Here is a basic version of my circuit. The concept is that the opto-coupler
is always on except when the amp output is within one diode drop (or less)
from the supply rails. The transistors should be high gain to minimize
the bias current. You can connect the opto-coupler output to whatever
circuit suits you (logic, timer, etc.). I use a micro with this design and
monitor other things, such as temperature. Anyway, feel free to comment or use the circuit to build on.
The input should be tied to the amp output before the relay, of course.
The opto-coupler can be whatever you can find. The PS2501 works
good, but cannot drive a relay directly.
is always on except when the amp output is within one diode drop (or less)
from the supply rails. The transistors should be high gain to minimize
the bias current. You can connect the opto-coupler output to whatever
circuit suits you (logic, timer, etc.). I use a micro with this design and
monitor other things, such as temperature. Anyway, feel free to comment or use the circuit to build on.
The input should be tied to the amp output before the relay, of course.
The opto-coupler can be whatever you can find. The PS2501 works
good, but cannot drive a relay directly.
I would be more than happy to email a copy of the Altec Lansing model 9442 schematic to any that would like to study it. It is also available at Altec Lansings unofficial web site under 9442 Power Amplifier service manual Page #4.
http://alteclansingunofficial.nlenet.net/proelectronics/proamplifiers/index.html
The protection circuit shows 2 thermal switches in series it also has a protection Led in the circuit.
http://alteclansingunofficial.nlenet.net/proelectronics/proamplifiers/index.html
The protection circuit shows 2 thermal switches in series it also has a protection Led in the circuit.
d3imlay said:
pinkmouse said:
A thermistor.
Or you could possibly use a semiconductor junction like a diode or transistor, I haven't studied the circuit in detail yet.
That's what I thought. My understanding is theremistors are often used on a board to limit inrush current, and then their value decreases based on the heat they generate. What I'm looking for is something with a tab that can be bolted to a heat sink.
Art,
Thanks for the kind offer. I was able to find the specifications on all three IC's and I am looking them over. I think the TA7317 will give the most bang for the buck. I would be most interested in your thoughts and comments.
d3imlay
In the Altec application they used a 190 F thermostat (TS1,2) which bolted to each heatsink. This application worked quite well and a similar part can be sourced depending upon the temperature you desire. Personally I always felt that the 190 F part was a tad too high.
Thanks for the kind offer. I was able to find the specifications on all three IC's and I am looking them over. I think the TA7317 will give the most bang for the buck. I would be most interested in your thoughts and comments.
d3imlay
In the Altec application they used a 190 F thermostat (TS1,2) which bolted to each heatsink. This application worked quite well and a similar part can be sourced depending upon the temperature you desire. Personally I always felt that the 190 F part was a tad too high.
burnedfingers said:
The testing I've done, which includes forcing an amplifier to fail, resulted in relay chatter under certain conditions. Sine wave testing, to determine trigger points, resulted in lots of chatter. This may not be real world conditions, but I figured if the relay trips, I want to find out why and not play pingpong with the relay.
zener_diode said:
How do you monitor temperature?
burnedfingers said:
The Phase Linear 400/700's had one of those thermal switches on the heatsink. It never worked. Maybe the trip point was too high and there probably should have been one for each channel.
I built up a prototype on one of those white prototype boards using the NTE7100/upc1237 and everything worked the first time, perfect. Trip points were right around -1.1 VDC and +1.3 VDC using the standard 56K voltage divider. I didn't have a cap in there because I only wanted to look at the DC trip point. Sine wave and music testing to pick a trip point will follow.
Does anyone have a recommendation for a music track to use?
burnedfingers said:
At my day job I work with relatively high power inverters up to about 100KW. We look at semiconductor temps and anything under 80C (176F) is cold. 190 F is about 90C. Max junction temps are usually around 125. You have to assume a few degrees of losses between amplifier transistor junction temp and the temp of the thermal switch. yeah, I think I'd rather see a lower trip point.
Incidentally, the Dynaco 410 used the thermal switches mounted right on the transistor.
The threshold of unbearable pain is around 55-60C. Generally speaking, if I can touch a part it's not too hot.
My favorite for testing is the 1812 ovature with cannon blasts. Caution, as it can be an amplifier killer!!!
My experience with the Altec series amplifiers goes back 17 years.
I have had some wierd experiences with this amplifier and the relay protection circuit hasn't failed. The only problem with this circuit has been C40 which is rated 1/50v cap which fails over time and thus R72 fails and CR15 fails. I install a 1/100v cap in place of the original and a 1/2 resistor in place of the 1/4 watt. I kept a log of all the Altec 9442 amplifiers that I modified and used it when I got into a Pi**ing match with some Altec engineers to prove my point.
On numerous occasions I managed to overtemp the amplifier and work the thermostats without a problem. Personally I like something a lot lower in temperature.
Your correct... the flame linears didn't work correctly but then they never sounded all that good either.
My experience with the Altec series amplifiers goes back 17 years.
I have had some wierd experiences with this amplifier and the relay protection circuit hasn't failed. The only problem with this circuit has been C40 which is rated 1/50v cap which fails over time and thus R72 fails and CR15 fails. I install a 1/100v cap in place of the original and a 1/2 resistor in place of the 1/4 watt. I kept a log of all the Altec 9442 amplifiers that I modified and used it when I got into a Pi**ing match with some Altec engineers to prove my point.
On numerous occasions I managed to overtemp the amplifier and work the thermostats without a problem. Personally I like something a lot lower in temperature.
Your correct... the flame linears didn't work correctly but then they never sounded all that good either.
d3imlay said:
I use a thermistor... connected as part of a voltage divider and connect
it to an A/D port on the micro.
One of the nice things about the circuit I posted is that it is scalable.
Anything from 5W to 500W or more can be accomodated by selecting
the appropriate transistors and resistor values.
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