Hey.

So I have built a TDA2030 bridge amp while completely following the schematic in the datasheet. I works pretty well when I play some music from my cellphone or when I plug in a guitar, but when I plug in my bass, the sound is pretty distorted when playing low notes. It improves a bit when I turn the treble knob all way up, but otherwise it distorts. Just for the record - when playing some music from the phone, if there is some more prominent bass in the song, there is distortion again.

This is when plugging in any device directly, with no preamp or anything between the device and the amp.

I tried using a simple booster circuit made with a TL072 (I think) IC. Now the distortion gets even worse on the bass side. Additionally, when the booster circuit is turned near to the max, there is some nasty sound on the output, even when there is nothing on the input of the booster (the guitar is unplugged or just nothing being played). In attachments there is a short track showing the actual noise generated. Also, the same thing happened when I use a distortion pedal and turn it up even a little bit.

The speaker is definitely not the culprit. I use the ±12V rails from a PC PSU to power the circuit. The max current on the -12V side is 0.8A (as from what's written on the PSU at least).

The chips are properly cooled.

I am unsure if this could be some grounding problem (I am using shielded cable on the input BTW), or just a bad power supply, or maybe a faulty board (I double-checked the connections though), so any help is appreciated.

Thanks!

 

Hi
I played bass in top 40 bands through my first two years of college for extra money.

OK, so you bridged two TDA2030 together to make a 25 watt amp, right?
Your negative 12 volt supply is rated at .8 amps. Each amp at 14 watts out draws .9 amps. This might be your first problem, not enough power supply.

Describe your bass speaker, speaker diameter, box volume, port size/no port.

Mark

 

I measured the current on the -12V line while the amp was at peak volume - it exceeded 1A. The PSU seems to provide the needed output current.

As for the speaker, I can't supply all the data right now, just I know the speaker diameter is 6".

 

I measured the current on the -12V line while the amp was at peak volume - it exceeded 1A........

Did you measure the voltage? How far did it drop?

Mark

 

The voltage while zero load is ~-11.2V and it dropped by ~0.5V when loaded.

 

how abput coupling caps on the amps? too small, and they will limit the bass response.

 

The voltage while zero load is ~-11.2V and it dropped by ~0.5V when loaded.

Did you use a DMM or a scopeto measure the drop? A DMM would not normally show sharp large dips in the voltage; rather, it would show a sort of average.

 

Here is the schematic I used: http://prntscr.com/3ynf4a

I have marked the cap that (I think!) is the coupling cap. I just followed the values recommended in the datasheet..

Did you use a DMM or a scopeto measure the drop? A DMM would not normally show sharp large dips in the voltage; rather, it would show a sort of average.

I just used a DMM; it's the best option I have..

 

Then my guess is that bass peaks are pulling the supply voltage way below 12V and causing the distortion. IMO a more powerful and/or better regulated supply is needed.

 

Makes sense. But there is something else; why does the same distortion appear when the volume knob is turned down so the chances the PSU is overloaded are small?

 

Most likely your TDA2030 circuit is oscillating at high frequency.

The TDA2030 is very sensitive to layout and will oscillate at any chance given.

I have a friend working as an EE at a germany company (ibp.de) that designs calibration standards and such for medical equipment and what not, and even he was unable to get a TDA2030 to work properly.

 

I agree with Alec. The -12 volts does not have enough current capability.

Here is something you can try to prove it. Replace the -12 volts with a car battery or motorcycle battery.

Also, if you can run this amp with a +-15 volt supply you will get a LOT more power out of it.

 

Most likely your TDA2030 circuit is oscillating at high frequency.

The TDA2030 is very sensitive to layout and will oscillate at any chance given.

I have a friend working as an EE at a germany company (ibp.de) that designs calibration standards and such for medical equipment and what not, and even he was unable to get a TDA2030 to work properly.

I would imagine optimizing certain parts' values could help if the circuit might be oscillating?

I agree with Alec. The -12 volts does not have enough current capability.

Here is something you can try to prove it. Replace the -12 volts with a car battery or motorcycle battery.

Also, if you can run this amp with a +-15 volt supply you will get a LOT more power out of it.

I was thinking about buying a transformer with both higher power and voltage, but it's not that cheap and I need to know that the circuit will perform well after I buy it.

Could there be a problem of any sort if I use two different power sources (like the PSU and a car battery, or maybe the +12V rail of another PSU, since I don't know if I can find a battery)?

Thanks!

 

Using a battery and a PC power supply is no problem.

Using two two PC power supplies (one inverted) is complicated. The common of all of the output voltages is connected to chassis and to the ground pin of the power plug. You would have to keep the two chassis separate and disconnect the ground pin (not recommended.)

Another way is to open up the supply and find where the output common connects to chassis/ground and break(cut) the connection. Leave the chassis/ground pin connection intact for safety.

Mark

 

Uhm, I'll probably just cut the wire that connects the board to the chassis, because the PSUs are pretty old, so anything that might happen to them wouldn't be a big loss, and the testing time will be pretty short anyways.. I just hope I won't attend a firework show.

Thanks for the help to this point!

 

You are not going to get proper bass from a 6" speaker.
Also the size and design of the speaker cabinet is equally important.
Posting a photo might help us to assess the situation.

I play bass in a band and my home made bass amp has a 450W 12" woofer in a bass reflex cabinet.

 

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).

 

Uhm, this is just a practice amp, and according to me 12"/15" speaker would be an overkill. I really don't need the best sound from this amp, just the fuzz part really messes everything up.

Nevertheless, I'll send over some pics of the speaker/cab tomorrow.

Thanks!

 

Looks like you've already been told what the problem is here by Fast Eddie, try improving the -12V side and then start with the component values.

 

Yeah, I forgot to mention that. Seems that the caps replacement didn't do the trick either, so I'll try the thing with the PSU today.

Erm, I uploaded a pic of the speaker & the cab, as you asked.

Thanks!