dB technologies Opera 405D

[Carlosraj]

Dear Everyone,

I am working on an Opera 405D powered 2 way speaker. The amplifier is Class D. The high driver has blown up, but the woofer is working fine. I opened up the amp and measured the voltage across the high driver terminals. It reads 35volts DC. The circuit uses a IRS20957S gate driver and 2 IRFR24N15D mosfets for the high frequency driver. I replaced the 2 mosfets but there is still DC voltage across the tweeter terminals. I did not have a new gate driver IC, so I took it out from another amp and replaced it. It is the same IRS20957S. There is still about 35 volts DC across the tweeter terminals. I am not very familiar with Class D circuits and I want to know what can cause the DC voltage to appear across the high frequency driver. Please advice.

Thanks

Carlos

[Enzo]

If there is +35 on the output, perhaps the -35 supply is missing. Open resistors can be just as bad as shorted transistors. You replaced the outputs. Were they bad? or was it just a guess? If they failed, there will be small parts involving the gates that may have failed. Are there ballast resistors? (the 0.2 ohm "emitter resistors") They go open when the transistors short. Read through the threads on similar models, Behringer makes a bunch, but so do all PA/monitor speaker makers. And they are all real similar.

[Carlosraj]

Dear Enzo,

I tested the 2 mosfets using an analogue multimeter and actually they tested OK, it is only as a trial that I replaced the 2 mosfets and the gate driver. I will check on the ballast resistors. I have tested all the transistors and doides on the board without isolating them and according to the resistance readings , I guess that they are all OK. I do not have a schematic for this amp. I cannot test the smd capacitors and I do not know their values. I will test all the resistors and get back to you.

Thanks

Carlos

[Carlosraj]

Dear Enzo,

I tested the 2 mosfets using an analogue multimeter and actually they tested OK, it is only as a trial that I replaced the 2 mosfets and the gate driver. I will check on the ballast resistors. I have tested all the transistors and doides on the board without isolating them and according to the resistance readings , I guess that they are all OK. I do not have a schematic for this amp. I cannot test the smd capacitors and I do not know their values. I will test all the resistors and get back to you.

Thanks

Carlos

Dear Enzo,

Today, I realised something, The woofer is working fine.
I switched "on" the amp and then this time took the voltage across the woofer terminals without connecting the speaker. I realise that there is about 28volts across the terminals. Then when I connect the speaker, the voltage goes off and there is sound. Before connecting the speaker, I also noticed that there is also about 28volts at the gate of one of the output mosfets, but after connecting the speaker, the voltage at the gate disappears and the meter shows a flickering reading. I guess that this means that there are pulses present at the gate which are coming from gate driver IC. When I connected the tweeter, there is a loud buzzing noise. When I checked at the tweeter mosfet gate, there is a fixed 28 volts. There is no flickering voltage . I guess the tweeter gate driver is not sending any pulses to the gate.

Is this because the tweeter gate driver is faulty or some component connected to the gate driver is faulty and causing no pulse signals at the mosfet gate. Please assist.

Thanks

Carlos

[Playloud]

Hello there,

I have noticed you are talking about the opera 405d.

I own a dB Opera 405d active loudspeaker and it broke.
The "symptoms" are that the speaker power on just fine. The speakers are working, they're not blown but there is NO sound
It just stopped playingwhile on a break I was playing some mp3s for the guests. NOT loud or anything
The service guy told me that it's the circuit board amplifier and it's not fixable
He said it needs replacing the whole amplifier board and that's gonna cost somewhere from 300 to 500€
Isn't that a little too expensive when the WHOLE speaker costs around 400 itself?
I'm just asking in case there is another way, or if the cost is cheaper and the lie to me
Is there any way I could find somewhere the spare parts, so my speaker is no more useless?
I am a professional vocalist/guitar player for many years, and the speaker is my tool. I know you understand


Thank you vey much for your time