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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 03 Nov 2016, 10:08 
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mwhouston wrote:
It's a universal design. But the design may slightly favour one tube over another.



It's only "Universal" because that is the name someone gave it.



To me it's paramount to putting big off road tires on a Honda Civic, yeah the car may still drive but the tires rub going around corners and the speedometer isn't accurate, not to mention PCM data is now incorrect and so it will mess up the shift points and fuel management etc............But the car still goes from point A to point B I guess.

Has nobody run into the issue of bandwidth in the real world with this preamp. The testing shows -3db at 40kHz but that is not going to always be the case with real world interconnects. Put a normal interconnect on there and with a parasitic capacitance of say 300pF and you will now be down-3db @ 8kHz, pretty bad.

Maybe a future addition to the project could incorporate a ganged switch where the switch changes plate load resistors and cathode resistors. This way you could shut the amp off, change from say a 12AT7 to a 12AU7, flip the switch and turn it back on and now it's optimised for the 12AU7. This would be a more fair way to compare the valves and their characteristics because it's my opinion that you can't judge a tube by plugging it into a circuit not setup of for it specifically.

A preamp that can't drive heavy loads whether it be resistive or capacitive isn't exactly "universal" if you ask me. But hey you can "roll" tubes I guess :|


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PostPosted: 03 Nov 2016, 17:04 
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Universal in the sense you can swap out 12A!! tubes only. We are all aware this simple preamp will not drive load under 100K well. That goes without saying. Fine for my tube power amps which are usually better than 250K input impedance. No one hear is trying to make out this simple design is so thing it's not. It was designed in the spirit of DIY fun and just adds a little extra interest to the hobby. I've built a few and sold a few of these. No complaints yet.

There is a few universal tube power amps on this site. Once more the amp is not optimised for any one power tube but may function better with one. Go ahead and design the ganged switch with the different biasing and tube loading. Can't wait to see what you come up with.

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PostPosted: 04 Nov 2016, 18:41 
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famousmockingbird wrote:
I still don't understand this preamp design?

You can't just plug a 12AU7 into a 12AX7 circuit they are completely different, this is ridiculous. The only similarity is pinout and heater characteristics, that's it. The circuit can only be optimal for one tube so why plug anything else into it?
The designs that people post here are, for the most part, not just random combinations of components, but either solutions to a specific problem, or experiments in design under particular constraints. Take this design for example. It did not simply spring from my mind fully formed, but rather was the result of a detailed design process undertaken to address a specific challenge. The component values and the topology were not simply something copied from a book or previous design, it was instead, the result of the aforementioned design process.

Had you reviewed the original thread here (http://diyaudioprojects.com/Forum/viewtopic.php?t=3266) you would perhaps have better understood the genesis of this circuit. It was not until post #109 where the first incarnation of the 4S "Universal" was introduced. The posts leading up to this one would, perhaps, help you understand the design more fully. I suggest you review them to aid in your understanding.

famousmockingbird wrote:
To me it's paramount to putting big off road tires on a Honda Civic, yeah the car may still drive but the tires rub going around corners and the speedometer isn't accurate, not to mention PCM data is now incorrect and so it will mess up the shift points and fuel management etc............But the car still goes from point A to point B I guess.
I must disagree with your assessment. This circuit is more akin to a properly designed set of tires that work well with a set of cars exhibiting similar characteristics. I would no more use this circuit to drive a low impedance or highly capitative load, than I would attempt to put a heavy studded truck tire on your aforementioned economy vehicle. In both cases, understanding must proceed actions.

In the project specific thread here (http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4628) in the fourth post you will find the load line designs for five tubes using this design (12AU7, 12AV7, 12AY7 12AT7, & 12AX7). These designs all demonstrate good performance at the resulting bias points. If your find fault with any of the calculated design points, by all means, enlighten us. We would be eager to hear your reasoning. If you read through both threads further you will find discussions of other tubes to which the circuit may be applied, and others which I recommend against for various reasons. And again, the goals of this circuit were never to be optimum in any way for all tubes, but instead to present a design solution to a particular circumstance, under stated constraints.

As to the issue of the output impedance. Again, in the various threads, you will find my reasoning for the chosen topology, and many in-depth discussions, plots, calculations, and design options relating to the trade offs between noise figure and output impedance in this design. You will also find that I have at times recommended an alternate topology with the volume control in front where a lower, fixed output impedance is desired.

And as to having an abnormally low high frequency 3dB point if the preamp is loaded improperly, this is an issue not with the design, but with a lack off understanding of the person using it. A lack of understand which could be corrected by spending an evening reading the background material.
famousmockingbird wrote:
Has nobody run into the issue of bandwidth in the real world with this preamp.
To answer this question, yes they have. And in each case, the issues were dealt with and those involved increased their understanding. And even more importantly, the circuit has been built by many individuals who have found it wholly adequate to suit their needs and satisfying in its performance.

If I may make a suggestion. In the future, before assailing the work of others based on your first impressions, you might be better served by researching the background of these designs, before recklessly loosing your opinions on those with more understanding. In this way, we would all be better served.

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PostPosted: 04 Nov 2016, 20:35 
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famousmockingbird wrote:
It's only "Universal" because that is the name someone gave it.

Yes. Much like a universal screwdriver and how most will understand that it will not be suitable for all nuts and screws.

famousmockingbird wrote:
To me it's paramount to putting big off road tires on a Honda Civic

Your example is extreme to the point that it appears to have impaired the logic of the analogy. Using a Honda Civic as an example, the car would be well suited for use with tires ranging between about 13 and 17 inches and would also accommodate a number of tire profiles. Each combination would have measurable performance differences - say fuel consumption and traction (ie. gain, distortion). In addition each car driver will experience a different ride. Someone with a skinny bum might not like small diameter low profile tire, but a portly individual might like it (ie. sound quality). Your example was more along the lines of trying to shove a 300B into a 9-pin socket.

If you read past the title, you should find that this project is very well documented and clearly shows the gain and distortion that can be expected with the various tubes.

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PostPosted: 09 Nov 2016, 15:52 
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Has anyone seen this thread at DiyAudio ?

http://www.diyaudio.com/forums/tubes-va ... esign.html

These guys are seriously dumping on the 4S design ?
I have built the 4S preamp and I like it a lot.

It is amusing to see some folks disparaging a design without actually having listened to it.
.........

Oops, Sorry, I intended this for the 4S preamp project forum.
Admin, please move to that forum.


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PostPosted: 10 Nov 2016, 08:34 
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That you like it should be enough. Putting value in the opinions of others when it comes to audio is dangerous unless you have established sufficient congruence to your tastes and experiences. And "expert" opinion is even more dangerous as such individuals typically have additional axes to grind when rendering their thoughts.

As to opining on something not heard - that is easy enough, and I will repeat an analogy. Early Dynaco ST120 solid-state amplifiers, while powerful for their day sounded like glass in a blender and tended to blow up by the numbers. I do not need to hear such a device to render an opinion on its behavior. However, this amplifier may be modified to sound rather nice and even to be reasonably reliable. I WOULD need to hear a modified device to determine if the work was successful. Many circuits are fairly standard - and an individual familiar with the circuit could opine on it without necessarily auditioning it.


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PostPosted: 10 Nov 2016, 09:40 
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Famousmockingbird is/was on this forum too and voiced this opinion in the 4S Universal thread. I've made two 4SU already and I'm happy. I don't care what audiophiles are talking about. This is 'my hobby' and I like how my amps sound.

As for putting big tires on a Honda, that's right up my alley too! I'm one of the fools on Grassroots Motors Sports forum. Doing wacky things with cars is all we do over there!

I generally subscribe to what Matt (Suncalc) says about audio and how we humans respond to it. I'm an engineer and I love the engineering he does to his designs and his reasoning.

There will always be people who think they are in a white castle looking down on the masses, but sometimes you have to make sure that even if you believe you're in the mud looking up at those people, you don't judge them any differently than the person next to you. I always try to appreciate someones different-than-my-own opinion.

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PostPosted: 10 Nov 2016, 19:24 
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Peter W. wrote:
And "expert" opinion is even more dangerous...
I have been designing and integrating cutting edge RF avionics sensors for over 28 years. In the company for which I work (a very LARGE company), if there is a radar question that people are having trouble answering, it generally works it's way around to me. In general, I can answer it. But when these people ask me if I'm a radar expert, I always say no. I will tell them that I am pretty knowledgable concerning radar systems, and I've been working with them for a very long time, but I don't like the word expert. The word itself carries a lot of baggage. And recently I can across what I think is just about the best working definition of an "expert" I've ever read.

"An expert is someone who thinks he knows so much that he becomes an a$$hole."
--Luke Rhinehart as voiced by the character Billy Morton.

So no, I'm not an expert. I realize that I will always have more to learn, and I should never ignore anyone's opinion. That is unless that person has given me a reason to do so. And refusing to investigate why something is the way it is, is in my mind, a very good reason. YMMV

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PostPosted: 11 Nov 2016, 04:07 
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Without pointing the finger, those who come in both guns blazing generally don't hit anything substantial rearly make friend. Thankfully I find most non-Australian forums very supportive, informative and instructive. And that's what I have experienced here. On a major Australian forum I find some aggression but even on the best balanced forums there is always one or two.

One or two compared with the great supportive camaraderie I/we experience here is but a drop in the forum ocean. Let's move on.

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PostPosted: 12 Nov 2016, 20:45 
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RossD wrote:
I generally subscribe to what Matt (Suncalc) says about audio and how we humans respond to it. I'm an engineer and I love the engineering he does to his designs and his reasoning.

I'm a Civil and see it exactly the same way. I doubt it's a coincidence! ;)

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