Hi All,

Does anyone have a simple (ish) circuit for amplifying the signal from a guitar / bass to the level required for headphones? I know there are various devices to buy from Vox and the like, but I fancy building one.


Thanks as ever,

Rich

http://www.maplin.co.uk/1w-amplifier-kit-220054

Makes a handy little cans amp. Feed it from 2x AA and a feebleMex Strat with get a bit of grind going. 9volts will make it cleaner and in fact loud enough for a speaker especially a~100dB/W guitar job.

Yes the input Z is an "improper" 10kish but it does not seem to matter. You could put a source follower in front if you were fussy!

Dave.

I recently built an amp from a circuit I found on Beavis Audio, http://www.youtube.com/watch?v=QdqlJVI2QM8. It was really easy to build, and my friend and I had a lot of fun playing with it. We didn't have the right ic, so we had to swap in a higher gain one, which is why it's so distorted, but you could experiment. Check out Beavis Audio.com, they have a ton of cool circuits.
*edit* the circuit in question is unbalanced to begin with, so you'll have no problem putting in a 3.5mm/ 1/8" jack if you want to use headphones.

Morning Andrew,
I take it that is the "noisy cricket" device? If so that is pretty much the Maplin amp based on the LM386 amp chip but with a FET front end and simple tone circuit. These parts could easily be added to the kit.

Dave.

+1 on a simple 386 circuit - check the data sheet - a cheap and cheerful, useful and fun little chip to play with and a great 'interface' for experimenting with other circuits with. the basis for many a crazy, cool and noisy fuzz box. google tim escobedo and nicolas collins for some nice add ons, ideas - uglyface, pwm, low rider, fuzzy dicer, etc. all very simple, minimal component circuits. keep it modular to start with, building block lego circuits to interconnect and play with - you'll soon be designing your own boxes around what you discover along the way.

and if you really must go to maplins (go online for bitsbox instead and save yourself a penny or ten) get yourself one of these: http://www.maplin.co.uk/ad-100-breadboard-5195 and buy the components separately. they are common enough that your local maplin may actually have them in stock, so long as you don't mind hopping home with one arm. great for experimenting with and when it's time to go permanently in a box get some stripboard, for which this may help: http://code.google.com/p/diy-layout-creator/

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i've just had a look at that maplin 386 kit linked to above and at maplin prices there are less than two pounds worth of components included in that kit which you can find online for half that price. so you would be paying more than four pounds for a (professionally made, quality) pcb and some vague instructions and a disposable plastic box.

if you are going to do it yourself, then do it yourself.

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ohm's where the art is

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i've just had a look at that maplin 386 kit linked to above and at maplin prices there are less than two pounds worth of components included in that kit which you can find online for half that price. so you would be paying more than four pounds for a (professionally made, quality) pcb and some vague instructions and a disposable plastic box.

if you are going to do it yourself, then do it yourself.

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Well that is fine IF like Will and I and probably yourself you have shedloads of odd components to hand. The DIY noob will not.

I believe as a first time entry into electronics a kit is the way to go and the price of 4 Stellas at Sainsburies is not a lot in my book.

Dave.

good point, dave.

but to be fair there's one chip, one mini pot, two resistors and five caps. not a shed load of components, really. all very common values and likely to be locally stocked items at any maplin at less than the kit price including the suggested breadboard, which will continue to be useful post project, and all components are evidently available cheaper online. the op would prolly also require extra switches, caps, pots, jacks, etc and an enclosure to complete his project which would need to be acquired separately anyway.

i get your point about the convenience of a kit but disagree with the economics. the kit is a bag of components and a pcb. and have you seen the 'instuctions'?

so there. ner.

(my dads bigger than your dad!)

Hi All,

Thanks for the advice - as ever the SOS forums are by far the most helpful places around.

It's a long time since I used a soldering iron other than for simple repairs, so while I'm not a complete noob I don't have shedloads of components either.

Sounds like the Maplin circuit is an easy starting point. Whether I get the kit or buy the components separately so it can be extended as required I don't know yet. Probably the kit route, then when it works I'll copy the design and extend it on breadboard. That way I get a working amp so I can actually use it,and experiment afterwards.

I can aford this route as I don't drink Stella

Cheers,

Richard

good response. welcome to sos. and good luck.

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ohm's where the art is

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good point, dave.

but to be fair there's one chip, one mini pot, two resistors and five caps. not a shed load of components, really. all very common values and likely to be locally stocked items at any maplin at less than the kit price including the suggested breadboard, which will continue to be useful post project, and all components are evidently available cheaper online. the op would prolly also require extra switches, caps, pots, jacks, etc and an enclosure to complete his project which would need to be acquired separately anyway.

i get your point about the convenience of a kit but disagree with the economics. the kit is a bag of components and a pcb. and have you seen the 'instuctions'?

so there. ner.

(my dads bigger than your dad!)

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Well, I make the component cost £3.53 and he still has to buy some stripboard and that is 3 quid for the smallest piece. Yes, Maplin's one off caps and R's are a rip off but it is the only game in town (this one anyway!). And my dad's dead, he wasn't very big but used to box for his squadran so watch it!

Richard: Should have said. fit all the components onto the pcb but not the chip, viz check then solder. Attach to power and check that the correct voltage and polarity is present at the correct pins on the holder. Diss' power and plug in chip..Rock and roll! (or get back to us p.d.q!)

Dave.

Got to agree with Dave that a kit is the way to go for a first time starter. The economics are irrelevant for a one off (besides, how much is your time worth trying to work out what to get and how to put it together).

Once you have at least one success under your belt then is the time to think about getting adventurous if you enjoyed putting the kit together. Otherwise it has cost you very little to find out you don't like the idea.

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It wasn't me!
(Well, actually, it probably was)

Hi all,

Thanks again. I've been reminded by my much better half that I still have to refit some skirting board and scotia in the breakfast room, so I may have to delay starting on this until after that.

A couple of other questions if I may:
What is the typical voltage output of a guitar or bass?
What is the recommended input impedance for a device connecting straight to the instrument output?

Regards,

Richard

Quote Dr R:

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Hi all,

Thanks again. I've been reminded by my much better half that I still have to refit some skirting board and scotia in the breakfast room, so I may have to delay starting on this until after that.

A couple of other questions if I may:
What is the typical voltage output of a guitar or bass?
What is the recommended input impedance for a device connecting straight to the instrument output?

Regards,

Richard

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My son's Mex Strat pounded chords into a Fluke DVM gives about 150mV, for electronical puposes 424mV pk-pk, say 500mV for jazz? Humbuckers and actives will be higher of course maybe 1-1.5V? (I only know of one instance of an amplifier that had a problem in this area and that only with VERY hard playing of a high output guitar and when the mains was at top dollar. In fact the problem was not even input overload but further into the circuit, post a valve stage that had given the signal a consderable boot up the jaxie!).

Input Z? ! Touchy subject, short answer, anything that sounds ok to you! The source Z of a passive guitar, all pots at max out is about 7-10kOhms, crank any pots just a little bit and it goes to H in a handbasket!

Build the kit as is and try it. If you don't like the sound fit the FET source follower, there is however a better FET guitar preamp circuit that gives about 4dB of gain (and a polarity flip which can be handy).

BTW:Cheers Will! Doing a B.O.M. for a project is an entirely different discipline I find and one I don't much care for. I am helping a guy (via email) build a fairly simple power supply. He has ordered the wrong bits, extra bits and generally spent more "office" than building time by a country klick!

Dave.

Edited by ef37a (08/06/11 08:19 AM)