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Old 14th June 2014, 06:54 AM   #21
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Old 15th September 2015, 08:16 PM   #22
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Default Speaker Protection

Quote:
Originally Posted by eskwadrat View Post
I finally received long waiting enclosure
How did this project turn out? Where did you have that custom enclosure designed and fabricated?

I notice that the Q-Watt has speaker protection designed directly onto the amp PCB. Why is that most speaker protection schemes are placed on a separate board?
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Old 15th September 2015, 08:36 PM   #23
rsavas is offline rsavas  Canada
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Yeah the costs do add up rather quickly. That case looks really nice.
I notice that the Q-Watt has speaker protection designed directly onto the amp PCB.
Quote:
Why is that most speaker protection schemes are placed on a separate board?
One reason is cost, due to duplication of parts like ac fail opto, bjts etc.

I did notice one room for improvement on the power supply. You are missing R/C snubbers for the rectifier circuit. Look up quasimodo by Mark Johnson in this forum and he also has a nice ps for chip amps, which could be used for this project.
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Old 15th September 2015, 08:44 PM   #24
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Originally Posted by rsavas View Post
One reason is cost, due to duplication of parts like ac fail opto, bjts etc.
Wouldn't it cost more to have a separate PCB made just for speaker protection?

From a technical and performance perspective, I wonder what the advantages/disadvantages are of having on-board integrated speaker protection built into the power amp PCB. e.g. is it bad idea to put AC on the power amp board? The measured specs of the Q-amp look pretty good, regardless.
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Old 15th September 2015, 08:55 PM   #25
rsavas is offline rsavas  Canada
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Quote:
Wouldn't it cost more to have a separate PCB made just for speaker protection?
Actually if you add up the pcb area for the circuits in duplication, it will be more, > pcb area = > cost.
Having the speaker relay on the p/a pcb is a good idea, as it saves on wiring. Wire directly to binding posts.
One fault that I saw was as you noticed, that they did bring the secondary ac up to the pcb. It is possible to reduce hum if it was not their, so it is a easy fix, just put the ac fail opto on the rectifier pcb and use the opto open collector output as your a/c fail signal in.
I am building something similar, but using the LME49830 and the Semelab laterals ALF16N(P)16.
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Old 15th September 2015, 09:05 PM   #26
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Quote:
Originally Posted by rsavas View Post
Actually if you add up the pcb area for the circuits in duplication, it will be more, > pcb area = > cost.
Ah, yes. Thanks for pointing that out. Because the Q-Watt PCB is so small to being with, Elektor could get away with integrated speaker protection at relatively low cost.

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Originally Posted by rsavas View Post
Having the speaker relay on the p/a pcb is a good idea, as it saves on wiring. Wire directly to binding posts.
To me, this is well worth it. Less wiring inside the chassis.

Quote:
Originally Posted by rsavas View Post
One fault that I saw was as you noticed, that they did bring the secondary ac up to the pcb. It is possible to reduce hum if it was not their
Yes. it might make more sense to put the speaker protection circuitry on the PSU to help reduce hum to the AC line.... Or spread the protection between power amp and PSU.
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Old 16th September 2015, 01:03 PM   #27
rsavas is offline rsavas  Canada
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Quote:
Or spread the protection between power amp and PSU.
that is what I am referring to in,
Quote:
just put the ac fail opto on the rectifier pcb and use the opto-coupler open collector output, as your a/c fail signal in.
This way the ac is not needed on the q-watt pcb.
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