Pop-free startup/shutdown

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#43
#47
I did, somehow..

In the end, i saw that ltspice sim, so i thought a supply is needed. To be honest, i don't know why all this is needed, as the TPA3255 EVM normally does not need any additional help to mute/unmute the amp due to the voltage-supervisor.

From my own experience, cap banks behind the SMPS are pretty much useless in this application. Even unrelugated toroid designs don't need excessive additional bulk capacitance as shown here:

http://www.diyaudio.com/forums/class-d/287470-tpa3255-diy-discussion-design-etc-32.html#post5192359

Btw. Creeping distance:

http://download.wecogroup.com/docs/en/TechInfo_F4_Creepage_distance.pdf
 
#48
doctormord said:
I did, somehow..

In the end, i saw that ltspice sim, so i thought a supply is needed. To be honest, i don't know why all this is needed, as the TPA3255 EVM normally does not need any additional help to mute/unmute the amp due to the voltage-supervisor.
Click to expand...


the idea is simply to unmute / un-reset the amp after all the other items (bluetooth receiver/minidsp) have started up, and mute/reset/shutdown again faster than they do.. in case they exhibit any bad behaviour.

also ive read in several threads that the reset function should be used during startup/shutdown to avoid pops/clicks from the 3255 amp.. cant find it now, but possibly it was even you advising to use it during start/stop..?


i was trying to find a very simple/automatic way to do it that i could handle with my limited skills, and Khron has very kindly provided a solution you could probably build on a postage stamp.

edit: im not considering capacitors after smps.. where are you getting that idea from?
 
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#49
I think the on/off noises on tpa3255evm are highly dependent on the power supply and input device used. And while those noises may not damage the board, they could damage fragile, high-efficiency speakers, and that is I think what @robinlawrie is after here.

The RESET function is far superior to other solutions for implementing speaker protection with this board. Big props to @Khron for sharing a circuit to implement.

Since you don't yet have your connexelectronic smps800rs power supply, you don't really know what on/off noises it may produce. It is a soft-switching supply and I don't have any of those to test with at the moment, but it might be worth waiting until you get it. On the other hand, better safe than sorry!

And some other observations on this supply: It does have overload (overcurrent) protection, but not over-volt protection or PFC. An 800W power supply really should have PFC. The efficiency is excellent, but since you'll be driving a subwoofer with one of your tpa3255evm boards, you might consider adding a quiet fan to your case. Even a small amount of air circulation can make a huge difference in cooling. Also be sure to use a fuse or circuit breaker on the mains before the power supply.

I have been using the 2x4 HD as preamp with my tpa3255evm and they sound great together. The 2x4 HD is the most flexible and useful audio device I have. Are you planning to use the 2x4 HD to control volume, or will that be an upstream device? If you leave the 2x4 HD at 0dB with upstream volume control, it can produce on/off noises as well.
 
#50
Just thought of something else...instead of having a separate "sense" transformer, can' you pull either 3.3V or 12V off the board itself? Those get voltage while the board is in RESET, and that's how the onboard RESET works.
 
#52
gmarsh did a very nice microcontroller implementation on his Wiener boards. For the TPA3250 version, aka Wiener PRO, I used a front panel DPDT switch to cut power and also trigger the (much faster) mute/stby feature. That tamed a mild turn off thump from a powered subwoofer in the system.




BK
 
#53
bk856er said:
gmarsh did a very nice microcontroller implementation on his Wiener boards. For the TPA3250 version, aka Wiener PRO, I used a front panel DPDT switch to cut power and also trigger the (much faster) mute/stby feature. That tamed a mild turn off thump from a powered subwoofer in the system.




BK
Click to expand...

thats a nice simple idea!


id guess that a dpdt switch driving a relay to the reset would turn the amp off before the power dropped enough to cause issues, but id still need a timer of some kind for the turn-on delay.. probably end up being a similar complexity level to the design provided by Khron.
 
#54
CCSS, ill be using the minidsp volume control.. ive got a nice hacky way to control it using front panel switches ( a second minidsp remote, stripped and mounted internally, with frontpanel switches connected to the remote board. )

-since ill be paralleling an external ir reciever to the original one on the board, to add a front panel receiver, the internal one will be available to receive signals from my internal "remote"


in any case its entirely possible for the system to be shut down with a signal present and the volume up, so i figure a bombproof automatic reset function will be useful.

bear in mind that the majority of audio this amp receives will be via usb from htpc, so apart from the pc volume controls, a pre-minidsp volume control in the amp would be impossible.

wrt the PSU, it will (i think) have the heatsink removed, and a block/heatpipe connecting it to the side panel of the case.
 
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#55
in any case ive now got a bigger problem. my projector (benq hc1200) just blew its lamp.

its only got 900 hrs on it, and an official replacement costs almost 300 euros. so now im navigating the sea of fakes and qc failures to try to find a genuine philips bare bulb at the best price i can, as quick as possible.

boooo!
 
#56
Ok so, amps have arrived, smps is on its way, and im ordering the last bits and bobs. Trying to find a place which sells all the little pieces tp avoid multiple orders and silly shipping prices. Frustratingly i cannot find one company that sells it all. Closest so far is Conrad, but they do not sell the 2n5401 transistor, or any of the recommended alternatives ive found online. Due to my lack of skills, im gonna need to ask for one more spot of advice:

Any of these do as replacements for that transistor in Khron 's nice circuit?
http://www.conrad.it/ce/it/Search.html?search=transistor+pnp+to92&searchType=mainSearchBar

Thanks a lot you lot. Nearly there!
 
#58
OK just reanimation this thread to say the circuit is working perfectly. Switched the amp out of reset half a second after minidsp finishes booting up.

One (maybe) issue is the sense transformer gets surprisingly hot. No idea if that's normal. After the amp is on for an hour or so, plastic case of trafo is 59 degrees c. I'd have imagined such a tiny one with such a minimal load would stay cool? Trafo is this one:
http://cpc.farnell.com/block/vb-0-35-1-6/transformer-230v-0-35-va-6v/dp/TF01286
 
#59
ok tested for 2 hrs and sense trafo arrived at 85 degrees.. surely thats not normal.

ambient temp in case is around 36 degrees.

is there an alternative to a small transformer that could be used with the circuit? a tiny encapsulated smps or even just a high value resistor?

its so hot that its warming all the other components up around it. id be scared to leave it on overnight..
 
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