Amplifier Load Box Project

Well, this is the start of my Headphone Amplifier load box project, Mouser just delivered all the parts.

Will have an 8 load values

  • 12 Ohms Aeon Flow Open (13 Ohms)
  • 25 ohms Ananda ( 25 Ohms)
  • 30 Ohms. Rad-0 (29 Ohms)
  • 40 Ohms Close to Arya( 41 Ohms) & HEDDphone (42 Ohms)
  • 75 Ohm Close to ELEX (80 Ohms) & Utopia ( 80 Ohms)
  • 120 Ohms. ( used in SPL Phonitor x mesurements)
  • 200 Ohms LCD -4
  • 300 Ohms Vertie & HD-6xx

Inputs

  • 4 wire XLR
  • 6.5 mm Stereo Headphone Jack
  • 3.5 mm Stereo Headphone Jack
    Output
  • two BNC outs for test equipment

Needed to 2 x 1 pole 10 selection pots to do selection for left and right load channels

The case i am going to use

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Very cool.

This will be a fun thread to follow. :+1:t4:

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Looks like an awesome project, looking forward to your updates!

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Nice, but box is fugly, my sg. is Hammond 1455N1602.

I’m not sure what you are trying to accomplish here. Ideally, the amp output impedance should be less than 1/8 the headphone impedance. I built a box that provided a 3 ohm output impedance that worked well for all my headphones. Output was taken from the speaker terminals of the amp.

A load box like that is to allow you to measure amplifier performance under a known, static, load - not to increase the effective output-impedance when using headphones.

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I see - you’re emulating the impedance of specific headphones for measuring, not trying to match the output impedance of an amp to the impedance of a headphone for listening. Makes sense, but what about the frequency-dependent impedance variations that most headphones exhibit?

Nice project.
I got something similar for general use in electronics projects.

Will you switch by replugging or by rotary switch?

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Plan on using Rotary switch, I thought about building a toggle bank like on old PDP-11 just for fun.

@Torq thank you for answering, work is a little crazy today, getting ready to fly out to see customer in Chicago.

@jnorris For this type of testing, you normally look at fixed-resistance but remember I have a pretty wide swing in resistance that would cover most state you see. Now I could put 475 Ohm resistor for the peak of HE-6xx for the issue you raise, also put in 600 Ohm resistor.

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Toggle bank sounds like a good (and expandable) setup.
Circuit would be like so:

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