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Old 7th April 2006, 05:26 PM   #1
msamkl is offline msamkl  Greece
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Question Looking for a DC Protection schematic...

Does anybody have a DC Protection schematic for Power amps?
I've built Gregs GB150D amp and I'd like to add a circuit to provide Dc protection to the loudspeakers...

Thanks in advance.

Thanasis.
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Old 7th April 2006, 09:06 PM   #2
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Default Re: Looking for a DC Protection schematic...

Quote:
Originally posted by msamkl
Does anybody have a DC Protection schematic for Power amps?
I've built Gregs GB150D amp and I'd like to add a circuit to provide Dc protection to the loudspeakers...

Thanks in advance.

Thanasis.

The simplest way to do that is using a servo for which there are many circuits around. More complicated arrangements use a comparator that in the presence of dc offset, will shut down the power to the amp.
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Old 8th April 2006, 01:38 AM   #3
VEC7OR is offline VEC7OR  Lithuania
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I've tried Rods http://sound.westhost.com/project33.htm
and it worked out real nice.
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Old 8th April 2006, 01:51 AM   #4
fab is offline fab  Canada
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Hi

Here is a DC protection that latches when Vdc at power amp output. IN addition there is an "in-rush" circuit (in bonus). It is incorporated in my power amp (I have 2 x 500 VA transfo).

When DC voltage reaches the threshold (+/- 3 V) RL2 contact opens then power voltage for output section is disconnected. RL3 makes the circuit to latch. You need a separate power supply for the detection circuit (same as for the audio driver circuit of the power amp). You may have to adjust components values to suit your amp voltages

It has worked fine since it is installed.

Good luck
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Old 8th April 2006, 05:17 AM   #5
djk is offline djk
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I have always liked the Hafler DH500 circuit.

I used to buy the board and use them in many other amplifiers (Adcom GFA555, DIY, etc).

http://www.hafler.com/techsupport/pd...00_amp_man.pdf

PC-9C board on page 16.

An inexpensive LM339 is the heart of the circuit. A couple of resistors set the DC trip voltage, turn-on delay, and it has a quick drop-out on power off. One resistor sets the relay voltage, I've used both 24V and 48V relays with a wide range of B+ voltages. A seperate supply is not needed. I use with a three pole relay, the third contact is used to short out an inrush current limiter.

The foil layout for the PC-9C is on page 19, it could be made smaller too.
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Old 8th April 2006, 12:57 PM   #6
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Like to look at this one ?

http://users.otenet.gr/~athsam/protection_2_EN.htm

I had some pcb for it (stereo)
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Old 8th April 2006, 02:49 PM   #7
fab is offline fab  Canada
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Unhappy Output Relay in series with load...

Small comment: if you want to preserve the maximum damping of your amp , if you pay attention, the circuit in post #4 has no relay contacts in series with the load as opposed to the the 2 previous posts circuit.

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Old 8th April 2006, 05:47 PM   #8
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Greetings from Norfolk

I like the idea of the post #4 in this thread, but can you clarify the connectivity / operation of the circuit around Q1, Q2 & Q3. The connections are not clear to me

Richard
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Old 8th April 2006, 06:08 PM   #9
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http://www.richie00boy.pwp.blueyonde...atic_small.png

SCHEMATIC COPYRIGHT VELLEMAN

good n simple one.giving active service.
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Old 8th April 2006, 10:42 PM   #10
djk is offline djk
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"Small comment: if you want to preserve the maximum damping of your amp"

Considering that this has no effect on how the bass sounds on an amplifier, I would rather have a relay (treated with de-oxit and a small bypass cap).

My McIntosh MC2120 has a DF of 14, and sounds tighter in the bass than direct-coupled high feedback designs that have DF in the hundreds, if not thousands.

DF is a huge red-herring.
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