My New Super Mini 14w-32w practice amp!! Cheap and easy to build!!

[Minion]

Hi Folks ,I was recently looking for a Low power Practice amp to build but not as low power as a Ruby or a Cricket so I came up with this simple design (sort of came up with it, it steals things from a couple different designs)that is versitile enough to get good tones and can be adjusted for several output powers and can be modded to taste.....It is pretty close to a DOD Distortion with the TDA App Note.....

I designed, built ,and tested this design yesterday useing a TDA2030 and a OPA137 and it sounds pretty good and has no hum or other issues, It is very small and could even be built inside a Large pedal enclosure...The PCB is aprox 2.5in x 3.1in and is single sided but there are 2 jumpers....



Mods:
A few mods that can be done are:

Changeing the Value of the Input cap on both the Single OPA and the TDA chip...
A small value cap can be placed in the Feedback loop of the Single OPA..(63pf-220pf..??)
The 0.22uf cap on the tone controll can be changed to get a different tone controll range, the Pot could also be changed to a different Value....
The use of different Clipping Diodes, and putting different diodes on a switch to change the clipping behavior..I used 1N4148...
Change the Gain by useign a Bigger gain pot and the gain of the TDA Chip can be changed with the 22k resistor in the Feedback loop....

Notes:

You can use a TDA2030 for up to 14w..12v,0v,12v-30Va Transformer
You can use a TDA2040 for up to 20w..14v,0v,14v-30-50Va Transformer
You can also use a LM1875 for up to 20w..14v,0v,14v-30-50Va Transformer
You can use a TDA2050 chip for up to 32w..18v,0v,18v 50-80vA transformer
If useing the Higher power chips then I suggest increaseing the 2200uF caps to 4700uF...


Any feedback is appriciated....Thanx

[tranceracer]

That's sweet cant wait to see / hear how it sounds after its all boxed up!  WOW 32W from that ckt!
Would you happen to have a link to a bigger schematic?
-bK

[FisTheGoon]

Seem interesting.Care to share the sample.Do you mind post the schematic only?cause the value seem to blur after zoom in.
Thanks.

[Dragonfly]

Very cool ! It looks like a nice adaptation for "guitar use !"

Might I suggest "linking" the original drawing as well, as the layout is a bit hard to read...or is it that way before resizing as well ?

It looks like others have been using the TDA2030 with great success....

http://eu.st.com/stonline/books/pdf/docs/1458.pdf
http://www.mitedu.freeserve.co.uk/Circuits/Audio/tda8.htm
http://www.e-dan.co.uk/electronics/TDA2030.html

[Mark Hammer]

The 2030, 2040, and 2050 constitute a huge share of the power sections in the various starter or practice amps you'll see from a wide array of manufacturers.  People keep buying 'em, and despite being in the hands of absolute beginners who are sure to abuse them, they last long enough to show up second hand on a regular basis.  For me, that's a sign of dependability.

[DougH]

Sounds cool!

I remember seeing a chip (guitar) amp demo on youtube a few years ago and it really sounded good.

Enjoy!

[Minion]

Hi, Here are some Larger pic (Hopefully as Photo bucket seems to resize them)...

here"s the schematic:



here"s the Parts overlay:



Here"s the PCB:



hope these look beter....

Thanx

I"ll try posting a sample after I get it boxed up and find a proper speaker for it...I"ve played it through a 12in stereo speaker and it sounded pretty good but it sounded like a Guitar player through a stereo speaker...you could hear the tones and the overall sound but it lacked that oomph that a guitar speaker gives....

Cheers

PS: also don"t forget that the TDA Chip needs a Heatsink...I used on that was about 3in x 2in and 1/2 cm thick with a TDA2030, bigger would be needed with the higher power chips....

[OnLyTNT]

If you plan to build high power version (32 W I mean), send-return connections may be added between vol-pot and c1 for other dist pedals. That also would be awesome.

[Minion]

I just wanted to give a little update....I just finished boxing it up, I had trouble finding a suitable speaker but was able to find an old 8in guitar speakerfrom an old busted Tube amp, it sounds really quite good, I was surprised becaise it sounded awefull through a couple of the speakers I tried but once I hooked up the 8in guitar speaker I got a much better sound....

I don"t have a way right now to record a clip as my recording computer and all my recording equipment is at my jam space and I am going out of town tomorow for 2 weeks but I"ll try to post a clip when I get my Sh*t together....

All I can say is it sounds good, I need to change a couple cap values cuz it is lacking a bit of low end, Ohh and it is Really loud and that is with the 14w version....definately worth the $10....

Cheers

[Minion]

Anothewr Update...I got rid of the 1N4148 diodes and put in 2 switches to toggle between Germanium diodes and LED"s and I have to say that it sound s MUCH better ...It actually sounds better than some amps I have played and it has a extremely heavey tone to it at full gain.....

CHeers

[earthtonesaudio]

Nice write-up and my compliments on the design.  One of the things I liked about the Noisy Cricket was that it distorts in a nice way when fully cranked.  In your experience, does the TDA chip distort nicely when it's maxed out?

(If you haven't blasted the input yet, no big deal... I'll probably order one of these chips eventually and then I can abuse them to my heart's content)


A couple other things I noticed, which you (or others who are interested) might find useful:

-It wouldn't hurt to have a fuse somewhere in your design.  The chip is internally protected from overheating and over-currents, but the preamp sections might not be so lucky.

-The tab on this series of chips connects internally to 0V (ground), so if you did a single supply instead of bipolar, you could connect the chip directly to the chassis ground with no insulator.  Someone more knowledgeable than myself might be able to comment on whether you can connect the tab to chassis ground when using a bipolar supply, as in your design.  I'm not sure about that one.


Anyway, thanks for sharing, and if you've overdriven the chip, please comment on the sound.   

[Minion]

Hi, Sorry I didn"t get to you earlier but I was out of town...While I was out of town I brought my amp and guitar with me and was able to get it up to about 5 (the thing is freakin loud) and it sounds great, I don"t notice any extra distortion from the power amp section compared to high and low volumes (general bedroom listening levels have the volume dial at less than one with the gain at 7) , but you do seem to gain a nice guitar tone with the volume cranked from speaker break-up...I"m useing an 8 in from an old Garnet knome tube amp...

Because the Clipping diodes clip the Voltage I believe that the output Voltage of the Preamp section isn"t enough to drive the Power amp into clipping so most of the distortion/overdrive comes from the Gain, Clipping diodes and speaker.....

I"m working on a bit better design with a 3 band tone and a makeup gain stage ,I might just make the tone controll active and drop the makeup gain stage....

Later....Cheers

[earthtonesaudio]

Cool, thanks for the reply, Minion.  Those who are interested should check out the R. Penfold design using the 2050 chip (in the book, "Audio Amplifier Projects").  Bare-bones simple (no preamp, just a pot to control level going in).  It helped me get an understanding of what's needed, what's not, etc.

[ambulancevoice]

Anothewr Update...I got rid of the 1N4148 diodes and put in 2 switches to toggle between Germanium diodes and LED"s and I have to say that it sound s MUCH better ...It actually sounds better than some amps I have played and it has a extremely heavey tone to it at full gain.....

CHeers

im very interested

btw, regarding power amp distortion, those TDA20*0 have low distortion
take a look at there data sheets
you probably could drive it by use a maxed out boost in front and with the volume pretty loud

[earthtonesaudio]

Yeah, I'm not looking at the data sheet right now, but I seem to recall something low like 200mV peak input signal before distortion.  Minion mentioned it sounded good with LED clippers, so that's letting through maybe 1.5 volts... if I'm remembering right about the amp specs, there's probably some distortion happening in the amp when the LED clippers are selected.  I'll have to check out that datasheet...

[arawn]

What if you cut the clipping diodes out and used a couple of cascaded fetzers in front of the power section. It would ideally give you a fender sound alike wouldn't it??

[Minion]

Yes you could definately drop the Diodes and use fetzers, you could do a lot of Things like take any Pedal you like and put in front of the Power amp section....

I have it set up now were I can disable the diodes all together which does increase the output Volume by quite a bit and it adds Opamp distortion and probably Power amp distortion but I have no way to distinguish the two...

It actually sounds good on all of the OD settings I have it set up so I can have no clippers and just use Gain to overdrive the Opamp/Poweramp and with Some Mystery germanium diodes which sound great if you are into that Muddy, feedbacky squeely sound (I like it) but with the germaniums the Output voltage is decresed quite a bit so i have to increase the Volume when useing the germanium clippers ,And then I am useing Orange LED"s which is the setting I use the Most ,it has a good new metal sort of sound ,easy to get Squeely harmonics and has a Pleasant feedback...I find myself not useing the Tone knob hardly at all ,It sounds best to me when at the 7 or 8 position on the dial...I spent about 4 hours playing it last night and I am really digging it, I"m sure I could even use it for Jamming if I used the TDA2050 chip and used a Nice 12in speaker but as it is it makes a great practice amp and I am working on a few Improvements while still keeping it simple, small and cheap....

I just wish I had my recording gear here so I could post some samples...I"ll see if I can grab some of my equipment later today....

Cheers

[earthtonesaudio]

Thanks for the report, Minion.  That's great that it sounds good even without the LEDs.  I got a chance to look at the datasheet, and it looks like the max input voltage is +/-15V.  That along with the fact that they aren't kidding about the "low distortion" properties of this chip (only 3% at 32W!), makes me think that the distortion you're talking about must be coming from the opamp, which is fine by me. 

I noticed something after I boxed up my 386-based practice amp... It would be really easy to mount it in a pedal enclosure, and have built-in effects (channels) or other presets (like your clipping diodes), and control them with footswitches!  And just run a speaker cable from your pedalboard to the speaker cabinet!  It might be weird to some people to not have a big head unit sitting on top of the speaker cab, but I just thought it was a really neat solution that I've never actually seen.  If someone has already done this, please let me know, cause I'd like to see it!


I actually have "extra" amps right now, so I'd have to sell one in order to justify building a whole new one... but if I did need one, this would be it!

Thanks for sharing,
Alex

[wampcat1]

What if you cut the clipping diodes out and used a couple of cascaded fetzers in front of the power section. It would ideally give you a fender sound alike wouldn't it??

I would do a mimic of a fender twin or deluxe reverb preamp using jfet's if it was me for this... the eq plays a big part on fender tonality circuit wise. Speaker and cabinet are VERY important too, IMO.

bw

[arawn]

Kewl I guess i'll Have to figure that out