The Subwoofer Conundrum
Subwoofers need a lot of power, and they are not to sensitive to high frequency noise. So speaker makers like to match their subwoofers up with some pretty low quality amplifiers, with switching power supplies and not much filtering. So whats the problem? The subwoofers sound OK. The problem we found is that you have to hook that subwoofer up to your ultra clean, ultra precision, perfect analog output from your DAC or Preamp. The presence of this noisy subwoofer amplifier just being hooked up to your DAC creates incredibly obvious noise and thus distortion on your main amplifier and speakers. Its like serving fine wine in dirty glasses. Its just intolerable.
The Nightmare Began
It all started when we had a customer demo our volume control in a Diamond DAC, and they preferred their preamp. Well that does not happen very often and we are always puzzled when it does, for in our experience, NO preamp sounds better than NO preamp. But suddenly we saw the pattern. An external powered subwoofer was present. We dug back into other cases where a preamp was preferred and sure enough, more powered subwoofers. So the testing began.
We hooked up an excellent speaker and external powered subwoofer and they sounded OK but certainly not what we had hoped for. We turned off the subwoofers and the sound came alive. Turned them on but disconnected the input. Still sounded great. Turned them on and hooked them up but turned sub level all the way down. Sounded horrible. It was not the sound of the sub that was the problem, it was the pollution caused by that nasty plate amp stuck in the back of the sub. Thus started a crazy time of desperate and incrementally more dramatic modifications to get both good bass, and completely transparent mids and highs. We finished and made music so sweet that no one who knew the speakers could believe what they were capable of.
The Solution is not an option but a necessity
The solution was a magic little box that provides a subwoofer output that is completely ground isolated from the source and blocks noise and feedback. We have made a whole range of these devices because when you are considering a powered subwoofer, the difference this kind of isolation makes is astonishing. So we have a configuration for every kind of system.
A Preamp Alternative
One of the roles of a preamp is to provide dual isolated outputs. But being an all purpose tool, it filters and isolates all the outputs. It blocks much of this sub feedback, but at the expense of the quality of the mains. This isolator allows a minimalistic signal path, with a single analog attenuator for volume control as the one we use in the DAC IV. So your primary AMP gets a perfect signal, and you still have an isolated subwoofer output without having to resort to active buffers. This passive isolator is not cheap, but compared to the quality of preamp you would need to obtain this level of isolation, its a real bargain.
Four Models - all $995 each.
Dual RCA In and Balanced Out (MSB DAC IV owners with Balanced primary AMP - recommended)
This unit is made for the MSB DAC IV users who use a balanced output for their main amplifiers and need a sub out. This module plugs directly into the dual RCA outputs on the DAC IV and provides an isolated balanced output for the sub. This is the best possible configuration.
RCA In and Out (MSB DAC IV owners with Single-Ended primary AMP and Single-ended SUB)
This unit is for use when you have a have a dedicated RCA sub output. It acts as a line filter. It is used on the MSB DAC IV if you are currently using the RCA output for your primary amplifier, and want to use the second RCA output for your subwoofer.
Balanced In and Out (MSB alternative)
This unit is for use when you have a dedicated balanced sub output. It acts as a line filter. It is used on the MSB DAC IV if you are currently using the RCA output for your primary amplifier, and want to use the balanced output for your subwoofer.
Balanced In and Dual Balanced Out (non-MSB DAC)
This unit is made for any DAC or Preamp user who have a single balanced output for their main amplifiers and need a sub out. This module provides a perfectly unmodified pass through, and a fully isolated balanced output for the sub. This is much better than a Y cable.
RCA In and Dual RCA Out (non-MSB DAC)
This unit is made for any DAC or Preamp users who use a single RCA output for their main amplifiers and need a RCA sub out. This module provides a perfectly unmodified pass through, and a fully isolated RCA output for the sub. This is much better than a Y cable.