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      04-25-2012, 09:08 PM   #68
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Drives: '08 335i
Join Date: Jul 2008
Location: JAX

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Originally Posted by E30 Racer
Originally Posted by taibanl View Post
Why is the high level input, reportedly superior.
I'd be interested in the answer to this as well.

My HD600/4 has the same issues as reported above, but I've determined its an input signal issue (present even with the OE HiFi amp). The car is an E82 with HiFi + Technic harness adapter. Taking the front channels from the harness to the HD in conjunction with the low input setting (gains at min), I get noise. Switching to high voltage removes the noise but as mentioned above, it returns when the gains of the amp are turned up.

Recently I ran the front channels from the Technic harness into a Mosconi 6to8 DSP. This processor has low/high input settings as well. Interestingly, I ended up using a high voltage input configuration to the 6to8 and retained the low voltage setting at the input of the HD. Other combinations resulted in what sounded like a really compressed signal; very poor sound quality with an unnatural dynamic range.
One thing I don't like about the HD amps is the proximity of the power terminals to the RCA plugs. I found out that the noise was being picked up at the RCA plug from the ground wire that was running within 1/4" of the RCA plug. If you run the power wires and RCAs in opposite directions, there is no noise.
Mobridge DA2 > JBL MS-8 > ARC XDi 600/4 > JBL Gti 408 Mids & Vifa OT19 Tweeters; PG Ti2 1600.5 > Morel HCW-10 & IDMax 15