My "audiophile" LM3886 approach

I finished assembling my RevC boards and began testing them today. They seem to work fine so far. I thought the LM3886 would get much warmer than it does, but it stays only moderately warm. However, I am surprised at how warm the 1k ohm resistors get on the board. Is this normal? I now understand the importance of keeping these resistors elevated above the board.

Although I haven't sat down to critically listen to the amps, I like what I hear. It's pretty gratifying listening to something you made--even if it was just soldering a kit together.

Now, on to the metal casework... (pictures forthcoming)
 
It is normal for resistors to get hot. It's not the most efficient supply for the LM318, but it works well with only a few inexpensive parts.

I know you will enjoy it, and I bet it's not the last audio component you will make 😉. Kit's are great way to learn..
 
orthoefer said:
However, I am surprised at how warm the 1k ohm resistors get on the board. Is this normal?
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Those 1K resistors supply the shunt regulator (the resistors plus the zeners) so they are passing a lot of current. It is quite normal for them to stay fairly warm(yes even hot). They will be dissipating around a watt each.

Cheers!
Russ
 
I mean, why stress further
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I couldn't agree with you more.

I've just designed a PCB layout for a simple but very good MC Head Amp ( by Marshall Leach, Jnr.) Granted I am a tad fussy, but it took me an age to do with graph paper. Making the PCB will no doubt take an age as well, and will be inferior to a professional job, such the excellent Twisted Pear boards.

Audie.
 
Russ White said:


Those 1K resistors supply the shunt regulator (the resistors plus the zeners) so they are passing a lot of current. It is quite normal for them to stay fairly warm(yes even hot). They will be dissipating around a watt each.

Cheers!
Russ
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I didn't assemble my resisters off the board. Am I going to run into problems? Should I consider replacing them. I have my boards built, but I haven't powered them up yet.

(K)
 
bikedude said:



I didn't assemble my resisters off the board. Am I going to run into problems? Should I consider replacing them. I have my boards built, but I haven't powered them up yet.

(K)
Click to expand...


You will probably be fine even with them mounted on the PCB. It is better for them to be lifted 1/2" or so, but it will probably not kill them if they get a bit warmer than usual. I would replace them when you can, but you could run them this way for quite a while, really probably indefinitely.
 
Humming

I finally completed one channel of my RevC. Powered up without a hitch, relay clicked, etc.
When I connect my test speaker, a *very* noticeable hum starts. I rechecked the connections, moved the trafo around, and changed the input polarity (now the center lead of the RCA goes to the ground input, I suppose that's wrong).
Now the hum is much lower, but the volume is low too.
If I touch the center RCA lead, the hum becomes unnoticeable, and the volume lowers.
If I touch the outer lead, the humming and the volume increases.

Any tips?
 
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