Audeze LCD-R: Can We Use Ordinary Headamps? Music for the Masses

A while back, Audeze released their ribbon LCD-R headphone to much fanfare: (https://www.audeze.com/products/lcd-r) The package was $2500 and included a Jotunheim-A, designed to drive the 2-ohm ribbon load. Generally, it's considered a bad idea to drive these kinds of loads from regular headphone amps because 2-ohms is pretty close to a short circuit. Maybe not as close as the RAAL ribbons at 0.2-ohms, but close enough to that, or far enough from today's super low Z planars at 8 or 15-ohms.



Evidently, at a recent corpo audio show, the Schiit guys brought along the Audeze LCD-R, and reported that a lot of attendees loved the LCD-R with the amps that they brought, presumably Magni Unity, Mjolnir 3, a few others.


What! The amps didn't blow up?

No they were fine. People really loved the LCD-R.

Show conditions right? Assuming people cranked it up slightly?

It wasn't that busy, but it was cranked up more than we typically listen at. One guy tried to buy the LCD-R from us on the spot.

Wait, doesn't the LCD-R come with a reverse 4-pin XLR so that it cannot be used with ordinary headamps as a safety measure?

It was re-terminated to a regular TRS phono.

What f**ktard did that?

You did, don't you remember?

Oh yeah, that's right. (I was testing stuff)


So this got me thinking: was this safe to do? Then I realized that there were other transducers that were just above 2-ohms. The Campfire Audio IEMs. The reason the CFA IEMs don't explode amps is because they are super duper sensitive to the point where microvolts are all they need. I plugged in the CFA Ara IEM into the Magni Unity (high-gain) and noted that volume position range at which I felt comfortable, around 9am-10am. I then did the same with the Audeze LCD-R, and noted 9:30am to 10:30am on the volume knob was where I felt comfortable. Hmm, so it seems that the LCD-R is pretty darn voltage efficient. A little less sensitive than the Ara with a less bit lower impedance. (It should be noted that the CFA IEMs impedance does steadily increase as the frequency rises whereas the LCD-R remains a steady 2-ohms).

I then proceeded to take measurements with the Magni Unity driving the LCD-Rs, at -20dBu and -30dBu. That would be 78mVrms and 25mVrms respectively. Yes, that's millivolts. For the load, I used the Audeze LCD-R. Yes, I used the headphone as the loud. FWIW, -20dBu produces roughly the same volume into the LCD-R as 0dBu (x10 more voltage) into the HD6xx (which is already hearing damage loud). I wanted to double check, to make sure were weren't clipping the Magni Unity (although clipping is just part of the story).


Magni Unity
High-Gain*
-20dBu 1kHz
Audeze LCD-R as load


Magni Unity
High-Gain*
-30dBu 1kHz
Audeze LCD-R as load


*High gain typically measures worse, but usually sounds better.

 

The next thing I did was put into a spreadsheet output level (dBu) -vs- load (ohms) to determine power output (mW). Yes, that's milli-watts. Knowing the wattage would give us a good idea how much current was being sucked, as power is proportional to current for any given voltage).

Even though I knew not much power would be required because of how voltage sensitive the LCD-R were, I just wanted to see it for myself. Even though the LCD-R would be expected to be used at very low voltage levels, probably between -60dBu and -30dBu, I decided to go up to plot the math up to 6dBu out of curiosity.

As we can see, higher impedance loads, like the Sennheiser HD6xx (300-ohms) barely make a dent with respect to power. Heck same thing for Grados and many orthos (most around 32-ohms). However, things start to change once we get below 20-ohms. By the time we get under 8-ohms, things turn SOUTH VERY QUICKLY. We can guess what happens if we push a few volts more: Pop! Smoke! And the smell of burning plastic! (And if the lid as off, pieces of plastic up on the ceiling).


1000mW at 2-ohms just under 2Vrms. Things go south quickly as we turn up the volume with lower impedance loads.

I think this is the scary part. I doubt people are going to crank up the Audeze LCD-R to earsplitting levels, same as with the Ara IEM. However, doing so is just a little bit easier with full-sized headphones.

That being said, I believe the Magni Unity. Magni+, and Heretic all have current sensing. You can try this yourself with cheaper cans, like the 15-ohm HFM HE400s. Just plug in a Loki, crank up the bass, and turn up the volume.

 

Next test. I'm not pushing it hard. Just -30dBu with a 37Hz signal. Left it like this for five minutes.

LCD-R 2-ohm load
-30dBu at 37Hz for 5 minutes
Output relay


LCD-R 2-ohm load
-30dBu at 37Hz for 5 minutes
Output transistor


LCD-R 2-ohm load
-30dBu at 37Hz for 5 minutes

Power regulator


Commentary:

• Temps for the output relay and regulators are "normal". At least compared to an HD600 driven with the same 37Hz tone, but at a higher voltage level (-10dBu).
• Temps for the output devices are about 2 degrees hotter with the Audeze LCD-R @ -30dBu. The HD600 @ -10dBu are about 38-39C.

 

OK, let's push it a bit. This time to -20dBu. In less than a minute, the temp reaches 46C. I bet they will settle around 50C. This probably isn't a big deal. I bet these transistors can get lot hotter. But we are starting to see big jumps in temps that the HD600 or even a 32-ohms ortho would almost never be capable of causing.

 

Piety is low power. I am betting half the power of Magni Unity. It also doesn’t have the current sense and protection of Unity. I suspect it would be fine unless you accidentally slip on the volume control and turn the Piety into weld mode.

Ferrum Oor is ordinary in the sense that it wasn’t designed to drive ribbons directly, although it’s got some hefty output. I’d still checkout the temps of the output transistors during a listening session with the LCD-R at typical volume levels.

We are probably far from arc weld mode, but sustained high temperatures or creep are a worry.

 

This is where these tiny things, cables, connectors, solder joints, insulation, adapters start to matter. I suspect the higher distortion in the L channel (measurements above) is the result of such as opposed to any imbalance in the amp.

 

No voodoo. My 45 custom has switch to use the 4-ohm taps. Studio B also has 4-ohm taps if you know where to connect at the Speakon jacks. Both amps are low gain, so mates well with LCD-R's super voltage sensitivity. The only issue would be with noise, but shouldn't be an issue if internal layout is good and quiet tubes are used. Finally, tube amps are indestructible, have gentler fail modes, and can be easily serviced. I had an ancient 45 tube that was shorted internally. All I needed to do was replace a cathode cap (it started spewing hot chemicals).