Lex*Toy

00 Nakamichi SC400 Radio

Interceptiing leads from the balanced headunit (HU) 4 positive and 1 signal ground. Converting to unbalanced system to add AUX line in directly to stock amps. Bypassing HU completely.

The issue is that while the door speaker amps are playing perfect, the subwoofer amp is very very very low. Unheard really.

Hooked up laptop to diagnosis, where the subwoofer played as normal only when ANY balance from L to R or vice-versa was enabled on the sound card.

Why is this? How can the sub amp cancel itself out?

engin_ear

iTrader: (1)

Probably because the sub amp is summing the left/right channels to create one single sub drive. You may have the polarity reversed on one of the lead pairs, causing the cancellation of the low-freq signal. If you set the balance off to one side, it makes one channel louder, and they no longer completely cancel. The solution is to check ALL of the polarities of what you've hooked up, and what the amp inputs are expecting.

Jerry

Lex*Toy

Can you please let me know what you mean by the last phrase? "What the amp inputs are expecting"?

Are you referring to voltage output or phase inputs? If phase, not sure how to check.

Lex*Toy

I was able to check all the polarities where it matched up.

Upon closer inspection of the standard 3.5mm input to L/R RCA Output, I noticed that the phase "cloud" eliminated itself and the system sounded clear immediately after removing either the Left channel RCA or Right channel RCA.

With either unpluged (Left Channel RCA or Right Channel RCA), both speakers sides (Left and Right) still played regardless of the fact.

Can anyone explain this?

Lex*Toy

Does anyone know?

engin_ear

iTrader: (1)

This is exactly what I was saying.
You need to make sure that the polarity of the signals (L & R) match, all the way from where you tap into them, to where they enter the amp. Make sure you know which one is the + wire, and which is the - wire for L & R channels. Carry them straight thru to the amp, and make SURE you have the L+ wire plugged into the L+ amp terminal, R+ wire plugged into R+ terminal, and likewise for the - wires. If you are goin thru any other pieces of equipment (other than just wiring between your headunit and amp, make sure you know which wires are the + and - going into and out of those units. Once you get them consistent, your audio will return.
Also check for any Phase Reversal switches on your amp. Set them to 0 degrees if any are there.

The problem is that the way you have it wired, the phase of the L channel is 180 degrees different from the R channel, causing almost complete cancellation of the bass waveform. When you unplug one, there can no longer be any cancellation, and the audio returns. Something is flipped in your wiring, or equipment. Check out all of the above and then report back, we'll wallk thru it and see where you may need to flip the + and - wires.

engin_ear

iTrader: (1)

If you are only coming out of a laptop with a 1/8" jack plugged into the sound card, and the other end of that cable has RCAs that you are plugging directly into the sub amp inputs, it's hard to have that wiring backwards. In that case, there is probably a phase switch for one or both of your amp channel inputs that you need to set correctly before your audio will return. Either that or someone worked over the amp and reversed something or put something back wrong.

Lex*Toy

Tell me if this sounds right.

I know this is very cliche, but it seems as if it was a grounding issue with the iPOD (Aux) neg. After researching more about the slight hum in the test setup, I made a seperate solid ground as close to the aux unit as possible instead of tying into the HU signal ground.

I decided to try this after reading an online article that audio circuits only "hum" when do they not know what silence sounds like. Only when there is not a clear negative reference.

After bolting-in a strong Negative, the phase seemed to adjust as normal, the hum severely diminished, and the bass response seemed to return.

Does this sound right to you? Seems almost to easy to solve all of the test issues. Thx.

Lex*Toy

Forgot to mention that this is a Nakamichi IPOD install between the HU and the factory amps with auto swtiching relays.

4 (+) speaker leads and 1 signal ground

Of course, Im pulling my hair out but it seems as if I have weathered the storm.

Will report back once SC400 integration is complete

engin_ear

iTrader: (1)

Your Nak headunit speaker outputs should have + and - balanced leads. The - is not signal ground. It is not a common ground system. The SHIELD for each pair is usually tied to ground. Don't know how this will affect what you are doing, gven the equipment involved. Make sure you've grabbed all of the + leads for the speaker outputs of the headunit!!! Still sounds like you need to trace each wire and double check what you've done. You're going to wind up with the "hack" method if you don't.

Lex*Toy

Give me some credit here, I do have a little bit of an electrical engineering background.

Since noone else is chiming in here, Im taking this to the PM.

See you there. Thx.