For the best sound, we recommend that you use headphones that have 100 ohms or higher impedance. Most high-quality headphones from companies like Sennheiser, AKG, and Beyerdynamic have impedances in the range of 200 ohms to 600 ohms. These headphones excel when driven by a Wheatfield Audio headphone amplifier.
Lower impedance headphones, like most Japanese brands, as well as Grado headphones, are more difficult for an OTL tube amplifier to drive. Their low impedance causes larger amounts of distortion, especially at high volume levels. For this reason, we don't recommend using the HA-2 with this type of headphone, unless you upgrade the output tube to a different type that provides a lower output impedance. (See the tube info page for details).
The HA-1 has a lower output impedance (around 35 ohms) and can drive 32-ohm headphones without any problems. If you are a Grado fan, this is the amplifier for you!
You don't have to spend a fortune to get good-sounding headphones... but you also can't get great sound from crummy headphones, even with the best of amplifiers. Check out the manufacturers and dealers listed below. We're sure you'll find something you like.
Sennheiser headphones are arguably the best headphones available to the audiophile. All Sennheiser headphones are good, but our favorite is the HD-600. We think they are flat out the best-sounding dynamic headphones made, especially when driven by a quality tube amp.
For a little less money, the HD580 is almost the same as the HD-600, at a very attractive price.
AKG is less well-known in the consumer marketplace than Sennheiser, but in the pro audio works, AKG is king. Although AKG makes some great "consumer" audiophile headphones, we like the K240 Monitor headphones, which are part of the AKG professional line. They are a great bargain... they can be found for under $100.00, and they sound great when driven by the HA-2! AKG claims that the K240 is the world's most popular studio headphone, so it's likely that the music you listen to was mastered using K240's.
Beyerdynamic is another European manufacturer that makes headphones similar in quality to AKG and Sennheiser. If you want sealed headphones (that block outside sound, and contain the sound from the headphones) Beyerdynamic makes some of the best. Check out the DT831.
Grado makes a full line of headphones for the audiophile. Definitely much brighter sounding (to us), all Grado's have a 32 ohm impedance. They work great with the HA-1, or with the HA-2 using a lower-impedance output tube.
One of the most comprehensive selections of audiophile-quality headphones can be found at HeadRoom. Check out their website!