Power up - loud snap

I had a similar problem with irs2092 based amps only it was on power down I got a huge thump or a siren type noise. I fixed it with a small PIC micro monitoring the psu and holding the 2092 in reset if the psu was too low.

You could try an RC on the shutdown pin to hold the chip off until power supply settles.
 
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Mark2727

Member
2009-03-23 12:53 am
Nigel,

I'm not understanding what you did. Could you give me a sketch and do you mean by "PIC", a printed integrated circuit?

Vacuphile I think the sound is ridiculously good for under $25, and really worth more money. I find everthing to be balanced and with no listener fatigue. Everything sound fast and detailed but not harsh. Two issues are this turn-on snap and also a small (and I mean really small) bit of background hum. I may up the value of the 470uF power supply capacitors to 1,000 uF if I get the go-ahead from someone more knowledgeable than I. Wouldn't you know it? I don't have any in the parts bin! This may only be an issue because I run La Scalas and they are really efficient. Bottom line: This was really easy to assemble, sounds great, and is a bargain.

tauro I don't know for sure, but I guess they are not. I'm no expert for sure, but I can see the circuit is pretty basic (and no doubt that's why it sounds so good). Sad part is I'm not getting much help from Jerry - he just says he's working on a solution. So, I'm just NOT turning the thing on and off at all really -- let 'er rip with my Pass B1 buffered preamp. Both amp and preamp use little electricity, so what the heck.

I have a delay device, but I couldn't get a measurement on it when I hooked it up, and the more I think of it, it probably would not work in this application anyway. Those are for tube filaments, then delay the main B+ power. So, you'd still get a big power "in" with this Jerry's Amp, only 40 seconds later. Right?

Mark
 

Mark2727

Member
2009-03-23 12:53 am
PS: It was suggested to me to put a capacitor across the power on/off switch. This of course, did nothing!

Additionally, I can tell you fellows that I'm awaiting a better power supply than what I've temporarily rigged. I ordered one of those sort of open cage looking affairs with the jacks to screw in your wiring. 24VDC, 2 amps. That was supposed to be here yesterday. Oh well. For the meantime I'm using a DC power pack type unit that is rated on the label at 12VDC, but I measured it at 18,4VDC. So, I'm waiting for the newer power supply to see if possibly the tiny bit of hum is being caused by the out of spec. salvaged one. Could be, but with my luck I doubt it.

Mark
 

Mark2727

Member
2009-03-23 12:53 am
The Velleman kit appears to require a separate power supply.

Looks complicated.

No English on the build manual.

There's got be another way. I have been told that something like a CL-90 won't work. Current rush limiter.

Other digital amps I have don't have this issue and are very small physically. I'm wondering what they do? Must be something built into the chip.
 
Hi,
I checked the schematic and it is not using the mute and also the shutdown pins. They are connected to ground means they are enable all the time.
I agreed with nigelwright7557 suggesting using a micro. You can use the Nano 8 from Basic Micro cost 2.98 and it is program in basic. You can control both pins Mute and shutdown easy with the micro. Just programming.
 

Mark2727

Member
2009-03-23 12:53 am
Nigel/Tauro:

Are you fellows telling me there's a pin/leg on the Texas Instruments chip that is running to ground, and should be run through some sort of microprocessor instead? And that that device must be programmed in BASIC?

Interesting. But it may be beyond my technical skills.

Look...I'm just a beginner. So sorry for the dumb questions.

Nevertheless, I'm off to look at a pin out of that chip.

Wow, this gets crazier all the time. Thanks!

Mark
 
Hi,
In the schematic the shutdown pin 2 it is connected to the + voltage means that the shutdown it is disable. Zero volts means enable. The mute pin 3 it is connected to ground. Zero means that the mute is is disable. 2 volts means that the mute it is enable. How much voltage your are using in you PS? I may come up with a schematic using the basic micro. I can make the circuit using the micro basic nano 8 if you are interesting. I will programming it for you. It is a simple program.
 
I usually use a dropper resistor and zener to power the microcontroller as it needs very little power.
The micro is an internal oscillator so is easy to use.

I think the micro will drive those pins direct.

When I did my circuit for the IRS2092 I had to use an opto coupler to drive its reset pin but you probably shouldn't need to do thi9s.
 
This problem must have an easier solution than the complicated schemes with external parts and programming. The application sheet says the following for the shutdown mode:

"The TPA3122D2 employs a shutdown mode of operation designed to reduce supply current (ICC) to the absolute minimum level during periods of non-use for power conservation. The SHUTDOWN input terminal should be held high (see specification table for trip point) during normal operation when the amplifier is in use. Pulling SHUTDOWN low causes the outputs to mute and the amplifier to enter a low-current state. Never leave SHUTDOWN unconnected, because amplifier operation would be unpredictable.
For the best power-up pop performance, place the amplifier in the shutdown or mute mode prior to applying the power supply voltage."

So place amplifier in shutdown mode prior to applying power. Use a 3 pole toggle switch that has the middle pole grounding an RC circuit tied to the shutdown pin with a suitable time constant to drain it prior to power on. The RC circuit takes a finite amount of time to charge and reach positive logic. The 3-pole switch then has to go to the third position ("on") to apply power to Vcc which then has to charge the RC circuit through a large R value so that the amp stabilizes before the shutdown is disabled. Assuming the amp stabilizes in 2 seconds and stated the logic value is 2 volts (p 3 of spec sheet), using the RC time constant equation: Time = 0.7 RC, set R=100k ohm, solve for C=2.0 sec/(0.7*10^5 ohm)=28 uF. Kind of a big cap, but easy with an electrolytic here.
Does this make sense?

You need a 3-pole switch, a 30 uF 35 V electrolytic cap, a 100 kOhm resistor. Problem should be solved. No programming or fancy external IC's.

EDIT: You can skip the 3-pole switch by putting a couple of 1 Meg ohm resistors in series to the positive electrolytic cap terminal to drain it to ground slower than the 100 k ohm charges it (20 x in this case). Then it is all passive.
 
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