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Electric bass headphone amp with PAM8403
Electric bass headphone amp with PAM8403
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Old 2nd April 2020, 03:39 AM   #11
PRR is offline PRR  United States
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Electric bass headphone amp with PAM8403
There *really* are better chips for headphone amps. You do not need class D for a milli-Watt job. You do NOT want bridge-mode output for common 3-wire headphones.
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Old 2nd April 2020, 04:34 AM   #12
cbdb is offline cbdb  Canada
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Probably doesnt have a high enough input impedance for a passive guitar. And its 5 watts into 4 ohms it will be a lot less into high impedance headphones.
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Old 2nd April 2020, 07:00 AM   #13
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by cbdb View Post
Probably doesnt have a high enough input impedance for a passive guitar. And its 5 watts into 4 ohms it will be a lot less into high impedance headphones.

You are right that it will be much less than 5W in high impedance headphones.

Without knowing much about headphones, 200mW in 32 Ohm should be quite decent. 200mW in 32 Ohm requires a voltage of 2.5Vrms which is possible because the PAM8403 has a BTL-coupled output.
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Old 2nd April 2020, 07:10 AM   #14
FauxFrench is offline FauxFrench  France
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Originally Posted by PRR View Post
There *really* are better chips for headphone amps. You do not need class D for a milli-Watt job. You do NOT want bridge-mode output for common 3-wire headphones.

I fully agree it is not an obvious or rational choice. The initial question from the OP was if it "would work" and my impression is that it is possible to make it work.
Sometimes you have such items lying around and like experimenting with their use. As a commercial product it is no good.

Last edited by FauxFrench; 2nd April 2020 at 07:13 AM.
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Old 2nd April 2020, 09:15 AM   #15
francescoboc is offline francescoboc  Italy
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Originally Posted by FauxFrench View Post
I fully agree it is not an obvious or rational choice. The initial question from the OP was if it "would work" and my impression is that it is possible to make it work.
Sometimes you have such items lying around and like experimenting with their use. As a commercial product it is no good.
Yes, that's exactly my situation. I found this little thing in a drawer (I don't even remember how/when I got it), and I thought I might try to build an headphone amp for my bass, since I don't have one (and since I am quarantined...). I could, of course, buy a better chip, but I think it would be fun to see what can come up with this one.

Unfortunately, I cannot really start right now, because I realised I am missing other pieces (the 470uF cap, and the female audio jack for connecting the earphones)... So for the moment, I am just gathering information.

For the headphones, I will be using Sennheiser HD 205, which have 32 Ohm impendance.

Could you guys/girls please elaborate on this statements? I don't really understand what you are talking about...

Quote:
Originally Posted by PRR
You do NOT want bridge-mode output for common 3-wire headphones.
Quote:
Originally Posted by cbdb
its 5 watts into 4 ohms it will be a lot less into high impedance headphones.
Quote:
Originally Posted by FauxFrench
200mW in 32 Ohm should be quite decent. 200mW in 32 Ohm requires a voltage of 2.5Vrms which is possible because the PAM8403 has a BTL-coupled output.
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Old 2nd April 2020, 09:27 AM   #16
chermann is offline chermann  Austria
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Hi Francesco.


i try point 2 and 3:
electrical power is the product of power P = Voltage U * current I => P=U*I
if you but in ohms law , U=I*R then you will get P= U^2/R or P= I^2 *R.


so the resistor = speakers impedance = headphones impedance , yours 32ohm at the same level of output voltage limit the current and therefore the electrical power. but as FF wrote enough for headphones.
P = U^2/ R = (2,5Vrms ^2 )/ 32R = 0,195Watt or 195mWatt
if you would use a 16ohm headphone- less resistance more current

P = U^2/ R = (2,5Vrms ^2 )/ 16R = 0,390Watt or 390mWatt


for point 1 by PRR i am not sure what he mean....but he will give us an answer

chris

Last edited by chermann; 2nd April 2020 at 09:52 AM.
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Old 2nd April 2020, 05:31 PM   #17
cbdb is offline cbdb  Canada
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32 ohm hps should be loud enough, I was worried they where over 100 ohms. The 2 problems I can think of are: guitars usualy need high impedance inputs, 1 meg, and most bass amps have a lot of bass eq.
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