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
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
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
Patrick
Or maybe this from Rod Elliott:
http://sound.westhost.com/project33.htm
Edit:
100µF bipolar electrolytic does not cost much. Or use two 220µF back to back instead of one bipolar.
http://sound.westhost.com/project33.htm
Edit:
100µF bipolar electrolytic does not cost much. Or use two 220µF back to back instead of one bipolar.
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?
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?
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....
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....
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/upload6/Amp_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
Hi Leolabs
The speed of this circuit is due to the speed relay.
Some high speed responce relay are very expensive,and the response time are approx. 5 m. sec.A standard relay have a response time over 15-25 m.sec.
When I have ended to mount my last high power amp I have disconnect the + supply rail from the supply,with a loudspeaker connected.
- 77 V DC on the output, the relay disconnect,and loudspeaker saved...
The speed of this circuit is due to the speed relay.
Some high speed responce relay are very expensive,and the response time are approx. 5 m. sec.A standard relay have a response time over 15-25 m.sec.
When I have ended to mount my last high power amp I have disconnect the + supply rail from the supply,with a loudspeaker connected.
- 77 V DC on the output, the relay disconnect,and loudspeaker saved...
Hi Chris
The blinking circuit is only for indicate when the protection is activated.
When using a quadruple op amp like this circuit,your current charge is not a problem, a LED indicator should be used for protection indicator.
His current charge are the same if it is supplied from the op amp,or directly (with the same value of resistor)by the power supply.
It is better to use a single quad op amp (like a TL 084) because this save cost, component number and spacing...
The blinking circuit is only for indicate when the protection is activated.
When using a quadruple op amp like this circuit,your current charge is not a problem, a LED indicator should be used for protection indicator.
His current charge are the same if it is supplied from the op amp,or directly (with the same value of resistor)by the power supply.
It is better to use a single quad op amp (like a TL 084) because this save cost, component number and spacing...
anatech said:Hi parsecaudio,
I like to keep things simple. Less to break.
I would attempt to reduce the op amp count to two anyway, use a transistor or two if you have to. That's just my take on these things.
Nothing worse than having the protection circuit fail and the amp is fine!
-Chris
On the same note I do not use ICs which contain too many transistors to detect simple voltage with no precision needed. Only a few transistors can do the job. The goal should be that the protection circuit be a lot more reliable than the audio amp circuitry...
Hi chris and fab
A simple question:
you are sure that he is simpler to mount a single quad op amp(14 pins=14 holes and/or solders points ) or some transistors(minimum count of 4 + their associated components= minimum 18 holes / solders point on PCB)?
Fab,it is right that a simple discrete transistors can do the same function.Are less expensive four transistors or one single standard operational amp?
No precision needed?Why?
When I designing a circuit,I like that it works as I want
Thank you very much for your answer
A simple question:
you are sure that he is simpler to mount a single quad op amp(14 pins=14 holes and/or solders points ) or some transistors(minimum count of 4 + their associated components= minimum 18 holes / solders point on PCB)?
Fab,it is right that a simple discrete transistors can do the same function.Are less expensive four transistors or one single standard operational amp?
No precision needed?Why?
When I designing a circuit,I like that it works as I want
Thank you very much for your answer
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.