly used ecc types, and seems pretty much independant of the voltage, as well as the gain

http://www.tubeampdoctor.com/images/File/TAD-Datasheet_RT005_030811-Version 1.0.pdf

doesnt that also imply its the more linear of them :confused:



edit, sorry, posted spec sheet on wrong tube, and now corrected
 
Many years ago i built a pre-amp using a pair of 12au7 SRPP's as a differential pair with a sand CCS at the bottom (B+ around 450v). Besides the pain of matching (and keeping matched) the 12au7's, it was one of the most amazing sounding pre-amps i ever heard. I ended up running balanced lines out to the amplifiers which had a true balanced input.
 
+1.

I disagree with wavebourn. SS devices don't have sharp corners in their characteristics, except when you completely run out of headroom, which is out of bounds anyway.

The problem is, I have MS in Electronics Engineering, and learnt physics of semiconductor devices in details... It disagrees with your statement. No other bounds except potential barriers in semiconductors. And all laws are exponential. :)
 
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Hi Wavebourn
How lucky that I see you around here.
Could you give me another trick to remove the magnet wire enamel?
I'm going crazy with an OPT, and I can't with 0.2mm wire.
Aspirin does not work because the enamel is polyester imide resin.
And tested with acetone, thinner, and up brake fluid !!!
Fire tends to ruin the wire, please, help me.
Best regards
Johann

The truth is, you are more lucky: we have great chemical scientist here on the forum, his nickname is SY. ;)
 
Speaking of the personality types, should I say subtypes, we are all DIYers. I like playing with the technology, I like playing with the cheaper end of the spectrum of vintage vacuum. So far most of the solid state stuff in the toys that I construct tends to be in the power supply and voltage regulators, or maybe a constant current source in a Long Tail Pair.

This 12AU7 SRPP circuit was stated to be a Line / Preamplifier and an experiment. An experiment perks my interest. For a line amplifier 2V RMS output is a lot, more than is needed to drive a power amplifier into clipping. This 12AU7 has a mu of ~ 17. For a line amplifier a mu of 17 is better than 33 for a 6DJ8. Perhaps this circuit has a gain of 10 which is still a little high to follow one of SY’s low distortion hybrid SS / Vacuum “His Master’s Voice” vinyl machines or a CD output. In this 2012 type of application there is seriously little distortion added. Not bad fun either.

If this circuit is used at higher voltage and distortion output to drive a power output stage there may be some of that equal and opposite cancelation thing going on here. This could catch on and become popular. Who Knows? Think of the ugly little duck 6CB6 pentode Pete Millett uses in his Engineer’s Amplifier.
DT
 
If it is a myth than it is spread by much more than wiki....i am not talking about driving a tube to clipping...just the slight amount of 2nd harmonics introduced....

You may search for "Harmonizer" here on the forum, I posted schematic few years ago. It has a knob to dial, from zero to max. Try for yourslf, which level of 2'nd order armonic sounds better. ;)
 
And all laws are exponential. :)

If you really have EE degree, you should know that it is mostly a case when you use bipolar transistors. FETs have very different laws, that is why they are used in designs by Nelson Pass and others. Moreover if several transistors are made on the same die, you can use circuits that change transfer function to something like hyperbolic sine, which is almost linear within relatively wide range of values. You can't use similar circuits with tube since there is no two tubes close enough for them to work.
 
If you really have EE degree, you should know that it is mostly a case when you use bipolar transistors. FETs have very different laws, that is why they are used in designs by Nelson Pass and others. Moreover if several transistors are made on the same die, you can use circuits that change transfer function to something like hyperbolic sine, which is almost linear within relatively wide range of values. You can't use similar circuits with tube since there is no two tubes close enough for them to work.

Yes, I really have EE, and I really did my diploma in Tomsk Institute of Semiconductor Devices, and I really believed that approximation of linear function is all that is needed for best sound reproduction, and I really designed several fully complementary, very fast and extremely low distortions (measured!) solid state amplifiers, but that stubborn Tesla Mono-130 tube amp that we had in our laboratory anyway sounded better. It measured worse, but sound was CLEANER! It was BAD, BAD, BAD amp!!! :D

It took me next 30 years to understand that I was wrong assuming that audible distortions corellate with measured distortions... They do, but not directly. That's why I wrote in my previous post abot SMOOTHNESS of transfer function vs LINEARITY. This is the key. Perception hears as distortion everything that slightly deviates from alterations of sound heard in nature. But if sounds are distorted wildly like reflected from some non-linear wooden surface, or transferred by non-linearly compressed air, they sound clean.
If ou deliberately add 2'nd order distortion you don't improve sound. But if you amplify the signal sacrificing linearity for 2'nd order (and higher orders with higher loudness!) distortions but don't add what people add struggling for linearity, you PRESERVE the sound.
Do you hear me now? ;)
 
For me the role of amplifier is to transfer signal without changing it in any other way other than volume. Otherwise it will become musical instrument by itself. But I want to listen EXACTLY to what authors (musicians, producers, engineers) intended. That is why any distortion has to be at level low enough not to be heard. It is not possible to achieve with speakers, but any electronic components in playback chain have to be transparent.
 
previous post about SMOOTHNESS of transfer function vs LINEARITY. This is the key. Perception hears as distortion everything that slightly deviates from alterations of sound heard in nature. But if sounds are distorted wildly like reflected from some non-linear wooden surface, or transferred by non-linearly compressed air, they sound clean.

This is a very important point sadly too often overlooked. Another example is our ability to hear the materials that the room around is made from. A wooden wall sounds very different from a sheet-rock wall, eyes closed (or from a recording).
How can this be? Because we're made to rapidly and automatically ignore *most* sounds, to allow us to react quickly to the tiger behind and above. We *hear* what doesn't belong.

Thanks,
Chris
 
This is a very important point sadly too often overlooked. Another example is our ability to hear the materials that the room around is made from. A wooden wall sounds very different from a sheet-rock wall, eyes closed (or from a recording).
How can this be? Because we're made to rapidly and automatically ignore *most* sounds, to allow us to react quickly to the tiger behind and above. We *hear* what doesn't belong.

Thanks,
Chris

Yes, that is why room treatment is not less important than choice of electronics and speakers.
 
For me the role of amplifier is to transfer signal without changing it in any other way other than volume. Otherwise it will become musical instrument by itself. But I want to listen EXACTLY to what authors (musicians, producers, engineers) intended. That is why any distortion has to be at level low enough not to be heard. It is not possible to achieve with speakers, but any electronic components in playback chain have to be transparent.

I agree with you that they have to be trasparent Transparent in terms of PERCEPTION. For example, if window glass absorbs UV and above, IR and below, is it transparent? According to measurements it is dirty. But according to human vision it is absolutely transparent. The same with sounds. Now, make it transparent from 1 Hz to the Heavenly frequency, will it be more transparent for vision? Not necessary. Means to increase such transparency can add something that eyes will see as a dirt, as if you see a picture in a frame, instead of a nature through the window. The same with music: either you hear band in your room, or you hear "Nice Sounding Speakers with Linear Amplifier".

I prefer to hear sounds. And enjoy when people say, "I want to buy a house near the creek, I like how frogs are singing on your backyard!" :D

And it is great reward, when I jump and turn around being scared by running water, then realize that it is a waterfall record from cheap dirty digital CD :D
 
Hi DualTriode
Thanks for your feedback and let me say that I must play with the cheaper end of the spectrum, I'm just a TV repairman.
I love the SRPP topology, but the circuit does not have anything extraordinary, I think it can be improved, as I said before the output impedance is too high to drive a power amp, perhaps adding a bypass cap in the bottom cathode resistor can help with.
A long time ago I made calculations with the same circuit and an ECC99, 2K2 resistors and a 470uF bypass cap, maybe I will do a sim.
Best regards
Johann
 
As explained in post #28 and #36 I consider demonstrated that the electron cloud/space charge affects the linearity of the triode.
Moreover, the curves speak for themselves!!!

Working with triodes, most of us use the information provided by the manufacturer data sheet and work below the dissipation limit curve, which in most cases is in the linear region, as I said in post #36 and #38.

I still have not finished my thesis, you can tell me I'm just a TV repairman if you want, but your PhD degree gives you no right to insult me that way.

Fortunately I am not your student, and I suggest you study a little bit more physics, lest they repent in your university.

Hi Popilin,

I thought this might be a useful link for you. Tubes 201 - How Vacuum Tubes Really Work

I know I found it interesting. I studied physics in some depth, but it's always fun to go back and read about something again.

I notice that this link refers to the fact that the space charge changes the electric field in a 'diode' so that it is no longer linear. Maybe this is what you were thinking of before. Anyhow, what ever the details, it's a fascinating topic.

Your high voltage approach looks interesting and in the true spirit of DIY.

Please don't be put off by the feeling you get from some posts on this forum. Even people who have good English skills are not always aware of how their writing will be received by somebody else. It is the same with email, it is a 'dangerous tool'. And some people just like a good argument :cool:
 
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