Gonna make a guitar chipamp

[polo16mi]

HI there:

I studing and reading this magnifical forum.  I downloaded the teemu´s book, and i reading it too. Great job, congratulations! It´s excelent stuff, but a little dificult to me in some´s point´s to understand, so... i chew a little of it every time i got a break.

I wanted to purchase a guitar amp, but i change my mind a little and here a couple of razons.

- I´m an technic electronic from the secondary college. Here i was studing in the ENET 2, from Neuquen, and i had graduated in 1992. I havent a lot of experience in audio but i work fixing computers and his related stuff. I had been working since that time in them. I love that kind of junk. I like to fix myself my car too, and i had make it several times with pretty nice results... I homebrewer too. So.... i like to mess around with anything else.... Its a shame for my that i cant make myself a ss guitar amp.

- I´m used to think that the cost of a trafo and a good speaker are too high and in adition, the work and time that takes to do the amp, dont make any sense to make one, and the best way is to buy one, but i get at a very good price a 24+24/6A tranny, and somes TDA 7294, a 3886, a TDA2005, and a couple of LM386 of a good friend of mine almost for free....... Still have the problem of get a couple of decent´s speaker for a guitar amp.

- I use to hit a old FAIM ( a cheap argentine copy of a STRAT)... not a very good player, but getting more experience with a teacher. We want to make an ensamble with other guys and just jam! So... we need an amp at least! The FAIM has some improvements such as Schallers and another neck. Not a big viola, but is my first girlfriend, i love it.

So, well....what the hell..... it worth the try.

Going to "the bifes".....i had looking around and reading somes datasheets of TDA7294, LM3886, TDA2005.....  I think that with this stuff and a few cheapers components i have enough to make a decent amp for jam with a drumer and a bassman.  If a could call for a wish to my hada madrina,  i want a 2x12" 100 RMS combo xP, with clean sound, and that the thing should be more "expresive" as a punch the strings! Kinda ACDC bluessy distortion if us permit me the term.

I plan to start making a Ruby or kind of it, something that looks simple, to practice and remember the cloruro, the soldering iron and all this stuff. Get practice and make a little amp for practice in a bedroom. Perhaps a simple preamp?

I thinking to make all modulars stage parts, so i can upgrade each with one more powerfull or better when i make a better part. Maybe a stage with the 2005?

At the end of all, i want to do the "big one" for the power stage..  I guessed that a good option are maybe a couple of 7294 in a bridge configuration, but i had reading around that isnt a good configuration. Them tend to explode in that bridge. Someone of us have one of them working in that configuration? I found a video at youtube, in that a mexican guy i guess, presents its chipamp and i says that he suppouse that the thing has BRIDGED TDA7294. 

In the second hand, i still have a LM3886T.  Looks like the net is plenty of well tested chipamp with it.

I confusing about if the path that i plan to follow is razonably or not. BTW,  i planing to purchase 2 12" of Mr FAHEY when i have the $$$.

Best regard for all of us and sorry about my english.  Sorry if i sound in any way bad for any of us, im not a great english writer 

[joecool85]

Welcome to the board!  Don't worry about your English, just try your best so we can understand you (you've done a fine job so far) and we'll be good to go.  We have several members on here that do not use English as their first language.

Sounds like you have a pretty good plan going.  Definetely start with a little gem or similar battery based circuit.  They are easy and help you with the basics, as you were hoping it would.  Also, the LM386 used in the Little Gem has been used as an effects pedal chip as well as a preamp chip with very impressive results.  So you could build a Little Gem, then when you are ready, you could build a LM3886 poweramp and plug the Little Gem into that as a preamp.  Throw on a simple preamp and you'd be good to go.

[polo16mi]

HI again:

Got some news from my desk.  I tried to do kind of Ruby, and after some fight with a proto-board and a few components, its sound pretty good!!!  I use first at all, a 8 ohms 2" speaker of a PC case, and it sound very poor, so i took a satellite speaker from my home theater. The differen is awesome.  Very clean sound for just a fist of components, and loud enough for bedroom practice playing. 

I found a nice work-point of it. The values, all of them, the original plans of the Ruby, but a 1K5 resistor between 1-8 pins. with the guitar volume at a half, it sound very clean til 3/4 of its trip. At full volume, the sound begin to break up to a nice distortion if i play a little bit hard.

I notice that when i play without hitting so hard the strings, the sound comes clean, but, if i go hard with them, its sound louder and little bit distortion. No bad sound. I like it. I can give to the sound nice variations just with the guitar volume pot.

I begin with the just the chip version, then, when it work, go for some more complicated, and add the MPF102 first stage to it.  First try, very bad, i misconected the drain with the gate i think, and it didnt work.  Reading the datasheet of the FET, solved the problem.

Now i have the two versions working already, but, maybe my ear is not good enough to percibe some diference in the sound of them. Thinking that changing the 3K9 resistor at the drain makes some difference. Any ideas?

I playing a lot with the pins 1-8 of the LM386, to see what appends with differents gains values, just for curious about it.  From open loop, to a 10uF cap and a 100K resistor, go the whole values that i have at the hand. No percibed so much variations, but the extremes of the tried values.

Now a thinking  to get  a 4" speaker  4 ohms  from some junk  and make a nice practice amp with all. Going to do the pcb, get the things in a box and finish my first project. I ll post some pictures in a while just to share the experience. No big deal, but maybe someone usefull.

Regards.

[joecool85]

I'll be looking forward to seeing those pics, I always love see how other's projects come out.

[sergscar]

Hi Polo,
Welcome to the board (I've already sent you a PM in spanish)

JoeCool is right abt the LM386's preamp. i've done one myself and plugged it into my 12W Dean amp, the sudden change was impressive.

Hope you continue posting your ideas and pictures, so everybody can see and discuss details.

Keep in touch
b'rgds,
Sergio

[mac_sama]

Hey Polo, I'm from Mar del Plata and I've already built a Ruby Amp. I use a 1k potentiometer to change the gain as pointed in runoffgroove.com; I've tried fixed resistors also, but the pot offers more versatility.

Just in case, I've recently buyed a 4'' 4ohm speaker for 20 pesos (~5 dollars) that works nice with the Ruby. Its not expensive and its worth the price.

[polo16mi]

Hi there:

Im polishing my final version of the ruby, before case it in, and im in a doubt  . Im making this version:



Im doing the same, with the follow diferences...
- Im fixed the gain with a 1K5 resistor. Maybe i ll  change it with a 5K pot if i get one.
- Im using a little bit more of tension. (around 12,5V), cause i using an ac adapter 220V-9V, made in china.  xP
- I had been trying differents values for the 47nf coupling capacitor, and the sound seem to going from very flat and "bassless" using a 47pf, to very cavernous bassy 470nf.  With the gain fixed, noted that with the highers values and the guitar volume at 3/4 or more, as i push hard the strings, the more distortion i got, specially at bassy notes like E5.  Looks like the clean sound loses with bigger capacitors. I tryied to reduce the distortion with the guitar volume, but as the distortion goes down, so do the volume     I tryied using the input volume pot that you see in the above fig, but the same.

Here is my doubt. How can i fix the capacitor value?  Why in the fig it has a 47nf value?    I want good clean volume til 3/4 of guitar volume wherever i hit hard or not the strings, and if i go all the way to full volume, distortioned sound if i play hard  .

Dont get me wrong, i very pleased and amazed with the results that i got, i just playing with the posibilities of this circuit, and i want to learn how to tailor the sound with differents posibilities.

BTW, a familiar of my give to me a microcomponet and it has 2x 4" 3,2 ohm, 2.5W speakers. Sound that is too few impedance for this circuit   .... If i shot a try.... buy another LM386?  NOthing says the datasheet about output impedance ranges. The page of rungroove says at least 4 ohms....

Best regards.
PD: good one matsama. i still looking around for a decent speaker here, in Villa La Angostura, but isnt easy to found (at least, purchasing one, nobody shells here)

[polo16mi]

Have an addicional question if you live me....

Thinking in and a simple tone control to the Ruby, see in the net the circuit that i attached.  If a fix the components that i marked between the 47nf cap and the pin 2, it will work? Should be?

[J M Fahey]

Hi Polo.
1) Very small amps have 2 big problems with bass:
a) They are used with very small and unefficient speakers, with no useful bass response
b) Bass requires higher power, which just isn´t there, and proper speakers, so they are not heard by themselves but distort everything in an ugly, farty way. The solution is to just cut them.
The 47nF, coupled to a 10K pot, cuts everything below around 320Hz, at 6dB/octave; that means that the lowest guitar frequency, around 80 Hz, gets attenuated by around 12dB, which is good. Different cap values will shift the cutoff frequency. You can try different *smaller* values (.022 , .01 , .0047 ....) to see which one gives you what you want: reasonably clean sound up to "6" (on a 0/10 scale) and "cleanly" distorted sound above it. Post your results here.
2) The Marshall MS2 tone control is only better than nothing at all, and by a very small margin. You have only "space" to boost highs, but if yiu cut them , there´s not much left.
Much louder/larger amps (Champ, GA-5) have no tone controls at all.

[polo16mi]

Thanks very much JM:

Very usefull info. :tu:

I guess that the 47nf cap and the 10K pot make some kind of RC filter. In this moment i dont remember so much about this stuff, so i looking around for some additional information in google. Unfortunatelly my secondary school notes is gonne. I guess that there is somewhere a formula that with the cap and resistor values tell us the cut frecuency of the filter.

Last night i had been trying to mix the control tone of the MS-2 as i posted above, with the Ruby, and surprisings results appends (for me, at least  ). I put the components that i marked in the grafic between the 47nf cap and the pot. Some observations are:

- I used 150K resistor and NOT 180K as the original. (I dont have 180K at hand).
- At the first try, it work, but, with a 1k5 resistor between pin 1 and 8 of LM386, the volume was very low, so i go with a 10uf in serie with a 25K or 100K pot in replace of it. (i dont remember right now the value exactly), but its seems to solved the issue.

The sound goes from very bright and rare (sounds like playing the guitar with the speaker inside a can  :duh ) to very bassy. Regardless of if i liked the sound or not, i ear an interesting variety of combinations of tones, and playing with the mics of the guitar, its sees very versatile (BTW, it has 3 simples mics, and dont have the classic 5 positions switch, it has an individual switch for each mic, so i have two adittionals combinations, mics 1-3 on, and all the three on) . Additionally, with this configuration of amp, the trip of the guitar volume pot that work without any noticeable distortion seems higher (> 3/4).   One more think, if i choose 2 mics on, the volume go down a little in comparison with just one on. 

I founded between all that sounds and combinations a couple that i liked, so, probably, this tone control, will go in the case!

I not sure if the fact of that i need to use the LM386 at higher gains values to compensate the lower volume obteined, is in some point a disadvantage for the circuit.... . 

It is perjudicial for the CI to use a 3.2 ohms speaker?

For now, its all. I ll keep trying diferents combinations...

[mac_sama]

http://www.muzique.com/schem/filter.htm

[polo16mi]

http://www.muzique.com/schem/filter.htm

Great one, mac_sama!!  :tu: :tu: