Amp for AKG 701

[pkduck]

I received AKG K701 as a gift.  Now I want to build a amp for it.  Is the stock Crack amp a good match? Or should I get the SEX instead?  I am reconfiguring the my old Sony Playstation 1 as the CD player (trying to build a poor-man/starter set).

[Lee Hankins]

Grainger I believe that you read Doc's info incorrectly.  The K701 have an impedance of 62 ohms.  The Crack with 6080 tubes is good for 120 ohms or greater, but "If you run 5998 tubes in your Crack instead of 6080s you can probably go as low as 70 ohm headphones".  Again the K701 are 62 ohms and would be better with the SEX amp, the K701 is not highlighted in orange.

Cordially,
Lee Hankins

[Grainger49]

Yup, it was a long afternoon of beating my head against a problem with my turntable.  The Crack page says 100 ohms or higher.

I'll edit my post.  

Edited it but the OP isn't following.  I deleted that response altogether.

[pkduck]

If I order the Crack from Bottlehead, how much will it be for the addition 5998 tube?

[Paul Joppa]

5998s are getting hard to find and expensive. Bottlehead doesn't sell them.

Stereophile did a review of the AKG 701 and it includes an impedance plot. That plot is quite flat, except at the highest frequencies; the inductance appears to be about 0.5mH in series with about 60 ohms. If the cans are designed for a low drive impedance, rather than the standard 120 ohms (similar to the Crack output with 6080 a tube), they might have a boost of 2dB at 20kHz due to that inductance.

In any case, response would be very flat up to 10kHz. If the boost is a problem, it can be removed with a simple Zobel, 62 ohms in series with 0.13uF, in parallel with each headphone. This will make the headphone impedance a flat 60-65 ohms at all frequencies

Not all headphones have such a benign impedance, but according to those measurements the 701 does.

[Doc B.]

The technical aspects aside, there are a few threads around the web these days that indicate the 701s and Crack are not as good a match as the Crack and higher impedance cans like Hd600s/650/800s, 880s, etc. The S.E.X. is always the safer bet when you are thinking of using headphones with an impedance lower than 300 ohms. When considering headphones that are somewhere between 32 ohms and 300 ohms you may just have to smoke it and see.

[pkduck]

SEX is just a little bit out of my price range (compare to Crack which is 1/2 the price after shipping and handling) .  Is Crack and the K701 really that bad of a match?  What if I upgrade the Crack with Speedball  and/or replace the the 6080 to 5998 down the road, will it be a better match and sound better?  I kind of building the amp around the cans instead of the other way around.  I am trying to get the best with my limited budget.

[levlhed]

You do not want to use a Crack amp with the K701.  I have K701 + Crack w/Speedball & 5998.  I am speaking from experience.

[pkduck]

I guess I will save up a little bit more money ...

[levlhed]

I really truly think it will be worth it. 

When I compare the sound I get from the HD650 vs. K701 on my Crack amp,  then listen to K701 on a solid state dac/amp I can say you will without a doubt be most happy with an amp that is best suited to lower-impedance vs. high impedance.