A while back I was working on designing a hybrid amp with a tube preamp and SS power amp. I'm finally getting around to finding components for it, and it is my understanding that the TDA2050 is no longer commercially available. I guess my first question is is there In fact no more legitimate source for this part? If not, does anyone know where I could get (preferably) a kit for a power amp IC? My circuit has one 35VDC rail, and I've only been able to find kits for dual-supply operation. I just want it to make a small signal bigger, so I'm not too picky; any run-of-the-mill, standard, boring IC will do just fine. Thanks for any suggestions!

I am deeply saddened to hear this news, Roly. I have only spoken with you through this forum, but you have been an immense help to me, not only from my direct interactions with you, but also in reading your responses to other posts. Aside from the direct help you provided me, I think my favorite thing I have learned from you is the art (and perhaps more so the science) of troubleshooting--to attack a problem by rooting out its cause rather than blindly guessing what the solution might be. That advice has been helpful to me in many more ways than just electronics, and I'm truly grateful for it and everything else you have shared throughout the years. I will be praying for you and your family, and I wish you joy and happiness as you visit with your loved ones in that beautiful country of yours. You will definitely be missed, but I'm sure I speak for everyone when I say that we are grateful to have known you. Take care, my friend!  :dbtu:


Matt

Oh, so if I'm understanding that right, the part of the pickup "outside" of the strings would actually be picking up more of the harmonics. Was I right, thought, in thinking that the signal would be stronger (higher voltage) with more of the pickup closer to the strings? If that's true, I'd think I'd be trading off the richness (fullness? quality?) of sound for a stronger signal. Which would maybe work better for a bass-type instrument? I will definitely try to rig something up to play around with it.

I'm currently building my 1-year-old son his own little guitar he can drag around and beat up since he shows much interest in my Taylor acoustic (which he cannot drag around and beat up). After I finish that project, I want to make one for myself. I have a humbucker pickup from an old Epiphone SG style body I acquired awhile back. These guitars only use three strings, so I was wondering of there would be anything beneficial to arranging the pickup so that more of the magnets are under the strings. That is to say, instead of setting it up in the normal fashion and only having half of it covered, I could angle it--or even turn it a full 90 degrees--so that the strings rest over all the magnets. What would this do for the signal? I'm inclined to think it would make it stronger. But I'm also inclined to think there could be some kind of phasing issue as well. But really, I have absolutely no clue, so I'm asking the experts.    Your thoughts?

You sound like you're asking a lot of the same questions I was asking when I started out learning about electronics (which was not very long ago). If you really want to get a better grasp on how this stuff all works, I'd suggest you start reading textbook type materials. One series of books I found is called "Lessons in Electronic Circuits" by Tony R. Kuphaldt. It's four volumes and each is about 500-600 pages long. Topics are DC, AC, Semi-conductors, and Digital. I found them as PDFs online somewhere. Whatever you find, keep reading a lot of it, because it probably won't all make sense the first time around, but it'll get easier the more information you pack in your brain.

If you don't have any in your junk bin you should check out your local thrift store. Not quite but ALMOST as cheap as your own leftovers.

As a fellow newbie to amp building, I've received much more from this site than I've contributed. Your questions seem like the kinds of things I was thinking about when I first started learning, so I thought I'd try to answer and maybe contribute something for once (hooray!).


I think what Roly was getting at is that you can copy someone's schematic and put together a working amp without actually having to understand what each individual part is actually doing for the circuit. Sort of a, "Connect this thingy to that doohickey, and you'll have a working amp," kind of deal. After you put something together, you can start to learn how to fix things that bug you about it, like if you want the EQ to sound different or want to adjust the distortion or something. Little by little you'll learn how to correct/change all these things until you actually know what you're doing (more or less).

Teemuk's book was a great read, but definitely a labor of love. I have read through it a couple of times now, along with many, many other pages on how electronics work. And let me tell you, the first time through, I probably only understood 10% of it. If you really want to get a grasp on it, my advice is to just keep reading, even if you don't understand. Eventually you'll read something that reminds you of another thing you didn't understand at the time, and it will suddenly click.



I think I have a grasp on headroom, so I'll give you my non-technical, layman's understanding of how it works. (Keep in mind this is not entirely factually correct; I'm just trying to hopefully get across the concept.) Your amp's power supply will put out a specific voltage, say 10 volts. That means if you want a clean, undistorted signal, the maximum voltage swing that signal can have will be 10 volts. If you try to amplify the signal to 20 volts, the amp can only get to 10 volts, so basically you're clipping off half of the signal, and when you clip a sine wave, that comes through as distortion. So the amount of headroom refers to how much room there is between the max voltage of the sine wave and the max voltage that your amp is capable of. Again, very technically incorrect, but hopefully that will help you get you going when you're reading how it actually works.


https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/clipping/page1.html

Wikipedia has a concise explanation on grounding classes that made a lot of sense to me when I was learning about grounding techniques.

http://en.wikipedia.org/wiki/Appliance_classes

Well if Metallica uses it, it must be good, right?  :cheesy:


Yeah, I've seen a lot of those types around recently. Pretty much exactly what I was looking for. Though I did see someone selling a beat up Marshall 15DFX for $20, which I used to own and really liked (I sold it to help pay for my wedding), so that one has had my eye for a couple of days now. It's a really nice day today though, so I might go out and see what all the yard sale people have to offer.

I'm wondering if anyone has any recommendations for a good practice amp.


. . . electrical modification practice, that is.  8|


I've been looking at various second hand websites, and I've discovering that one can buy any number of entry lever guitar amps dirt cheap (<$20 US). I was thinking it would be fun/educational to pry one of these open and try to make some changes to it. Is there any particular amp(s) that stand out as being commonly modified to improve the sound a little? Not necessarily improve the sound, but make it somewhat at least noticeably different (e.g., doing something to reduce the hum). I figured I could work on my circuit skills, and worst case scenario I bought a bin of parts useful for twenty bucks.

Your thoughts?

For instance, I've been playing around with this circuit this afternoon. It's three basic common-emitter stages with negative feedback. I basically copied a textbook example three times and added feedback. Neglecting tone controls and such, would this be good enough to drive an output stage? What problems might arise from this set up in real life (as opposed to the perfect linearity from the simulation)? These are the kinds of questions my mind is circling around right now. I'm also working on a simple long-tailed pair circuit, but dishes don't clean themselves (yet?), so that one will have to wait.

I have been re-reading @Teemuk's book "Solid-state Guitar Amplifiers," and it makes a lot more sense the second time around. Well, a lot more makes sense, that is. I don't have much time for projects, but I've been thinking of putting another one on the back burner: making a solid-state amp. I've been playing around with LTspice to test my understanding of theory, and it seems to be going pretty well (things mostly do what I expected them to do).

Anyway, the issue facing me right now is that I don't know how complex I should/need to go. After learning basic topologies, all the articles I read start talking about how to improve them, and it gets pretty complicated pretty quickly. I'm not against having difficult circuits to build, but what I'm wondering is at what point does it become so elaborate that it would make sense to just use an op-amp circuit instead? Or how simple can a circuit be made that is still serviceable? Put in different terms, if I were looking to build myself a car, I could make a hot rod and optimize the entire engine, but my '88 Tercel has all the basics and gets me around just fine. (And it got GREAT gas mileage. Too bad it was totaled a few years ago . . . )

I hope you understand what I'm getting at with my question. It seems that with tube amps (which is what I've been looking into mostly before now), there are only so many options, making it a little easier on beginners, but with solid-state designs, there are a thousand different ideas on how to put it all together, so I can't figure out what the "introductory" method might be.

And again, I can't recommend Teemuk's book enough. It's been a tremendous help so far on this journey, and I haven't begun to understand even half of it yet.

So what would happen if you made it so it was +/- 19 volts with the center tap and also put a load from +19 to -19?

That makes sense about making the +/- rails. With this setup, would it also work to power a load between the + and - rails (skipping the ground rail), so the load sees 38 volts?

I've been designing a tube/SS hybrid amp. I based the power supply on running at 50 volts max as per my device limitations. At 50 volts of rectified DC, I was going to need a transformer with about a 35 volt RMS secondary (50V pk/1.414=35V RMS). So I designed in a 36 volt transformer, but I didn't really understand how the 50 volts was going to get there; I thought that it would be running at the RMS value and somehow I had to just know that the peak value was going to be higher and I had to keep it in mind when choosing components. Then I built a simple string of LEDs for my coat closet because our doorbell transformer sticks out of the wall in there and was begging to be more useful. After running some experiments to figure out voltages with a diode rectifier wired in, I realized that the peak voltage BECOMES the DC output when rectified, and the AC voltage goes away (save for a little bit of ripple voltage). So after I put a rectifier and the proper capacitor in, the system will be running off the PEAK voltage of the secondary, not the RMS voltage.

I don't know how common that misunderstanding is, but I went through it so I thought I'd explain how I figured it in case that helped someone else starting out figure out how to design a power supply. My biggest advice (which others repeat constantly) is to actually build the circuits so you can see how the theory/math actually works and if it doesn't, you can start to figure out why not.

Anyway, that was the helpful part of my post; now on to my actual questions. 

I decided for now that I'm just going to stick to the 35V design instead of re-figure out all the other components. I actually found a 25.2V transformer at Radio Shack that would be cheaper than buying one online with shipping and everything. My question is about VA rating: through my reading I have learned that the DC amps drawn by the circuit will actually draw more AC amps from the secondary (by a factor of about 1.6, as I understand it). So if I expect my circuit to draw 500 mA, I should actually make sure my transformer is rated for 500mA x 1.6 = 800 mA. Am I understanding this correctly?

My second question is more theoretical, but the transformer in question is center tapped so each side of the CT is at 12.6V. That got me to thinking: Is there any reason one couldn't wire up the center tap as some sort of reference voltage? I was thinking maybe there's a way to make a bridge diode between the two outside leads and one between the "ground" lead and the center tap or something like that. My gut tells me that there's some obvious reason why it wouldn't work, but it also seems like it *should* so I thought I'd ask people who actually know what they're doing.