System "Hiss"

Hello,
FINALLY finishing my install in a 2017 Ford F-150. I am using the factory 8" Sync 3 source. I have Dynaudio tweeters in the A-pillars and E650's in the doors. I'm doing 2 way active. Front stage is run off a Mosconi AS 200.4 and subs are 2 Stereo Integrity BM MK V's run off a Helix SPXL 1000 all run through a Helix DSP Pro. I noticed hiss when nothing is playing. I turned the gains way down on the Mosconi to get rid of it. Then I noticed the system gains in the Helix software were set quite high. This is my first time using a DSP so I am still learning. I turned the gains down to -25db in the software. I could then turn up the gains on my amp some...... but i still have them below probably 30% and that is with the Helix system gains set at -25db. If I unplug the rca's from the Mosconi I can turn the gains all the way up and no noise. When I plug the DSP back in to the Mosconi the noise returns. If I unplug the high level inputs from the DSP the noise is still there. So I am assuming the noise is being introduced from the DSP. Am I missing something? Is there something software related I need to change? Any help would be greatly appreciated. Thanks!

When you turned down the gain on the Helix did the hiss get quieter or stay the same? I'm not familiar with the Helix but does it have an input and output level adjustment? If so did you try lowering both?

It got quieter when I lowered the gain in the software. As far as I know there is only the gains for the independent channels in the software. I could be wrong though.....

Then keep lowering it in the software until the noise is an acceptable level. Don't worry where the gain is on your amps or anything else, all you need to be concerned with is finding the combination with the lowest noise while still reaching your desired output level.

Try -10 in the DSP...
and other values...

You want the DSP as high as it can go with clipping, but I do not know on your DSP how you figure where that setting happens.

It sounds like your input gain is way too high and needs to be properly set in the Helix. This is not done in the software, but by opening up the unit and changing jumpers to high level input and then adjusting the sensitivity pots. In the manual, look at page 18 section 3 for more details.

https://www.backesljud.se/produktfil...elixdsppro.pdf

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Originally Posted by jrwalte

It sounds like your input gain is way too high and needs to be properly set in the Helix. This is not done in the software, but by opening up the unit and changing jumpers to high level input and then adjusting the sensitivity pots. In the manual, look at page 18 section 3 for more details.

https://www.backesljud.se/produktfil...elixdsppro.pdf

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What is the range of selections for the input gain?
It is likely too high, or too low...
(i think maybe it's too low., so we have a 50/50 shot at being right... or it could be ok where it is?)

Let me rephrase. The input (from the source HU speakers) is too high a voltage while the Helix input is set for a lower voltage (default for Helix is 5-10v for speaker highlevel input), hence causing too high a gain because the Helix is, for example, set for a max of 6v when the highlevel input is maybe sending up to 14v. So the signal is getting over amplified and clipped, because the Helix was expecting a max input of 6v not 14v.

Following the instructions in the manual and using a 0 dB 1KHz test tone at 90% HU volume, the correct gain input for the Helix can be determined. It's possible OP has to change the input jumper to the 10-20v input and adjust the pot until he sees the clipping light turn on and then back off until it just turns off. At this point the Helix is then at the correct input. You'll know you need to change the jumpers if when adjusting the gain pot, you can't ever get the clipping light to turn off.

OP, before doing the gain pot adjustment, make sure any gain adjustments you made to the input in the software is back to 0.

^Well said.^

i guess if he had a way to measure it then it would be easy... or the does the DSP have some input clipping indication?

The helix does have internal clipping notification. It's a red light on the input side.

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You'll know you need to change the jumpers if when adjusting the gain pot, you can't ever get the clipping light to turn off.

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This might be wrong. It might be the clipping light never turns on when on the lower voltage jumper setting. Point is you need to make the clipping light turn on, and then back off the pot until it just turns off. This may require you to change the jumpers or it may not, depending on your input voltage from the HU.

you shouldn't have to crack the case and set gain pots.

helix dsp software -> dcm tab -> pc-tool configuration: ensure source level control is enabled.
helix dsp software -> io tab -> every input should be 0db (control is next to the input label on the left).

your per-channel outputs shouldn't be above 0db if possible and there shouldn't be any overall EQ boosts above 0db until you're more familiar with tuning.

my experience with the helix pro mk2 and helix mini:
- you can go up to +5db on input levels without adding any floor noise/hiss
- you can go +2-3db on the output levels without having clipping problems, doesn't seem to impact floor noise/hiss.

should be able to set amp gains at least 1/4 of the way up without introducing noise.

Thanks for all the help! I will delve into the suggestions tomorrow and report my findings.
Thanks again!


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Originally Posted by nadams5755

you shouldn't have to crack the case and set gain pots.

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Then why is that exactly what the Helix manual tells you to do? And it isn't "cracking" the case, which makes it sound like you aren't supposed to be opening it. It is 4 screws on the input side to remove the side panel and then the bottom panel can be slid out. He's running input from his HU speaker wires which are probably over 10v and that is why he must manually change the jumpers to high input 10-20v and adjust pots to compensate.