[-=Germania=-]

Better yet, make the sound on the amp adjustable. Tube amps allow a lot for this, but not much in SS without making decisions which can adversely affect the sound.

There are those of us who prefer to have just one killer amp than 4 or five home amps.

 

[NelsonVandal]

There are a lot of tweaks you can do to alter the sound of SS amps. The choice of transistors have a major influence. You can even alter between bipolar, JFET and MOSFET if you make the design versatile enough. By adding CFP and/or cascode the sound is altered. You can also play around with local feedback to reduce the open loop gain. The use of ground channel or active grounding via shunt regulators will also have a major influence. Complementary or single end, differential stages, folded cascode... so many choices that all will influence the sound, in SS amps as well.

 

[mcmurray]

Quote:

Originally Posted by FloydCouncil /img/forum/go_quote.gif Yeah, I've done a course on Signals & Systems which dealt with Transfer Functions and stability of systems. We only dealt with very simply circuits though, such as simple filters and just general systems (2nd and 3rd order) without much context. Next semester, I've got a course on Control which I'm really looking forward to. I can find out a transfer function of a circuit with an op-amp, if I assume the Op-Amp to be ideal and all. But if I don't, I don't understand where to get the real transfer function for the op-amp.

The transfer function for any transistor circuit can be determined by using mathematical models (AC equivalent models) for each transistor stage. This gives you a clear insight (after a bit of simplification) as to what effect each component has on the characteristics of the amplifier in terms of frequency response, phase response, noise peformance, input/output impedance etc. It's quite fascinating really.

BTW there are more advanced models for OP-amps, depending on just how accurate you want to get. It is possible to use a schematic diagram for the op-amp, treat it as a discrete circuit, and derive the transfer function that way.

Usually an analogue electronics subject will cover this material after the foundations of signals and systems have been covered.

Quote:

Originally Posted by FloydCouncil /img/forum/go_quote.gif When designing systems, do engineers exclusively use Control theory and then after the transfer function is figured out they design the circuit using it or what?

That's the basic idea, yeah. Or you may have a specific transfer function in mind and you want to design a circuit to reflect that. For example, for the condenser microphone, an integrating amplifier was required so the circuit was manipulated to give a 1/s frequency response curve. Once you've got the transfer function nailed you need to address the biasing requirements and stability of the amplifier, etc.

 

[joneeboi]

More reading material for OP:

HeadWize Library - Projects

Audiologica

How come nobody mentioned Tangent?

Reading through his articles will definitely help you integrate the theory with the practical knowledge.

Plus, do you have your own copy of "The Art of Electronics?"

 

[FloydCouncil]

Quote:

Originally Posted by mcmurray /img/forum/go_quote.gif The transfer function for any transistor circuit can be determined by using mathematical models (AC equivalent models) for each transistor stage. This gives you a clear insight (after a bit of simplification) as to what effect each component has on the characteristics of the amplifier in terms of frequency response, phase response, noise peformance, input/output impedance etc. It's quite fascinating really. BTW there are more advanced models for OP-amps, depending on just how accurate you want to get. It is possible to use a schematic diagram for the op-amp, treat it as a discrete circuit, and derive the transfer function that way. Usually an analogue electronics subject will cover this material after the foundations of signals and systems have been covered.

Ah, that makes sense. I'll try reading up on transistor models. I understand that by looking at the op-amp circuit one can figure out the transfer function, but is it also possible by looking at the bode plots in the data sheets?

Is there any book you'd recommend for analog design, one that uses control theory/transfer functions in its methods?

I already have a copy of Art of Electronics, which is brilliant but I feel is more focused on building blocks of circuits than strictly on design.

 

[kipman725]

I am just finnishing my first year of EEE and this is rearly not that complicated, you have learnt about diffirential amplifiers, common collector/emitter amplifiers, various outputs stages and variations of all these with active loads. A complete audio amplifier is just aload of these strung together with bias components (zenners, current mirrors, etc). The trick is just to read everyone elses work and then you don't end up re-inventing the wheel or doing something dumb and in the case of the internet (mostly) not beliving everything you read.

 

[Juaquin]

Quote:

Originally Posted by kipman725 /img/forum/go_quote.gif I am just finnishing my first year of EEE and this is rearly not that complicated, you have learnt about diffirential amplifiers, common collector/emitter amplifiers, various outputs stages and variations of all these with active loads.

Having "learnt about" amplifiers and designing high-end, stable audio amplifiers as a finished system are completely different beasts. It's not as simple as you seem to think it is. Sure, you can figure out a design based on theory (with quite a bit of hard work). But what happens when you put it together and it isn't perfect? How do you fix it? There are some things that theory alone does not teach, and unfortunately most university educations (mine included) do not sufficiently address these real-world circuits as well as they should.

 

[pdupiano]

Its nice to know that there are a lot of EE's here on board. But sorry to burst your bubble folks but having an ee background can be a bit of a hinderance from my experience. Unless your school focused exclusively on hands on work you'll quickly find yourself in deep... well you know. A lot of my electronics knowledge/background that allowed me to understand how the mini3, m3, zapfilter, etc... work are from practical knowledge I got from HS -not an ounce came from my EE background. I've also been getting a lot of info on Tubes from a good friend of mine who's about 30 years older than me who works as a machinist and is an old electronics tinkerer. He's got the original RCA manuals on Tubes (same as the ones on Pete Millet's site). I've come to realize that I haven't applied a single bit of theory/class work at all in working on amps and other diy projects. What I've come to realize though, is that I can now see schematics for what they are after working with them constantly. For example, if a series of opamps and components or transistors are arranged in a particular way, I can now see if its a buffer or some type of stage in a process. The sad part is, while they tell you what these things are in school, they never give you enough time or practical work with the material so that you can begin to "see" these components together.

If there are EE's out there interested in audio work and design, I suggest taking as much time and putting in as much effort as you can to collect the following:
1) USB Oscilloscope (you can opt for an old oscilloscope, or if you're rich get a regular one)
2) Signal Generator
3) Bread Boards
4) Random Electronics Components (resistors, caps particularly 22 and 47uf)
5) Old Books. Libraries throw them away and I was able to get a handful of books on tube designs from books they were going to throw away.

As you go through your academic career, focus on practical design, scour through the diy forums here, diayaudio, headwize etc.. And also play around, mess with opamps and see what happens. I got a chance to do this while studying EE (before I joined head-fi) because I worked on building robots and other automated devices (even worked on my school's Darpa challenge for a bit). Your EE degree can hinder you because a lot of the work will begin to pile up especially near your third and fourth year. But just find the time to mess around, and knowing practical applications helps with the theory + it helps with your senior design project.

 

[kipman725]

Quote:

Originally Posted by Juaquin /img/forum/go_quote.gif Having "learnt about" amplifiers and designing high-end, stable audio amplifiers as a finished system are completely different beasts. It's not as simple as you seem to think it is. Sure, you can figure out a design based on theory (with quite a bit of hard work). But what happens when you put it together and it isn't perfect? How do you fix it? There are some things that theory alone does not teach, and unfortunately most university educations (mine included) do not sufficiently address these real-world circuits as well as they should.

true, my main issue is various circuits with feedback deciding to oscilate, I understand why this is but find I have to use a simulator to spot the osiclation and then just fiddle till it's gone. A pretty weak aproach. For example in a high voltage floating regulator I designed I found that with output capacitance <100uF the regulator liked to oscilate at between 70 - 400 khZ. My solution was to bump up the output capacitance but HV capacitors are expensive so this is a suboptimal solution.

 

[FloydCouncil]

Quote:

Originally Posted by pdupiano /img/forum/go_quote.gif 1) USB Oscilloscope (you can opt for an old oscilloscope, or if you're rich get a regular one)

Could you please recommend a USB Oscilloscope?

 

[pdupiano]

Can't really recommend one from experience since I havent owned one. I got myself an old Techtronix and it suits me fine. I've seen other students use usb scopes and they're happy with it. My recommendations are that you find one with Dual Channels and is sensitive enough for the audio range. Most usb scopes are able to do logic operations and also capture wave forms for further analysis. It something that I wish my old scope could do so I may be looking forward to a digital scope in the future or maybe a usb scope as well. If I purchase a usb scope I'll certainly give my impresions on it. goodluck with your search.

 

[Juaquin]

Quote:

Originally Posted by pdupiano /img/forum/go_quote.gif Its nice to know that there are a lot of EE's here on board. But sorry to burst your bubble folks but having an ee background can be a bit of a hinderance from my experience. Unless your school focused exclusively on hands on work you'll quickly find yourself in deep... well you know.

Totally agree - that's why I'm here. I do a lot of fiddling with circuits and breadboards, especially Arduino related stuff and the audio stuff here. It's actually helped quite a bit - I've had lab partners who have no experience with hands-on electronics. I've had to explain how a breadboard works a couple times. A lot of EE programs focus on theory (transfer functions, semiconductor physics, theoretical circuits), but there isn't a whole lot of hands-on labs, real-world application, or circuit design. I know a couple professors are trying to change that, but change is slow in the world of academics.

 

[pdupiano]

The change will never happen because of ABET requirements. My school actually created a separate program with the intent of teaching more hands on than theory work. Its called EE-Tech Basically you learn half the theory, and you get more hands on work. But you don't graduate with an engineering degree I think you might even end up with a BA instead of a BS. I think the best bet, if you're really interested in audio is to go through the hands on approach through DIY material around here. Besides, no school teaches Tube design, and most schools focus on digital and will only offer one or two courses on analog design.

 

[digger945]

I bet if a feller could set down with Alex Cavalli he could learn a thing er two.

 

[cr0ntab]

I just recently built myself a Bantam DAC and a Mini3 amp, that was a great learning experience. I reversed the wallwart polarity on my Mini3 and blew that up....haven't had time to see what went wrong and what I need to do to fix it though.... =(

I went to CanJam today and got to meet Ti Kan, super genius....really knows his stuff. I got to look at all the various amp designs he had on display and that really got me inspired to look into it some more. A lot of the resources given here are gold mines of information thanks to all that provided!