Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Schematics and Layouts => Topic started by: n9voc on January 19, 2008, 01:55:11 AM

Title: TDA2003 based Guitar Amp
Post by: n9voc on January 19, 2008, 01:55:11 AM
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, 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, 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)
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on January 23, 2008, 10:17:00 PM
Front and back pics of the Bug Eyed Monster!
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on January 23, 2008, 10:21:28 PM
The "innards" of the Bug Eyed Monster.  Yep, 5x7 Roadmaster speakers from Waly World (20.00 for the pair), scavenged transformer and computer grade filter capacitors.  In the second pic a closeup of the "buisiness end" of the boards - note the HOT GLUE board mounting.  (Glue Guns - not just for crafties anymore).  The heat sinks on the TDA2003 chips are anodized aluminum.
Title: Re: TDA2003 based Guitar Amp
Post by: joecool85 on January 24, 2008, 07:32:20 AM
Why such giant caps on the power supply?  (The ones as tall as the transformer lol)
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on January 25, 2008, 06:38:11 AM
Simple reason for the BIG caps - I got them FREE, and had the space in the case. 
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on February 19, 2008, 02:13:16 AM
Attached is an improvement I made in the B.E.M.   Moving the injection point for a tape player/CD/external audio seems to work better in the new location. 8)
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on April 16, 2008, 07:36:53 AM
i dont really understand electronics, but from what i see, the front stage was with a FET pre-amp, can i eliminate this, and use other pre-amp? or the FET stage is critical?

I have built the tda2003 stage, and put an 8ohm speaker on each output, plug it to my electric-acoustic guitar, it already made a loud sound.

the pre-amp that i was thinking is the Tonemender from

Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on April 16, 2008, 10:46:00 PM
Yes, you certainly can use a different preamp with this unit.  I used the FET as an impedance matching device only, to give me a higher "front end" impedance going into the amplifier.
I use this ampifier with both electric and acoustic (piezo pickup) guitars, and the EXTEREMELY high input impedance is a MUST for the piezo pickup.
The FET preamp section has NO gain to it, typical of a source follower circuit.  In fact, I have measured the output voltage at the high end of the Volume Pot and the voltage is approximately 90% of the input voltage.
The buffered output is simply an additional feature that I use to daisy chain amplifiers together. (or to go to a "house" system).
Good luck and good building!
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on April 30, 2008, 09:39:02 AM
I succesfully build the amp, also the preamp using the tonemender. I try to plug my guitar directly to the amp, it produce great clean sound, but when i try to hook up the tone mender before the amp, withouth plugging in my guitar it produce noise sound and humming.

Is pre amp design prone to low frequency signal? like RF signal sometime giving oscilation or something?
Title: Re: TDA2003 based Guitar Amp
Post by: teemuk on April 30, 2008, 10:28:46 AM
Many amplifiers hum when their inputs are left "floating". You need to use a switching input jack that grounds the input when the cord is not plugged in.
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on April 30, 2008, 06:38:37 PM

Glad to hear you had a successful build.  I designed the amplifer to be squeeky clean in its original inception, and haven't tried putting any pedals other than my chorus in front of it.  The chorus pedal does NOT have a "shorting when unplugged" input to it and if I turn the amplifier on with only the chorus pedal plugged in and on, I also get HUMMMMM.

If you look at the third paragraph of the first post, you will see that I recommended a "shorting when unplugged" input jack to the amplifier.  Most commercial amplifiers (the good ones, anyway,) have this type of arrangement on the input to keep hum down when the guitar is not plugged in.

Teemuk has it right on the money!  I'm certain that the hum you hear is the high impedance input picking up the powerline frequency.

The noise should go away when the guitar is plugged in.  It is for this reason the "old timers" in the music scene recommend plugging in the guitar BEFORE turning on the amplifier - stops hum and "connection noise".

Hope you enjoy it! :tu:

Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on April 30, 2008, 08:56:26 PM
without the tonemender no noise coming out from the amp. when i plug my guitar a short hummm is normal. without the guitar attached to the pre-amp (tonemender) noise is coming out from the amp. my intention was to build a tonestack before the guitar. and yes, the guitar input was grounded when no jack is plugged.

I guess i just build a simple 3knobs tonestack with a transistor pre-amp, maybe this would solve my problem.

thank you all for the help, lets see how it goes.
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on May 01, 2008, 07:38:37 PM
by the way, can I bridge the output from two TDA2003 into one 4ohm speaker?
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on May 01, 2008, 10:08:38 PM
RE: Bridging TDA2003

Indeed you can, take a look at the datasheet for the chip, some versions of it on the net have the bridge circuit included.
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on May 01, 2008, 11:27:59 PM
hey, thanks again, i found the datasheet and i will try to bridge my 2xTDA2003 amp. Regarding to the tonemender i builted, maybe using TL072 was the problem, should change to a better low noise dual opamp.

Basically, I only need a preamp with tone control.
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on May 02, 2008, 05:05:22 AM
Your quite welcome!

Just a thought for you - have you tied the DC ground of your system to the "earth" ground plug on the mains?

Second notion - do you have your preamp exposed to the air and not running on the same  DC supply as the amplifer (thus common ground)?  This could be the source of hum as well .  Try tying all circuit power grounds together.

With most of my FET input devices, due to the high impedance present, if I don't have the DC ground tied to earth, I get some hum - with a lot of metal at DC ground and the DC ground not tied to Earth, I get a LOT of hum when running on the mains.  I do recommend bringing all the grounds to a single point (google "star grounding") then tying that point to the earth ground.

The advantage of single point grounding for hum reduction was illustrated to me when I had two of my amplifiers daisy chained together through the "buffered output" of the first.  I had one in one room, and the second about 30 feet away in another room.  Each was plugged into the wall, but the wall circuits are on different breakers. When I had the second one plugged in, it hummed something awful.  Fortunately, it was a battery backup unit and I unplugged it from the wall, running that unit on battery - eliminating the ground loop between the signal cable and the two "earth" ground points - hum disappeared.

hope this helps! 8)
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on May 03, 2008, 03:36:27 AM
thanks again for the suggestions. a little bit of humming is fine i think, due to sometimes in a lot of places, earth ground zero-ohm is hard to achieve, so there should be something like 0.44ohm is the best thing you can get.

Now, i have read somehwere on the net, split supply for the DC source might help to overcome hum and noise problem, is this true? haven't tried it, maybe i will try it just for proof  :D

I only built half of your circuit, which mean only using 1xTDA2003 on a 4ohm speaker, not too loud but enough. For the preamp, i took a schematic of MicroAMP circuit, i have tested them, works well. But before that, i did try to make a bridge configuration from the datasheet schematic, not successful, everytime i plugged in the power, noise coming out of the speaker, couldnt figure out why.

anyway, TDA2003 is very simple amp to build...!! thanks! now i am building my seffect (distortion-compressor-reverb) in one box.
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on May 04, 2008, 05:11:33 AM
quick question, does TDA2003 or TDA2005 need a regulated powersupply?
Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on May 18, 2008, 12:15:24 AM
question,  how do i make an attenuator? seems that from my guitar directly to the amp, when i crank up the volume, without an effect, the guitar sounded a bit distorted.
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on May 22, 2008, 12:35:41 AM

Almost any solid state circuit can benefit from a firmly regulated supply.  Caveat - be certain regulator can deliver at least twice the expected full steady state load, and have a minimum of 1000 uF post the regulator to insure that it absorbs the fast rising currents until the regulator can catch up.

Secondly, bear in mind the circuit has a voltage gain of 100 as it is straight up.

With a 12 Volt supply, the absolute maximum producable signal by the amplifier chips is 12 volts peak to peak before the waveform distorts due to supply rail limitations. (actually a hair less than 12 V, but we'll say we have ideal amplifiers for this example)

12/100= 0.120 volts p/p maximum input before distortion.

I have measured 0.750 volts p/p out of my electric guitar.

As you can see, doesn't take much to drive the output to distortion.  The FET input of the original design maintains the high input impedance that guitars like to see in an amplifier and the 10-50k volume pot then serves as an attenuator.

lacking the front end impedance match, here is a high impedance attenuator schematic:

Title: Re: TDA2003 based Guitar Amp
Post by: casiomax on May 23, 2008, 02:50:29 AM
I am forgetting the other important key to have a good amp, speaker. I have purchased vintage 30g12 replacing the one i have, suprisingly.... sounds a lot more better! nothings wrong with the input or my guitar.

but on my amp, i did not built the buffer stage, would this affect anything?
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on May 23, 2008, 05:42:19 PM
If you talking about the buffered output - that is strictly optional, and will have no effect on the amplifier performance.  It simply allows an output that is electronically isolated "buffered" from the rest of the amplifier.  you could put a short across the buffered output to ground, and the amplifier will still run.

If you are talking about the FET guitar input buffer, then it will simply affect the input impedance of the amplifier - if you have another preamp that is between the guitar and power amp stage, don't worry about it.   Without the guitar input FET circuit, the input impedance of the amplifier is the potentiometer, in this case 50 kiloohms.

Title: Re: TDA2003 based Guitar Amp
Post by: Anirvan on April 30, 2019, 06:03:13 AM
I have two questions-

1. As shown in the diagram, the inputs are shorted to make a single input. Will it damage the ICs ?

2. If the 470 uF capacitor at the pin 2 is replaced with a 220 uF capacitor then what difference will it make in the circuit ?
Title: Re: TDA2003 based Guitar Amp
Post by: n9voc on May 01, 2019, 09:15:45 PM
Wow!  Eleven years since I last revisited this topic!


The inputs are AC coupled together, but not DC coupled.  This protects the IC from damage. in the eleven years since last posting - neither or nor the current owner of the amplifier has had any issues with this arrangement.

If you are speaking of the RCA and 1/4 inch jack, Those are isolated from the IC by the FET.  Again, no problems known. :dbtu:

Regarding the 220 uF vs 470 uf in the feedback circuit - the Xc of 470uF is about 4.2 ohms at 80 Hz, and Xc of 220 uF is about 9 ohms at 80 Hz. 

Looking at the feedback resistive setup - i think that going with a 220 uF would reduce the bass amplification response of the amplifier - by how much?  I have not a clue. :cheesy: