Distortion

[Mukhalled]

Hi

I've built preamp + amp :
http://www.electronics-lab.com/projects/audio/039/index.html
http://www.electronics-lab.com/projects/audio/006/index.html

I've coupled them together and they work, but I get very high distortion when I increase the volume (when the bass is full ).
My question is : what can be the cause? Should I use larger speakers?

Thank you all for supporting me ;D

 

[audioguru2]

Hi Mukhalled,
What supply voltage, speaker impedance and speaker size did you use?

Philips datasheet for their TDA1554Q states that it produces typically only 12W per channel with a 13.2V supply into a 4 ohm load, with fairly low distortion. It also shows that it loses 30% of its power when the supply voltage is reduced from 14.4V to 13.2V (1.2V less). Therefore you could assume that again it would lose 30% of its 12W when the supply voltage is reduced another 1.2V down to 12.0V, so its power would be only 8.4W per channel.
Unfortunately, our project shows 12V as its supply.

If you use 8 ohm speakers, the power will be about half, which isn't much.

It is not a very powerful amplifier, about the same as ordinary car radios, so keep its volume turned down below distortion.

View attachment 36563

 

[Mukhalled]

Hi Audioguru
I used 15V DC , 6 ohms impedance and 12 cm diameter (2-way speakers).
Do you think 4 ohms impedace will do better? And what is the typical voltage supply do you think?
I believe you Theory Expert ;D.

Best Wishes
Mukhalled

 

[audioguru2]

Thanks for the compliment, Mukhalled.
I am glad that you are using 15V instead of only 12V as in our project.
Your problem is that your speakers are too small to have good efficiency and bass, and 4 ohms would produce more power than 6 ohms.

If it is for a car, get 6" X 9" (15cm X 23cm) 4 ohm 2-way car speakers with big magnets. Mount them on the back shelf so that the entire trunk is their box. I did that and it sounds very good and loud, with excellent bass that I can feel.

If it is for your home, get or build 8" (22cm) 4 ohm 2-way pretty-big speakers with tuned ports for good efficiency and bass. Usually home speakers are 8 ohms, so parallel them or use 8" 4 ohm car speaker-drivers. For many years that's what I had at home with an amplifier like yours and it sounded fine. Now I have a much more powerful amplifier that rarely gets turned up. Visitors ask me, "It sounds great, where's your sub-woofer?" I don't have one, just a little bass-boost circuit that I built. ;D

 

[Mukhalled]

Thank you so much Audioguru for the explanation ;D