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Multi-Way Conventional loudspeakers with crossovers

JBL LSR305 tweaking
JBL LSR305 tweaking
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Old 4th May 2019, 10:24 PM   #81
etalon90 is offline etalon90  Canada
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Join Date: Mar 2004
Location: Cold Lake, Alberta
Hiss on mine is minimal and inaudible from my listening position.

If your bead help, I"ll replicate for sure.
on RTA, mine exhibit peak 15khz (usb mic limit higher than 20khz measurement) Seem like the high frequency garbage is there on mine too.

I read people using ferrite on the tweeter wire to replace the doughnut used by factory. Awaiting delivery...

Last edited by etalon90; 4th May 2019 at 10:26 PM.
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Old 6th May 2019, 08:45 AM   #82
z1024 is offline z1024  Russian Federation
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Those ferrite filters on the speaker wires are there for EMI compatibility to pass FCC(and other similar) regulations. Basically so it does not interfere with AM radios.

It is unlikely they will help with the hiss. I'm pretty sure the hiss is caused by the STA350BW itself. I saw other people suggesting it is caused by switching frequency leaking into the ADC input, but that seems unlikely as well. Something fishy is going on with the 384kHz carrier. Initially I thought it is the AM spread spectrum feature of the chip, but in this "noisy" mode the 384kHz spike is even higher, and with proper spread spectrum all spikes should be much lower and broader.
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Old 15th May 2019, 10:42 PM   #83
z1024 is offline z1024  Russian Federation
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Ok those ferrite beads on the PLL filter power supply lines had exactly zero effect on hiss.
Though PLL filter power now is super clean. No digital noise, just some 15mv 200khz sine waveform. Can be reduced to about 2-3mv with a 2.2uf cap in parallel, but also have no effect on the hiss.

So my only remaining theory now is that the STM8 MCU writes something to the STA350BW's registers that causes it to behave that way.

I don't have a proper logic analyzer to dump the I2C traffic from the MCU to the amplifier chip.

Could the that spread spectrum thingy I mentioned. It does seem to reduce the spikes in the > 1MHz range. Though I couldn't care less about EMI compatibility. I'd much rather it not hiss.
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