Bridged vs Stereo/Mono (Series vs Parallel)
I've been thinking about running the sub and amp at 8 ohm and bridged to start, since I'll be running a single sub (Dual 4 ohm voice coils).
The NU3000DSP is rated for the same wattage in 8 ohm bridged mode as it is for 2 ohm stereo/mono mode. While I expect that I'll build another of these, I don't think it will happen for a while, and I'm thinking 8 ohm bridged should be easier on the amp than 2 ohms on one channel.
I am also going to run a 12/3 cable just so I can have 1+, 1-, and 2+ available from the amp whenever I need them, without having to rewire my speakON cable to change loads.
That said, I don't want to have to pull the driver and re-wire the voice coils when the time comes to add another sub either, so I had been thinking about installing an impedance switch to switch the load over to 2 ohm (parallel) down the road. It then occurred to me that:
1. I may be running a single sub for quite some time,
2. It may be impractical and overkill to have a heavy duty switch that may only be used once, or even never.
3. Accidental switching could
happen, causing the amp to run bridged into a 2 ohm load!
Thinking about these issues, I decided that rather than use the standard DPDT switch for series/parallel selection, if I used a 3PDT switch I could easily switch between Channel A @ 2 ohm (on 1+ and 1-) and bridged @ 8 ohm (on 1+ and 2+), while making it impossible to run bridged into 2 ohms (a DPDT switch can switch between series and parallel, but for amp safety I need the 3rd pole to switch between 1- and 2+).
That would take care of my third concern, but it still leaves 1. and 2., so I decided to find another solution that would eliminate the switch altogether, while still allowing me a somewhat painless method to change the wiring (or not
change it, as the case may be).
I will install (two) 4 Position Molex jacks wired to the terminals of the speakON jack, with a single matching plug coming from the voice coils.
I can then plug into one jack (Jack 2) and be connected in series for 8 ohms from the bridged output of 1+ and 2+, and down the road simply remove the speakON jack (4 screws) to access the wiring, switch the plug to the 2 ohm parallel jack (Jack 1) and button it back up. I can do this for under $5 in parts.
(the panel mount ears will be removed):
I more than likely will only switch jacks once, but I will always have the option to switch back. The jacks I chose are about 1/2 inch tall x 1/2 inch wide, so they should easily fit through the speakON jack mounting hole. The jacks will be wired and loomed together in tandem with only two wires between them, for a lower profile and so that one doesn't interfere with the other when inserting or removing them through the speakON mounting hole. I drew the schematic out (see below) using an inline 4 jack and plug layout to make it easy to follow, but I will be using a 2 x 2 plug and jacks (shown above) to fit through the hole. If it still proves too tight, I will fabricate a mounting plate for the speakON jack and just make a larger access hole.
Here is the wiring layout:
I don't need to explain this for most of you, but I do so for the electrically challenged:
2 ohm stereo/mono, wired in parallel
Current flows from 1-
on the speakON (black wire) into Jack 1
, which has a jumper between Positions 2
. This routes the signal into the negative side of both
voice coils (in parallel, via the blue wires), out the positive sides, returning (red wires) to Positions 1
, which then continue back to 1+
on the speakON.
8 ohm, bridged, wired in series.
When plugged into Jack 2
, current flows from 2+
(green wire) through Position 2
into the negative side of the first
voice coil, continuing from the voice coil into and through Position 3
, then across the jumper to Position 4
, where it then is routed through the second
voice coil (a series connection) and back out through Position 1
on the speakON.