A picture of the finished unit.  I used the grill from the TV speaker and a piece of masonite for the front panel.  The handle came from a hardware store (a drawer pull)  on/off switch is part of the IEC power connector on the back side.

Finally got my digital camera up and working.
Attached is a shot of the front panel of the "Ampenstein" model.  I originally called it the ODE SKOOL #2, but it got renamed after the "enhancement".
Front panel is of sheet aluminum, drilled and painted black - connected to safety ground.

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

The following is my humble opinions, these with about $5.00 will get you a cup of coffee at most restaurants!

Couple questions you need to address:
1) How much power do you want your new "Auxilliary Amp" to put out?
2) Do you want to use the power supply of the FM-65 to power the "New Amp" or do you want to add your own supply?

The answer to #2 will depend highly upon your electronics skills!

(I believe that it would actually take MORE skill to modify the old supply than to install a totally new one, especially if the Fender has only one board that contains all the electroncs, amp/effects/power suppy)


First, I recommend that if you have any electronically savvy friends, get them to help you with this project!

THEN:
I suggest that you remove the "Guts" from your FM-65, leaving the fuse, power switch, line cord, a volume contol, input jack and line cord intact.

Then I suggest you install a power supply (either modify the old, or build up a new from the old one's parts as well as new parts), and then build up a power amplifier module.

BE CAREFUL!!   The mains voltage can severely damage or even kill!!

There are several good power amplifier kits from Canakit.net that can handily provide you with the power amplifier module.  (also available from several other suppliers).  They and several other suppliers give you a board, components and heat sink for the power supply module section - makes life simpler than building the power amp section on a "vectorboard" solely from a schematic.

Then connect up the power supply assembly.  Then connect the input jack and volume controls to the power amplifier module and the speaker to the output of the PA module.

I do recommend that you get some "aluminum tape" and cover up ALL the extra holes that you will have in the front of your amplifier (to keep out dust and other "junk")

If you take a look at the "Schematics" section and some of the posts there, you will find some ideas for complete amplifiers - including the power supply circuits.  Since you don't need the high impedance input, you can insert a volume pot before the power amplifer module, and this will give you control over the output volume.

Final note - as you build, TEST each section before integrating it into your amplifier, it is a BUNCH easier to correct a miswired connection on a board on a bench than to take the board out of the completed amplifer and try and diagnose where the problem is!  (Yep, I still find miswired connections on my project boards, the final note IS the voice of experience!)

Good luck in your project!

As mentioned above, this is the second part of the "Ampenstein" schematic.

I didn't want to "tear down" the board I had built up  above (it had power supply, Input/output, power amp, headphone amp all on one project board).  To increase the maximum power for the "Ampenstein" from 1 Watt to approximately 3 watts, I built up the below schematic on another project board, connected it to a ribbon cable which had an 8 pin IC socket I soldered onto it.

I pulled the LM386-4 I had in the main board, plugged in the socket/ribbon cable assembly attached to the below board and viola!  I had increased the maximum power out without having to rip the old board apart.  If the power supply is beefy enough, this idea would work for any "Ruby" type amp.  Kind of nutty, but effective!

Good Day again!

Thought I'd share a last "Ruby inspired" design with ya-all!

On this post you will find attached page one of two of the "Ampenstein" amplifier I built and current have in use in my living room attached to my computer (but works great as a portable guitar amp!)

Note that the power supply begins with a laptop 'brick" that I had left after a old laptop of mine crashed out that goes into the standard regulator circuit.  You might say this was a "Junkbox Special" because I designed it around the parts I had on hand in my "junkbox" at the time.

If you drop an LM386-4 into the socket, you have an amp with a maximum output of 1 watt. 

I decided that I wanted more "Max power" so I built the circuit shown on post 2 - three LM386 amp chips in parallel, routed to an IC socket that plugs into LM386 socket on the main board below.



With a 5 amp/hour gel cell, this unit can run approximately 10 hours once batteries reach full charge

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!).

Good Day!

I designed this unit to fit in a smallish box, using the LM386 and a "cube tamer" power supply circuit.  You will note there is no "on" switch, it turns on when you plug a "Wall Wart" into the power jack.

As noted, any "wall wart" AC or DC with a voltage from 12 to 30 volts can be used to power this practice/personal amplifer - or it can be plugged in via an auto adapter.

C2 (.1 uf on input) really isn't necessary, but I determined that post the build - thus it is on the schematic.

I hope that you-all can get some ideas for your own amplifers from these posts, pictures will be forthcoming of the completed units later (as I get my digicam up again!)

Thanks for checking them out. 

FYI - the program I use to make my schematics is a free download from www.expresspcb.com.  It is really an excellent CAD program for schematics! There is also a PC board layout program included with the package.  They offer a prototyping board service, but I have built all of mine on "Rack Shack" project board stock.

Here's the "Mini":

Good Day All!

In my harvesting of speakers from old television sets, I ran across this 32 ohm speaker, 4 1/2 inch in diameter.  Kept it around for a while, and was experimenting with using the LM386 in a bridged configuration.  I found out that the chips get prohibitively hot when running 12 volts and a speaker load of less 8 ohms.  I tried 16 ohms, and though the chips got "good and warm" under full operation, they were survivable.  With the 32 ohm speaker, they work GREAT.

I put this in a kind of small box, thus the title "The Mini".  I was still experimenting with values for the headphone amp portion, and have since determined that changing 10 kilohms to give the headphone amp a gain of 10 works better.  Holding it at 15 kilohm gives it a gain of about 7, which is tolerable, but not best.

R1 and R2 determine input impedance, set to 5 Megohm in the Mini2.  The buffered output provides a means of connecting this amplifier to another unit or a house system.  It's output is approximately 80% of the voltage level of the input to the amplifier.  I use this for guitar, as well as for general listening purposes.

I like the independent headphone assembly, that can be utilized as a secondary "line out" if necessary.

The power supply is a regulated "wall wart" design, similar to that found on the "Mini".

Anway - enjoy!

 Good Day AGAIN!

My last post for the day -- gotta run

All my DYI amplifiers had NO reverb.  I looked up Craig Anderton's Stage Center Reverb, and came across an unknown reverb tank (got it as a gift!).

I did my usual "tweeking" on the schematic and built the result - I LOVE IT!  It works with my guitar and most useful to me with my dynamic microphone!

I changed the chip from a TLO-74 to two NE-5532 op amp chips.  With the kinds of loads the  NE5532 can drive, I believe that this unit would drive and recover from almost any Reverb Tank out there.  Note the power supply on this one - with a rail splitter - rail splitter can deal with 200 mA without problems.  Also note that I, again, set it up with a high impedance input --Just "cause I like High Z inputs for guitars and mics! (be certain to use "shorting type" input jack with shorted to ground with no plug inserted).

When you run the "dry" down and bring up the "wet" - it can get SCARY with the reverb, and even feed back through!

The reverb tank I used was a two springer, similar to an accutronics type 1.
(Do visit the accutronics website, they KNOW spring reverb!).

Humbly submitted to share

Mensur,

(The following is my humble opinion, that and $5.00 will get you a cup of coffee almost anywhere.)
As with any chip amp, I believe you can use this as the power amp stage of a guitar amplifier.  However, with a closed loop gain of 30-35 dB (per spec sheet) you will need a pre-amplifier for this unit.  I do recommend putting a 10k Log pot right up front of the power amplifer stage to allow for easy adjustment of amplifer level.  I am unfamiliar with the pre-amp mentioned, but in my little world - an electron is an electron is an electron.
Couple-three of things to be aware of:
1)  The rated power will only be developed across the rated speaker load (in this case, 2.7 ohms)
2)  Be certain and have more than sufficient heat sinking on the chip - or it's "fried chip time".
3) The rated power can only be achieved with the rated power supply voltage (in this case +/- 40 volts)
4) Make certain that power supply can supply at least 2 times the necessary current needed to run the amplifier at full rated output. (100 watts out, 80 volts (+/-40), is about 1.25 ADC - I would not try to run this circuit with less than a supply that can produce +/- 40VDC at a current level of 3 amps minimum - try for 5). 
5) I do recommend a voltage regulated supply for this - ABSOLUTE maximum voltage for the chip is +/- 50 volts.

The data sheet for the chip can be found here: http://www.st.com/stonline/books/pdf/docs/1057.pdf

Finally, below you will find a suggested schematic to interface the output of the pre-amp to the TDA7924

Hope this helps!

Good Day, Again!

Attached is the schematic of my favorite amplifier I have built and use regularily.  I call it the "Classy Lassy" because the speakers are "recycled".  The 8 inch and the tweeter were from an old Magnavox tube type console record player.  The 6 inch is a Bogen speaker that was used as a studio monitor at a now defunct radio station from a local college.

I use a lot of "recycled" speakers in my little amplifier projects - the sources are quite varied.  I have found that old televisions usually provide highly usable speakers, that also give it a neat tone.

I have found that multiple speakers, each driven by an amp chip provide a MUCH "bigger" sound punch per watt than a single speaker device.  Also, by mixing speaker sizes and shapes, one can shape the tone out of the amplifer.

Well, Here's the 'lassy:

Good Day All!

Attached is a schematic of the amplifier I made I call the "Bug Eyed Monster" because the grills from the Roadmaster 5x7 speakers I bought at Wal-Mart give it that appearance!

About 8 to 10 watts RMS capable per speaker in this configuration.   Again, Mouser.com for most parts, I build the cabinets for these from scrap lumber and use hardware store handles and rubber furniture feet for the amplifer feet.  When I get my digital camera operational, I'll post some pictures of these amplifers I am providing schematics for - They are in use!

Again, the input is from "The Ruby" by runoffgroove.com, and the P.A. portions are from the datasheets for the chips, with my own "tweeks" added.  "Astro-Peke Music" is the "pen name" I use if I am building an amplifier for someone else, but I folded it as a small business - not enough time with my full time job to give a side business proper care!

To repeat from my first post -  I like high impedance inputs, and to keep hum and such down, you need to make certain and use a switched input jack that shorts the input to ground when there is no plug inserted.  (personal preference, in all my designs the input impedance is determined by the input resistor pair - feel free to modify as you see fit)

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".