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Old 19th November 2006, 07:17 AM   #1
rsbay is offline rsbay  Germany
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Default Short the Output of an Aleph X

Hello,

I want to implement a relay to short the output of the Aleph X amplifier during run up and as a security device for my loadspeakers when the differential offset gets to high.

There are two ways of doing it :

1. short the plus and minus output to ground
2. short the plus and minus output together

Can I use one of both ?

Regards

Ralph
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Old 19th November 2006, 08:33 AM   #2
Netlist is offline Netlist  Belgium
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A carefully build and aligned AlephX should be stable within the 100mV range offset.
The McMillan resistors and the big output resistors to ground will greatly help in stabilizing the DC.
Besides that, Im not sure relays are happy with switching DC voltages in the long run.
As far as I know, there are no reports of AlephXs who ever damaged speakers so Id concentrate on good and careful alignment instead of output relays.

/Hugo
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Old 19th November 2006, 08:52 AM   #3
Duo is offline Duo  Canada
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Or stick a non-polar electrolytic cap in series with the speaker.

-- Yeah... I know.... sorry...
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Old 19th November 2006, 02:15 PM   #4
EUVL is offline EUVL  Europe
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Ralph,

Short plus to minus. Check amp stability with shorted outputs with an oscilloscope (i.e. it does not oscillate).

And make sure the relay has sufficient current rating.
I use automotive relays.


Patrick

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Old 19th November 2006, 06:21 PM   #5
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Hi Ralph,

I am building an Aleph X myself, and am just starting on DC protection.

A problem is that most DC protection circuits are not differential, but measure DC against zero. The only one that claims different is Euvel. Check out his post:

http://www.diyaudio.com/forums/showt...018#post434018

When you short-circuit + against - you have no in-line contacts. One of the relays that can handle the DC load is: Amplimo . Check under Amplifier Modules, down at the bottom.

Please keep us "current" with your solution.

Greetings, Harry.
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Old 19th November 2006, 07:02 PM   #6
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by harryeng
Hi Ralph,

I am building an Aleph X myself, and am just starting on DC protection.

A problem is that most DC protection circuits are not differential, but measure DC against zero. .......................

Greetings, Harry.

try uPC1237 for that
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Old 20th November 2006, 04:40 AM   #7
rsbay is offline rsbay  Germany
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Thanks for the informations - I will shorten + to -

I think about using a microcontroller and measure the voltage of both output against ground. Than I get the information about the differential DC offset over the load and the absolute offset of each output.

Regards

Ralph
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Old 20th November 2006, 05:44 AM   #8
EUVL is offline EUVL  Europe
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uPC1237 measures DC offset to ground, so not differential.
Of course you can change the input circuit, but as Harry pointed out, I have already published a full differential circuit. It works without a hitch for 4 years (not that I needed it at any time). It is much easier than a P, and I do not particularly like HF circuits near my analog amp. You need to adapt the circuit a bit for different relays (in terms of coil current).

If you want readout, 2 (or even 3) multimeters from Reichelt at 6 Euros each is the easiest solution.

And the quality of the relay contact for a shunt protection is not important. It just has to handle a hugh pulse current (say 200A min.). You can also short to a small power resistor (say 0.1 ohm 50W) to make life a bit easier for the relay.


Patrick
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Old 23rd November 2006, 01:19 PM   #9
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Quote:
Originally posted by EUVL
uPC1237 measures DC offset to ground, so not differential.
...........................................

download pdf and you'll see (if I understand it correctly ) that 1237 don't need gnd for sense.
both legs for sensing (L and R in stereo connection ) are virtual ground .....L for R and vice verse;
perfect for diff use
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Old 24th November 2006, 01:40 PM   #10
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> perfect for diff use

When Pin 2 is 0.7V above pin 5, pin 6 will go open, turning the relay off. In operation, Pin 6 goes to Gnd (=Pin5).

In the circuit published, the 56k resistors plus the 330F cap form a low pass filter to isolate the DC component of the amplifier output, which if more than 0.7V will trigger the protection circuit.

So let's take your suggestion and connect the +ve output of an Aleph-X to the Rch point in the circuit, and the -ve output to the Lch point. A 2-V common mode absolute DC will certainly trip the relay, but a symmetrical differential DC across the outputs will do nothing, as the 56ks form a pontential divider which gives you a nice 0V at the +ve pole of the 330F cap.

Or you have something else simple in mind which does not require a differential amp (opamp or otherwise) ?


Patrick
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