Howdy!
I like to use my main Solid State amplifier (posted under "outboard amp") and a tube type Fender "Champ" clone I built at the same time.  To facilitate this, I built a splitter (schematic attached).

The power transformer came out of a junked HP 310.  It was mostly from my junk box, and is indeed a bit over designed.  My idea was to have the guitar signal split without any loss o f signal to either amplifier, or loading down the guitar.  Thus the input impedance of 1.35 Megohm, and the use of the opa2134 FET input opamp.  I had some 2134's, but I am certain it would work as well with a TLO72. :tu:

The power supply is overbuilt, but again, I used parts I had on hand.  The use of the split power supply allowed the use of noninverting input, without concerns of trace impedance variations used by an "artificial ground".  The positive and negative regulated power supply is rock solid, and dead quiet.  In fact, the entire mixer is "overbuilt". (But then again, I started by opening my junkbox, and seeing what there was available for use in making my mixer.)

The upshot is that the combined sound coming out of both my amps at the same time is just simply AWSOME!   :tu:

The splitter circuit could be used for virtually any audio circuit with a maximum signal level of about 2 volts p/p.  The power supply voltages are the limitation on the maximum signal used.  Respectfully submitted for your edification!

The second item is the "Transmogrifier".  It is a passive mixer cable assembly that I and many others locally use to play our MP3 players through our amplifiers.  The resistors provide a channel isolation, preventing possible shorts from one channel to the other.  Just a combiner cable without the resistors may work fine, but with the "transmogrifier" the system is virtually "bulletproof" to enjoy my music through my existing mono amplifers.

The input impedance of most of my amplifiers ranges from 50,000ohms to over 1 million ohms.  The signal lost across 91 ohms is insignificant compared to the voltage present at the amplifier input.

Just thought I'd share and start this "gadget thread".

I'm working on a guitar mixer, allowing two guitars to be played through one amplifer -- without loading either guitar down -- more on that later!

Anybody out there got some gadgets they use that answer their little needs like these do for mine?

Hello, fellow solid state amplifier buffs!

Been awhile since I've posted, and I conceived of an amplifier project – and thought it would interest the members of this forum to see the process of the project from inception, conceptualization, design and final build.

Thus, I started this thread.  I'll be posting to it as the project progresses – with photos, schematics and commentary – I hope that you find it enjoyable as well as informative to "get inside the head" of this builder and player for this project.

As I describe each step, I am aware that there are probably better ways to go about the design, and ways to get "more" out of the design.  However, I am not designing this for production, but rather for performance and ease of build using components on hand as much as possible – in other words, with as little cash outlay as possible and still make a serviceable amplifier.  With those caveats out of the way, here we go!

The Project:

I want to build an amplifier that will be the bottom of a "half stack" configuration with my 3 watt "Classie Lassie" amplifier I built earlier.  I want to be able to add 20 to 30 watts of capability to the "Lassie", and have the amplifier stack look good, like the "Classie Lassie" amplifier does.  (See attached pictures of the "Lassie" below, and further information on this amplifier can be found under my post of "my favorite practice/small group amplifier")

First – The "footprint" of the upper amp (the "Lassie") is 17 inches long by 11 inches wide.  The "footprint" of the amplifier she'll be sitting on must be at least this size, to match in looks.  Height of the bottom (outboard) amplifier will be determined later.

I dug into my junk box and came up with the parts shown in the picture below, from left to right I have laid out:  (some materials to work with!)

A power transformer pulled form a defunct 150 watt power mixer, dual center tapped secondary with dual primary for configuring to 120V or 240V.

Some "project board", LED's, IEC power connector, a fuse holder, some bridge rectifiers and a good set of filter capacitors for the power supply. The big blue one is 18000 uF at 25VDC rating, computer grade.  The others are either 3300 uF or 4700 uF.

Two FK607 boards (an amplifier module based on the TDA2004/2005 chip),  a couple of TDA2003 amplifier chips, a heat sink, some ¼" jacks, several NE5532 op-amp chips, and cabinet hardware pulled form the aforementioned power mixer.

Speakers:  An 8", 8 ohm 10 W speaker from a JWDavis ceiling fixture, a couple of 5", 6 ohm speakers with big magnets, pulled from a defunct studio monitor set – estimate at least 50 watt capability – and an aluminum plate to mount controls upon.

From this array of parts, an idea of triple PA (one power module per speaker),  op-amp preamp amplifier design suggested itself.

I am now ready to begin conceptionalizing the amplifier, sort of pre-design work based upon the materials at hand.

**** Continued Next Post ****
Images:

http://img523.imageshack.us/img523/4832/bea2fq5.jpg
http://img523.imageshack.us/img523/1153/bea1fg1.jpg
http://img523.imageshack.us/img523/2935/bea3py7.jpg

Hello, fellow solid state amplifier buffs!

Been awhile since I've posted, and I conceived of an amplifier project – and thought it would interest the members of this forum to see the process of the project from inception, conceptualization, design and final build.

Thus, I started this thread.  I'll be posting to it as the project progresses – with photos, schematics and commentary – I hope that you find it enjoyable as well as informative to "get inside the head" of this builder and player for this project.

As I describe each step, I am aware that there are probably better ways to go about the design, and ways to get "more" out of the design.  However, I am not designing this for production, but rather for performance and ease of build using components on hand as much as possible – in other words, with as little cash outlay as possible and still make a serviceable amplifier.  With those caveats out of the way, here we go!

The Project:

I want to build an amplifier that will be the bottom of a "half stack" configuration with my 3 watt "Classie Lassie" amplifier I built earlier.  I want to be able to add 20 to 30 watts of capability to the "Lassie", and have the amplifier stack look good, like the "Classie Lassie" amplifier does.  (See attached pictures of the "Lassie" below, and further information on this amplifier can be found under my post of "my favorite practice/small group amplifier")

First – The "footprint" of the upper amp (the "Lassie") is 17 inches long by 11 inches wide.  The "footprint" of the amplifier she'll be sitting on must be at least this size, to match in looks.  Height of the bottom (outboard) amplifier will be determined later.

Having worked with and in electronics for the last 30 years, I at times develop a pretty well stocked "junk box". I knew I had a lot of the "basic" parts – resistors, coupling capacitors... etc, but did I have of the "expensive" stuff to keep the cost of this project down in my possession at this time?

I dug into my junk box and came up with the parts shown in the picture below, from left to right I have laid out:

A power transformer pulled form a defunct 150 watt power mixer, dual center tapped secondary with dual primary for configuring to 120V or 240V.

Some "project board", LED's, IEC power connector, a fuse holder, some bridge rectifiers and a good set of filter capacitors for the power supply. The big blue one is 18000 uF at 25VDC rating, computer grade.  The others are either 3300 uF or 4700 uF.

Two FK607 boards (an amplifier module based on the TDA2004/2005 chip),  a couple of TDA2003 amplifier chips, a heat sink, some ¼" jacks, several NE5532 op-amp chips, and cabinet hardware pulled form the aforementioned power mixer.

Speakers:  An 8", 8 ohm 10 W speaker from a JWDavis ceiling fixture, a couple of 5", 6 ohm speakers with big magnets, pulled from a defunct studio monitor set – estimate at least 50 watt capability – and an aluminum plate to mount controls upon.

From this array of parts, an idea of triple PA (one power module per speaker),  op-amp preamp amplifier design suggested itself.

I am now ready to begin conceptionalizing the amplifier, sort of pre-design work based upon the materials at hand.

**** Continued Next Post ****

Hello All!

I'm looking for a schematic for a Sunn SR8520P powered mixer.  Does anyone out there have one?  I do have a pdf of the owner's manual, but still need a schematic.  The SR-8520PD is available through Fender for only $5.00, but I have a pdf of the owner's manual for that one as well, and it seems to be a different animal.  (I am quite willing to share that pdf too!)

For reference, I am attaching pictures of the front and rear of one of these boxes.

Thanks for any help!

Good day!

I have attached a schematic and pics of a high impedance input (5Mohm) booster circuit.  If I want to play my electric and not worry about imput impedance of the amp, this does the job as a preamp.  As you can see, I have the knob marked at the x1 and x5 positions. 

Enjoy!

Good Day All!

Joe had asked about if I had tried the LM1875, and I found my schematic for one of the first successful amplifiers I built based upon an LM1875 design - I called it FrankenAmp, because I used a relatively cheap practice amp for the chassis and amplifier hardware.  It is Frankenamp 2.0, because I made a new enclosure and completely reworked the innards.

The original of the attached schematic was generated as the unit was built and evolved with a lot of "cut and try" ideas along the way.  I finally got tired of messing with it and the result is as seen below. It works good, and my son uses it regularily.

There are a few changes I will make to the below design before I create another LM1875 based amplifier, but I haven't gotten around to writing them out yet - or building a prototype.  The speakers in Frankenamp 2.0 are a 5 1/2" and a 6x9" purchased at Wal-Mart for around $10.00 each.  The tweeters were from an inexpensive "miniboombox" radio from Dollar General.

Most of the rest of the parts came from my "junk box" at the time.  I used OPA2134 op amps in the design because I had handful of them at the time.  The R19/R20 combination was an adjustment to the R20 value to get a good sound level out.

Enjoy the schematic and pics that follow!

Good Day!

Attached are pictures of one of the most unusual builds I've done to date - a little amplifier I call the "Cube of Sound" - speakers on three sides.

It began with a TDA7053 amplifier kit, two excess computer speakers (by Boston Acoustic) and two 3.2 ohm speakers from garage sales.

I wanted to have a second input that I could run from a mic level to a line level in, and thus the Cube of Sound was born.  A drawer pull for the handle, and rubber furniture cups for the feet came from the hardware store.  With such an unusual look, I just HAD to paint the backplate rather than clear coat it!

Ive attached a schematic of a little combiner box I made up for use with interfacing a guitar or other mono input amplifier with a stereo, dvd, headphone or satellite receiver.  It can combine the signals through the RCA jacks to either a mono or stereo 1/4" jack.  The resistors in line assist with the mix, as well as keep a certain level of separtion between the channels. The can be anything from about 32 ohms to about 100 ohms.  To interface with a 1/8" headphone, I picked up a 1/8" stereo to twin RCA plug cable from radio shack.

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

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

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".