Threshold S/300 Used In Mono Mode

Hello All,
I love the Threshold S/300 I brought used so much I plan to purchase a second one and use them in mono to drive the Magnapan 1.6 I plan to buy as soon as I relocate.

My question is, can these amps be used in this manner and how can I accomplish this feat? Is it a difficult thing to do? Is there anyone using these great power amps this way at present? By the way, I am using a Classe DR-5 pre amp and the sound I am getting is wonderful, full and very musical. I believe the sound will be greatly improved when I get the Magnapans involved.

My music preferences tend towards small and large scale orchestral and choral classical works as well as large a small scale modern jazz works and big band music. I love a wide, tall and large soundstage with plenty of front to back depth. I look forward to all comments and suggestions. Thanks all.

I suggest you relocate before you decide on speakers, especially planar speakers, then think about amplification. Should you decide to go with mono Thresholds, the SA 1's might be a better way to go.
I agree with Unsound..I would personally look for a pair of Threshold SA-1 or similar quality Monoblocks for the long haul..Even though you might get more power with the second Threshold S/300 you may noy achieve the sound quality you expect by using two S/300 amps in mono...Just my gut feelings on the subject..
Hi Bob,

Glad the amp is working out well for you.

I don't recall if the S300 has provision for operation in bridged mono mode; perhaps one of the others can clarify that.

Most amps which can be used that way have a switch on the back to select stereo or mono operation, and I don't think it has one. When mono operation is selected with the switch, the polarity of one channel is inverted, and the speaker is connected between the two red "hot" output terminals, with an identical input signal (corresponding to one channel, either left or right) being fed into both of the amplifier's inputs. That results in twice the voltage being applied across the speaker, compared to the normal stereo configuration in which the speaker is connected between one hot terminal and ground.

There are a few designs which don't have such a switch but provide for bridged mono operation by always inverting the signal in one channel; having the black output terminal of that channel "hot"; and the red output terminal of that channel in common with ground and the black terminal of the other channel.

But in any event I don't think you would want to operate in bridged mono mode with the Maggies, if they are what you end up purchasing, for three reasons:

1)While bridged mono mode substantially increases the power the amp can put out, it results in the amp seeing the speaker's impedance divided by two. Since the 1.6's are nominally 4 ohm speakers, the amp would see a nominal 2 ohm impedance (undoubtedly even lower at some frequencies), which very few amplifiers can handle gracefully.

2)The S300 in normal stereo operation can put out 300 watts into 4 ohms (twice its rating into 8 ohms).

3)It is generally believed that most stereo amplifiers do not sound quite as good when operated in bridged mono mode, compared to stereo mode.

As an alternative, though, you might want to consider bi-amping, which the Maggie's have provision for. See the comments on bi-amping by the noted designer Steve McCormack (Stevemcx) in this thread:

-- Al
I would give Jon Soderberg a call to see if it is possible to modify your amp for mono operation & to find out what his recommendation is on the best way to proceed.
This is great and substantial feedback. It is what I need to move forward and will help me decide what my next step will be. Initially, I had intended to run a pair of Magnapans using a single Threshold S/300 but throught two would be better and provide more power.

I do recall reading somewhere that running stereo power amps in mono mode may not sound the best. I would certainly not want two S/300's to sound worse than one by itself. It would now appear that I should consider using my single Threshold until I can purchase a mono pair of amps. Thanks again all for providing me this great information. I do very much appreciate your time and comments.