Hi Damir,
Can you explain to me how the protection circuit works? How does it hook up to the speakers and how does it protect them?
Thanks, Terry
Hi Terry,
Somewhere in this thread I already explained the function, but in few words it works like this.
First why this is not a regulator with fixed voltage? Instead a zener reference it uses resistor divider and capacitors only as a reference(R1, R25,R2, C1, C2 in plus side, similar in minus side). It acts as a capacitance multiplier in a way because it filters the input voltage, but follows slow input voltage change as slow change in the mains voltage or prolonged sagging under heavy load.
There three types of protection implemented:
1. Over current and short protection. Q6 is a sensing transistors reading voltage drop on R9(same in minus side) and when conducts triggers combination of Q8 and Q9(acts as SCR) and activate Q7 and shut down Q14, Q13 and output. In the same time the minus side is shutdown too via D105(the same action happens if the minus side collapses and thus close the plus side. This is actually 2. protection, always both sides are closed simultaneously.
3. Loudspeaker protection from a power amp DC offset on the output. Q11, Q12,Q101, Q102 are sensing transistors connected to the power amp output(LL, LR on the schematic). There is big RC time constant(R19, C5, R119, R105) to prevent to be triggered with music signals. Those transistors trigger the same transistors (SCR) Q8, Q9.
There is one more feature, master slave behavior as the minus side follows the plus side via P1 connected o the plus side. P1 adjust the minus side on the same plus side voltage.
BR Damir
Hi Terry, there two inputs, LL and LR(Loudspeaker Left, Loudspeaker Right) look the schematic. I use PS regulator with three inputs for mine three channels amp.
Yes I use a bridge rectifier ad some caps http://www.diyaudio.com/forums/solid-state/182554-thermaltrak-tmc-amp-6.html#post2910364 and the photos here http://www.diyaudio.com/forums/solid-state/182554-thermaltrak-tmc-amp-7.html#post2960995
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In the circuit, are R26, D9 ad D10 important? If so, how critical is it that D9 be 22V?
Thanks, Terry
D10 red LED indicates when the PS Regulator was switched off in case of an error triggering the protection. This schematic shows a regulator with 45 V DC input and 40 V DC output(about 5-6 V was dropped on serial transistors Q13, Q113) and D9 chose for that voltage but it's not critical, for higher voltage regulator this zener voltage should be increased accordingly. This regulator can work with higher input voltage, up to the transistors type used(BC546/556 in this case), but could be adopted for even higher voltage using higher voltage transistors.
BR Damir
D6 should be reversed, D6 and D7 are 10V zener connected back to back and if difference between + and - polarity is bigger than 10V it will trigger protection. To test the regulator first disable the protection on both polarities, by shorten R13 and R113. After that you have to adjust - polarity with P1 to be the same as + polarity (outputs of course). After that remove shorts from resistors. To test the loudspeaker protection, touch one output with one hand and with other touch in the same time one of the loudspeakers input(LL or LR). The protection should trigger and shut down the outputs. To reset the protection switch off the power and wait a bit to discharge big caps.
BR Damir
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I'm using MJL21193/94 for the pass transistors but I have 0VBE on the MJL21194 so only about -5V output on that side. I will try shorting the protection in the morning and see it that helps find the trouble. I already spun D6 and that didn't fix it. All the transistors test right with a diode test. If I can't find the issue I will mark up a schematic and let you take a look.
Thanks, Terry
Thanks, Terry
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If + and - outputs are not equal (>10 V difference) than the protection triggers and shut down both output.
BR Damir
By the way, it is good to have some loads at the outputs during testing, let say 330R 10W, or 470R 5W.
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Hi Damir,
I tried shorting R13 and R113. I still have a issue on the - rail. I created a spice file so I would have something to compard it to but I can't get the spice file to work right. Perhaps you are someone who is better at Ltspice than I am can take a look at it and hopefully get it working so I will have a reference to help me track down what is wrong with my board.
Thanks, Terry
I tried shorting R13 and R113. I still have a issue on the - rail. I created a spice file so I would have something to compard it to but I can't get the spice file to work right. Perhaps you are someone who is better at Ltspice than I am can take a look at it and hopefully get it working so I will have a reference to help me track down what is wrong with my board.
Thanks, Terry
Hi Terry,
I have my spice file. Just came from Classical music concert and if you put the voltage on the schematic you've got I will take a look in the morning, it's late here.
BR Damir
OK Terry, you don't need a variac here, no danger to burn something is not an amp. The voltages values will help. The simulation is a bit different than to simulate an amp.
Did you use a resistors to load the output. I'll be back tomorrow morning.
BR Damir
Hi Terry,
I thought that you talked about real regulator and that you can show some voltages, but OK here are spice files: normal work, overload, and loudspeaker protection triggered.
V3 or V4 can be used to simulate an amp DC offset, used very low frequency of 0.1Hz.
BR Damir
PS. You have to click on the voltages or current to get the waveforms and values.
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