DC-Protect Circuitry

[Fritzell]

Hello! Been a while

I'm getting some more expensive speakers and if my homebuilt amplifier decides to breakdown at some point I don't wan't to burn the speaker. So I was thinking of adding a DC-protect circuit. I know there was some big thread about this a while ago, but I'm not intending to to the most perfection but just a simple protectcircuit that is reliable and deactivates the amp or the speaker when DC is at the output. I alredy have other protectioncircuits for overload etc.

It's the detection circuit I'm intrested in mostly. The breaking-circuit can be some in many ways. Breaking the output with a relay or with solid-state components, or cutting the PSU from the amp. The simplest way I believe is to break the output.
Anyway, I was googlin' some and found this:
http://www.amb.org/audio/epsilon12/epsilon12_sch.png

Any comment'? I'm having problems finding those big cap's for some reasonably price.. (100uF non pol) Would'nt it be possibly to increase the resistor and use a smaller capacitor instead?

Thanks.
Fritzell

[EUVL]

Make a search in this forum or google for TA7317P (speaker protection IC from Toshiba). It has enough features in one chip. No longer in prudction, but you can still get them, e.g. from www.reichelt.de.

Patrick

[4fun]

Or maybe this from Rod Elliott:
http://sound.westhost.com/project33.htm

Edit:

I'm having problems finding those big cap's for some reasonably price.. (100uF non pol) Would'nt it be possibly to increase the resistor and use a smaller capacitor instead?

100µF bipolar electrolytic does not cost much. Or use two 220µF back to back instead of one bipolar.

[Fritzell]

Aha thank's for your replies. I think I will build Rod Elliots design But instead of relay I will probarly design a Mosfet transistors circuitry instead.

Oh I didn't find the electrolytic bipolar capactitors on Elfa.se at first but now I found them. I was looking on the Mkt 100u before But these others are not very expensive so it's ok.

Thanks!

Btw: In the schematic: http://sound.westhost.com/p33-fig1.gif
Can 1N4002 be used for D1-D4?

[4fun]

I hope that you won't intend to switch speaker output with some mosfet circuit instead of a relay.
You could use 1N4148 100mA diodes instead, so low current there so it's no danger.

[parsecaudio]

Hi to all
This is also a good solution for DC protection.
It is very reliable.

[fab]

Originally posted by parsecaudio
Hi to all
This is also a good solution for DC protection.
It is very reliable.

one question: What will happen if you have full max DC on the output of audio amp...?
I think that the maximum DC voltage that X1 can take at its input is 2 X VC (or VE) since greater than taht X1 may latch up or could be damaged...

[parsecaudio]

Hi fab
I have tested this circuit for this.
The high value of the resistors in input stage limits the currents on the inverting and non inverting input of the op amp.
This high value protect the inverting input in case of DC voltage.
Also you must to use an I.C. without latch-up problems.
The test that i have made is for 85 V DC....

[Fritzell]

I hope that you won't intend to switch speaker output with some mosfet circuit instead of a relay.

I don't see this as a big problem out of Audio aspect, and a relay (10A+ DC) is expensive and takes a lot of space (which I don't have in my amp ) And Mosfets are alot faster, so a solid-state solution is good, maybe less practical though. Instead of breaking the output I think it feels better to cut the DC supply from the poweramp because it's not nice to have electronics on the output as you said...

The DC sensor:http://files.upl.silentwhisper.net/u..._DCprotect.pdf

The DC detect circuit looks like this. In normal mode, The last BC556 to the right will be open and send a "protect-voltage". When DC is applied to the circuit-input (from amp-output) the same transistor will cut off. Only minor changes from Rod Elliots design (A Led that indicates)

The PSU: http://files.upl.silentwhisper.net/upload6/Amp_PSU.pdf

Don't bother the circuit to the left, it's just a softstart and is longtime tested.

Anyway, when protect voltage (+33V in my case) comes to "Protect" it opens so that current goes between the rails through the zeners and opens the mosfets. When Protect-voltage is cut, the Mosfets will cut also. The mosfets should handle up to 10A without any problems. I think this design should work. But feel free to comment

//Fritzell

[Leolabs]

Originally posted by parsecaudio
Hi to all
This is also a good solution for DC protection.
It is very reliable.

A little bit expensive but should be a nice one in term of response.