Using McCormack DNA-0.5 Deluxe as Mono Amps

Hi Morgandogge -

There are a variety of ways to use a matched pair of stereo amplifiers to run your main speakers. There is no “Mono” switch on the DNA amps, but you can simply use one channel per amp (leaving the other channel unused), or you can use one amp per speaker in what is called a “passive vertical bi-amp” arrangement (passive horizontal bi-amping is also an option, but I do not recommend it).

Passive vertical bi-amping works very well and is easy to do if you have a matching pair of stereo amps, but does require that your speakers have bi-wire inputs with the jumpers removed. You simply assign one DNA-0.5 amp per speaker, use a Y-connector (typically) to run the same signal to both inputs, and connect one channel output to the speaker's high-pass input, and the other output channel to the low-pass input (which obviously requires a total of 4 independent speaker wires). The power each amplifier produces does not change, but now each speaker has its own amp so the net system power and dynamic headroom is increased.

Because you have a TLC-1, you have an additional option: you can use the passive output to connect to the high-pass channel on each amp, and use the buffered output to connect to the low-pass side. This requires a total of 4 independent interconnect cables which should all be the same for best results (along with the speaker cable). The potential advantage of this is the slightly superior bass performance of the buffered output. Connect the side of each amp being fed from the buffered output to the low-pass input on your speakers. If you don’t have 2 matched pairs of interconnect cable, skip this idea and just use a good quality Y-connector to bridge the signal across each amp’s inputs.

I often see people trying to use this technique while playing “mix-and-match” with the speaker cables and/or interconnects. Please do not allow yourself to fall into this trap. It may seem like a good idea, but it usually is not. The way this idea works best is when all of the connections are matched as closely as possible.

Finally, there is the option of having your DNA-0.5 amps converted to true monoblock operation. This is one of the upgrade options from SMc Audio. It provides balanced / unbalanced operation, and the power goes up to 400W @ 8 Ohms per amp. I like this option a lot and feel that it gives the best overall performance, but it requires sending the amps in for upgrade work. You can try the passive vertical bi-amp for free (or fairly low cost) and see what you think.

Have fun!

Steve McCormack
SMc Audio

I've been running the passive vertical biamp arrangement Steve describes for a couple of years now and have had great results (I'm using Electron Kinetics Eagle 4 amps, not DNA 0.5). I considered converting them to monoblock but after asking the speaker designer which to use, I was advised biamping with 125 w/c would be better than a 400w monoblock, so I saved my money. FYI my speakers are Von Schweikert VR4genIIIs, and I think your results are very speaker dependent as I received the opposite advice when asking the same question about my Totem Mani-2's.

Could they be parallelled with jumpers? Maybe using a small resistor (<1 ohm) between the outputs to reduce circulating current?

There would be an advantage driving low impedance speakers this way. Less voltage but more current than bridging.

Steve: Greetings! Would you be willing to comment on why you do not recommend "passive horizontal bi-amping"? Thanks, Din

In theory, paralleling the outputs of a stereo amplifier (with both channels being driven by the same signal) will double the current available to the load. This would seem like a simple way to make a high-current, mono amplifier. In practice I do not trust or recommend this technique. I feel that there are too many opportunities for things to go wrong, become unsymmetrical, and end badly (with a lot of smoke). It might work well for a while, but I just don't trust it.

Hi Din -

Passive vertical bi-amplification is defined as using one amp per speaker, while horizontal bi-amping uses one amp for the highs of both speakers, and another amp handles the lows. The "passive" part refers to using the speaker's own internal crossover network to do the range splitting and signal conditioning, rather than an external electronic crossover.

Passive vertical bi-amplification is easy to do (and works well in my opinion) so long as you use a matching pair of stereo amps, along with matching interconnects and speaker cables (4 separate lengths required). The trap that many audiophiles succumb to is to start mixing-and-matching different cables with the thought that some are better for highs and others are better for lows. This may seem like a good idea, but it usually just messes-up the system coherence. This is actually the reason why some high-end speaker designers refuse to provide bi-wireable inputs - it gives the user the opportunity to screw things up.

In my opinion, passive horizontal bi-amping will never work as well as the vertical option. Ok, why? Let's assume you are using a matching pair of stereo amps. In the vertical approach, both channels of each amplifier see the same input waveform, and the only difference in the output is the amount of current vs. frequency. There is no difference crosstalk across the common power supply and ground system, and that's a good thing.

In the horizontal approach, each amplifier sees a different left channel / right channel input (just as it would in a normal full-range setup) so you do have the usual crosstalk and signal interference across the power supply which degrades performance to some degree (unless you have a perfect amplifier - good luck!).

Ahh, but you have the solution! Just use 2 different amps - one chosen for the highs, and another that has great bass. That should do the trick! Well, sorry - we're right back to that whole "loss of coherence" problem, and we've complicated the issue by adding the need for separate level controls to match the amp's volume. This simply doesn't work well (or very rarely) with speakers whose crossover point is usually somewhere in or close to the midrange. This is not to say that it can't be done, but having it turn-out well and actually conferring an advantage is difficult and unlikely in the extreme. But this has not stopped a lot of folks from trying. Hey - it's a hobby after all, and monkeying around with this stuff can be a lot of fun and a worthwhile learning experience. You've been warned ;-)

Best regards,

Steve McCormack
SMc Audio