Need Battery driven Guitar AMP

[J M Fahey]

Basically any N-channel Fet. You might find the J111/112/113 easier to find.
Whatever you use, download and check the datasheet because pinouts often differ.
Good luck.

[trialabc]

Would it be possible if i use transistor instead? Since I lived in HK, tt is quite hard to find these electronic components as most probably no one will DIY a guitar amp here.

[rowdy_riemer]

Well, JFET's are transistors. If you mean bipolar transistor, then yes, but it will have to be biased differently. Your best bet is to try to order what you need online from mouser.com or jameco.com or any other electronics part vendor. Of course shipping might be a little pricey for you if you order from jameco or mouser or any other American supplier, but I bet you can find an online parts supplier reasonably close. If you do use a bi-polar transistor, be sure to research how to bias them. http://en.wikipedia.org/wiki/Bipolar_transistor_biasing . Any low current BJT  in an emitter follower configuration should be fine. However, you will not have the high impedance that you would have with the jfet input. In fact, you might not get much better results then you would have by leaving out the buffer stage all together, like with the Little Gem. You could also use an op-amp buffer instead of a source follower or emitter follower. It would be best to find a jfet with the same pinout as the mpf102. Then, you will be able to use the PCB layout  provided by ROG. Good luck on the parts search.

[rowdy_riemer]

Here's a couple of listings for mpf102's from Hong Kong suppliers:

http://www3.hkinventory.com/public/OfferInventResult.asp?search=offerinvent&MainCate=&SubCate=&Order=&keywords=&words=3&SearchType=offer&pnums=mpf102&btnSubmit=Search

http://hk.farnell.com/jsp/search/browse.jsp?N=500002+1002727&Ntk=gensearch_001&Ntt=mpf102&Ntx=mode+matchallpartial

It also looks like mouser isn't a bad bet either. http://hk.mouser.com/Search/Refine.aspx?Keyword=mpf102

[trialabc]

Thanks for the links guys. It should come handy whenever I needed "rare" components. :tu:

Since all I lack is the buffered input, may I used op-amp to make a voltage follower at the input of LM386?
It seems to be a bad choice to me since this way just consume more current. However, if i just simply use a capacitor to separate the input and LM386, would that be possible? or will the performance become very poor?

Thanks in advance!

[J M Fahey]

Hitrialabc.
I find it *incredible* that, of all places in the world, you find it difficult to find electronic components ... in Hong Kong !!! 
Yet, maybe the minimum order is one million pieces each value , so .....
You may build this bipolar transistor buffer, which uses *any* NPN, TO92 general purpose transistor, *any*.

[rowdy_riemer]

JFETs aren't rare. I would imagine they are as easy to find as an LM386.

[trialabc]

I finally have time to built it and test it.

Since I am lazy, I first try it without using any buffer to the input of LM386.
In other words, I just use a 0.01uF cap connect to the guitar input, then a 10k ohm variable resistor. Then the rest remain the same as the RUBY schematic.

Everything seems okay, except it continues giving out a small static noise.
I wonder if this is the design problem? (meaning without the buffer)
Or because of the bad soldering, routing problem? --> this is because I am too excited to start and forget to plan first before soldering the components

Thanks in advance!

[J M Fahey]

Congratulations for finally building it.
Some small static is normal, very probably captured by the guitar itself.
Does it dissapear when you set guitar volume and tone to "0"?

[trialabc]

Yes.

The problem is when I turn on the maximum volume control, the static noise also increases.
Maybe later I should add back a buffer to see if the input noise can be reduced.

[rowdy_riemer]

Do you have everything housed in a grounded metal housing? The buffer is for frequency response, and I do not think it will reduce the noise.

[trialabc]

Nope. Currently it does not have any housing.

There is one things seems not good.
When I play chords harder, the sound could become so loud that become distorted to the output. (just like having a overdrive)

I wonder if that's why buffer is added.

Another question is a larger size speaker gives larger SPL?

[J M Fahey]

Well, it *is* a low power amplifier, and thus easy to overload. That's life.
Later on,  if you want mor power, to play on a busy commercial street, a subway station, places like that, start investigating louder amps that can be powered by a 12V7A alarm type gel battery, the best weight/power/pportability/price/availability compromise there is.
I'm an old timer and only used TDA2005 (20 loud/*real* watts into 4 ohms), but there is a TDA-something that's the same and uses only 4 or so external components.
Maybe somebody can point to it.I think it was the TDA1519.
Check on my "Callejero" (Street Man) amps
http://www.ssguitar.com/index.php?topic=1212.msg7641
you have links to Photobucket pictutes.

[trialabc]

I have gone through the specification of TDA2030 which seems great for my further testing. Moreover I can buy it easily through stores.

Since TDA2030 requires higher voltage, maybe I can try TDA2003 or TDA2004 first which I can also easily buy from stores. (Seems also cheaper then Farnell.  )
Though Fahey have mentioned about TDA2005, I don't find it from those stores that I visit.

Probably I would move on to use 12V 7VA battery for my "battery driven guitar amp" project. Maybe later need to make DIY charger for that slightly heavy battery.

In the mean time I am really unhappy about static noise that my prototype RUBY amp, is there a way to eliminate the static noise? Like adding a passive filter? or should I simply buy a better "guitar wire"(the wire connecting the guitar and the amp)?

Thanks in advance!