| matheprat |
I've built one channel of a Gainclone (LM3886). At medium-high volume, the sound starts to crackle at a definate point, below which is fine. I tried putting a zobel network (100 nf and 10 ohms) across the output and it seemed to reduce the noise, but it can still be heard.
What else can be done to help?
Many thanks. |
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| peranders |
| How about cooling? Maybe it's the protection circuits that you trigger? |
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| burnedfingers |
| Gain clowns sound very bad when they clip. It is very possible that you are clipping the amp. |
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| AndrewT |
Hi,
give us some constuction/compatability details.
Transformer VA & Vac
Dual or single bridge
Smoothing uF
Inverting or non-inverting
Speaker impedance & sensitivity |
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| Nordic |
| How big is your heatsink? |
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| AndrewT |
Hi Mat,
have you fitted a heatsink, or have you gone quiet while you are fitting one now?
Let's hear from you. |
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| Nordic |
| I think we killed another one, Andrew. |
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| matheprat |
Sorry, been asleap.
Yeah, I have a large heatsink fitted to the chip. 4 x 2 inches. It gets slightly warm to the touch, so I don't think the chip is overheating.
The transformer is 160 va, and the power rails are +- ~38v. The caps are 5600 uf, and the amp is non-inverting. The speaker inpeedence is 8 ohms.
Many thanks. |
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| burnedfingers |
What is the speaker efficiency? Your speakers how many db with
1 watt@ 1 meter? |
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| matheprat |
I don't know. How can I find that out? It's not on the speaker anywhere.
Many thanks. |
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| AndrewT |
Hi Mat,
have you eliminated air from the gap between heatsink and chipamp?
You want the gap as small as possible (0.0001inch=0.002mm) and FILLED with thermal transfer compound.
+-38Vdc is towards the top end of supply voltage for 8ohm speakers but if the correctly coupled heatsink is not getting beyond warm then it indicates that excess heat is not the problem.
Could it be oscillation brought about as output voltage hits a threshold? What would be the symptom? internal triggering on detection of excess HF?
My discrete Crimson has a thyristor lock out on detection of HF @ the VAS. It ONLY ever latched when pushing 50kHz at near full power :xeye: I didn't try that again:eek: |
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| markiemrboo |
| quote: | Originally posted by AndrewT
if the correctly coupled heatsink is not getting beyond warm then it indicates that excess heat is not the problem.
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Or that the chip isn't making good contact with the heatsink? Maybe unlikely, but possible :)
EDIT: Ah, oops. Missed you asking whether the poster had got rid of the air gap with paste and all that!
I heard mine make a crackle noise once, but then it didn't seem to happen again, so I am quite curious as to what it is :) |
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| AndrewT |
Hi,
I'm not too good at this debugging stuff, so I'm glad you're keeping an eye on me. |
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| batcat |
I had a similar problem with my bi-amp system where all channels would crackle at moderate listening levels. Trouble shot that one for quite some time.
As it turned out the power switch was defective, arcing or something internal when I tried to run some current thru it. Now I use a power strip to do that chore. Problem solved.
Hope this helps.
David |
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