[dBs]

I'm just about to graduate with my BSEE in the next couple of days. I decided a year ago that after graduation I wanted to design, test, and build an amp from the ground up. You know, do something for me after all of this hard work. I bought and have been reading through a book on SS amplifier design and my book on valve amplifiers just came in today. What I am wondering is if anyone on here who has some solid experience to kind of help guide me along the way as I understand the theory and basics but not the real world implementation of those. I think it will be a good experience for me and maybe even a learning experience for my mentor/s as I would be willing to try some really out there things.

I am hoping to make the results of all of this work a DIY project for anyone (likely without profit but that's negotiable, my priority is learning along the way and making a very fine end product). At this point I haven't started anything major so the design is completely up in the air. I just got the valve book so that door is open to me now as well. Valve, SS, hybrid, whatever. If the person/s deciding to help me own a store or something, I have no problem selling the end result out of it as DIY or completed builds (though I do ask that the product be DIY for those who wish).

I should give some perspective about me for whatever poor sap/s decide to take me up on this invitation. I have taken the advanced electronics class so I know the basics. I have had no background with valve design at all. No experience in PCB design. I also have two very solid jobs lined up after graduation so I will likely be working as well, so this will be a free time venture, no pressure for anyone involved.

If there are any other thoughts/questions/etc feel free

 

[Uncle Erik]

You're beyond me in understanding electronics, but for what it's worth, you should devote some time to the layout and construction of tube amps. Morgan Jones wrote a good book on the topic. Designing the circuit is one thing, but you have to carefully plan the chassis and layout, too. Pay attention to the materials you use to build the case - sometimes you can get coupling from ferrous cases. And keep an eye on RFI, which can be a tricky demon in sensitive audio circuits.

I'd also give some thought to learning how to work point-to-point. There are a lot of advantages to using it for tube amps. The best way to get a feel is to restore an old tube radio. If you're up for a challenge, get an old "boatanchor" communications receiver from Hallicrafters, Hammarlund, National, Drake, Collins, etc., and restore it. Get the Photofacts, which will give you the parts list, schematics, alignment info, etc. You'll get to see firsthand how engineers in the golden age laid out tube gear. What's nice is that you can get boatanchors working great with $50 of Orange Drops and resistors. Tubes are very reasonable, too. Also, listening to shortwave is a hobby in itself and you might be surprised at the quality of AM when you pass it through a high end receiver.

Anyhow, good luck, keep us posted on your progress and congrats on the degree!

 

[digger945]

First let me join Erik in congratulating you on completing your degree. You sound like an ambitious person who should no doubt go far. While it may not be impossible to come up with a completely new circuit altogether, you can draw much inspiration from the work of Ti Kan, Alex Cavalli, Kevin Gilmore, and many more like the ones Erik mentioned. Other references for tubes would be the RCA Radiotron Manual version 10, bonavolta, and the Navy NEETS manual.

 

[NelsonVandal]

I've built several solid state amps from the ground up, without any knowledge at all - I've picked it up along the way. Looking at schematics, hanging around Diyaudio.com and playing around with LTSpice have done it for me. There are so many options. All of them will measure well and sound OK, but the problem is to get the sound you want. Trial and error is the only way to learn what different tweaks, topologies and components do to the sound. There are some very good opamps out there like LME49xxx and AD797, so you really have to struggle to beat them with a discrete design.

 

[Juaquin]

I'm a year or so from graduation with a BSEE myself and I wanted to do just this thing. Good luck!

 

[digger945]

Congrats to you as well Juaquin. Looks like we are assembling a team here.



Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif so you really have to struggle to beat them with a discrete design.

Wouldn't be any fun at all if it were easy

.

 

[pabbi1]

Pete Millett built a page just for you. His HA-4 could be a smash with a technical refresh.

 

[dBs]

Great info so far everyone thank you. And thanks for all congratulations.

I can design basic amps well enough from what I know, negating valve amps. Hopefully with the book I got, Amazon.com: Valve Amplifiers, Third Edition: Morgan Jones: Books I will soon be able to do the same with valve amps.

The things that I suspect I will have the most trouble with is where and why to (seemingly) insert random capacitors, zener diodes, etc. Looking over any major schematics from amps in any of my books, from AMB, etc all have them and the reason for their presence is not usually intuitive.

The next aspect is what parts to choose. This problem is pretty self explanatory. These two hurtles are ones that are usually only overcome by experience or many years of learning. I guess I'm hoping to tap the experience of a superior to shortcut some of those years =)

 

[Uncle Erik]

The Morgan Jones book is quite good - you will learn a lot. You should also pick up Bruce Rozenblit's "Beginner's Guide to Tube Amps" as well as take a look through Bruce's site. I'm posting from the phone and can't paste the URL, but Google Transcendent Sound and you'll find him. Also Google the Tube CAD Journal and read that - it is excellent.

Another designer you might want to chat with is Craig Uthus, of Eddie Current. He's friendly, sharp and has produced more than a few good designs. You might want to talk to Frank Cooter, too. He designs and builds his own amps and has made some impressive gear. A newcomer you might want to talk to is Donald North. I don't know him yet, but he seems to know what he's talking about and has some experience. I've been tied down a lot lately, but I want to meet him, check out his amp and get to know him.

 

[LingLing1337]

I have no technical knowledge of this whatsoever, but one piece of advice I would like to give is, during the testing phase, test the amp with as many different (hi-end) headphones as possible. Too many amps these days seem to synergize perfectly with one 'phone and do poorly with another.

 

[AudioCats]

Quote:

Originally Posted by LingLing1337 /img/forum/go_quote.gif Too many amps these days seem to synergize perfectly with one 'phone and do poorly with another.

but who wants a "jack of all trades" amp?

 

[mcmurray]

Not exactly what you're looking for but I did a (nearly complete) design for a low noise condenser microphone preamplifier for my thesis. It should be of some help with your design especially for minimizing noise and transfer function analysis. It's also a good example of how to design a very custom amplifier suited to a particular transducer by the use of a mathematical model.

PM me if you would like a copy of the thesis.

I think as part of EE degrees they should have the students design an audio amplifier from the ground up as a learning experience. IMHO there's too much focus on the fundamentals and not enough on practical application. Out of a 4 year degree I only had 2 units that covered analogue electronics!

OT: does anyone know of good books that cover DAC design including analogue IV stages? I'd like to design a high end DAC from the ground up.

 

[FloydCouncil]

I'm currently doing EE as well and agree with mcmurray there just isn't enough design. I'm only about to enter my 2nd year, so hopefully I'll see some design modules in my course.

Besides that though, in my spare time I'm trying to design an amplifier by studying other published designs - especially the one's at tangent. We haven't really covered transistors yet, but I try to learn by myself and get by. But thankfully, I understand the bits about op-amps so far, in most cases. I can understand the schematics on Tangent's website, but on amb website, I can't quite figure out the M^3.

And there are things which confuse me about all designs - for instance, why do almost all the amp's I've seen have an active ground?

So far, my design is just a non-inverting amplifier (which really isn't a design at all). I'm thinking of biasing it into class A by the use of the JFET Cascode current source. But beyond that, I'm completely lost.

I would really like advice on where to go from here. I got into EE because I want to design circuits - not analyze them all the time!

 

[mcmurray]

^ have you done any work with transfer functions, pole/zero analysis as part of your degree yet? That was a a bit of an eye-opener for me.

 

[FloydCouncil]

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.

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?