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Impedance considerations for Yamamoto HA-02?

post #1 of 9
Thread Starter 
I have a Yamamoto HA-02 on order. It will go into my primary headphone rig in which I am using 600s as my can. I have never fully understood impedance (mis)matching and would appreciate some additional guidance from forum members. Specifically, with this amp, how would the 300 ohm 600s function relative to a lower impedance can. I have attached a link below, as well as some excerpts from the review with the specs on the HA-02. I appreciate your help.

"The HA-02 wires it as a feedback-less pentode which benefits from ultra-quality in-house-wound transformers adapted from the accoladed A-08S. 50-ohm headphone and 8-ohm speaker secondaries connect to the front-mounted ¼" socket and rear-mounted speaker binding posts. Delivering 300mW @ 50 ohms at the former and a mere 240mW @ 8 ohms at the latter, a speaker driven from the HA-02 will have to be efficient and used in the extreme nearfield, say in a desk top PC setup. The HA-02 ships with an audio-technica designed interconnect terminated on the source end with a mini stereo jack. Hello iPod or equivalent.

Gain of this headphone amp is 9.5dB into 50 ohms, 1.5dB into 8. Frequency response is 30-21,000Hz and 45-17,000Hz respectively. Noise at the ¼" terminal is given as 100 microvolts. Everything about this device spells high class and the promise of noise-free, high resolution, ultra musical thermionic headphone addiction."


From a review posted at 6moons: http://www.6moons.com/audioreviews/yamamoto4/ha02.html
post #2 of 9
Well, headphones become easier to drive as their impedance increases, not harder, so it's just a question of whether it'll have enough output power for 300Ω cans. 300mW into 50Ω is probably cutting it close, but should be just enough for them, but that's just a guess.
post #3 of 9
Yeah, what Carl said. Even though it's a bit counterintuitive, a higher impedance is a more friendly load for an amp to drive. Less current required, and even though the max volume may be less, it will be clean, unclipped volume.

In general, one wants the output impedance of the driving amplifier to be less than (preferable), or equal to the impedance of the headphone driven. If the amp has higher output impedance than the headphone, that is a mismatch just asking for trouble.

The Yamamoto HA-02 specs suggest a 50 ohm headphone output impedance, but is not conclusive. It also has the 8 ohm speaker terminal spec, so may tolerate less than 50 ohm headphones (Grados).

You may be the first Head-Fi'er to get one (curses, Brian from Venus HiFi has not gotten back to me yet), so your ears will be leading the way.
post #4 of 9
Thread Starter 
Thanks for your thoughts.

I will post some thoughts on the amp once I receive it.
post #5 of 9
[QUOTE=agile_one;2510952]The Yamamoto HA-02 specs suggest a 50 ohm headphone output impedance, but is not conclusive. It also has the 8 ohm speaker terminal spec, so may tolerate less than 50 ohm headphones (Grados).
QUOTE]

Given the 6 Moons review it seems fine with 40ohm phones at least(W1000) which doesn't necessarily mean that it'll like the fairly similarly rated Grados.
My Mapletree loves the RS1s but doesn't work so well with the ATs.
It's a beautiful amp and I'm sorely tempted.
post #6 of 9
The output power should be enough for headphones. Earmax Pro has an output power of 0.32 mW at 35 ohm, 1.2 mW at 100 ohm and 6.3 mW at 600 ohm according to measurements in a review in audioXpress 9/02. It is not a powerful amplifier but it is usually enough. The official spec was 150 mW and maybe few would bye it with the real specs!

The 8 ohm specs for Yamamoto probably refer to the speaker output, but could be the same for the headphone output. Anyway, good luck and listening impressions are welcome!
post #7 of 9
From the Yamamoto web site

"the optimal load impedance is 50ohms, but it can respond to the headphone of the wide range impedance from 8ohms to about 600ohms."

that should cover most headphones.

Looks like I've talked myself into ordering one also. I must be one of the few who likes the W1000 and this seems like a good mate for it.
RS1 with Mapletree HD100 and W1000 with Yamamoto, think I'll be a happy Headfi camper.

Just a side note, I have been dealing with Mr Yamamoto direct as there is no dealer in this part of the planet and I need a 240V version. He has been very prompt in his replies. There is around 7 weeks wait for one on the downside.
post #8 of 9
Thread Starter 
I will certainly try it first with the HD600s. If they don't match well, it will give me a chance to add to the collection.

On my interest list are the 701s and W1000s, but I will wait to hear what others experience in matching cans with this amp.
post #9 of 9
Sounds great with my hd650, akg k701, and Grado rs1i. Ha-02 just sounds really great to me. smily_headphones1.gif
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