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Bubba Zanetti 12th December 2005 02:53 PM

TDA 7294 amp with horns problems

I made chip amp based on TDA7294 about 8 years ago - it was very well made with large power supply and with my old floorstanders (DIY 2 way, with 6.5" poly cone and 2" soft dome tweeter ,around 88db/w sensitivity) it gave me years of very pleasent and relaxed sound.

I recently made Beyma "The Viech" back loaded horns and when I connected them I instantly noticed strange harsh sound at low listening levels that I never heard before - I thought it was maybe due bad recorded CD or Beyma 2nd resonance peak and went on with listening, but after few days of listening - the things are like this:

- on every CD that annoying harsh sound exist, it can be heard especially on guitar passages, on electronic music it's little more pleasent but is still there,
- it sounds very similar to clipping,
- it's noticable only on particular low to normal listening levels - I measured with DMM it's happening always under 1 volt on amp output,
- it raises midrange output and bass is sometimes so distorted that I thought couple of times that amp went dead ,

I am thinking is it possible that I am hearing crossover distortion due 96dB Beyma sensitivity that I never noticed before with my old speakers ?

Sound is excellent BTW in all other listening levels - extremely loud and extremely quiet...clean, powerful and undistorted.
Amp heatsink is always cold or slightly warm in case of very loud listening volume.

Beyma driver already played music over 200 hours , so it is already broken in...

Tnx for help in advance !

Bubba Zanetti 30th December 2005 03:00 PM

Hmmm, it seems that problem is in fact related to proper operating temperature of the amp.:)

I noticed that after cca 4 hours of listening sound always became much different:less harsh and more balanced, much, much better.

With old speakers that effect existed but it wasn't SO obvious, with horns almost 70% percent of my CD's are unlistenable when amp is just turned on and cold...:mad:

And one another interesting thing, even with high efficiency speaker and 70W amp I still prefer larger capacitance in power supply: bass is much tighter, defined and stronger, I can't imagine how can somehow live with 1000uF per rail + under 90dB/W speaker combination as seen in many GC's, maybe only for vocal music - bass must be extraodinary weak...but anyone has it's own taste, I assume.

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