TDA7266M Amplifier, little/no base - Page 1
Forum section: electronics / projects

author: spilihps
author_rank: Regular Contributor
timestamp: October 20, 2018, 12:17:19 pm
content: Hello!So i "wired" up a small and simple amplifier project on a prototype board. For a little radio project im working on.To much of my surprise it really sounds good. Both very low noise and the clarity is really great.However, the bass is very low or almost none existent. Firstly i thought it might me my Si4703 FM chip that is not tuned properly. So then i tried both my mobile phone, and a regular stereo as input. And its really really low base on those also.Im not sure what im missing, My output is a regular Samsung 6ohm 20w bookshelf speaker.The circuit consists of the two diagrams attached to this. The TDA7266m is from the datasheet, and the tl072(used as a pre-amp) is from the link in the picture.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: October 20, 2018, 01:12:50 pm
content: Try with a bigger cap on the input; with those 0.22u and the input impedance, you have a high pass with a -3dB corner freq. of 24Hz. Go with 1u for a try

author: MasterT
author_rank: Frequent Contributor
timestamp: October 20, 2018, 03:25:29 pm
content: TL072 can't work at +5,Quotehttp://www.ti.com/lit/ds/symlink/tl072.pdf

author: Audioguru
author_rank: Super Contributor
timestamp: October 20, 2018, 03:30:12 pm
content: EDIT: Its (+) inputisbiased at half the supply voltage.Of course the TL072 needs a minimum supply voltage of 10V but more is better.Why is the preamp inverting with an extremely low input impedance of 1K? The datasheet for the radio IC says that its minimum allowed load is 10k. Maybe that is why the bass is cutoff.All my preamps are non-inverting with an input impedance of at least 100k.

author: spilihps
author_rank: Regular Contributor
timestamp: October 20, 2018, 03:38:03 pm
content: Sorry, i might have attached the wrong schematics on the 072.I do remember that i changed the design due to a problem with the first one i tested.I am out right now but will confirm this when i get home againBut it is fed with the same supply as the TDA about 12v.

author: spilihps
author_rank: Regular Contributor
timestamp: October 20, 2018, 08:09:46 pm
content: Thanks guys for your help.I can confirm that i posted the wrong TL072 circuit.Also tried to feed the main amp directly and the bass is back.However, always fun to learn something new, so why not.So the problem is in the pre-amp that i have apparently failed miserably withSo instead of hunting down what circuit i did go for i better just hook up a new one.Do you guys have an idea or pointer on a circuit that would be suitable?

author: MasterT
author_rank: Frequent Contributor
timestamp: October 20, 2018, 09:32:50 pm
content: http://www.redcircuits.com/Page60.htm

author: spilihps
author_rank: Regular Contributor
timestamp: October 20, 2018, 10:01:24 pm
content: Thanks! That’s a great link with information also.However it calls for 20v minimum. I would like to be at 12V or 15V. would it be to far off?

author: MasterT
author_rank: Frequent Contributor
timestamp: October 20, 2018, 10:17:18 pm
content: Anything between +10 and +30 is fine

author: spilihps
author_rank: Regular Contributor
timestamp: October 20, 2018, 10:34:51 pm
content: Great! Thanks.Will try to build this and report back. Really like the bass-boost feature, going to be fun to play around with!