Education and pre amp tubes

[Venusblue]

Hey, I was just wondering what kind of education most of you guys on here have. Everyone seems extremely knowledgeable of electronics here... I'm still getting my associates of electrical engineering and get lost in some of the formulas and things I see floating around here.

Also I was wondering if there is a large difference between 12ax and 12ay tubes when used in pedals. Does it really affect tone that much? I've even heard people go so far as to say that the tube in most pedals are more of a gimmick and contribute very little to the tone.

[tubelectron]

Hi Venusblue,

Hey, I was just wondering what kind of education most of you guys on here have. Everyone seems extremely knowledgeable of electronics here... I'm still getting my associates of electrical engineering and get lost in some of the formulas and things I see floating around here

I am an engineer graduate in mechanics and automation, but it has not much to do directly with the electronics of tubes, amps and stompboxes... Moreover, many of us here (should I say : including me) are only skilled and talented techs which have no other background than what they have learnt by studying part-time and expererimenting. What we would call : Passion.

Also I was wondering if there is a large difference between 12ax and 12ay tubes when used in pedals. Does it really affect tone that much? I've even heard people go so far as to say that the tube in most pedals are more of a gimmick and contribute very little to the tone.

Right and Wrong...
There's probably no large difference between 12AX7 and 12AY7, I say probably because it depends on the design of the circuit itself.
There is usually a contribution to the tone from the tubes in stompboxes, I say usually because it depends on the design of the circuit itself.
The guys who pretend that " the tube in most pedals are more of a gimmick and contribute very little to the tone" means that adding a tube in a pedal doesn't mean it is a good pedal - the tube mystique/magic is strong, indeed...

I have built and experimented many tube circuits since 1978, from amps to pedals : some of them works amazingly, many others are "double-triode worthless junky tube mystique members". Tube is not magic, I agree... But...

Here is one example I own and experimented separately which can be considered an excellent sounding device : the Westbury W-20 The Tube (1978-1982). It is a HV powered unit (plate voltage circa 250V), and look accurately : you will see that there is a diode clipper... Nonetheless, this hybrid design works amazingly well, and can cover from subtle to deep sustained overdrive, but always smooth and singing. (pictures from my unit, schematic thanks to R.G. Keen)





A+!

[mth5044]

I have a BS in food science and am going for my Masters in the fall 

I suppose for your second question, refer to my first answer. I have no idea.   

[amptramp]

Electrical engineer specializing in small-signal analog electronics.  This board is my home!

As for the difference in 12AX7 and 12AY7, the biggest difference is the µ of 40 for the 12AY7 and 100 for the 12AX7.  (RCA quotes the µ as 40 for the 12AY7 whereas GE quotes it as 44.)  The lower gain of the 12AY7 occurs at a higher plate current of 3 mA vs. 0.5 to 1.2 mA for the 12AX7.  The 12AX7 can use contact potential bias i.e. the negative grid voltage which occurs because the grid has a cloud of electrons on one side that will impinge on the grid.  This provides the -1 to -2 volts negative bias which is enough (with a large grid return resistor like 10 megohms) to bias the stage with no cathode resistor.  Bias on the 12AY7 is -4.0 volts and you will not get that from a grid resistor; you need a cathode resistor (or negative bias supply) to achieve this value.  The µ is the voltage gain of the tube before the effect of the plate resistance and other parallel resistances are included.  If cathode bias is used, a value from 1000 to 1500 ohms would be usable for both tubes, so some circuits may accommodate both tubes.

[Venusblue]

many of us here (should I say : including me) are only skilled and talented techs which have no other background than what they have learnt by studying part-time and expererimenting. What we would call : Passion.

Ahh that's good, I felt really overwhelmed at first, thinking "Wow these guys know so much... I doubt i'd be able to do stuff like that without my masters". I'm able to piece together circuits and recognize what parts do now... I haven't started on my actual engineering classes yet, just my basics. I chose electrical engineering for my love of working with tubes, actually. I'd like to work with high voltage.

The guys who pretend that " the tube in most pedals are more of a gimmick and contribute very little to the tone" means that adding a tube in a pedal doesn't mean it is a good pedal - the tube mystique/magic is strong, indeed...

I've heard a lot of people say that it literally contributes nothing, though. That the same EXACT tone is achieved with a silicon transistor, which I had a hard time imagining. Also I can only imagine how beautiful that overdrive sounds... God i'd love to make that some day.

Electrical engineer specializing in small-signal analog electronics.  This board is my home!

Oh wow, I'd really like to do that. Is there a large market for things like that? I assumed that most electrical engineers worked on more like computer systems and things anymore. Like I said, I'd like to work on high voltage, but that's also something i'd really be interested in. Recently some one told me that in electrical engineering, you'll be lucky to get some one to even glance over your resume if you don't have your masters. Is that true?

I understood bits and parts of your second part, but i'm still googling a bit of it. I've also heard a lot about the "Starved tube" effect, and that it contributes more to the tone of a pedal that way. Would that just be supplying it less power, or is that more of some kind of choke?

[sault]

There are some circuits where solid-state roughly does match tube in terms of tone. If the tube is biased to operate in a very linear region (and perhaps has a significant amount of negative feedback) and doesn't stray out of that region, then there is little difference between the two. When used as a buffer (aka for solid state you've got the BJT emitter follower, for the JFET you've got the source follower, for tubes you've got the cathode follower etc), there isn't always a large difference in terms of tone. Again, a large factor is where the operating region lies - in general, more current tends to mean a more linear operating region. In general, the more the device goes into saturation the more the differences between tubes and solid state becomes apparent.

Starved tube literally means feeding a tube less voltage than normal. Referencing what I just said about current == better linearity, it follows that less current and less available voltage means less linearity, and more of a 'tubish' coloration to the tone. There are a number of pedal projects on this board that use a starved plate configuration, and they seem to do just fine.

My personal opinion is that people who say statements like that need to either be understood in a certain context (audiophile? power amp? phase splitter? starved voltage buffer vs op amp buffer? wild bias or ignorance?) or make clear what they're referring to. It is certainly not the rule across the board.


To sum: Sometimes they're similar, sometimes they're not. A lot of times they're not, especially when they start to saturate, ie, when you push 'em harder. A lot of the time, it really does depend on the circuit.


Saul T

[PRR]

> "...I doubt i'd be able to do stuff like that without my masters".

Oh, bull-poop. 90% of audio is KIDDY-stuff. When you KNOW YOUR BASICS (few do), it can all be worked-out. It helps to READ EVERYTHING: most audio is the same old stuff done different each time, and you learn the patterns.

By sophomore year you should be able to (without SPICE!!) sketch a modest 1-transistor amplifier, show that it does (or does not) have useful gain and impedances and is not wasteful of power. Or to be able to shape frequency response in a general way ("less highs"). You will probably have to ace the junction-theory quiz to predict distortion from scratch; alternatively an alert but untutored dabbler can estimate THD with a few rules of thumb not taught in school (because the audio assumptions are a very small subset of the total world an EE must know).

> "...my masters".

Conversely, the EE degree prepares you to begin to learn many amazing and wonderful things which mostly are NOT useful to everyday audio design. Note: "prepares". The average company expects a fresh EE to need several years to be "productive". Partly because the commercial leading-edge moves so fast, and largely because the intense teaching of theory leaves no room for practical messing-around. I've known EE grad students who could not put an actual capacitor on an existing resistor to make a fixed tone-mellower.... they started writing arcane equations instead of grabbing a clip-lead.

Audio electronics is really simpler than building houses. Me, my contractor, and his lead man have a total of ZERO hours formal training but about a combined century of whacking wood and cursing toilets. We get stuff built. Sometimes mighty good.

I have 13 hours of 200-level transistor-amp class.

Around that time I was "designing" my own amps, based on analyzing and modifying GE and Fisher ideas, backed by perhaps 2,000+ hours of omnivorous reading and meditation. Since then maybe tens of thousands of hours pondering audio electronics. Sounds like a lot as a number, but any musician who has played several decades has about the same amount of time and insight into his music.

[Steben]

I studied engineer-architect. A rather awkward combination degree internationally, but typical Belgian.
My father however studied engineer electrotechnics, hence ....

[Mike Burgundy]

Interesting quetion - hope more answers turn up, I'm kinda curious too
*edit - okay, that got me rambling. Sorry for the long post

Dutch schooling is structured differently, but after "scientific high/college" (VWO-beta) and getting thoroughly confused about options and wishes (even considered music (which I soooo wasn't ready for, I know now) and acting) After getting the short straw on med school (lottery!) I started university electical engineering because I was totally in love with what MIT was doing at the time with robots. I soon found out I was in the wrong place. This particular flavour of EE was almost exclusively advanced math, and desinging bits of chips. Nobody knew what a tube was. Met a great professor, who proudly showed me what he had been working on for the last 5 years - final test batch of chip die just delivered. It was a *part* circuit - a building block for chips. It would go into a library as a black box. I realised I needed something to show people what I had done, not a bit of library space.
Short straw for med school again. Then trained as an industrial design engineer for quite some time, never finished my masters. Now have my own company in interior construction (fancy name for building IKEA furniture - we supply their buildup service).
During my uni days I've spent lots and lots of time on music, audio engineering, studios, tinkering with electronics, building guitars, etc. First pedal I built was during highschool - a generic distortion (from some EE mag from the library) which didn't work. Gave up for a bit. Started again at university. FuzzFace, Didn't work. Got mad. Got sad. accepted it. Built it again, and it worked. At this time the net was coming up fast, and I soon found Jame Heilman and (through Jamie) RG's schems, Aron got started, and the DIY bug took.
I actually incorporated more of what I learned DIYing into my industrial design projects than the other way round.

I think a LOT if not most of us started with some technical insight and a healthy dose of enthusiasm, but no more. Like PRR says - it's all in the reading, and thinking about what you've read. I don't do that enough, but if you want to get a *major* head start on any random EE (as far as music electronics are concerned) he's right - learn the basics (Ohms law, take it from there), then seek out all you can find on certian circuits. RG's "technology of..." series are a GREAT start. Then use those to take it a step deeper - see *why* a transistor stage is built that way (so find out about transistor biasing, how and why), what the filtering stages do (Ohms law, but with capacitors). Same for opamp stages.Etc. The internet is a *truly* wonderful resource. Do this for a while, and you will develop a deeper grasp of music circuits then a "generic" EE - because he's thinking about very, very different things.

[StereoKills]

I've been working at a small biotech startup company for 3 years as an electronics technician. I got the job because I "had experience with electronics", in other words, I could wire a guitar. The EE I work with is also a guitar enthusiast and actually just finished rescuing a old Earth Sound Research 100W amp. I also am pursuing an education online majoring in Biology. Pretty handy that I also work with several biologists if I can't figure out some homework.

[bluesman1218]

Electronics hobbyist from my teens (late '60's), various mechanical trades. Started working on tube amps before pedals, they're a lot simpler to me. Loving learning more about pedals and these forums and guys like RG Keen, Jack Orman are a fantastic resource. You're in the right place!

[Zipslack]

I don't have much of a presence here, but here's my background.  Engineering school drop-out (too much theory, little to no practical - ran into too many Senior-level students who couldn't wire basic circuits).  Got interested in electronics as a teenager to mod my guitar (Thanks, Craig Anderton!) and keep my old junk amp running.  Eventually went back and got an Associate Degree in Electronics and then worked as an Engineering Tech. for a company that specialized in EMI/RFI Filters and relay-control power controllers.  I used to train fresh EE's when I worked as an Engineering Tech so they could do USEFUL work.  An education just shows that you CAN learn and prepares you TO learn.  Been teaching high-school electronics for 12 years now and just recently started working on my B.S. in Information Technology.  I also do some repair work for a local music store, which got me into tube amp build/repair.  Compared to a lot of guys on here, I don't know squat - but I'm reading and studying and maybe in another twenty years I'll be good enough to hold Enzo's schematics while he works...

[Astronaurt]

Hey, I was just wondering what kind of education most of you guys on here have. Everyone seems extremely knowledgeable of electronics here... I'm still getting my associates of electrical engineering and get lost in some of the formulas and things I see floating around here.

Also I was wondering if there is a large difference between 12ax and 12ay tubes when used in pedals. Does it really affect tone that much? I've even heard people go so far as to say that the tube in most pedals are more of a gimmick and contribute very little to the tone.

Well I'm just in my first year in my City college's Sound Arts Program (which really has more to do with working with Analog and Digital audio systems and than the actual circuitry that makes 'em work, but hey it's close ) I totally second tubelectron, I didn't start out with much knowledge at all but I've got a ton of passion for this stuff. I started out with building pedals when I saw the schematic for the old Vox Clyde McCoy Wah pedal one day and was just completely baffled why it costs upwards of $100 to buy a Wah pedal when the parts cost around $15. I probably wouldn't have gotten hooked so awfully bad on electronics if my first try at making my own Wah pedal wasn't a complete and utter success. I'd say I'm addicted to this stuff, but then again maybe the solder fumes are just starting to get to me...

On the subject of Tubes though, THE BEST resource I've come across is Merlin Blencowe's books on Tube pre-amp and power supply design. They have tons more useful information than most electrical engineering textbooks I've read, and don't READ like electrical engineering textbooks. I kinda freaked out my family when I told them all I wanted for Christmas last year was "Designing Tube Pre-amps for Guitar and Bass" and I've since read it cover to cover about 8 times. If you want to learn about Tubes and tube circuitry applicable to Amplifiers or stompboxes, that's what you want hands down.

here's a link to his site where you can look at some chapters from his books and order 'em. He's also a pretty frequent poster on this forum if I'm not mistaken.

http://www.freewebs.com/valvewizard/

[geertjacobs]

If you want to learn about tubes, here's a great document with basic theory.
It explains the working of a simple tube amp.
Ax84.com P1 theory document

[defaced]

Also I was wondering if there is a large difference between 12ax and 12ay tubes when used in pedals. Does it really affect tone that much? I've even heard people go so far as to say that the tube in most pedals are more of a gimmick and contribute very little to the tone.

The tubes are different, their effect on the sound of the pedal will be dependent on the circuit.  Running a tube a 12v or at 100v or at 350v will all do very different things to the tube's characteristics.  I'm sure at some voltages, particularly low ones, the tube is not doing what it was designed to do.  Read up on "starved plate" designs. 

Oh, I'm a welding engineer.  Pretty much everything I've learned about electronics above the basics has been self taught over the course of the past couple of years.

[Venusblue]

Wow! Thank you guys very much for all the replies, I thought it died and didn't check it for a few days, as I don't get on here as often as I would like...

Thank you all for the information, I'll be reading over all of this and every link posted... I have been reading everything I could get a hold of, on this website and otherwise. I've been picking up books to read on engineering too.

I feel like i'm the exact opposite... I can wire a guitar, I enjoy experimenting and have a lot of experience with working on electronics, just no as much theory as I would like yet... But yeah I have heard a lot of stories about EE's who have their bachelors and don't know how to solder. How the helll....?

[Incubusguy]

Wow! Thank you guys very much for all the replies, I thought it died and didn't check it for a few days, as I don't get on here as often as I would like...

Thank you all for the information, I'll be reading over all of this and every link posted... I have been reading everything I could get a hold of, on this website and otherwise. I've been picking up books to read on engineering too.

I feel like i'm the exact opposite... I can wire a guitar, I enjoy experimenting and have a lot of experience with working on electronics, just no as much theory as I would like yet... But yeah I have heard a lot of stories about EE's who have their bachelors and don't know how to solder. How the helll....?

Oh, you wouldn't believe...  

I'm just finishing the third year of my Masters in Electronic & Electrical Engineering. At no point has the art of soldering ever been mentioned; it's considered a job for the labourer and not the engineer.

Although soldering is, in my opinion, an essential skill to have (not least just for prototyping purposes) I've noticed many more worrying things in my time on this degree: people forget the basics as quickly as they learn them. Many people in my year could happily design the building blocks for a comms system involving a QPSK wireless link with correlation receiver, followed by an optimised fibre-optic link with pulse shaping; however, ask them to design a simple low-pass filter or one-transistor/IC amp and I guarantee they will stare at you with a blank face. The worst case of this is something I experienced a few weeks ago: I had to teach a fellow Masters student the concept of a potential divider and how to calculate its output   Honestly, it actually makes me both angry and sad that these are the next generation of engineers.

While one could argue that anyone looking for a high-paid electronic engineering job will be asked to do the former more than the latter given the current technological trend, lacking the basic skills will absolutely catch you out when it comes to real-world engineering. I've done a few different work placements and you can't expect to just slot together these separate building blocks they teach about; the inability to factor such basic things as impedance between stages will seriously hamper your work effort.

Interestingly, I would say that a good 75% of my electronics knowledge comes from this forum and general hobby interest over the past 7 years or so. Without trying to sound boastful, I would consider myself more knowledgeable than some on my course, but this just highlights the main issue: in my experience, electronic engineering degrees will definitely make you better at maths and you'll become aware of higher-level concepts such as the ones I mentioned earlier, but don't expect it to have any bearing whatsoever on the things we DIY'ers do. As Zipslack said, it will only prepare you to learn; no more.

Frankly, I think it's embarrassing and a big step backwards when you don't absolutely hammer home the basics; in some exams, I've been in the situation where I haven't learned the solution to a problem (if you can memorise solutions parrot-fashion, you WILL get a good degree classification, regardless of actual ability - but that's a whole different topic I could rant about!), but I've deduced the solution by working from first principles. Sure, I might end up with the same mark as someone who spent hours memorising and it takes me a few more minutes in the exam, but I saved myself a few hours outside the exam and get the real satisfaction of glimpsing the feeling of discovering something for the first time.

Referring back to the thread topic, there has been one mention of tubes/valves on one slide of one set of lecture notes in three years of study so far. Modern electronics rarely calls for valves outside of audiophiles and certain HF applications where they become preferable to silicon, but even just one lecture on the technology and simple design techniques would be helpful, if not just to create a more rounded engineer.

Oh, and PRR: while your projection of a sophomore student's ability may be accurate for that year, don't expect them to remember those skills after that year's exams, at least in my experience!

[sault]

Many people in my year could happily design the building blocks for a comms system involving a QPSK wireless link with correlation receiver, followed by an optimised fibre-optic link with pulse shaping; however, ask them to design a simple low-pass filter or one-transistor/IC amp and I guarantee they will stare at you with a blank face.

In a word - tragic!

Is it a case of over-specialization? To ignore what are seemingly vital fundamentals just seems criminal.

I was a Boy Scout - "be prepared". I have low-level paranoia - "assume the worst will happen". I've learned already that you can't assume ideals when designing circuits in the real world - a good design allows for non-ideal components, operating conditions, and variation in component values. Being hobbyists and low-volume producers, to some extent we can skip some of these precautions (hand-selecting components, manually-trimming bias points, etc), but still... a good design should have a degree of resiliency.

My philosophy, at least. I would expect at least as much from any EE... disappointing to hear otherwise...


Sault

[Incubusguy]

Many people in my year could happily design the building blocks for a comms system involving a QPSK wireless link with correlation receiver, followed by an optimised fibre-optic link with pulse shaping; however, ask them to design a simple low-pass filter or one-transistor/IC amp and I guarantee they will stare at you with a blank face.

In a word - tragic!

Is it a case of over-specialization? To ignore what are seemingly vital fundamentals just seems criminal.

I was a Boy Scout - "be prepared". I have low-level paranoia - "assume the worst will happen". I've learned already that you can't assume ideals when designing circuits in the real world - a good design allows for non-ideal components, operating conditions, and variation in component values. Being hobbyists and low-volume producers, to some extent we can skip some of these precautions (hand-selecting components, manually-trimming bias points, etc), but still... a good design should have a degree of resiliency.

My philosophy, at least. I would expect at least as much from any EE... disappointing to hear otherwise...


Sault

In the first year we were taught all the fundamentals so they weren't ignored. Every year onwards, it's assumed that we remember everything we are taught so we progress onto more advanced topics. Since people are quite able at forgetting topics covered in previous years (myself included), it results in people with considerable high-level knowledge but whom are rusty on the basics.

I think part of the problem lies in the desire/need for a university course to cater to the current climate in the field. We are in the age where wireless communication and heavy software dependence is common, so the university will naturally try to ensure that its graduates are well-versed in these areas to give them good employment prospects and to satisfy industry demand. In order to fit all that in, there's no time to refresh the basics every year.
To a point, I don't blame them because they can't teach everything they might like in 3/4 years, so some things have to be sacrificed. However, given that most companies will educate a new-starter anyway, it would make more sense to me to ensure that the graduate has a solid founding in the basics; everything can follow on from there. I'm not so sure we're in danger of losing any skills, though, since they'll probably be reacquired on the job through experience.

I can't say that the overspecialisation is common-place since I only know what I've experienced in my own degree course; I'd like to think/hope that it's an anomaly! I do know of a number of coursemates who would make capable engineers, but I know at least as many people who have drifted into this degree and hoped they would get interested along the way.

Interestingly, times don't seem to have changed much since you were at engineering school, Zipslack! I constantly complain to people about how little practical work we do and the overspecialisation mentioned earlier.

I think it's worth pointing out that these words come from an engineering student; I would expect a practicing EE to adhere to the concepts you mentioned so, assuming they do, perhaps you need not be so disappointed!