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Old 17th June 2010, 10:35 PM   #1
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Question Bass distortion ..!!

hi
i wanna ask what`s the reason behind distorted bass at a little high volume . i built a tda7294 bridge amp with pre amp TLo72 it sounds great even at high volumes but bass isn`t deep enough so,i decided to use a tone control circuit based on tda1524a the production of bass is now deep enough at low volume but at a little high volumes it became distorted although i am using 25-0-25 10amp. transformer with 22000 mf per rail . is the reason behind this distortion is the type and wattage of speakers _as i am using two 8" brandless speakers -??
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Old 18th June 2010, 01:13 AM   #2
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When you use the tone control to get more bass, that means that the signal level of the low frequencies is much higher than the overall signal level.
Therefor, when you turn up the level, the low freqs are the first that get to the max output signal level of the amp and the amp will clip the low freqs. That causes the distortion.
Increasing the wattage or amperage of the transformer or the value of the caps doesn't help; the only thing that helps is either speakers with higher efficiency (they sound louder with the same signal level) or an amp that can deliver more signal level - which in practise means higher supply voltage meaning a higher power amp.

What enclosure are the speakers in?

jd
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Old 18th June 2010, 11:33 AM   #3
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hi
thnx for ur cooperation,it`s dual 8" in sealed enclosure every one is 8 ohm and i am connecting them in parallel to get 4 ohm load
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Old 18th June 2010, 11:52 AM   #4
asbjbo is offline asbjbo  Norway
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If your amp is in bridged configuration, it will "see" half the actual loudspeaker impedance. In other words, you are asking the TDA7294 to drive a 2 ohm load in a frequency band where efficiency is quite low. That will need a lot of current.
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Old 18th June 2010, 01:01 PM   #5
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Quote:
Originally Posted by asbjbo View Post
If your amp is in bridged configuration, it will "see" half the actual loudspeaker impedance. In other words, you are asking the TDA7294 to drive a 2 ohm load in a frequency band where efficiency is quite low. That will need a lot of current.
Yes, good point! That may trigger the protection systems (which will sound bad).
Maybe a solution is to 'unbridge' the amp and let each amp drive one 8 ohms speaker.

jd
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Old 18th June 2010, 01:57 PM   #6
asbjbo is offline asbjbo  Norway
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I looked at the datasheet at http://www.st.com/stonline/books/pdf/docs/1057.pdf. It says:
Quote:
Another application suggestion is the BRIDGE
configuration, where two TDA7294 are used, as
shown by the schematic diagram of figure 25.
In this application, the value of the load must not
be lower than 8 Ohm for dissipation and current
capability reasons.
It seems like a better idea to use each chip to drive one 8" speaker, as suggested by janneman.
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Old 18th June 2010, 02:16 PM   #7
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ok i`ll do this and see the result thnx again
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