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Old 7th November 2012, 01:55 PM   #1971
rsavas is offline rsavas  Canada
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Default Wire Amp Muting?

Hello folks,

Been following this thread, as i am working on my own version of this design. Thanks for the feedback, helps me figure out some design issues I have in my implementation.
So based on this Mute issue, I take it that you need to have a AC present & absent detector.
A simple transistor ckt to ground the mute pin quickly in the absence of an input AC voltage, sounds like what you are requiring. That and a mute delay at power up. This is why we prototype, test and then improve, all part of the design process, know one is at fault here, so strong words are not required.
I am undecided how I will do my speaker protection part of the design. Contemplating a full speaker protection ckt, AC line detect, o/p DC detect, over current detect, turn-on delay, relay for the speakers? I understand the reasons to have these features and why not. All part of the design process. If anyone has input for me please express it in the thread that I have created, rather than de-rail this thread
LME49830+LatFET, yet another for design review

AndrewT, not sure why you are saying that the zener "Z1", 12V is not needed. It has to be there to limit the input voltage to the LME49830 mute pin. Looking at the LM49830 spec, I can not determine the maximum V the mute pin can tolerate, they only say 120uA min to put the part into play mode. So I assume that Owen (OPC) just followed the guidelines from the data sheet and app note info.

Hi Owen, thanks for your design contribution, helps me alot in my efforts. If you are open to me asking you some questions about my design, I would appreciate it very much. We could do this off line. Who knows one day I might be able to buy you a beer or two/lunch/dinner, I realize that you are in Ottawa, so I am not that far from you or if you are in the GTA at some time in the future.

Regards
Rick

Last edited by rsavas; 7th November 2012 at 02:03 PM.
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Old 7th November 2012, 02:07 PM   #1972
opc is offline opc  Canada
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You don't need the zener if you calculate the resistor value properly:

IMUTE = (VMUTE VBE) / (1kΩ +RM) where VBE ≅ 0.7V

The problem lies in the fact that the calculated resistance only really works with one supply voltage (over a reasonable range) and needs to be adjusted as per the above formula for different supply voltage.

Using the zener simplifies this as you can use any rail voltage you want and the current into the mute pin is always the same.

If you were designing this into a product with a set rail voltage, it would be cheaper and easier to simply calculate the right resistance and omit the zener.

Cheers,
Owen
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Old 7th November 2012, 02:38 PM   #1973
IanAS is offline IanAS  England
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So...

Another resistor can be inserted between the capacitor and the mute pin. The relay joined to the mute pin. This way, when the relay earths the mute pin, the capacitor discharges slowly and doesn't weld the relay contacts.

During the period of earthing there will be some small current flowing through the resistors, via the relay, to earth.

Would that do it?

Same relay can also be operated remotely from, say, a pre-amp. (by interrupting the voltage to the relay)

Last edited by IanAS; 7th November 2012 at 02:41 PM.
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Old 7th November 2012, 03:15 PM   #1974
rsavas is offline rsavas  Canada
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Default LME49830 mute circuit

Quote:
IMUTE = (VMUTE VBE) / (1kΩ +RM) where VBE ≅ 0.7V
Ya, it would help if I looked at the LME49830 block diagram to see the 1K res in series with the diode to gnd. I am a real Homer Simpson at times :-)
I guess they could have spec'd the maximum current into the mute pin node, but I am sure is not to be over say ~100mA.
See why I am asking for help!!
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Old 7th November 2012, 03:20 PM   #1975
opc is offline opc  Canada
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National specifically states that exceeding 2mA into the mute pin could damage the IC, so that's your limit. If I were designing it, I would target about 900uA at nominal Vcc since that's in the middle of the specified allowable range. The last thing you want is the IC muting during a large transient that loads the supply rails, or getting destroyed under high line conditions.

See the appeal of the zener?

Cheers,
Owen
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Old 7th November 2012, 03:24 PM   #1976
rsavas is offline rsavas  Canada
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Yes sir, that just cost me one beer, do you have a preference? Gotta learn how to read, damn, right there in print on p12.
Thx Rick

Last edited by rsavas; 7th November 2012 at 03:47 PM.
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Old 7th November 2012, 03:31 PM   #1977
qusp is offline qusp  Australia
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Quote:
Originally Posted by rsavas View Post
Yes sir, that just cost me one beer, do you have a preference?
Thx Rick
I gather asking that sort of question of opc could get expensive...
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Old 7th November 2012, 03:57 PM   #1978
rsavas is offline rsavas  Canada
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That' s okay, I am having fun with it & I don't even know if he (Owen) indulges in such activities. Has not taken me up on my offer, so I do wonder. By the sounds of my stupid ?'s you'd think I was already toasted, it's only just noon here & I am at work today.
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Old 7th November 2012, 04:00 PM   #1979
qusp is offline qusp  Australia
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oh he does, the commonality of good beer, good coffee and good audio was discussed earlier in the thread, or was that the LPUHP thread? hmmm one of the myriad wire threads anyway
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Old 7th November 2012, 04:01 PM   #1980
opc is offline opc  Canada
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Quote:
Originally Posted by rsavas View Post
That' s okay, I am having fun with it & I don't even know if he (Owen) indulges in such activities. Has not taken me up on my offer, so I do wonder. By the sounds of my stupid ?'s you'd think I was already toasted, it's only just noon here & I am at work today.
I wish

I'll take one of these... definitely the nicest triple at the LCBO right now, if you can find one.

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Cheers,
Owen
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