LM3886 design
Re: LM3886 design
Some of the heatsink manufacturers have their catalogs on web sites. These usually include the thermal resistance for each type. It appears that Aavid bought Thermalloy. They have a web site at www.aavidthermalloy.com. This site also has a fair amount of application information. Another posibility is Thermalloy (who apparently bought Aham Tor) at www.wakefield.com. They seem to concentrate mostly on extruded heat sinks.<p>The Aavid heat sinks listed for the TO-220 package seem to start at 2.7 deg/watt and go up from there. Without an insulator, the total thermal resistance would be still about 3.9 deg/watt.
Re: LM3886 design
3 questions:<p>1. When I use the amp, turning the pot all the way from min volume to where it stops reduces the volume very much. It only reaches full volume with the pot about 1/8 of a turn away from the point it stops. What causes this problem? Is it because I am using a linear taper 25K? I do also have a 100K audio pot? will that make a difference? Could it be that I have the input mixed up (ground to positive, positive to ground)?<p>2. If I wanted double the power, could I just build another amp that is exactly the same as this one, split the input to both amps, and connect the positive output from both to the speaker? Would the two amps have to share the same ground?<p>3. I normally have the amp connected to a plain portable cd player. When it is connected, there is no buzzing. When I disconnect the cable, it buzzes very quietly. I can deal with that problem, but the other problem is when I use my laptop as the input, I get a loud, annoying buzz, that can be heard probably miles away! 
If a MP3 is playing, the buzz is still noticable. How do I stop it? <p>Thanks for any help, Mike
If a MP3 is playing, the buzz is still noticable. How do I stop it? <p>Thanks for any help, Mike
Re: LM3886 design
Mike:
Which configuration of power supply did you finally end up using, the single supply or the dual supply and at how much DC input voltage ?
On your problems on the volume , I’m suspecting that you used a linear type of pot for your vol control instead of the prescribed logarithmic audio taper type. As for deficient volume output, you may not be driving the amp enough, and might need a stage of preamplification if your drive source is the fixed output of a typical AF CD player.
So you may not be getting the prescribed power output, potentially already there, but not attainable by virtue of that shortcoming of input drive level.
As for your hum…..chum….…look into ac ground loops between your two power sources, if AC power plug mechanical polarization permits you to do so, reverse the AC power line plugs one at a time until the lowest…or nonexistent hum level results. Also confirm properly coaxially shielded audio cables being utilized on low level lines. Specifically, not a cable that is two opposed RCA plugs with Zip cord between them….normally intended to be utilized for interconnecting smaller wattage remote speakers. If the portable unit is battery powered and not utilizing an aux AC line power pack…. AC hum should not be a problem As for your #3 source of extraneous noise, I would suspect that to be from the switch mode supply and all of the subharmonics from that units power supply as well as a lot of lower freq digital hash from the MP3’s electronics You might initially take a low level AC meter reading...or ideally, a scope probing… between the two units chassis grounds and see what you read, but I would suspect an adequate ground being established by your common grounded AF line interconnecting cable. As another approach, try looping (multi looping {according to its available core dia}) the low level AF cable thru the center hole of a ferrite RFI balun/core, in case you were hearing digital trash in your audio from the MP3 unit.<p>
73's de Edd
[email protected].........(Interstellar~~~~Warp~~~Speed)
[email protected]........(Firewalled-Spam*Cookies*Crumbs)
However, in lieu of typical 90% system down time ever since the
buyout and conversion over by Comcast..more apropos would be:
[ UNSTELLAR !~~WARPED !~~SPEEDLESS ! ]
Which configuration of power supply did you finally end up using, the single supply or the dual supply and at how much DC input voltage ?
On your problems on the volume , I’m suspecting that you used a linear type of pot for your vol control instead of the prescribed logarithmic audio taper type. As for deficient volume output, you may not be driving the amp enough, and might need a stage of preamplification if your drive source is the fixed output of a typical AF CD player.
So you may not be getting the prescribed power output, potentially already there, but not attainable by virtue of that shortcoming of input drive level.
As for your hum…..chum….…look into ac ground loops between your two power sources, if AC power plug mechanical polarization permits you to do so, reverse the AC power line plugs one at a time until the lowest…or nonexistent hum level results. Also confirm properly coaxially shielded audio cables being utilized on low level lines. Specifically, not a cable that is two opposed RCA plugs with Zip cord between them….normally intended to be utilized for interconnecting smaller wattage remote speakers. If the portable unit is battery powered and not utilizing an aux AC line power pack…. AC hum should not be a problem As for your #3 source of extraneous noise, I would suspect that to be from the switch mode supply and all of the subharmonics from that units power supply as well as a lot of lower freq digital hash from the MP3’s electronics You might initially take a low level AC meter reading...or ideally, a scope probing… between the two units chassis grounds and see what you read, but I would suspect an adequate ground being established by your common grounded AF line interconnecting cable. As another approach, try looping (multi looping {according to its available core dia}) the low level AF cable thru the center hole of a ferrite RFI balun/core, in case you were hearing digital trash in your audio from the MP3 unit.<p>
73's de Edd
[email protected].........(Interstellar~~~~Warp~~~Speed)
[email protected]........(Firewalled-Spam*Cookies*Crumbs)
However, in lieu of typical 90% system down time ever since the
buyout and conversion over by Comcast..more apropos would be:
[ UNSTELLAR !~~WARPED !~~SPEEDLESS ! ]
Re: LM3886 design
I figured out the Volume problem. I had the ground and out to amp backwards, so the input is on pin 1 (left), the ground was in the center (pin 2) and the out to amp was on pin 3 (right). All I had to do to fix it was switch the connections on pin 2 and 3. The loud hum when plugged into my laptop also disappeared. The only problem left is quiet buzz when no sound is input. How I have it set up is the input is connected to the crossover, the crossover is connected to the amp, and the amp is connected to the subwoofer speaker. When there is no sound playing, a quiet but noticable buzz is heard from the speaker. When sound is playing, the buzz is gone. Could it be that AC is getting into the amp? I am only using 1300uf caps for my power supply, is that not enough? Or is it a different problem? Oh and I am using a split supply. The trans produces 24-0-24. So, what do I do about that small buzzing?<p>Thanks again, Mike
Re: LM3886 design
Mike:<p>I had info on mis-wiring of the vol control on my previous post ,but deleted it due to the fact that I figured that you would have detected that by the squirrrely action of the control on end to end adjustment.
“When sound is playing, the buzz is gone”…probably not, just not discernible , due to the higher audio input level obscuring it over.
Assuming that you don’t have long lead lengths associated with the vol control to pick up extraneous /unwanted signal(s).Disconnect your audio input source and then try placing the vol control at absolute minimum vol level and see if your buzz is still there. If not its source potentially could be the amps electronics circuitry picking up stray fields ( bench AC wiring/florescent lamp noise/dimmer ckt noise, etc) in its close proximity if the unit is built in breadboard config and unshielded./OR/the problem also could be inadequate B+ filtering of your power supply introducing in 120 ~ hum.
Alternatively, if the buzz disappears when the Power Amps input was disconnected the crossover network could be introducing the pick up as unshielded inductors are a good pick up medium if LC was utilized instead of RC components.
Lastly, do what I do if I’m trying to locate a noisy stage in a line up of several of them. Take a 10 ufd elect at ~ 50VDC WV with short leads and bypass the power amp input to ground and if your problem disappears, that point back towards the speaker is OK so move to the next stage forward and do the same .When the noise stays after bypassing that stages input….there is your noisy stage. Usually there is no DC charge imparted into the cap , but to be on the safe side, discharge it before moving between stages.<p>
73's de Edd
[email protected].........(Interstellar~~~~Warp~~~Speed)
[email protected]........(Firewalled-Spam*Cookies*Crumbs) <p>
However, in lieu of typical 90% system down time ever since the
buyout and conversion over by Comcast..more apropos would be:
[ UNSTELLAR !~~WARPED !~~SPEEDLESS ! ]
“When sound is playing, the buzz is gone”…probably not, just not discernible , due to the higher audio input level obscuring it over.
Assuming that you don’t have long lead lengths associated with the vol control to pick up extraneous /unwanted signal(s).Disconnect your audio input source and then try placing the vol control at absolute minimum vol level and see if your buzz is still there. If not its source potentially could be the amps electronics circuitry picking up stray fields ( bench AC wiring/florescent lamp noise/dimmer ckt noise, etc) in its close proximity if the unit is built in breadboard config and unshielded./OR/the problem also could be inadequate B+ filtering of your power supply introducing in 120 ~ hum.
Alternatively, if the buzz disappears when the Power Amps input was disconnected the crossover network could be introducing the pick up as unshielded inductors are a good pick up medium if LC was utilized instead of RC components.
Lastly, do what I do if I’m trying to locate a noisy stage in a line up of several of them. Take a 10 ufd elect at ~ 50VDC WV with short leads and bypass the power amp input to ground and if your problem disappears, that point back towards the speaker is OK so move to the next stage forward and do the same .When the noise stays after bypassing that stages input….there is your noisy stage. Usually there is no DC charge imparted into the cap , but to be on the safe side, discharge it before moving between stages.<p>
73's de Edd
[email protected].........(Interstellar~~~~Warp~~~Speed)
[email protected]........(Firewalled-Spam*Cookies*Crumbs) <p>
However, in lieu of typical 90% system down time ever since the
buyout and conversion over by Comcast..more apropos would be:
[ UNSTELLAR !~~WARPED !~~SPEEDLESS ! ]
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