2v HU Pre-out doesn't seem enough for Helix DSP

[chilly]

Hi all,

Another new member here with a problem.

My Kenwood HU has 2v RCAs. I've checked the clipping point with a scope and it seems to clip at 34 (of 35) while playing a 0db 1000hz sine. At that point it is outputting very slightly over 2v. Below 34 the voltage drops very quickly.

At volume 34 when I try to set the input gain on the Helix Mini DSP I can turn the gain screw all the way up without the clipping light coming on.

I should also mention that I get an awful alternator whine which I presume is as a result of the DSP gain being set so high.

Any suggestions please?

[Haakono]

Some questions:

1. Is the Helix not outputting a decent signal to the amps, or are you just upping the input gain to the max to try to having it clip, and then turning down a bit?

2. You can also adjust input gain in the PC-Tool software, from -10db to +10db, at what level is it now?

[chilly]

Thanks for the reply.

1. I'm getting huge alternator whine which I didn't have with my Bit Ten. It feels like I'm having to crank the Helix Input gain all the way to max and even then the clipping light isn't turning red. This makes me think the voltage from the head unit is too low maybe?

2. I've looked everywhere in the PC-Tool but I can't see anywhere to adjust input gain. I'm sure I'm just missing it. Where do I find that?

[Haakono]

The input gain adjustment in the software is here:


Try setting the gain control on the actual DSP halfway down, and adjust the gain up a bit in the software to see if anything happens to the alternator whine. Which is a separate problem that needs to be adressed, but boosting the gain to the max will probably add to the issue.

However, does the gain need to be that high to achieve enough output signal for the amps? Are you also maxed at the output levels for the RCA outputs in the software for the amps? The higher the gain is set, the more noise and interference is picked up along the way, including alternator whine.

[goatpanda]

The Helixes have a selectable ground lift switch, maybe try a different ground setting to see if it helps with your alternator whine? From the manual:

Ground lift switch
The signal ground of the HELIX DSP.3 is galvanically decoupled from the power ground. In many cars this setup is the best way to avoid alternator noise. Nevertheless, there are use cases where it will be necessary to directly connect input and output ground or to tie both grounds together via a resistor.

Therefore the Ground lift switch has three positions:
- center position: input and output ground separated.
- left position: input and output ground tied together.
- right position: input and output ground connected via 200 Ohms resistor.

[jtrosky]

Just a heads-up - the input gain in the software will only show up if you have "Source Volume Control" setting set to "enabled" under DCM->PC-Tool Configuration. So if you don't see it, check that setting - it probably needs enabled.

Also - the Audiotech-Fischer US reseller (@dobslob) mentioned that a recent software update changed the default setting for the ADEP.3 Configuration "Compatibility Model" setting under DCM->ACO Featrues (if your Helix is an ACO-enabled mode - and the DSP Mini is) - and that it was causing ground-loop-related nosies. So also check to make sure the ADEP.3 "Compatibility Mode" setting is set to "Disabled".

[chilly]

Thanks for the help guys. I would never have found that software gain control let alone how to enable it.

I'll have a go at reducing the hardware gain and increasing the software gain tomorrow (if it ever stops raining!)

I didn't mention that my vehicle has two large batteries (factory fitted) so I guess it has a pretty high output alternator. I have a feeling I might end up having to fit a suppressor in the DSP power feed.

I've ordered a new Kenwood HU with a 4v Pre-Out. Hopefully that might help a little too.

Now I just need to try to figure out why I get the message "Desired Devitation Not Reachable" when I use Auto Tune.

[Haakono]

The input gain on the DSP mini is adjustable from 2V to 4V, meaning that with the gain set at max, you will need 2V to max it out, and probably some margin over that before clipping. So; gain set to minimum = 4V to max it, gain set to max = 2V to max it. Usually the gain control on an amp set to max, will only need about 200mv (0,2v) to max/clip the input driver. So the Helix DSP is a bit different compared to the input level/gain control on typical amps.