Ok im trying to get my head round how to ensure my speakers are safe, using my new diy amp.
Setup is as follows: 2x tpa3255 evm boards, signal from minidsp 2x4HD bare board in same case. All powered by one connex smps 800w psu.
Obviously with one psu and a traditional "kill the mains" power switch, i cannot easily do a startup/shutdown sequence, or use the "reset" jumper on the 3255 boards. How do other people deal with this issue? I cant be dealing with multiple on/off switches and a specific "sequence" its gotta be kid, and powercut proof.
I also need something simple, budget is finished, and there is barely any space left in the box!
Setup is as follows: 2x tpa3255 evm boards, signal from minidsp 2x4HD bare board in same case. All powered by one connex smps 800w psu.
Obviously with one psu and a traditional "kill the mains" power switch, i cannot easily do a startup/shutdown sequence, or use the "reset" jumper on the 3255 boards. How do other people deal with this issue? I cant be dealing with multiple on/off switches and a specific "sequence" its gotta be kid, and powercut proof.
I also need something simple, budget is finished, and there is barely any space left in the box!
Might something like these help?
Loudspeaker Protection and Muting Figure 3, in the "Muting" section
Project 104 - Preamp/ crossover muting circuit
Power Supply for Preamps The "top" part, with the "AUX" output
Loudspeaker Protection and Muting Figure 3, in the "Muting" section
Project 104 - Preamp/ crossover muting circuit
Power Supply for Preamps The "top" part, with the "AUX" output
The speaker thump at startup occurs bcos the cap bank at zero charge is a short circuit for the trafo and causes a sudden inrush of current.
What you need is a soft start board, which puts a set of resistors in the AC path so that the sudden inrush of current at startup is avoided.
After some time duration, a relay switches the resistors out and direct power goes to the trafo.
What you need is a soft start board, which puts a set of resistors in the AC path so that the sudden inrush of current at startup is avoided.
After some time duration, a relay switches the resistors out and direct power goes to the trafo.
I don't suppose you've taken a peek at any of the links i posted, have you? 
Granted, if you're using an SMPS to power everything, you might need the smallest transformer you can get your hands on, just enough to power a small relay or two (since the simplest circuits rely on AC detection, and it's not the most "healthy" option to hook them up directly to unisolated mains).
Granted, if you're using an SMPS to power everything, you might need the smallest transformer you can get your hands on, just enough to power a small relay or two (since the simplest circuits rely on AC detection, and it's not the most "healthy" option to hook them up directly to unisolated mains).
Sorry, yes i did, its interesting using the ac directly from the switch to trigger fast disconnect of relays. However it seemed that the circuit proposed was drsigned to also provide dc detection and was (possibly?) more complex than what i need.
I guess i should also investigate using a similar circuit to trigger the reset/shutdown function of the 3255, as this would avoid needing high power relays for 6 channels of output. To be honest im surprised this aspect of speaker protection is not automated on these latest-generation chips..
I guess i should also investigate using a similar circuit to trigger the reset/shutdown function of the 3255, as this would avoid needing high power relays for 6 channels of output. To be honest im surprised this aspect of speaker protection is not automated on these latest-generation chips..
From what i can see, that aux trigger circuitry uses the half-wave rectified AC as the signal, and one of the DC rails to actually supply the power to the relay (if that's the route chosen).
Since your setup is a single-supply deal, the second version of the circuit (single-supply) would be closer to your scenario. You should be able to use one of the already-existing DC rails for that, but as i mentioned earlier, you would need the (physically) tiniest transformer you can find (for a decent price), simply to provide the "trigger signal".
Since your setup is a single-supply deal, the second version of the circuit (single-supply) would be closer to your scenario. You should be able to use one of the already-existing DC rails for that, but as i mentioned earlier, you would need the (physically) tiniest transformer you can find (for a decent price), simply to provide the "trigger signal".
I had power up/down problems with a irs2029 system.
On power down I would get a siren type noise for 1 second then a massive thump through the speaker.
I found out it was mainly to with too big smoothing capacitors causing slow discharge.
I got in touch with IR and they said I needed a reset circuit to put 2092 in reset mode on power down.
So I added a small PIC micro with a2d. It monitored VCC and when it got below a certain voltage it put the 2092 into reset mode.
This worked great.
I guess you could do the same with a comparator circuit.
On power down I would get a siren type noise for 1 second then a massive thump through the speaker.
I found out it was mainly to with too big smoothing capacitors causing slow discharge.
I got in touch with IR and they said I needed a reset circuit to put 2092 in reset mode on power down.
So I added a small PIC micro with a2d. It monitored VCC and when it got below a certain voltage it put the 2092 into reset mode.
This worked great.
I guess you could do the same with a comparator circuit.
OP says that he uses an SMPS of 800W, what does this have to do with inrush? These things are designed to ramp up when turned on, unless it is very very crude. Even the El-cheapo ones on eBay uses a chip that ramps up over a few seconds precisely so it would not take out the output devices..
I read this on their web site:
This power supply is only suitable for BTL amplifiers, which use single rail supply, or other applications where a single output of 36V, 48V, 60V or 72V is required. It is not suitable for Class AB or class D amplifiers which are configured in Single Ended operation mode, for these amplifiers, consider using the SMPS800RE which is almost identical except the output section.
This power supply is only suitable for BTL amplifiers, which use single rail supply, or other applications where a single output of 36V, 48V, 60V or 72V is required. It is not suitable for Class AB or class D amplifiers which are configured in Single Ended operation mode, for these amplifiers, consider using the SMPS800RE which is almost identical except the output section.
I'm a bit new on this stuff and not up to date. Years ago we used Thermistors ie inrush limiters to stop the pop . This is a common device that cost about .40 us in volume. Check out NIC. A relay on a timer can be used to remove the device after start up. KISS here. I just bought a Lepai 2020TI and it's a nosy rascal. Some day, when I have the time I'll try adding this to the input. A wall wart switcher ,12V 3 amp came with the Lepai. Not a bit familiar with Class D or PS's currently in use so it's a work in progress.
If you use a SMPS, and if the cap bank is big, the phenomenon still occurs, but the SMPS isnt able to cope, and it shuts down.
the smps i have selected actually features a thermistor, and soft start.
im more concerned with random startup noises coming from the minidsp, connected bluetooth receiver , power amps, or connected htpc (connected to minidsp via usb)
and random shutdown noises.
i believer the psu switch-on thump should be minimal to non-existant with this psu.
maybe it will all be fine without any extra protections, but i have seen suggested that the tpa3255 does pop a bit if you do not use the "reset" switch during start/stop.
ok so, if i am understanding correctly, i can use some variation of the "aux" part of the circuit described here:
Power Supply for Preamps
running from, say the 12v regulated dc im using to supply the minidsp.
i would then provide an unrectified AC source from a tiny transformer as the signal.
the output of this circuit would be used to drive a relay to disconnect the speakers..
would it be ok to use the output of such a circuit to drive the "reset" function of the 3255?
as far as i can understand, using the "reset" function of the boards correctly during startup and shutdown i should negate the need for relays on the speaker outputs? rather useful if so, as with 6 channels to switch, a relay board for the power side of things would get quite bulky.
Power Supply for Preamps
running from, say the 12v regulated dc im using to supply the minidsp.
i would then provide an unrectified AC source from a tiny transformer as the signal.
the output of this circuit would be used to drive a relay to disconnect the speakers..
would it be ok to use the output of such a circuit to drive the "reset" function of the 3255?
as far as i can understand, using the "reset" function of the boards correctly during startup and shutdown i should negate the need for relays on the speaker outputs? rather useful if so, as with 6 channels to switch, a relay board for the power side of things would get quite bulky.
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