Basic Amp Build for teaching electronics

[Justin Thomas]

I won't argue with that... But just because everyone else is willing to settle for less doesn't mean I have to... And having owned a 1962 Zenith tabletop bakelite radio, well, let's just say the bass tone in that old piece of crap SPANKED anything else out there, including Mom's $400 Bose Wave Radio.

Justin

[rjb]

And my 1932 Philco cathedral table top radio... still worked, last time I plugged it in (yes, after reforming the caps with a variac).

Going off on my own tangent:
2.5W Class D amp (can run on batteries), $3.95.
Maybe not much of a learning project, though.
https://www.adafruit.com/product/213...vbEaAnVI8P8HAQ

[nosaj]

I won't argue with that... But just because everyone else is willing to settle for less doesn't mean I have to... And having owned a 1962 Zenith tabletop bakelite radio, well, let's just say the bass tone in that old piece of crap SPANKED anything else out there, including Mom's $400 Bose Wave Radio.

Justin

Here's my wifes Ipod player using the phono input on back.

[Enzo]

I enjoy a Scholz Rockman, but it does nothing to drive my strings into sustain, even if I play right next to my headphones.

Peavey makes a couple interface modules, one for smart phone, the other for computer. Includes emulation of various effect pedals and amp simulations.
https://peavey.com/products/index.cfm/item/1346/118572

[nosaj]

I enjoy a Scholz Rockman, but it does nothing to drive my strings into sustain, even if I play right next to my headphones.

Peavey makes a couple interface modules, one for smart phone, the other for computer. Includes emulation of various effect pedals and amp simulations.
https://peavey.com/products/index.cfm/item/1346/118572

Put a Big Muff in there.

nosaj

[rjb]

Let's imagine that OP is still set on doing a simple amp project.
As Justin has alluded, largest effort and expense would likely be on enclosure and speaker.
Can someone recommend decent speakers for low-power amp, and/or "simple construction" tips?

-rb

[Chuck H]

I think the focus of the project is obviously educational? In that regard the simplest amp that can accessibly have some principals explained seems like a logical choice. At the same time the OP's goal is to exploit the cool factor to help engage the students. In these lights I think Justin has a good idea with the small tube amp, BUT... The high voltage IS a problem, as noted by Enzo and others. In fact the inclusion of ANY power supply that has to process wall voltages is going to be dangerous for an inexperienced teacher and students. So my vote is for the wall wart or battery powered mini amp or effect. In fact I can't imagine unleashing any wall AC power supply construction on an inexperienced instructor and students as a classroom project. There's probably some kind of regulation against it! JM2C

I think a battery powered ear bud amp, ala Rockman, would be a great idea. Though I'm a tube guy and mildly SS impaired so I can't really contribute. But there are certainly people here that can

I envision construction of a voltage amp to drive a "module" and then a current power amp to run the ear buds. Simpler than a Rockman by a stretch, but still very useful depending on the "module" features. The educational lesson would be in the implementation of the pre and post amplifiers. This even seems in keeping with more contemporary repair circumstances in this new age of module based devices as it applies to blue collar repairs. JM2C on that too.

[Mick Bailey]

The more I "hear" the substitutes offered & proffered for real moving-air analog amplifiers (of which we are becoming more and more afraid), the more the substitutes "sound" okay... But they don't FEEL the same, and they carry no authority.

The catch in this is that we collectively listen to (say) Eric Johnson, Hendrix, EVH or whatever on digital media. I listen to Eddie on my CD player and it's a wholly digital construction. Yet these recordings sound good, and when I put the same tracks through PA speakers, sound even better. So we end up back to the discussion regarding digital v analogue. If it was possible to recreate that sound heard on CD/MP3 etc in precise enough detail, would that sound be good enough?

Would this change your mind that these things carry no authority;

https://www.youtube.com/watch?v=uKdcwTMAeNg

[Chuck H]

In Justin's defense I'm pretty sure he's talking about the creation end of the music rather than the reproduction end. The difference isn't moot. At the creation end, as it applies to guitar and particularly rock, electric guitar there are a lot of physical phenomenon that signal level devices just can't exploit. And, IMHO, in the digital arena there is a loss of the "feel" related to these physical phenomenon even when amplified in volume because of the 'once removed' nature of several aspects in the replicating process. At least that's what I believe I detect. If I had to come up with an analogy, sort of like playing a sports based video game vs. going outside and playing the ACTUAL game. YMMV. And that's not insignificant because equipment familiarity WRT the creation of art is only a small part of the artists challenge. Something Stan has pointed out here many times. The younger generations will learn on many direct input, digital modeling systems and THAT will become their medium. Probably to the point that they would find our loud, heavy, chaotic and brash amplifiers cumbersome and incompatible. This is a significant and unavoidable reality (even though it's never going to be mine or Justin's). I guess I'm just outlining Justin's very valid position, but recognizing it's dated philosophy in the same post

[Justin Thomas]

While I find the creation end to be of vastly greater import, I mean reproduction too. It's a matter of TOO MUCH detail. Sure, it's "clear." All that "def" is also aesthetically unpleasing to me. The whole 20-20KHz thing I just don't buy. It was the compromises inherent to the technology, that slurring, the loss of the highest and lowest end, the lack of crystalline clarity that makes my old crappy tube radio worth listening to. I turn the bass and treble on my car stereo down all the way most of the time, because it's all artificially enhanced and produced, and the fake nature of it just grates on me.

While it may all be an unavoidable reality, and I may have to "live with it" because nothing lasts forever and I don't have the means to buy everything I want for my "perfect" world, it doesn't mean I have to say "eeeesss ze beeessst! Eeeessss fantassteeeek!" Maybe it's all like the fluorescent light hum - it doesn't bother everyone, but it sure bothers some. But just because it's not universal doesn't mean it's not real.

As I said, I can't sit here and cite studies and formulae. I don't have anyone else's ears, and nobody else has mine. And I understand the necessity of compromise, but I'm going to call it just that - compromise.

Mick, I'll have to get to my computer for the video.

Justin

[bbsailor]

Hi, I am a Physics teacher and guitar player. I have some students (14-16) who are also guitar players and also interested in electronics/building stuff. Next year I want to undertake a project with them to get them to build a really simple amp, just to get them enthusiastic about building stuff and electronics. Can anyone suggest a really simple amp project that may be suitable. Cost will obviously be an issue. I have some very limited electronics experience so simple is better. Many thanks for any help you can give, thanks Simon

Simon,

As a former college faculty member, I taught an audio and TV production course.

The logical place to start is at the signal source... microphones of all types. They all work on the the principal of induction with the microphone diaphragm being attached to the coil moving in a magnetic field. Then, with the ribbon microphone the diaphragm is the the coil in a strong magnetic field being directly transformed in a step up transformer (1:39 to 1:50 turns ratios) to bring the 0.1 to 0.2 Ohm ribbon impedance up to the typical microphone impedance of up to about 300 Ohms (max). Get a miniature matching transformer 8 Ohms to 10K up to 50K. Alligator clip the 8 ohm side across a string on an acoustic guitar (behind the nut and behind the bridge). Attach the high impedance side of the transformer to the guitar amp input and hand hold a magnet near the string. Plunk the string and listen. This works like the ribbon microphone.

If you then expand this into making guitar pickups, you can safely explore the sound sources of low impedance, low level signal sources and then evolve into higher level, high impedance signal sources. These devices will be rather quick to make and then begin to capture the students interests into the types of amplifiers that these pickups can effectively feed.

Any homemade pickup can be easily mounted on an acoustic steel string guitar to play with your new DIY pickup. Wind 500 to 600 turns of AWG 34 on a plastic pickup bobbin and connect it to pins 2 and 3 of an XLR microphone connector and that works well into a low impedance microphone mixer input.

Use the search feature on this forum and look for:
flat pickups
thin pickups
low impedance pickups
moving coil pickups
Alumitone pickups
CSE187L current transformer

There is a wealth of knowledge that you can choose from that will get you started. Then, you can logically move into various amplifier types, their input impedance range of input sources, signal levels and noise levels.

I hope this offers another alternative to stimulate young minds.

Joseph J. Rogowski

[Justin Thomas]

Not seeing the rest of the band, meaning a real drum kit, and other players, and assuming that all the other tracks used were similarly produced and pre-recorded, no, it doesn't change my mind... I also wasn't there to see it. Also, I'm acknowledging that I had to listen on laptop speakers. The PLAYER has authority and a command of his instrument, but I bet he'd carry more with a living, fire-breathing monster at his back.

Justin

[J M Fahey]

Like the OP, also read the other answers and noted the objections

Agree with many of them:
* forget tubes, they won´t be allowed anyway,
* a "toy" will quickly lose interest
* should still be simple and buildable
* I *guess* construction will include cabinet an speaker? If so, "something else" may/should be repurposed, to avoid complex carpentry, tolexing, etc. which will complicate construction and in any case is not "electronics"
* it should sound good by itself, but also be usable amplifying a smartphone app or even a notebook running "guitar rig".
* being portable so usable for busking *might* be an interesting extra.

Given all above constraints I would suggest:
1) build the Marshall Lead 12 / 5005 preamp : KILLER sound, used by many Guitar Gods (such as ZZ Top Billy Gibbons) live and in recordings.
This is the sound I am talking about:

2) do not build the Lead 12 power amp, but a 15W one based on a TDA2030

3) add a "CD input" which is a direct input to the power amp; it allows two useful functions:
a) the Musician can play along a CD/MP3 of his favourite band or download backing tracks , many "everything but the guitar" are available
b) he can avoid the built-in Marshall preamp and just play straight through his smartphone

4) the day he´s bored with playing guitar, he may leave it in its case and just play music or games sound through this amplifier, period.

5) IF you think it useful, you can build *two* TDA2030 amps in the same case, driven from a single preamp, or stereo CD inputs, fed from the same supply and of course each driving its own speaker.
A truly multi purpose amp, good and powerful enough to , listen to music at home, throw a nice little party in an appartment and even used as some kind of Home Theater when watching some movies on a Notebook or Tablet .

6) Jensen MOD speakers are very good sounding and relatively inexpensive, available in 5" , 8" , 10" and 12" , all are acceptable Music reproducers on their own .

7) IF busking is found desirable, replace TDA2030 which require roughly +/-12 to +/-15V symmetrical supplies by TDA2005 (boy am I old) or any modern "12V car audio" power amp, build the proper power supply and they can be fed from cheap 12.6V lead acid "gel/alarm" type batteries, not the most modern technology available and more heavy than modern ones but still widely available and cheap.
Did I mention *easy* to recharge?
Go for modern LiPo ones or whatever technology suits you, of course.

8) to avoid wasting time and resources on carpentry and tolexing, become "creative" with cabinet ideas.
Of course, include amplifier in cabinet to simplify things.

a) you can go to IKEA or something and get cheap well finished wooden flower pot holders or whatever, you assemble them but cut speaker holes and slots to mount chassis (which can be strips of aluminum or even 2mm plastic or hardboard, just coat one side with aluminum paper for shielding and grounding)

b) use gallon jugs, the thicker walled ones are preferred


c) old briefcases or discarded luggage:




d) cool old Tupperware will definitely supply some cool enclosure in the proper size:


e) if you want classic "covered wood" for peanuts, you can adapt some car type carpeted enclosure: the real thing, cheap and plentiful, resists moving here and there and 90% of the work already done, just cut proper slots for electronics.


Just one caveat: do NO repeat NOT let kids (or untrained or clumsy adults) anywheare near saws of any kind, either reciprocating/jigsaws or even worse, rotary ones, which cut through bone (let alone flesh) in 1 (one) second.
Just watch your local butcher going through beef bones with his ribbon saw, same thing.

Or add to the project budget 1 million Dollars per cut finger ... not kidding.

Last week a woman got U$ 70000 from Starbucks because she ordered a takeaway cup of coffee, *she* fumbled with its cover while driving a car, spilled hot coffee on her legs and sued them, not kidding, so imagine the price per cut fingers involving minors.

[Jockster]

Hi, can I just thank you all for all the answers above, they are very much appreciated. I have got a lot of investigating to do based on all the really helpful information you have given. I will come back with some questions when I have absorbed some of the information. Many thanks once again, cheers Simon

[Gingertube]

Cheap component cost students project - Manyof these built, main designer actually runs occassional amp building "school" where students build these.
AVA101 The Lamington
Cheers,
Ian