OK, your speaker/cabinet is marginal for a low level bass guitar practice amp. So, I think your distortion is coming from your amplifier. How is your power supply fix coming?

Mark

 

I think it's time to beg or borrow an audio sine generator and a 'scope to see the waveforms.

Without those it is a lot of "guessing in the dark" and that's a lousy way to try to fix things.

 

OK, your speaker/cabinet is marginal for a low level bass guitar practice amp. So, I think your distortion is coming from your amplifier. How is your power supply fix coming?

Mark

I would say it's a bit better with both +12V and -12V levels being powerful enough. Still, there is some distortion present when the circuit I use as a preamp is turned almost all way down, and if I turn it up a bit it sounds like I have a fuzz box cranked up to it's max instead.

I am thinking about buying a transformer for the circuit. However, it's a 30W one (I am unsure if that is enough, but the next available power is 60W and that is double the cost of this one). Also, it has ±12V and ±18V. However, as far as I know the voltage is multiplied by a certain factor after using a diode bridge to convert it to DC, so I'll probably get ±14-15V. Please let me know if the 30W one will be okay.

I think it's time to beg or borrow an audio sine generator and a 'scope to see the waveforms.

Without those it is a lot of "guessing in the dark" and that's a lousy way to try to fix things.

I am afraid I can't find an o'scope any time soon....

 

and if I turn it up a bit it sounds like I have a fuzz box cranked up to it's max instead.

That is probably a result of the amp input stage being over-driven.

 

That is probably a result of the amp input stage being over-driven.

Can higher supply voltages (>=15V) help?

 

Can't say without seeing the amp schematic. You risk letting out the magic smoke if the volts go above the designed/rated value.

 

The circuit can definitely handle at least ±14V, because that's what written in the datasheet (actually ±18V for the chip, but for the bridge configuration it's ±14V, so it could possibly go even higher).

 

...
I am afraid I can't find an o'scope any time soon....

Little "DSOnano" 'scopes can be bought brand new all over Ebay for about $73;

 

STOP!!!

Do NOT NOT NOT buy any of those so called pocket scopes!!! They are merely kids toys and are TOTALLY USELESS!!!

Schools and institutions are more or less giving away good but old _CRT based oscilloscopes these days.

 

for 73 dollars you can get even quite high end tektronix brand scopes if you look hard enough.

 

I know that buying any o'scope for ~75 bucks would probably be a good investment since it could come handy for some other circuit too, but if I was willing to spend that money at the moment, I'd rather buy an amp with an equal, if not better quality than the one I working on at the moment.

I'd like to ask again; would a 30W transformer be enough for this circuit (with ±18V on it's outputs, which I might lower down to ±15V, but the current draw would stay the same).

Thanks!

 

And even a 12" driver is considered less than optimal, most bass players will go for a 15" driver. Especially in heavy rock with 5 string Bass guitar (low B string).

Yes, anything smaller than a 15" is too small.

I say anything under 1000 Watts and run through 2-18" folded horns, is too small for Bass.

In the 1960s anyway!

 

My 12" is better than your 15". It's not the size but the quality that counts.
It's the driver behind it that matters.

 

STOP!!!

Do NOT NOT NOT buy any of those so called pocket scopes!!! They are merely kids toys and are TOTALLY USELESS!!!
...

That's a very strong (and LOUD) opinion!

They are not "totally useless" they are extremely useful for audio frequencies. They also perform measurement and averaging features, logic analysis and frequency readout etc, many features that you just won't get on an older analgoue 'scope.

The screen size is 320x240 pixels which was a standard for full-size desktop digital 'scopes too for many years. So you can;t really blame the screen resolution making it "useless"...

In fact once you add in the pocketability its FAR better than an old analogue scope in just about every way apart from high MHz bandwidth.

Which his bass amp doesn't need.

 

My 12" is better than your 15". It's not the size but the quality that counts.
It's the driver behind it that matters.

For a lot of years, I ran a Rickenbacker 4001 through 2-500 Watt amps in stereo.
Each cabinet held 2-15"s. One cabinet on each side of the stage.

But, the best was through 2-18" folded horns. 1200 Watts.
Then, on to the house PA.

That rig was heavy, and bulky as hell, but you could feel the Bass in your gonads and heart.

Played all styles of music, but it really excelled at the old, Classic Heavy Metal, such as Black Sabbath, Foghat, Queen, AC/DC, etc., "Arena Metal".
That rig was so versatile, I even used it in Jazz, top 40, and Country bands.

Nowadays, I run through a 1-15" Peavey cabinet, and another Crate cabinet with 1-18" and 2-10"s.
Very versatile set-up.

What I cannot stand, is those cabinets with 8-10" aluminum speakers. Makes a Bass amp, sound like a guitar amp.
No Bottom or Balls.
They will never replace the old Ampeg, 8-10s paper-woofer, cabinets.

 

The 18 inchers separate the men from the boys!

I've got a single 15" in a nice little portable 100W RMS amp. Quite capable of shaking all the windows, and good down to a low B, but that's in a house... Not suitable for a stadium.

 

I agree with THE RB about the DSOnano scope. It has a 1 MHz by 12 bit sample rate. It is perfect for audio trouble shooting. If you like building stuff like this, you will love having it. And guess what, if you can build it, you can repair it, which will always be a source of income. In my early years, music stores always had amps that needed repair, which turned into good money for me. A musician with electronic talents is valuable. Go for it.

Mark