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Old 30th December 2006, 12:12 PM   #21
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Quote:
[i]
I use parallel series 0.47R because I haven't found non-wirewound power resistor.
Thanks for help [/B]
I don't understand the need for .23 ohms in series with the speaker, what does it do?
Besides wirewound resistors are not inductive, if this was a concern.
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Old 30th December 2006, 02:05 PM   #22
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Quote:
Originally posted by Nico Ras


I don't understand the need for .23 ohms in series with the speaker, what does it do?
Besides wirewound resistors are not inductive, if this was a concern.

It is actually there to sense current for feedback.

Please read this Nico: http://www.diyaudio.com/forums/showt...645#post702645
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Old 30th December 2006, 02:36 PM   #23
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Quote:
Originally posted by Nico Ras
.....Besides wirewound resistors are not inductive......
wire-wound resistors can be made two ways.
inductive or less inductive.

The way they are wound determines into which category they fall.
The easy, cheap way is to wind a coil on a former and weld on the lead out wires. This is inductive.

The alternative methods involve winding coils that oppose each other to cancel the magnetic field. This cancellation will never be perfect but a substantial reduction in inductance can be achieved. Anything better than 90% reduction will cost more than the inductive wound type.

BTW,
1uH has a reactance of 0.13ohms @ 20kHz.
Imagine (or calculate/simulate) what effect this might have on emitter resistor feedback when the Re is of similar resistive value.
What happens when the frequency of interest is one or two decades higher?
Even 1nH starts to become significant cf 0r22.
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Old 30th December 2006, 03:26 PM   #24
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Quote:
Originally posted by Russ White



It is actually there to sense current for feedback.

Please read this Nico: http://www.diyaudio.com/forums/showt...645#post702645
Dear Russ,

very interesting reading thank you.

Kind regards

Nico
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Old 30th December 2006, 03:28 PM   #25
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Quote:
Originally posted by Nico Ras


Dear Russ,

very interesting reading thank you.

Kind regards

Nico

You are most welcome, its not exactly easy to find. It is very good read though. I have actually done several Howland pump type amps, one using discrete components(not chipamp).
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Old 30th December 2006, 11:52 PM   #26
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I have soldered and assembled amplifier but it doesn't work
I think that this is due to SMD (very difficult to solder accurate) or burned LM3886.
I don't know what to do with this. I'm so tired from LM3886 (I already have made 2 amplifiers that work ok) but 3rd was unlucky one.
Maybe I should forget about that chipamp and try to make a discrete amplifier. What do you think about this?
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Old 31st December 2006, 12:27 AM   #27
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Quote:
Originally posted by Stanley Drake
I have soldered and assembled amplifier but it doesn't work
I think that this is due to SMD (very difficult to solder accurate) or burned LM3886.
I don't know what to do with this. I'm so tired from LM3886 (I already have made 2 amplifiers that work ok) but 3rd was unlucky one.
Maybe I should forget about that chipamp and try to make a discrete amplifier. What do you think about this?

Or you could use a PCB that is tried and true. I posted a single side PCB PDF file on the MyRef thread.
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Old 31st December 2006, 01:31 AM   #28
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Thanks for advice but I think it's time for something more complicated
My fault that I used SMD. I will never use SMD again in amplifiers I'm unable to produce a good looking PCB with SMT
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Old 31st December 2006, 01:41 AM   #29
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Stanley, by all means build another amp, but don't give up on yours. Learning to troubleshoot things like this is an invaluable skill, and can even be quite fun, (in a month or so, once the frustration has gone).
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