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Battery/Line Powered Practice Amp

Started by n9voc, January 19, 2008, 01:43:24 AM

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n9voc

Good Day All!

Attached is a JPG of a battery/line operated practice amplifier I have built and used.  Good sound, capable of running as long as 10 hours on a full charge.  The battery "float" charges whenever unit is "Plugged in".  The high input impedance (5 Megohm) means you need to use a switched 1/4 inch jack for the input that shorts the input to ground when there is no jack plugged in (to avoid hum and such).  Made quite a few variations on this theme - more to come in later posts.  Suggest Mouser for parts, Unless you have a pretty well stocked "junkbox".


joecool85

Nice variation on the ruby amp there.  Are you going to share it with the guys at runoffgroove.com?  If you do and they post it, they'd give you credit.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

n9voc

Joe,

Thank you for the kind words! I'd LOVE to share it with Runoffgroove.com. After all, it was "The Ruby" that inspired me to start working on all these variations I have posted here, and those still in development.  They came up with the central Ideas used here for ALL my LM386 designs, I just took it and tweaked it for my own use -- one of the reasons I give them credit on the schematic.  However, I do not know how to contact them.  I'm not worried about 'credit", I just hope someone else can have as much fun with these ideas as I have! As you probably guessed from my ID, am a "Ham" operator and experimenter, - as well as VERY amateur musician. (Not so good at it, but I have a lot of fun!).

joecool85

Last I knew they still had an email address on the site, I contacted them a while ago about something that way.  They responsed within a day or so.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

n9voc

Thanks,
I just checked and there is still an E-Mail there.  I'll zip up the images that I have presented here and send them their way

noobiePT

hello all, just a doubt, is this amp capable of driving a 10 or 12inch speaker??

teemuk

It's capable of driving any speaker load with it's rated output power. The size of the cone has nothing to do with that.

joecool85

teemuk has it correct there.  I've used a little gem (1/2w amp very similar to this) to drive a 10" 8ohm Dean Markley speaker cab that can take 50w RMS, it sounded great.  Much louder than on the 4" speaker that maxed at 2w RMS.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

noobiePT

though that the bigger the speaker the more power it would require to function... newbie here  :) thanks
other newbie question, im not really used to read this type of amplifiers schematics, so forgive this stupid question but what is the SP1/SP2 ??

numpsha

The lm386 played a big part in my (ongoing) electronics learning curve - low financial and safety risk for early wacko designs ("So what if I did reverse the battery in my DuoRotoPhase S***Fire?") I avoided playing with mains powered stuff until I learned WTH I was doing, but there is much to be learned from low voltage circuits. For me, component datasheets and application notes have been a great place to start: Google the component part # of your choice plus the keyword data and get something like this:

http://www.national.com/ds/LM/LM386.pdf

See the typical applications and application hints? Look familiar? Also interesting is the Equivalent Schematic and Connections Diagrams for the chip -- if I'm not mistaken, one could build a discrete amp using this as a basic blueprint. (Not practical for a BBB delay, unfortunately. :-))

A quick search of the DIY forums will show this little amp chip has been tweaked to death for use in tone and gain controls, preamp stages, distortion/compression/octave effects, etc.. BTW, these come in 3 different power ratings.


teemuk

By the way, parts R4, R15, R14 and C15 seem pretty useless.

noobiePT

thanks for your comment, so seeing that link you gave it looks like SP1/SP2 are speakers lol...  ;D
now i feel a bit bad...

syndromet

#12
Just a quick comment.

The volume the speakers put out are not directly a result of the speakers watt rating. You should look at the speakers efficiency rating. That gives how many db the speaker output at 1watt at a certain frequenzy in a given distance. The higher the efficiency, the higher the volume. A speaker rated with an effiecency at 100db and 2 watt will play way louder with the GEM than a 50 watt speaker rated at 95 db at the same impedance.

http://everything2.com/index.pl?node_id=1523585

n9voc

#13
Quote from: teemuk on February 14, 2008, 01:35:21 PM
By the way, parts R4, R15, R14 and C15 seem pretty useless.

I agree, the circuit will probably work fine without these components, however, when I create items for myself, I typically overdesign - because I am a "belt AND suspenders" kind of a guy.  ::)  And, because I am not designing this for commercial builds, and am not that concerned with either parts count or cost of parts.

my reasoning for each:
R4 & R15 - to GUARENTEE that the current will remain limited in the FETS - I just get nervous hooking a FET or bipolar directly to a rail.
R14 - to limit the input impedance of this stage to 5 Megohm - because I like it that way.
C15 - to GUARANTEE DC isolation of the output buffer - in the event of C3 being shorted.

Thus, my friends, don't be surprised to see some components in these schematics that may not be absolutely necessary for function, but are there because they help my sense of security with the design!

(Yes sir, that is just a bit neurotic :duh, but hey - I never claimed to be fully sane!)