hi tom!
i guess i was kind of looking for a plug and play solution to take the led from the smps to the front of the chassis. something like a lead with an led plug on it. i guess just soldering wire to the pins will be the easiest solution. sometimes i forget that i recently learned how to solder .... well the basics at least.
i have another question regarding the testing of the lm3886dr. if i test it using a voltmeter, should it be hooked up to speakers at the same time? i have a feeling that turning it up to an output of 10v ac could get very loud and i don't want to damage my speakers...
apart from that i already gave it a test drive which i described in post #211.
today the enclosure will arrive from italy
i guess i was kind of looking for a plug and play solution to take the led from the smps to the front of the chassis. something like a lead with an led plug on it. i guess just soldering wire to the pins will be the easiest solution. sometimes i forget that i recently learned how to solder .... well the basics at least.
i have another question regarding the testing of the lm3886dr. if i test it using a voltmeter, should it be hooked up to speakers at the same time? i have a feeling that turning it up to an output of 10v ac could get very loud and i don't want to damage my speakers...
apart from that i already gave it a test drive which i described in post #211.
today the enclosure will arrive from italy
The first/main thing to test is DC offset. This is the voltage measured across the speaker terminals without speaker connected and no input How to Measure DC Offset: 5 Steps (with Pictures) - wikiHow
i just measured DC offset and it's 3,9 mV for the left channel and 3,2 for the right. the manual says it should be below +/- 10mV os I guess I'm good.
i noticed that the dc offset actually rises as soon as i turn off the power supply. It's currently at 210mV. That's about 5 minutes after turning off the amp. why is that?
and back to the original question:
if i test the gain using a voltmeter, should it be hooked up to speakers at the same time? the manual says to turn up the input signal to 500mV to get a 10V output signal. I have a feeling that turning it up to an output of 10v ac could get very loud and i don't want to damage my speakers...
i noticed that the dc offset actually rises as soon as i turn off the power supply. It's currently at 210mV. That's about 5 minutes after turning off the amp. why is that?
and back to the original question:
if i test the gain using a voltmeter, should it be hooked up to speakers at the same time? the manual says to turn up the input signal to 500mV to get a 10V output signal. I have a feeling that turning it up to an output of 10v ac could get very loud and i don't want to damage my speakers...
so the building process slowed down a bit because i dislocated my shoulder the other day and that doesn't really make working on an amp much easier.... :-(
i just finished putting all the components in the enclosure and they all fit fine. the back is still open as i need to finish drilling all the holes for the inputs and outputs.
i did a gain test and with an input of 8,7mV from my iPad one channel (out) reads 178,9mV and the other 178,4. so i guess that equals a db gain of 26 which would be according to spec.
there's still a little noise coming from the speakers - well apart from the music that is it's really faint and sounds like an rf interference or something. it's not a big thing but it really bothers me. let's see if it goes away as soon as i finish the enclosure.
i just finished putting all the components in the enclosure and they all fit fine. the back is still open as i need to finish drilling all the holes for the inputs and outputs.
i did a gain test and with an input of 8,7mV from my iPad one channel (out) reads 178,9mV and the other 178,4. so i guess that equals a db gain of 26 which would be according to spec.
there's still a little noise coming from the speakers - well apart from the music that is
it's really faint and sounds like an rf interference or something. it's not a big thing but it really bothers me. let's see if it goes away as soon as i finish the enclosure.
"An RF interference or something"? I'm guessing "something" as the RF is attenuated by the input filter (-40 dB at 8 MHz).
Is the noise white? I.e. a faint hiss? Or is it more of a buzz? Or is it hum?
Does the "something" go away when you short the inputs? I.e. connect the RCA centre pin to the RCA shield with a shorting plug or piece of wire?
The LM3886 is not the quietest amp in the world, but with 40 uV RMS that I normally measure, I can't hear any hiss when I put my ear against the speaker. If you're using medium-efficiency speakers (85-90 dB SPL @ 1 W, 1 m) your setup should be pretty quiet. How efficient are your speakers?
Tom
Sorry if i might have used the wrong term. I'm having a bit of a hard time describing it.
It's definitely not white noise or hum. I'd say it's more of a buzz with some higher pitched peeps - it's not constant. It reminds me of the sound you got holding an older mobile phone close to a radio.
My speakers are rated at 89db.
No, I have not tried shortening the inputs. I'll try that tomorrow morning.
It's definitely not white noise or hum. I'd say it's more of a buzz with some higher pitched peeps - it's not constant. It reminds me of the sound you got holding an older mobile phone close to a radio.
My speakers are rated at 89db.
No, I have not tried shortening the inputs. I'll try that tomorrow morning.
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Are you referring to the connection between the grounding lug on the power supply and the Chassis?
I tried shortening the inputs - no difference. I turned of my wifi without noticing any difference. The only thing that did make a difference was unplugging my fan which i use in the same room - the noise from the speakers almost disappered. Also i noticed that the noise increases as soon as the amp is connected to a sound source. Even if the source is turned off.
Another question for Tom: Can you tell me what the input impendance of the lm3886dr is?
The input impedance of the LM3886DR is 47 kΩ.
Some fans emit a fair amount of noise when they run. Putting the amp in an enclosure will likely help there. If the noise increases when you connect the signal source, you're either hearing the noise of the source being amplified or you're dealing with a ground loop. Do you have the ability to lift the ground on either the source or the amp?
Tom
Some fans emit a fair amount of noise when they run. Putting the amp in an enclosure will likely help there. If the noise increases when you connect the signal source, you're either hearing the noise of the source being amplified or you're dealing with a ground loop. Do you have the ability to lift the ground on either the source or the amp?
Tom
Thanks, Tom!
To be honest I wouldn't know how to "lift" the ground. I'm not sure what it means. If it involves disconnecting some cables inside the amp I'd be able to do it if I'd only know which ones. Sometimes it really does suck to not know what I'm really doing here....
But hey there's also good news. Apart from the unwanted noise from the speakers (which is completely inaudible as soon as the music is on) everything works just fine and I'm really enjoying this amp. So I already reached 95% of my goal. I'll post some pictures as soon as I made progress with the enclosure.
To be honest I wouldn't know how to "lift" the ground. I'm not sure what it means. If it involves disconnecting some cables inside the amp I'd be able to do it if I'd only know which ones
. Sometimes it really does suck to not know what I'm really doing here....But hey there's also good news. Apart from the unwanted noise from the speakers (which is completely inaudible as soon as the music is on) everything works just fine and I'm really enjoying this amp. So I already reached 95% of my goal. I'll post some pictures as soon as I made progress with the enclosure.
Ground lift or Loop Breaker, see here Earthing (Grounding) Your Hi-Fi - Tricks and Techniques