New! WNA MKll Head-amp kit. - Page 9

Nice job you've done there Alick!

Sorry about the time taken to congratulate you on your fine build but I've been unable to access Head-Fi the past few days. My MKll is down in Nottingham at the moment and you only know just "how good" it is when it's gone! Captain has done a comparison between the WNA and ANT Amber in the amplification forum and I tend to agree with a lot of what he has to say about it, I don't know if you've read it but if not, have a read.

It really isn't a good amp to compare side to side to a more immediate sounding "in your face" amp....... the WNA is wonderfully neutral and it's only after a prolonged listen that its qualities begin to shine through..... that's usually the way of it.... equipment that sounds upfront and "thrilling" through a comparator in a Hi-Fi shop usually ends up turning out to be harsh and fatiguing once you've bought it and listened to it for a while. The neutral gear may not give you an immediate "in yer face" hit but over a period of time the subtle nuances make the hairs on the back of your neck stand up.

Give the MKll a couple of weeks Alick..... It's a creeper and once it kicks in it's a definite keeper. My MKll should be back from the Nottingham meet one of these days (no hurry Kirk) I've got a couple of AD 843's to try in it, Looking at the spec sheet I don't expect great things from the AD 843 but you never know...... others here are rating the 843 so may as well give it a go. As I say I'm not expecting fireworks.


All the best.

Mike.

First off...... Welcome to Head-Fi sorry about your wallet Henry Morgan (a traditional greeting I have never understood...... why should this place make me want to part with money?)

Strange,

I actually found the LM6181 to provide an even leaner, tighter and more musical bass than the LM6171. I haven't listened through Grados but through HD-6**'s and AKG K-501 the bass certainly can't be described as "heavy"...... there is the possibility that I'm going deaf however.

I'll roll in the LM6171's once the amp is back with me and will "really" go to town comparing the 6181 to the 6171...... as it stands though (from memory) the LM6181 has an airier, pacier and lighter bass than the LM6171 (with 300R and 120R phones)

What value output caps are you using Henry?

All the best.

Mike.

I did go AWOL but it was compulsory absence if you catch my drift?

Hi Henry,

1000uF is ideal, Maybe the LM6181 "is" bassier than the LM6171 with the Grado phones but with the senns and AKG phones the bass is even tighter than it was with the LM6171. I'll have a real good listen to the 2 opamps again once the amp returns.

Mike.

LM6181 / 6171 update

The amp arrived back safe and sound from the Nottingham meet and I couldn't wait to hear music through it so I connected her up and was very underwhelmed indeed It was not how I remembered it at all sounding pale, thin and lifeless. I scratched my head for a bit and could only come to the conclusion I must have "got used" to the LM6181 prior to sending the amp down to Nottingham.

Everything about the sound seemed different to what I'm used to hearing from the WNA... for starters the volume control had to be turned up to about 2 o'clock to get any decent level of sound out of it, the bass was very light and the overall sound was thin and lacked dynamics and "grunt"

I tried listening to my AKG K-501's powered by the LM6181 WNA and it was an absolutely lifeless listen.... no bass, flat midrange and .... well, just plain "weedy" even turning her up to the 4 o' clock position on the volco couldn't provoke anything decent from the K-501.

hmmmm....... weird stuff! I must admit (prior to the Nottingham meet) that It was necessary to crank the volco up a couple of extra notches with the LM6181 but I didn't realise, at the time, just how weedy the sound actually was compared to the WNA with LM6171 onboard.

I confirmed this last night by removing the LM6181, I retrofitted 1K in R2 and 3.3K in R3 and rolled in the LM6171.... connected her to my source, plugged the phones in and "bingo" the balance, the body, the volume.... everything was back to normal as if by magic... 11 o' clock on the volco got the senn HD-600's pumping my eardrums loud style! More like it!!

Tried the K-501's and, quite franky, still pretty thin sounding though nowhere near as watered down as they sounded with the LM6181 on board.... LM6181 is crap with the K-501, full stop.

The HD-600 and LM6171 combo is pure magic of that there's no doubt. In an attempt to inject a little extra drive into the K-501 I upped the quiescent current by 25% (replaced R5 (120R) with a 160R and R6 (75R) with a 100R

Very little effect on the K-501 but certainly a big improvement with the HD-600!! definitely more drive, more energy and more pizzaz to the sound.... not just a slight improvement but a marked one..... I may even up the quiescent current another 25%, may even improve the Senns further... what the heck it's worth a try

Once I've finished playing about with the quiescent current and am satisfied that all's well with the LM6171 / Senn HD-600 combo I'm going to give the Burr Brown OPA627's another shot in the MKll. I've ordered the military grade OPA627BP's so the DC offset should be pretty close to zero..... I think it's worth giving them a tryout in the MKll, they sounded a bit syrupy in the MKl but it may be a different story with the MKll, who knows...... it's worth a try!

The good weather must have returned I've got an insatiable urge to opamp roll!!

Rock and roll!!

Pinkie.

EDIT: If you up the quiescent current by 25% it's probably best to fit clip on heatsinks to the transistors as the core temperature rises from 60c to 80c

I wasn't overly impressed with the 627's in the Mkl but you never know, they may be better in the Mkll. One thing I have been experimenting with today is the value of R11 (R9 in the MKl) at the moment it's a 12V incandescent 60mA lamp... I whipped them out and they measure 21ohms so, in effect, the output resistance of the WNA is 21ohms.

As we all know some amp manufacturers fit 120ohm output resistors in accordance with IEC 61938 international standards which recommend that headphones should expect a 120ohm source regardless of the headphone's own impedance. Other manufacturers try to get the output impedance as close to zero as possible.

Well, I started off by removing the incandescent lamps and replaced them with zero ohm links....... sounded good through the HD-600 though, for some reason, whenever the volume control went past 11 0' clock it introduced hiss but "only" when my finger was in contact with the volume knob.... as soon as I removed my finger all was ok

I then went to the opposite end of the scale and fitted 120ohm resistors, slightly deeper bass and more accentuated treble.... one things for sure, the 120R output resistor makes a difference, whether it's good or bad I've yet to decide...... looks like the next few evenings will be spent evaluating the best value of output resistor to use with the Senn HD-600's

Are there any output impedance experts in the house? Some manufacturers swear by zero ohm output impedance whilst others insist on 120ohm as per IEC 61938 international standards. What would be the best "catchall" value to use? (cause less offence to a wide range of headphones) I notice that quite a lot of the commercial manufacturers go with 120 ohm output impedance whereas the majority of DIY'ers prefer as close to zero as is possible output impedance...... What output impedance would make the amp more "bullet proof" with all headphones....... zero ohm or 120ohm (I don't mean which OI will sound better but which output impedance is the most "stable" with all headphone impedances?)

Let us know your findings Udo and be sure to upload pics of the 10 Farad caps

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