LM3886 Very Loud Buzz

colindj69 · 1st September 2008, 11:07 PM

Hi all - I recently aquired a few active speakers made by DAS. These use the LM3886 based amp. 2 x lm3886 for bass, 1 for top.
The problem is that when the amp is powered up, it produces a full volume buzz on the 2 x lm3886 side (bass), which I think is at mains frequency but cannot be sure.
If I connect the bass cone to the to the (1 x lm3886) side, the cone just pushes forward, lots, as if DC voltage was being sent to cone.
I've measured the output at the speaker leads with no load attached and am getting 70v on the bass side, and 32v on the other side.....

The volume controls make no difference at all....

Any help would be greatly received...

Many thanks

Colin

Nuuk · 2nd September 2008, 06:29 AM

It sounds like one rail is disconnected somewhere. As it is the same for both sections, I would be looking at the PSU, but without a circuit diagram or pictures, I can't be any more specific.

Puffin · 2nd September 2008, 06:31 AM

It would seem that all is not right. Were these working when the last person used them?

If there are 2 LM3886's for each bass unit, it would seem that these may be running in bridged or parallel mode for more power.

The measurements you have taken are not what you would normally expect to see at the speaker terminals. Anything over 100mv is too high, so 70v cannot be right. Are you sure that you have measured the voltage at the right points. The readings you have are more ikely to be the rail voltages. These chips normally run at +35v,0v -35v.

Mooly · 2nd September 2008, 07:26 AM

Bridge mode or not there has to be zero volts across the speaker points. Find the data sheet for the IC's and carefully measure the rail voltages on the IC pins. Sounds more like a zapped IC to me.
Are they hot even with no speaker attached ?

1st September 2008, 11:07 PM	#1
colindj69 diyAudio Member Join Date: Sep 2008	LM3886 Very Loud Buzz Hi all - I recently aquired a few active speakers made by DAS. These use the LM3886 based amp. 2 x lm3886 for bass, 1 for top. The problem is that when the amp is powered up, it produces a full volume buzz on the 2 x lm3886 side (bass), which I think is at mains frequency but cannot be sure. If I connect the bass cone to the to the (1 x lm3886) side, the cone just pushes forward, lots, as if DC voltage was being sent to cone. I've measured the output at the speaker leads with no load attached and am getting 70v on the bass side, and 32v on the other side..... The volume controls make no difference at all.... Any help would be greatly received... Many thanks Colin

2nd September 2008, 06:29 AM	#2
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	It sounds like one rail is disconnected somewhere. As it is the same for both sections, I would be looking at the PSU, but without a circuit diagram or pictures, I can't be any more specific. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
4 ch esp p3a psu Buzz	kjb	Solid State	7	4th August 2008 11:53 AM
Melos triode and computer as source: BUZZ BUZZ BUZZ	zigo3	Tubes / Valves	4	28th November 2007 02:11 AM
buzz noise from loud speakers	vibeline	Multi-Way	9	7th January 2007 06:19 PM
Loud buzz and hum from one monoblock!!!	victor1	Tubes / Valves	5	12th June 2006 05:32 PM
Car audio amp, LOUD buzz. what is wrong?	silentblackhat	Chip Amps	2	12th April 2006 05:49 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

2nd September 2008, 06:31 AM	#3
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	It would seem that all is not right. Were these working when the last person used them? If there are 2 LM3886's for each bass unit, it would seem that these may be running in bridged or parallel mode for more power. The measurements you have taken are not what you would normally expect to see at the speaker terminals. Anything over 100mv is too high, so 70v cannot be right. Are you sure that you have measured the voltage at the right points. The readings you have are more ikely to be the rail voltages. These chips normally run at +35v,0v -35v.

2nd September 2008, 07:26 AM	#4
Mooly diyAudio Moderator Join Date: Sep 2007	Bridge mode or not there has to be zero volts across the speaker points. Find the data sheet for the IC's and carefully measure the rail voltages on the IC pins. Sounds more like a zapped IC to me. Are they hot even with no speaker attached ?