I have built a LM3886 amplifier with part of SMD components, however, oscillation occurred. What can I do?
I haven't got an oscillscope in my home to detect the details of the osc. however, the ICs generate heat at a short moment after I have connected the power. Thus I'm quite sure it would be in oscilliation.
Could anyone help me to rectify this problem, many thanks.
Cheers
I haven't got an oscillscope in my home to detect the details of the osc. however, the ICs generate heat at a short moment after I have connected the power. Thus I'm quite sure it would be in oscilliation.
Could anyone help me to rectify this problem, many thanks.
Cheers
It would be best to describe the test setup. Load connected, no load, is there input connected, schematic, etc.
you have to be an editor to pick it up:
this is clipped from the bottom of the article you referenced:
<em><b>transration by Yoshi and Irene Segoshi</em></b>
yeah, I was an editor in a prior life.
this is clipped from the bottom of the article you referenced:
<em><b>transration by Yoshi and Irene Segoshi</em></b>
yeah, I was an editor in a prior life.
Hi Rachel,
Which LM3886 circuit did you built? There are a few floating around and I have built quite a few (for the bedroom amp and for the TV speaker replacement). Very fortunately (touch wood), I did not encounter any oscillation problem.
I suspect you have hums (i.e. ground loops) in your system, instead of oscillation caused by positive feed back. Maybe you may need to describe the symptom a bit more.
Which LM3886 circuit did you built? There are a few floating around and I have built quite a few (for the bedroom amp and for the TV speaker replacement). Very fortunately (touch wood), I did not encounter any oscillation problem.
I suspect you have hums (i.e. ground loops) in your system, instead of oscillation caused by positive feed back. Maybe you may need to describe the symptom a bit more.
Amplifiers want to be oscillators!
In their heart, amplifiers want to be oscillators!
In their heart, oscillators want to be amplifiers!
Sometimes it's hard for us to make circuits do what we want.
Here is a list of questions, some to ask yourself, some to post the answers to the group.
a) Have you built more than one channel? Do they all oscillate or just one.
b) Does it get real hot, real quick? That is to hot to touch within seconds.
c) Is the output sound volume about normal?
d) Is the sound fuzzy, noisy or distorted?
e) Do you have a test meter? A $20US multi-meter with AC / DC Volts and ohms will be fine.
I only have the LM3876 but I think that the circuits are similar.
f) Is the DC Voltage at the supply pins of the IC correct?
g) Is the metal tab part of the IC case connected to anything? Remember that it's internally connected to the minus DC supply.
h) Have you read the National Semiconductor instruction book? It has at least 12 paragraphs on the subject.
i) Do you have a ground wire from the power supply to near the IC chip?
j) Lots of DIY-mod problems are caused by skipping some of the parts the the IC mfg. called for (remember it wants to be an oscillator) or by substituting high priced audio couplings capacitors for power supply bypass capacitors (tantalum and monolithic ceramic capacitors are good in a power supply)
k) Put all the mfg. suggested parts in and get it working, before you remove or substitute anything.
In their heart, amplifiers want to be oscillators!
In their heart, oscillators want to be amplifiers!
Sometimes it's hard for us to make circuits do what we want.
Here is a list of questions, some to ask yourself, some to post the answers to the group.
a) Have you built more than one channel? Do they all oscillate or just one.
b) Does it get real hot, real quick? That is to hot to touch within seconds.
c) Is the output sound volume about normal?
d) Is the sound fuzzy, noisy or distorted?
e) Do you have a test meter? A $20US multi-meter with AC / DC Volts and ohms will be fine.
I only have the LM3876 but I think that the circuits are similar.
f) Is the DC Voltage at the supply pins of the IC correct?
g) Is the metal tab part of the IC case connected to anything? Remember that it's internally connected to the minus DC supply.
h) Have you read the National Semiconductor instruction book? It has at least 12 paragraphs on the subject.
i) Do you have a ground wire from the power supply to near the IC chip?
j) Lots of DIY-mod problems are caused by skipping some of the parts the the IC mfg. called for (remember it wants to be an oscillator) or by substituting high priced audio couplings capacitors for power supply bypass capacitors (tantalum and monolithic ceramic capacitors are good in a power supply)
k) Put all the mfg. suggested parts in and get it working, before you remove or substitute anything.
I've seen this before.
Rachel,
I have seen this in a project that used LM1875's. I can't remember if the ocsillation frequency was 375 kHz or 3.75MHz, it doesn't matter anyway, the ocsillation was eventually atrributed to grounding problems. The signal and the power shared too much of the same ground path. No ground planes, and use single point grounding with as large a wire or trace that is permissible.
Check out page 15 of the following document:
LM3886 .pdf file.
Later,
Rachel,
I have seen this in a project that used LM1875's. I can't remember if the ocsillation frequency was 375 kHz or 3.75MHz, it doesn't matter anyway, the ocsillation was eventually atrributed to grounding problems. The signal and the power shared too much of the same ground path. No ground planes, and use single point grounding with as large a wire or trace that is permissible.
Check out page 15 of the following document:
LM3886 .pdf file.
Later,
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