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Power Amplifier -> Headphone Adapter

17 Jun

Power Amplifier -> Headphone Adapter

2016/06/17 by Joshua Harris


Here is a quick little project that I pulled together so we could see just how power hungry headphones (like Hifi Men and their ilk) sound on our lovely sounding directly heated triode amplifiers. With the DC filaments on the StereomourII, the results were quite nice. The parts I used are all available from a variety of online vendors.

I wasn’t taking notes or pictures when I put this together, but this is an easy enough project to put together once you see the parts for yourself.

First order up the parts. I used these part numbers, but you could use any quad microphone cable you like, different connectors, et cetera. Markertek sells all of these exact model numbers; other vendors may or may not carry all three.

• Rean NYS508-R NYS508-B dual banana plugs (one of each, about $2 each)
• Neutrik NJ3FC6 cable mount TRS jack (one, about $7)
• Mogami W2534 (about $1.30 per foot, purchase to desired length (I used about 3 feet))

Strip the outer jacket and shielding (braided copper if the Mogami is used) off each end. I did about 7″ (178mm) on one end, which is long enough for the ends to reach the binding posts on a Kaiju. The other end I stripped as needed by the plug, so it may vary.

Disassemble the TRS jack. The one shown has a screw as well as the screwed on strain relief. Slide the strain relief and connector body over the short stripped end.

Strip the blue and clear wires on the short stripped end about ¼” (7mm). Solder one blue wire to the tip lug, and the other to the ring lug. Solder both clear wires to the sleeve lug.

Strip the blue and clear wires on the long stripped end about ½” (14mm). Use the continuity checker on your meter to determine which blue wire is on the right channel (ring terminal). Mark that pair with tape. Confirm continuity on the left channel (tip terminal) and grounds while you’re at it.

Reassemble the TRS jack. Feel good that you don’t have anything on the other end of the cable when you realize you left a piece off…

Disassemble the banana plugs. The ones shown are held together with a black screw in the plastic body. Once the body is apart, you insert a small flathead screwdriver into the individual bananas to loosen a setscrew that will secure the wire in a small hole. I found the fit to be better if the end is folded over on itself before inserting. Take the pair of wires marked as belonging to the right channel and insert the blue wire into one post and the clear wire into the other, securing with the setscrews. Assemble the red banana plug around these connections. Mark the blue wire with a “+” and the clear wire with a “-” on the outside of the the plug. Repeat for the left channel. I recommend using the same positions for the + and – bananas as used on the right channel, since the black plastic is hard to mark.

That’s it. Of course, you could use whatever cable dressing you like (tech flex, cable pants, heat shrink, et cetera), but that’s all you need to do to make a functional cable.

1) There is no protection of the headphones provided as built. Use this adapter at your own risk. Headphones can easily be damaged by a strong signal; do not hot swap interconnects with headphones on your output! Use of this kind of device with high powered amps is not recommended.

2) We do not recommend this for AC heated SET amps.

3) Directly heated triodes are a microphonic; you will hear some ringing when you touch the amplifier or the surface it rests on.

4) You certainly can use this with low impedance, high efficiency headphones. You will hear some tube rush and other noise. Wire your output transformers to the lowest impedance for the best signal-to-noise ratio.

5) Most important! This project is presented as a DIY solution to a problem.

That means •Do •It •Yourself!.

There is no technical support offered for this project. There is no advice offered for this project. There is no recourse if you screw it up (see note 1).

It costs about $15 dollars to do this project with the pieces suggested. You could probably get that down to just over $5 if you use cheaper parts and a short cable. Time investment is minimal as well. If you want to know how it works, TRY IT. This project is far simpler than any kit we offer, or ever will offer. It would make a great warmup project for a first timer, or just a useful thing to have around an audio house.

BeePre Input Transformer Modification

01 Sep

BeePre Input Transformer Modification

2014/09/01 by Joshua Harris

First, buy the necessary supplies:

2 x CMLI-15/15B (CMLI-15/15B2 will also work) transformers, ordered from Be sure to order as a single 3/8″ stud

2 x 22KΩ 1/4W resistors (Mouser 660-MF1/4DC2202F)
2 x Neutrik female XLR jacks (Mouser 568-NC3FD-L-1)
1 x 5-lug terminal strip (Mouser 158-1005)


Remove the plastic hole covers. Trim the wires off the RCA Jacks closest to the transformer holes. Mount the XLR jacks with the existing hardware and add a 5-lug terminal strip to the back hole of the front XLR jack. The terminals are numbered from front-to-back.


Mount the transformers using the hardware supplied with the transformer — insert the post from the top side of the chassis and secure below with the lockwasher and nut. Do not fully tighten the transformers.


Attach and solder the red wires to pin 2 of the closest XLR jack.

Attach and solder the brown wires to pin 3 of the closest XLR jack.


Attach and solder the black and white wires to the ground tab of the closest XLR jack.


Attach the green solid wire to 1U, the green striped wire to 2U, the brown solid wire to 4U and the brown stripe wire to 5U. Do not solder any of these terinals


Attach a 22KΩ 1/4W resistor between 1U and 2U. Do not solder.

Attach a 22KΩ 1/4W resistor between 4U and 5U. Do not solder.


Attach and solder the orange wires to 1U and 4U. Attach and solder the yellow wires to 2U and 5U.

Return the BeePre to your system and power the system on. Switch the selector to the position for the balanced input and listen for hum. Rotate the transformers to minimize hum.

Enjoy your balanced input!

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