Replies to This Discussion

Permalink Reply by Mark on October 11, 2009 at 8:08am

PS. I just discovered the strand "Simple Underground Electronics" - rather than re-post everything there I posted a link flagging up that I've put some questions here. If people feel it's unhelpful to have separate strands then I could delete this and try to move it over there.

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Permalink Reply by HOGS GRUNT on October 11, 2009 at 8:12am

If you are going for an amp kit and have been looking at Maplins why not check this out:-

http://www.maplin.co.uk/Module.aspx?ModuleNo=10502

By the time you have bought all the bits needed you might just as well go for something like this and you will get more power output.
Just a thought so tell me to shut up if the info is not what you are looking for.

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Permalink Reply by Jkevn on October 11, 2009 at 8:52am

I'm putting a few links for amp kits here - thats the easy way. As far as lm386 based amps and the small cap @ pin 7, it helps to isolate the high-gain stage of the IC from noise from the power supply etc. when the output load is heavy. The "ruby" calls for 100n, but values up to about 4.7uF may work better depending on the power supply used....battery versus wall charger.

http://store.qkits.com/moreinfo.cfm/FK617
http://www.goldmine-elec-products.com/prodinfo.asp?number=C6238

My favorite "cheap" method has been using old computer speakers to make amps. Everythings already put together, you just have to put it in a cooler box....most are 12v, but speakers that connect to a computer's USB port are powered by 5v, and will work off of 9v.

http://www.premierguitar.com/Magazine/Issue/2007/Dec/The_5_Travelin...

http://buildinggadgets.com/index_key.htm

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Permalink Reply by John Sims on October 11, 2009 at 9:50am

The Bypass capacitor removes "AC" noise or filters any alternating current from the DC portion of the circuit, making it more stable and eliminating hum.

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Permalink Reply by Mark on October 11, 2009 at 9:54am

I've looked at those kits and might give them a try later on. For the moment the LM386-based ones suit my purpose - among the advantages they have are that their low power consumption makes them suited to battery power and there's already a fair knowledge base out there in terms of a variety of designs by people who've used them as guitar amps. I've also found that 1w amps can be perfectly loud enough for the situations I have in mind.

HOGS GRUNT said:

If you are going for an amp kit and have been looking at Maplins why not check this out:-
http://www.maplin.co.uk/Module.aspx?ModuleNo=10502
By the time you have bought all the bits needed you might just as well go for something like this and you will get more power output.
Just a thought so tell me to shut up if the info is not what you are looking for.

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Permalink Reply by Mark on October 11, 2009 at 10:03am

Thanks for that, I think I might be on my way to understanding pin 7 now. As I'm using a battery supply I was assuming there wouldn't be much noise from it - am I missing anything there? I presume there could be other sources of noise in the general environment. I also read on one of those links that a capacitative link to ground on pin 7 helps avoid oscillation at high gain.

Jkevn said:

I'm putting a few links for amp kits here - thats the easy way. As far as lm386 based amps and the small cap @ pin 7, it helps to isolate the high-gain stage of the IC from noise from the power supply etc. when the output load is heavy. The "ruby" calls for 100n, but values up to about 4.7uF may work better depending on the power supply used....battery versus wall charger.

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Permalink Reply by Wes "I'm Baaaaack" Yates on October 11, 2009 at 10:35am

I did the ruby amp as a preamp in my Oliva box. Works well but get the right components. Tho will work, the right components help the gain and should keep interference down. Mine picks up FM signals when the volume is 0.

Ground the strings and bridge and anything else that might pickup signal.

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Permalink Reply by Jkevn on October 11, 2009 at 10:40am

Anything taking electrical current and using it to provide "work" is gonna create noise, even on a minute scale like this. Those capacitors, input and at pin 7, try to shed unwanted electrical thuds and thumps to ground where they don't:
a: get amplified into bigger thuds and thumps
b: begin the endless oscillation death-spiral.

Are you using a gain pot or strapping out pins 1 & 8?

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Permalink Reply by Mark on October 11, 2009 at 11:01am

I'm using a gain pot - seems to be the best way to allow some adjustment of the sound/distortion. I'm wondering about the capacitance in this: The datasheet seems quite clear about the need to put a capacitor between pins 1 and 8 if you're changing the gain (either with or without a resistor in series), but I notice the "Little Gem" and "Ruby" just have a pot there.

Jkevn said:

Anything taking electrical current and using it to provide "work" is gonna create noise, even on a minute scale like this. Those capacitors, input and at pin 7, try to shed unwanted electrical thuds and thumps to ground where they don't:
a: get amplified into bigger thuds and thumps
b: begin the endless oscillation death-spiral.

Are you using a gain pot or strapping out pins 1 & 8?

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Permalink Reply by David L. on October 11, 2009 at 3:39pm

Hi,

I have built a few mini amps that I have added to CBGs as on board amp/speakers. I have tried several ones and found the smokey schematic works as well as the more complex designs. Without the overdrive function the LM386 amp sound is really weak, but with it the sound is ok for bedroom playing. With the smokey amp if you want a cleaner sound you have the volume turned down more.
http://www.bitsbox.co.uk/kits/projectkits.html sells a 1W amp kit based on the LM386 for £4.49 and the seller is a top bloke - very helpful and usually next day delivery.
For a stronger clean sound the £5.99 Maplin 3W mono amp kit is good http://www.maplin.co.uk/Module.aspx?ModuleNo=2904 and works fine with a 9v battery (no overdrive circuit though). For simplicity Maplins sells a 3.5W Universal Amplifier Module for £6.99 you just need to solder a speaker and a 9v battery http://www.maplin.co.uk/Module.aspx?ModuleNo=37734.

The main improvement you can make whatever schematic you use is to use bigger speakers rather than the 500mW paper speakers - I prefer the mylar ones you can get off ebay such as http://cgi.ebay.co.uk/Mylar-Cone-Speaker-2W-77mm-Round-Alarm-Sounde...

One useful thing I did was to get a breadboard (solderless prototyping board) off bitsbox so I could have a play around with different circuits and still be able to reuse the components.

Good luck,
David

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Permalink Reply by Mark on October 16, 2009 at 11:57am

Re: the 7w TDA2003-based Maplin kit suggested by HOGS GRUNT - I've now given this a go and I think it might have the potential to be a usable compact guitar amp. It certainly packs plenty of volume while still running comfortably off a 9v battery. And by adjusting resistance values I seem to be able to crank the gain up and get some nice distortion. However I still need to play around a bit to get the altered components just right because, if I push the gain too far, it sometimes goes into oscillation.

Re: The 3w Maplin kit - it sounds interesting for clean sounds (which might suit my piezo-fitted tin can banjo) but it looks to me as if there isn't a neat way to get it to distort nicely. Unlike the chips in the other simple amps the TDA7267 at the heart of this one doesn't seem to have any way to alter it's gain.

It seems to me the great advantage with the LM386 chip is that other people with much greater expertise than me have done a lot of work on creating practical circuits based on it.


HOGS GRUNT said:

If you are going for an amp kit and have been looking at Maplins why not check this out:-
http://www.maplin.co.uk/Module.aspx?ModuleNo=10502
By the time you have bought all the bits needed you might just as well go for something like this and you will get more power output.
Just a thought so tell me to shut up if the info is not what you are looking for.

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Permalink Reply by Mark on October 21, 2009 at 3:15pm

Just completed my first amp - the "Choc-O-Cube". The internals are a modifies 7w TDA2003-based Maplin kit and the enclosure is an old cholocate tin.

http://www.cigarboxnation.com/photo/the-chococube?context=album&...

Next project is to try to fit an LM386 circuit into a much smaller tin.

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