[12796]

PF,

I am thinking of trying the ad8067 in the headamp but its only stable at gains >8 - what is the defualt gain in the headamp? Also when you tried the ad8065 was that in the version of the headamp with both sets of caps?

Thanks,

Nick.

 

[FritzS]

Quote:

Originally Posted by PinkFloyd As I say... you can connect to pin 4 of the LM6171 which is -12V (or near to the pin on the same track) Mike.

My suggestion - use a additional opamp for lower the DC offset.
Some amps use a integral opamp circuit DC loopback like http://www.borbelyaudio.com/eb804419.asp
Q9 & Q18
This eliminates the outgoing DC and a little of ingoing offset too.

 

[FritzS]

Quote:

Originally Posted by FritzS My suggestion - use a additional opamp for lower the DC offset.

 

[PinkFloyd]

Quote:

Originally Posted by biovizier PF, I am thinking of trying the ad8067 in the headamp but its only stable at gains >8 - what is the defualt gain in the headamp? Also when you tried the ad8065 was that in the version of the headamp with both sets of caps? Thanks, Nick.

Hi Nick,

The gain on your amp will be the standard 4.3

To change the gain to 9 replace the 3.3K resistor in R3 with an 8K resistor. Alternately, replace the 1K in R2 with a 500R which will give you a gain of 8.6 The gain is worked out by G = (1 + R3 / R2)

When I tried the AD8065 I believe the amp was capless at both ends... it was certainly tried without output caps, I can remember that.

Mike.

 

[12796]

I tried swapping in the ad8065 as is - it doesnt seem to be completely stable. Which is annoying as it seems as if the ad8065 might beat the ad843 - which is why I asked if you tested it capless. In the cmoy the ad8065 gave the ad843 a sound thrashing as well.

 

[PinkFloyd]

Quote:

Originally Posted by FritzS

Cheers Fritz!

I put your last suggestion to Dr. White and he responded:

"Yup that works, its called a dc servo. I'd be interested to hear from anyone who tries it, because opinion is divided as to whether it's better or worse than an output capacitor. From the various analyses I've seen I would conclude that a dc servo degrades the low bass to a greater extent than an output capacitor, but I'd be happy to be proved wrong. I considered using a dc servo in my phono stage but didn't go ahead because of the reservations outlined above."

 

[12796]

I have completed testing the ad8065 v ad843 v ad847 in the capless WNA and also in a cmoy. The results seem pretty close:

ad843 then ad847 then ad8065 in order of increasing performance in both amps. I would be curious to get your view in this setup Pinkie - do you have a wna amp at the moment?

 

[PinkFloyd]

Quote:

Originally Posted by biovizier I have completed testing the ad8065 v ad843 v ad847 in the capless WNA and also in a cmoy. The results seem pretty close: ad843 then ad847 then ad8065 in order of increasing performance in both amps. I would be curious to get your view in this setup Pinkie - do you have a wna amp at the moment?

Hi Nick,

So you prefer the AD8065? I tried that ages ago in the Mkl and it was my second favourite to the LM6171 sounding warmer and smoother. I don't have an 8065 to hand but will try and find the thread where I commented on it... will link to it when I find it.

Mike.

 

[PinkFloyd]

Here you go nick:

AD8065 2

 

[rickcr42]

The AD843 may be getting a bit long in the tooth (old) but still manges to get more right than it does wrong.I also like the "old" AD825 chip which again usually errs on the side of musical rather than the trend of most "newer" more modern chips which always seem to trend to the bright and slashy when caught out on busy sections of music with a lot of peak content in combination with a low level music foundation.They seem to lose the low level details while attempting to hit the massed peaks but fail even there mostly.

Just an opinion of course.YMMV.

On to servoed designs.I do not like them personally even though many swear by them.The servo in combination with negative feedback to me is a stage alwys trying to catch up and perfect instead of just passing along what is there.Play,compare,eliminate.play,compare,eliminat e,play,compare.......

With a discrete output stage DC coupling is attainable but again no eeasy path and there is parts aging which will cause at some point a D.C. offset requiring re-adjustment.this last is not within the capabilities or desire range of most headphone users so would be out for a commercial product but even for the DIYer who would want to always be paranoid about the D.C. and instead of enjoying music worrying about his and checking for D.C. conmtent ?

So what is left ? Capacitor coupling or transformer galvanic isolation.The first is the cheaper path and one that can provide good results depending on the capacitor selected.Being a single part it is super easy to pop out one cap and pop in another to check the sonics and once you arrive at a good result-solder that puppy in and close up the box then go enjoy some music.
The second option is neither cheap nor is there many oiptions out there though why i do not know considering the amount of headphone amp activity lately from all the major players.Sowter has one that goes dead flat from 15hz-30khz and is 10 ohms effective as seen by the circuit so a possible solution but to my knowledge the only headphone specific transformer readily available.Oh you,it will cost about 10X the cost of even the most expensive caps so not a cheap option though potentially a better option sonically.

Just adding to the conversation folks

 

[rickcr42]

BTW-a D.C. Servo done right is not run full banwidth but is low pass filtered so it only effects the below audible range frequencies.Probably start it around 5hz and flat to D.C. (0.1hz).This means the opamp used for the servo must have superior low frequency response itself and not just grab any and stick it in.You also do NOT want an ultra-high-speed lightening fast/high slew rate device.These frequencies where it will be used are neither fast nor are they ultrasonic so if the stage is limited to the narrow band where it is to do the work again it is D.C and low frequency performance thatdetermines suitability.

I think the OP27 worth looking into for this area.

 

[12796]

Pinkie,

Well the ad8065 in the Mk II with both lots of caps removed (and series resistor on the output replaced with zobel compared with Mk I and no resistor accross pins 2 and 6) doesnt sound warm or smooth at all as far as I can tell. It doesnt get confused sounding either. It just sounds exactly right. According to Dr White it was a close call between ad843 and lm6171 in my headamp - and Mrs White prefered the ad843, so the ad8065 should be a long way ahead. Look forward to hearing your findings with your next headamp! Do you have a wna unit currently?

Regards,

Nick.

 

[PinkFloyd]

Hi Rick,

The two 10M resistors and 100K work fine and the DC offset stays at 0.00mV whatever the ambient temperature so I don't see the need for a DC servo... sometimes the simple "cheap" way is the best way. Since removing the output caps and zeroing the offset by means of the 10M and 100K trimpot the amp has never sounded better and I just am happy to listen to the music... you can spend ages messing around with components and find yourself listening to the amp instead of listening to the music. I am, once again, listening to the music (and enjoying it) and for the first time in ages I am frightened to go under the bonnet and change anything in case I mess up this glorious sound I'm enjoying.

I've been listening with the Marantz CD-10 Trichord modded CDP and Grado SR-325i and am pretty bowled over by just how "analogue" like this combo sounds..... The WNA is typically "British sounding" and excels in the timing and detail departments and doesn't seem to over emphasise things like some of the "beast" amplifiers do..... It's just sounding so neutral which I love! It doesn't grab you by the balls and inject spadeloads of excitement into your ears (Spadeloads of excitement is good for a 5 minute listen but that soon turns to fatigue) no this little puppy sounds unexciting on initial listen, It's only after you've heard her for a few hours that you realise this unassuming, seemingly flat sounding amp is doing the right thing..... there are no bells and whistles attached to this amp just good old down to earth "music" is outputted with nothing added and nothing subtracted.... acoustic guitar sounds like acoustic guitar and not like a bouzouki, bass lines sound like musically individual notes and not like someone farting low level into a microphone, rim shots are like someone firing an ouzo SMG and not like someone firing peas out of a pea shooter, vocals are silky smooth and not searingly sibilant and well recorded live concerts come across as palpable and sized to scale and not puny and compressed sounding.

This is slightly off topic but I, for one, just had to say I'm enjoying the music and have no intention of doing any more to this amp. It's a super DIY amp in stock (kit form) guise but It's a very great amp once you remove the belt and braces (bullet proof) components from it. I'll say it again.... compared with Graham Slee Solo, MF X-Can V2 (modded), Chiarra / Andante and Sugden Headmaster the WNA blows them into the dust when it comes to sound quality..... I can't wait for a MKlll (if there will ever be such a thing?)

Keep up the good work Dr. White.

Mike.

 

[12796]

Its funny you should mention that ... my new version of the volco has something very interesting under the hood!

 

[rickcr42]

Quote:

sometimes the simple "cheap" way is the best way

more like all the time.so many spend far too much time trying to over think a problem that the solution is often worse than what they were trying to fix.

"the operation was a total success but the patient died"