Making my 1st AMP! (40/60w Bass Amplifier)

[Shakal]

Hello people!

As you can see I am new here. I'm brazilian, 19, in College, Bass player and trying this little adventure in the world of "Made by Myself". I'm gonna pre-apologize for any english mistakes that I will make or already made...

This AMP will be like a prototype for any furthers. I gonna use it just for study and playing at home.

I choosed this one: http://www.redcircuits.com/Page66.htm
Amp:

Pre-amp:


The power supply (that I didn't buy yet) gonna be a 24+24V by 3A that will be more than enough.

The darlingtons I changed for TIP142 and TIP147.

The PCB layout isn't ready yet but I will use a software to do it, like Ultiboard or something like that. To start it up I'm just waiting for the transformer and then I'm gonna have an idea about the space inside the chassis.

Talking about chassis... This is one of my questions:

I wanna know what type of material to use, Aluminium, Stell... and the thickness I can use. I think I gonna use a plate in a shape of "+" and fold it into a little box with 200x200x100mm.

I'm thinking about to screw the PCBs in the chassis with a circundal hard-paper between the Chassi and PCB. The transformer directly in the chassis and the cover with 4 screws with a "L" Support in the chassis.

I drawed this... It s***s I know but just to illustrate what I'm thinking about.



So, what do you think about it? It's good enough? Any ideas to improve it? Any sugestions?

Thank you for reading this and... don't be ashamed in replying.

See ya!

[geminni]

You say that you will make supply with 2x24v? But the amplifier on schematic has only single supply, 60 volts, not 2x30v! Don't make symmetric power supply, you'll have +24v, -24v with separate ground. Your amplifier needs +60v with ground!

[destroyer X]

Have you watched your brazilian brother thread, the Dx amplifier thread!

Qualé amigo, prestigia nossa gente..... ei!.... eu tou aqui!!!!

Hello my friend...your people is here.... can you see me?

You need power to bass amplifier.... several times more power than your mid range amplifier.

65 percent for bass
25 percent for mids
10 percent for treble.

So...having 1 watt amplifier, a full range unit... a portable player using a small computer speaker as amplifier, for instance, you will need a 6.5 watts amplifier to bass...unless you will have unballanced sound.

In the real world, we use 4 times the mid plus treble power...as you see the subwoofer systems doing this way...the good ones, unless those ones have that proportion.

I will invite you to visit Dx amplifier thread.... green and yellow thread man...people there talks portuguese...qualé amizade?

"Eu morei em Cambé e em Londrina, trabalhei como Chefe de Operações na TV Coroados, hoje pertence à TV Parana eu imagino."

I have lived in your place, your state, Cambé and Londrina were the place i have lived when had the charge of technical manager responsible for the televisions operation.... Enginnering department manager may be the name.... the television name was Coroados (crowded) and now belong the Paraná Network of Broadcasting.

Pisei na terra vermelha amigo...e não prestigias?

regards,

Carlos

[Shakal]

hehehe foi mal camarada! Agora que fui ver, quanta gente postou lá hein! Pode deixar que vou participar na thread verde e amarela!"

"Sorry dude! I just saw that, so many people replied huh? I gonna participate in the green and yellow thread!"

Thanks for the answers guys!

geminni, I know a little bit about these transformers... Please correct me if I am wrong:
In a normal transformer, I have the 2 wires... The +48 and the Ground... Actually, i think it doesn't matter, because it's AC.

In a central tapped transformer I have +24V, Ground, and -24V. Taking the tap to be the reference, I will have 2 times 24Vrms. But if I leave the tap unconnected I shall take one of the wires(+24V or -24V) to be the "reference" or ground. Then I'll have 48V rms in total, or a 67.9V peak. Retify it will give me 66.5V peak (losing 2x0.7 because of the diodes resistence). Then after filtering it by the Capacitor, assuming the frequency of the main supply 60Hz, the Current of 3A and the capacitance of 4400uF (2x 2200uf)... I will have 5.7V between the Vmax and Vmin. In the end... "5.7V / 2 = 2.85" and "66.5V - 2.85 = 63.65V" that is my Average Voltage, that if I'm right, is the 60V that the guy of schematics says.

Is that right, or I am totally nonsense?


destroyer X,

"So...having 1 watt amplifier, a full range unit... a portable player using a small computer speaker as amplifier, for instance, you will need a 6.5 watts amplifier to bass...unless you will have unballanced sound."

I think you mean 10 watt, right? But what I am trying to do is a Bass Amplifier, the instrument... I won't use any mid or treble.

The transformer is 48V and 3A, its 144Watt. Assuming a 20% of losses I will still have 115Watt. Twice of what I need to a 4ohm speaker.

Well... I think that's it! If I said something (or everything) wrong, PLEASE CORRECT ME!'

See ya!!

Obs: é estranho falar em "inglês" com um brazuka aUhaUhaU

[destroyer X]

Estranho é .... demais!................ very strange..and a lot!

O teu caso é especial..esquece do meu amplificador...não é bem indicado para você...na bôa!

Not your need..forget my amplifier... it is not good for your purposes...you can believe me...not good for instruments.

regards,

Carlos

[Shakal]

OK, thanks anyway for your help... But I won't forget ur amp... I want to make one of those too, when i finish this project maybe!

Sugestions for my project please?? Is everything OK? What I said about the power supply is right? What about the material and thickness!?

I need HELP!

[destroyer X]

Not more than 35 watts over 4 ohms and not more than 20 watts over 8 ohms.

It is not good to guitar amplifier too, as has not enought transistors in parallell to hold the enormous distortion guitar can produce.

Enormous overdrive too into the input.

Those darlingtons are not so strong as we use to think, and they normally oscilate till the destruction if you not solder a 560 picofarads condenser or even more from the colector to the base...in both darlingtons you have in the output.

To guitar, you have to find amplifier that have "overcurrent protection".... they are 2 small transistors that senses the voltage developed over the output emitter resistances, and reduces the signal into the earlier stage, reducing by this method, the output level and current.... this will protect the output devices.

This amplifier may be good for your first "do it yourself" amplifier....mine one need some previous knowledge...some basic experience.

Take a look in the schematic i am providing you....your supply will fit...not problems..... the strange transistors numbers you can replace by BD139 when NPN and BD140 when PNP..

I am talking about the protection...that Q9 and Q10...this will be needed for your bass work.

Good to start...but to be really happy you must use the Krell Klone made by Jan Dupont...and biased class AB....because you can increase supply voltage and produce a good power that is needed to a bass amplifier....you need more than 200 watts to use it as a professional...of course, to home use, a TDA2003 producing 10 watts RMS will be enougth.

Dx amplifier will not fit your need.

regards,

Carlos

[gaetan8888]

Hello

Maby that one would fit your need;

http://sound.westhost.com/project27.htm

Gaetan

[Minion]

I am actually in the process of building this very same Amp for Guitar and Bass....I have allready done the PCB design for the Pre and post stages and am useing the MJ11015/16 T0-3 transistors.....

if you want the PCB designs let me know.....


Cheers

[teemuk]

I built this amp once. Frankly put, it's horrible: The bias circuit doesn't work right since the Hfe of BD139 is too low for those component values - you will have plenty of nasty crossover distortion unless you redesign it. This circuit can also blow the amplifier if the wiper of the trimmer lifts during bias adjustment. There is no mains fuse (easy fix but still), there should be a buffer between volume control and the power amp, there is no output Zobel, there is no short circuit protection, the gain stages of the preamplifier had some mystical problems that kept them in constant saturation, etc. (I built the guitar version of this circuit where the tone controls and "harmonic modifier" were copied from Heathkit TA-17). I don't know whether it was due to an impedance mismatch or what but the tone control circuit was afwully "voiced". It's totally useless. 60 watts for bass doesn't sound like much.

I usually don't like to hammer down a design like this but this is just... bad. There are better designs and I dearly suggest you try one of them instead. Rod Elliott's guitar amplifier looks a lot more promising than this one.