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Pre amplifier

S-fr

New Member
I was wondering if i can use pam8403/8601 as a pre amp so that the audio volume wont go down due to bass, is it a good idea?
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Sorry, not enough information.

The PAM8403 is a Class D (switching, PWM) power amp intended to directly drive a loudspeaker or headphones, it's not really suitable as a preamp in any way I can imagine?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Well, as already pointed out, you've provided almost zero information - and attempting to use a power amp as a preamp is a really silly idea, which is unfortunately commonplace across the Internet, with projects from people without a clue.

However, (from what I can 'guess' from your lack of information) it sounds like your power supply isn't up to the job. As bass volume goes up, current consumption increases - greatly - voltage drops, volume drops.
 

S-fr

New Member
Well, as already pointed out, you've provided almost zero information - and attempting to use a power amp as a preamp is a really silly idea, which is unfortunately commonplace across the Internet, with projects from people without a clue.

However, (from what I can 'guess' from your lack of information) it sounds like your power supply isn't up to the job. As bass volume goes up, current consumption increases - greatly - voltage drops, volume drops.
Im using tpa3116d2 on a 4ohm load with a 18v 6a power supply, it is not a huge but a noticeable drop on volume, i saw some video on YouTube where people use 3w power amplifier as a solution for this, so i am just asking if its safe, because of the frequency output from 8403 seems quite high for 3116d2
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Im using tpa3116d2 on a 4ohm load with a 18v 6a power supply, it is not a huge but a noticeable drop on volume, i saw some video on YouTube where people use 3w power amplifier as a solution for this, so i am just asking if its safe, because of the frequency output from 8403 seems quite high for 3116d2
Just use an opamp - simple, cheap, and high quality. I've no idea what you mean by 'frequency output', it makes no sense.

But if you've got an audible drop in volume it would be better trying to find out why, rather than 'bodging' it.

It could be that you're overloading the power amplifier?, and increasing the drive to it will only make it worse.
 

audioguru

Well-Known Member
Most Helpful Member
When the power supply cannot produce enough current causing its voltage to drop when the amplifier plays bass frequencies then the output volume does not change, Instead the output becomes severely clipped with very high distortion if the output level is high.

Your power supply is 18V x 6A= 108W. The datasheet for the TPA3116 shows 35W per stereo channel into 4 ohms.
The amplifier is 88% efficient so the heating per 35W channel is 5W for a total power of 35W + 35W + 5W + 5W= 45W.
Then your power supply has a transformer and/or filter capacitors too small for the amplifier to produce 70W of bass.

OR you are playing acid rock "music" that has so much distortion that you cannot hear when your amplifier is clipping.
 

audioguru

Well-Known Member
Most Helpful Member
All the You Tube sound system videos from India and Pakistan and have no enclosures for the woofers so of course they produce no bass when powered with only 2W per channel from a PAM8403 amplifier. Then the PAM8403 is used as a preamp and they make a very powerful amplifier to overdrive bass into the woofers.
 

crutschow

Well-Known Member
Most Helpful Member
When the power supply cannot produce enough current causing its voltage to drop when the amplifier plays bass frequencies then the output volume does not change, Instead the output becomes severely clipped with very high distortion if the output level is high.
Wouldn't a Class D amp, as this is, possibly just reduce its output with a drop in supply voltage rather than significantly increasing distortion (assuming the Class D modulator stays operating normally)?
 

audioguru

Well-Known Member
Most Helpful Member
Wouldn't a Class D amp, as this is, possibly just reduce its output with a drop in supply voltage rather than significantly increasing distortion (assuming the Class D modulator stays operating normally)?
I have never tried a class-D amplifier, BUT the output distortion rises as steeply as a linear amplifier above clipping.
The TPA3116 datasheet shows distortion vs output power with a 24V supply and and 8 ohm load.
At 1kHz the output power is 31W when the severe distortion begins at 0.06%.
At an output of 41W, which sounds only a little louder, the distortion is horrible at 10% due to clipping.
 

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