Trial and error is easiest 🙂
To calculate is OK in theory, in practice you probably would alter it.
You need to know the max output of the amp... say volts rms before clipping, and the maximum output of the PC at an audio level of 0db, which is an absolute in the digital domain.
Knowing the gain of the amp, you calculate what input would correspond to clipping point and design the attenuator to give that level when presented with a "0db" max signal level.
Why no good in practice... because many recordings are at an average level way below the 0db point and you would find that the system wouldn't be loud enough on full volume... so trial and error is far better.
The easiest way is just use a pot, see what setting works best and then measure the resistances to the wiper and select nearest fixed resistors.
To calculate is OK in theory, in practice you probably would alter it.
You need to know the max output of the amp... say volts rms before clipping, and the maximum output of the PC at an audio level of 0db, which is an absolute in the digital domain.
Knowing the gain of the amp, you calculate what input would correspond to clipping point and design the attenuator to give that level when presented with a "0db" max signal level.
Why no good in practice... because many recordings are at an average level way below the 0db point and you would find that the system wouldn't be loud enough on full volume... so trial and error is far better.
The easiest way is just use a pot, see what setting works best and then measure the resistances to the wiper and select nearest fixed resistors.
I'm glad you mentioned this. This is what popped in my head when I realized I would need to attenuate the signal. This seems like it will take the least amount of time to dial in a good level.
Go for it. The chips are cheap and the build is easy. I'd like to know what you think of it.
Let me know if you want my PCB file. I can give you an Eagle file or just send you PDF's for etching the board.
That would be great a PDF file would be awesome.
that way I could just send it right to the printer.
thanks! jer
that way I could just send it right to the printer.
thanks! jer
No problem. I currently have three jumpers in the layout so I could easily remove the components from Mute1,Mute2,and ST-BY from the circuit. (found out I can remove Mute1 and Mute2, but ST-BY is needed for normal operation)
Would you like me to remove the jumpers or leave them for you?
I'm sure the jumpers would okay.
But I plan on using the amp without any mute or standbuy circuits active so that it is on at all times.
do you need my email address? jer
But I plan on using the amp without any mute or standbuy circuits active so that it is on at all times.
do you need my email address? jer
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Yeah, PM your email address and I'll send it out. I went ahead and took out the jumpers and components you won't need if running active in stereo mode. I increased the size of the pads a bit to make drilling easier. Board is ***really*** simple now.
Forgot to mention that there is no startup pop from this amplifier. Apparently this is built in but not mentioned in the DataSheet. I also notice in the DataSheet that the description seems to abruptly cut off with:
"The extremely reduced components count"
The extremely reduced components count what? Don't leave me hangin'!
"The extremely reduced components count"
The extremely reduced components count what? Don't leave me hangin'!
found the rest of the sentence after the absolute maximums table:
"allows very compact sets."
so:
"The extremely reduced components count allows very compact sets."
Phew! The suspense was killing me!
Update regarding noise from PC power supply:
I had already determined if a separate power supply is used with the PC, the noise is eliminated. I thought maybe its just the power supply on the PC I'm using so I tried 2 other PCs. Both had noise as well.
Today I discovered that if I used the PC power supply but supplied the signal from an outside source such as a laptop, the noise was gone.
At this point I suspect a ground loop as the common factor. I hook up a ground loop isolator on the signal and sure enough no noise. 😀 Yippee!
I would like to incorporate a ground loop isolator on my amplifier. Off to the internets I go for the best way to do this...unless one of you fine people can point me in the right direction. 😎
I had already determined if a separate power supply is used with the PC, the noise is eliminated. I thought maybe its just the power supply on the PC I'm using so I tried 2 other PCs. Both had noise as well.
Today I discovered that if I used the PC power supply but supplied the signal from an outside source such as a laptop, the noise was gone.
At this point I suspect a ground loop as the common factor. I hook up a ground loop isolator on the signal and sure enough no noise. 😀 Yippee!
I would like to incorporate a ground loop isolator on my amplifier. Off to the internets I go for the best way to do this...unless one of you fine people can point me in the right direction. 😎
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques
The ground loop breaker is at the bottom of the page.
The ground loop breaker is at the bottom of the page.
Hmmm, I'm thinking isolation transformers to eliminate ground loop may be the wrong approach. For one thing I can tell there is more than ground loop going on when the amp is hooked up to the same power supply the PC is using. I can hear noise from actions such as mouse scrolling. Also, this individual was able to overcome the noise issue with one 10 Ohm resistor:
4x15 Watt quad audio amplifier
Does anyone know if a similar solution could be applied to the TDA7393 I am using?
4x15 Watt quad audio amplifier
Does anyone know if a similar solution could be applied to the TDA7393 I am using?
Attachments
Ah, thanks.
I hope it works. I emailed the site owner for the amp build I posted and just received a reply. He had the following to say:
I'll give it a try and post back.
I hadn't noticed that. In that case you actually should not apply that resistor, because the supply current would flow through it and lead to a big voltage drop across that resistor.
What you can try to do is to provide only one GND connection between amp and PC. You have four GND terminals on your PCB. Disconnect the GND wires from the input and stand-by terminals and see, if the noise becomes less. For a loop you need at least two paths. Is the heatsinking tab isolated from the computer case to avoid another path to the PC's GND?
What you can try to do is to provide only one GND connection between amp and PC. You have four GND terminals on your PCB. Disconnect the GND wires from the input and stand-by terminals and see, if the noise becomes less. For a loop you need at least two paths. Is the heatsinking tab isolated from the computer case to avoid another path to the PC's GND?
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