TDA7265 Over 18V at 4 ohms

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Sh00pus

Member
2011-03-09 11:03 pm
I decided to build an amplifier with the TDA7265 with a 12.6-0-12.6V transformer which will give me roughly +/- 17.8V. But i know that transformer are not made perfectly and there will be some range, so my question is, what if my transformer ends up outputting more than 18V on each side. I looked the the output power vs. supply voltage for 4 ohm load and I see it ends beyond 18V. Will something bad happen or will it just have a higher output wattage?
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
what if my transformer ends up outputting more than 18V on each side. I looked the the output power vs. supply voltage for 4 ohm load and I see it ends beyond 18V. Will something bad happen or will it just have a higher output wattage?

Higher output power comes with bigger volume. The rated (max) output power brings very high distortion. You don't want to hear that. You may be disturbed cranking the volume, so expect only volume opening to give less than 10W.

But if you're crazy enough trying to hear the loudest sound, then before reaching max output power, the chip total dissipation will climb much faster and may break the chip. The lower the load (worst case is output short) the faster this to happen. So, monitor the chip temperature to find out the likely maximum volume for a known speaker.
 

johnr66

Member
2009-03-05 1:55 pm
With a 12.6-0-12.6 2.5a 63va transformer, you will get around 11 - 12 watts per channel with 8 ohms or 15 - 16w @ 4 ohms. This is continuous sine wave, both channels driven, no clipping. No problem at all as you are running the IC with a low supply voltage.

I'd rather run them a bit low rather than push them with near the limit supply voltages. If I need more power, I move on to a higher power IC.
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
BTW, what is your maximum power expectation (some of us are happy with 3W). I'm trying various chip amps to find the best one. My current amp (have been 2 days) is a TA... eww I forget. It is rated for 6W/8R/1%. But with carefully selected good parts, it is very good and you will agree that THD number is not as bad as it looks.

I will temporarily finalise it today and move to TDA2030V (previously I tried TDA2030A), or may be TDA7265, I'm not sure.
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
TDA7265 sounds OK on bass/mid duty but way too dull at the top.

If I'm not mistaken, that was the reason I didn't go with TDA7265 for my "extreme" project.

TA82XX is a better candidate. But I want to try TDA2030V first because I know how good it is.

New lessons learned from the latest/current project:
1) Sanyo Oscon is not good in signal path compared to regular BP/NP. But it is good as FB cap, as long as it is given a few hours to break in :D
2) Holco resistor is not good only in series FB resistor, but also in shunt FB resistor. "Better" than the gray Caddock resistor.
 

johnr66

Member
2009-03-05 1:55 pm
Isn't TDA2030V just a particular form of lead bend on what's the same die as TDA2030A? Or am I missing something? Seems to me that amps with LTP in the input stage are always hamstrung by that. Degeneration helps though - many of the LM3xxx have resistors in the LTP.

The TDA2030 is an IC with max supply voltage of +/- 18 volts. It can be in H or V suffix for mounting position (lead bend). Not sure if it is active or not. The TDA2030A seems to be only available in the TDA2030AV vertical mount according to the ST current datasheet. The A suffix denotes a part with a supply voltage of +/- 22 volts max.
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
If I'm not mistaken, that was the reason I didn't go with TDA7265 for my "extreme" project. TA82XX is a better candidate. But I want to try TDA2030V first because I know how good it is.

My small chip amp is an LA4270. Go search the datasheet, it doesn't have anything special. It's THD at 10K is 0.23% for 2W output. Acceptable still.

It took me two and a half day to tweak the amp for best sound. Tried several bypass cap values and brands, feedback resistor values and brands, input BJT buffer transistors, and at last it can sound beautiful enough.

So I built a TDA2030V several hours ago with basic parts. No way it can compare to my LA4270. Then I use better parts (BC/Philips for supply caps, Oscon for feedback cap, vishay 0.01% for FB resistors, Sanyo NP for input caps). Still, the LA4270 is way special.

From my experience building chip amps, it is impossible to get special sound without preamp. That's why I often use a single transistor in the input as a minimum substitute for the preamp. Haven't done this to the TDA2030V. I think TDA2030A is better than this TDA2030V.

So what chip amp next? I tried to check the datasheet for TDA7296. No way this chip can sound good. Here is a little secret of a good/bad sounding amplifier (example is a bad one, for TDA7296):
 

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Its probably the RF susceptibility of the input stage, that's the reason you find you can't get decent sound without a preamp. Try TDA8566, this is giving me the special sound without any preamp, but you do need very good PSU decoupling - ceramic caps I've found work well.

Looking at a THD vs level plot, what I think indicates bad sound is sharply rising THD at the lowest levels (<1W on this plot you're showing).
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
Its probably the RF susceptibility of the input stage, that's the reason you find you can't get decent sound without a preamp.

I have no idea. With chip amp I prefer a lower gain as chip amp distortion is relatively higher compared to discrete amp or preamp. With lower gain the drive suffers, also the amp more easily oscillate.

High frequency issues play an important role for a good/bad sound. Much more than most people know/realize I believe.
 
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