I own a Peavey Valve King 100 Amplifier and would like to hook this up to my audio card's line-in without blowing stuff up, so I thought I should get a loadbox with a built-in speaker simulator. I will only be using one of the speaker outs of the amplifier as the loadbox only has one input.

The amplifier itself has the following specs:

  • 100 Watt RMS
  • Adjustable Resistance (4/8/16)
  • Two speaker out ports (parallel)

The load box/speaker simulator has the following specs:

  • Type: Passive
  • Dummy load impedance: 16 ohms
  • Input type: Unbalanced
  • Output type: Balanced, unbalanced
  • Max. load: 100 watts RMS

Would this imply that I should set the adjustable resistance on the amplifier to match the load box? Or should I only get an 8 ohm loadbox since the speaker outputs on the amplifier are parellelled?

Sorry for the extreme layman's terms.


2 Answers 2


First and foremost I would recommend consulting your owner's manual - amps with parallel output jacks usually have a list of common scenarios and how best to connect the amp.

Most parallel-out jacks on amps are switched, which means that if you only use one (and your manual should tell you if there's a specific one to use), the output transformer only sees the load on that jack. It's not waiting for a second load on the other jack to meet that impedance. So your simplest solution is to set the impedance to 16 ohms and run one line directly to your 16-ohm load box.

Just as an aside, stock PC audio cards are generally not very good for line-in recording. You will likely encounter latency issues and lower quality vs a sound card or interface specifically for audio recording. If you're just getting started, this won't necessarily be a problem, but just be aware of this going forward.

  • \$\begingroup\$ Great, thanks for the swift help! I do own a M-audio 2x2 interface (so soundcard was probably bad wording on my part). The annoying part is that I don't have the manual and the amplifier is quite old so I can't seem to find any documentation online either (probably because there is a new version nowadays). My biggest concern was the parallel-out jacks, so this was a good answer! \$\endgroup\$ Commented Apr 4, 2017 at 20:02
  • \$\begingroup\$ And also, say that the parallel-out isn't switched; what's the worst possible outcome of running this setup? \$\endgroup\$ Commented Apr 4, 2017 at 20:04
  • \$\begingroup\$ If it isn't switched (extremely unlikely), you'd see a finite cabinet load on one jack in parallel with a near-infinite load on the other jack, which would give you a near zero total load. That would wreck your output transformer. You should never run a tube amp unloaded because of this (solid states usually have some internal protections). It would be a serious design flaw on Peavey's behalf to not use switched on the output, as that would require you to always use both outputs. \$\endgroup\$
    – Chris M.
    Commented Apr 4, 2017 at 20:13
  • \$\begingroup\$ Edit: I did that wrong. If it's non-switched (or rather non-shorting), you'll end up with a near-infinite load on your transformer. Your tubes will then try to put normal amounts of current into some insane load, voltages will spike, the transformer will likely go up, and maybe some of the tubes as well. Same bad output, wrong reason. \$\endgroup\$
    – Chris M.
    Commented Apr 4, 2017 at 20:25
  • \$\begingroup\$ I see, then I feel fairly confident running this setup. Thanks a lot! \$\endgroup\$ Commented Apr 5, 2017 at 14:53

If the amp has a serial effects loop (i.e. Send and Return) then I would use Send output because it gives pure preamp tone. And speaker simulation can be done via software according to your tonal taste. So no load box is required. Also load boxes with resistive dummy loads do affect the tone (e.g. decreasing treble and high-mid response).

Anyway, if you insist on using the load box then yeah, output impedance of the amp should match to the load box.


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