Redirecting stereo speakers into mono

[Hamilton]

I have a Spark modelling amp that has no line out, or speaker out capacity. I wanted to put in a speaker out jack, taking the signal from the 2 inbuilt speakers. My concern is that if I run both speakers feeds into a mono lead, each speaker will produce a resistance load to each other and possible damage the amp? Is there a way to do this safely? I want to be able to plug into the amp, and run the speaker out to a larger cab with 12” speakers. Many thanks in advance for any wisdom

[Mick Bailey]

The only safe way I can see to do this is to run each speaker output individually into a stereo cab, making sure that the internal speakers disconnect - either by using switched sockets or a separate switch for internal/external. Depending on the output topology, connecting the two outputs directly into a single mono output could destroy the output stage in one or both power amps. The amps are rated into 4 ohms. In addition to the impedance issue, an amplifier does not expect to see any voltage other than its own at its output. Apart from this there are other issues regarding sound quality that may arise from the phasing of the stereo outputs when combined.

[glebert]

I'm assuming you want to get more volume or fuller sound than the internal speakers? Have you tried running the headphone out from the Spark into another amp, preferably one with a stereo aux input?

[J M Fahey]

You can NOT combine speaker outs, period.

Since you mentioned "cabinet with speakerS" split them and connect individually to different channels, but not in between.

Do not even share ground wires, modern SS amps typically use ground current sensing resistors (0.1 ohm to 0.33 ohm 5W) which must also be kept separate.