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Mini3, what did I do wrong? right channel only

post #1 of 10
1/24/10 at 3:37am
Thread Starter 
Hello everyone,

I just finished assembling my AMB mini3 amp for the first time and gave it a whirl. Immediately, I noticed a staticky hiss when the amp is turned on with the source playing but the hissing disappear when I turn the knob further for more juice. Is that normal?

The biggest issue I have so far is when I plug my earphones all the way in the mini3, I can only hear the music from my right monitor clearly but the left monitor is quiet.

But when I pull the earphone cable out of the mini3 and gently press the 3.5mm earphone plug partially into the mini3 out socket, only touching it, then I can hear from both ears. Only when I press the earphone plug completely into the amp, that's when I can only hear from my right monitor. Any ideas?
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post #2 of 10
1/24/10 at 9:32am
I don't know about the hiss, but I guess that when you completely plug it in the 3.5jack makes a bad contact. This could be a fault in the jack.

You say that the R = ok
the L = ok when partialy out of the channel.

Are you sure that when you say that you can hear with both ears when partially plugged in, that it isn't just the same right signal on both sides? When partially plugged in it could be that the contact of the R channel in the onboard jack touches both L and R of the 3.5Jack at the same time. If so, this could indicate that the onboard jack is bad or the whole L channel, which is even worse.

If the signal is indeed just as it should be (stereo) and the L channel comes through as it should when you partially plug it in, then it's probably just a bad female jack.

Dries
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post #3 of 10
1/24/10 at 9:48am
Sounds like you've killed the U5 opamp which is a bit of a pain to fix. I'm guessing when you're part way into the jack you've got the same channel in both ears, when you're the whole way in and the left ear is soft it's probably crossfeed in the earphone cable.

Check your current draw and DC offset and see if it's normal.
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post #4 of 10
1/24/10 at 2:56pm
I'd agree with Menisk... you are probably listening to one channel on both. Go through the initial check section of Amb's website: The Mini³ Portable Stereo Headphone Amplifier
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post #5 of 10
1/24/10 at 3:21pm
Thread Starter 
thanks for the quick replies, I'll go check it out.

you guys might be right about hearing the right channel on both ears when its partially plugged in because when I tested it out with Baba O'Rielly by the Who, I could not hear the piano playing at 0:49
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post #6 of 10
1/24/10 at 3:23pm
Long story short; I had a similar problem, and it turned out to be
a fault with the board that was shorting out one of the channels.

Before you start replacing things, check your board very carefully.
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post #7 of 10
1/24/10 at 6:15pm
ewynn, you'll have to follow the initial checks on the Mini3 site and if/when you get a result that doesn't line up with the result expected, paste your result here and we can go from there.
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post #8 of 10
1/25/10 at 5:00am
Thread Starter 
Quote:
Originally Posted by CodeToad View Post
ewynn, you'll have to follow the initial checks on the Mini3 site and if/when you get a result that doesn't line up with the result expected, paste your result here and we can go from there.

thanks codetoad! I'll try to do it
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post #9 of 10
1/25/10 at 2:57pm
I faced almost the same problem when I was building mine. I am sorry to say but I think your U5 opamp is gone. It is a pain in the but to replace, just make sure you have checked all other obvious stuff like shorts cold solder etc.. before you attempt to replace the U5.

I wonder if there are any other more robust opamp to use in the mini in place of the two versions recomended by AMB.
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post #10 of 10
1/26/10 at 1:34am
Quote:
Originally Posted by gabriel-dan View Post
I wonder if there are any other more robust opamp to use in the mini in place of the two versions recomended by AMB.
The two versions were carefully chosen to provide the best combinations of output voltage swing and output current capability, given the low supply voltage. One skews more toward outright performance while the other toward battery saving, but both could swing all the way to the rails and give respectable current output. I've yet to find any other opamp combos that satisfy all these requirements.

The chosen opamps are quite robust once the build is done and cased. Virtually all blow-outs are due to mistakes during assembly and testing.
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