[12796]

the headamp mods are finsihed but it is being held back while i await the ad843 to slot into the phono to test against the lm6171. Once that has been finalised david will send me both units with my choice of opamp installed. ad843 takes ages from farnell...

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Did you try the ad843 without both sets of caps and still preferred the lm6171 with one set of caps is that correct?

Yes, it turned out that way Nick but I shall be building another WNA around the 843 in due course... simply rolled in the 843 sounded superb so It's worth extracting its full potential in another dedicated 843 WNA and then comparing them side to side.

I also want to have a go at building a valve amp and maybe another Chiarra or a Dynahi so I can have a few amps on tap to compare.....

Mike.

 

[boodi]

Quote:

Originally Posted by PinkFloyd Yes, it turned out that way Nick but I shall be building another WNA around the 843 in due course... simply rolled in the 843 sounded superb so It's worth extracting its full potential in another dedicated 843 WNA and then comparing them side to side. I also want to have a go at building a valve amp and maybe another Chiarra or a Dynahi so I can have a few amps on tap to compare..... Mike.

I'm looking forward to read you

please if/when you start a new wna843 thread or a comparison thread , post a link here
thanks

 

[l_simon_l]

I completed my WNA headamp yesterday, and I must say it sounds awsome. But then I don't have much experience with headphone amps. The only other amp I've heard was the sugden headmaster, and it failed to impress me, but I'm very satisfied with the sound coming out of my WNA. This was the first time I've soldered anything other than cables.... this was fun, and I'm already thinking about maybe modding the amp a little and perhaps adding a simple bypassable crossfeed.

I just have one question, It seems I have some issues with grounding. When I touch the chassis and/or volume knob I get a grounding noise. When I don't touch the amp it isn't there. Is this normal? If not, what can I do to fix it?

 

[l_simon_l]

Well now the hum is gone! Shortly after I posted my message here I got an email from david where he said he had read my post here on headfi and told me how solve my problem ( I had missed a paragraph in his manual about grounding). I must say I'm very impressed with how Dr. White treats his customers.

And the amp is excellent!

 

[PinkFloyd]

Quote:

Originally Posted by l_simon_l I completed my WNA headamp yesterday, and I must say it sounds awsome. But then I don't have much experience with headphone amps. The only other amp I've heard was the sugden headmaster, and it failed to impress me, but I'm very satisfied with the sound coming out of my WNA. This was the first time I've soldered anything other than cables.... this was fun, and I'm already thinking about maybe modding the amp a little and perhaps adding a simple bypassable crossfeed.

Hi Simon,

My apologies for not congratulating you on your build sooner, I only came across your post today (I really must subscribe to this thread!) I'm glad you're happy with the amp, give it a few weeks to burn in fully it gets even better!

If you are considering "modding" the amp then I highly recommend you remove the output caps and fit the 10M resistor and 100K trimpot.... it totally transforms the amp IMO and I would never go back to a WNA with output caps.... never! My absence from this thread the past few weeks means only one thing.... I'm happy with the amp and am enjoying the music

The WNA has remained switched on for over a month now and I've measured the DC offset almost every day and it hasn't drifted from 0.00mV (even on very warm days) so I think It's safe to say that removing the output caps and fitting 10M /100K trimmer is the way to go.


Quote:

Originally Posted by l_simon_l I just have one question, It seems I have some issues with grounding. When I touch the chassis and/or volume knob I get a grounding noise. When I don't touch the amp it isn't there. Is this normal? If not, what can I do to fix it?

Sorry to hear that Simon, I've just read your post saying you've managed to sort it.... It's quite a common thing but once you ground the pot to 0V it usually gets rid of it.

Keep us updated if you do decide to mod the amp.

All the best.

Mike.

 

[12796]

Arrived today! Fitted into a new case with space for 4 9V batteries (now on order). Currently running off a switchie. Pinkie - I notice there is still a single opa134 inside - is this the rail splitter? Is there anything to be gained by replacing this and what have you tried? It beats my cmoy like it was a red headed step child after the pub on a friday night. Nice bit of work you did inside! very tidy. In a months time I will be swpping in BG and vishay just to test out how much difference it makes before I consider upgrading the rest of my kit.

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Arrived today!

Great, at last! Sure has been gone a long time Nick.

Quote:

Originally Posted by biovizier Fitted into a new case with space for 4 9V batteries (now on order). Currently running off a switchie.

Cool

Quote:

Originally Posted by biovizier Pinkie - I notice there is still a single opa134 inside - is this the rail splitter? Is there anything to be gained by replacing this and what have you tried?

So David didn't replace it with an LM6171

LM6171 is probably the best opamp to use in the railsplitter (according to brokenenglish who's compared many opamps in the rail splitter) I usually bung whatever I have into the rail splitter and on this occasion it appears the OPA134 went into yours.... perfectly good opamp for the job but you can try LM6171, OPA 627 etc. in the rail splitter and see which one you prefer. It's easy to roll the opamps in so you won't have to send the amp away.

Quote:

Originally Posted by biovizier It beats my cmoy like it was a red headed step child after the pub on a friday night. Nice bit of work you did inside! very tidy. In a months time I will be swapping in BG and vishay just to test out how much difference it makes before I consider upgrading the rest of my kit.

Glad you like it Nick, keep us informed if you do decide to fit black gates etc.

All the best.

Mike.

 

[12796]

courtesy of a 3 week delay on ad843 due to ups! I hate those guys.

Think I will try lm6171, ad825, ad8065...

I have ad843 in the phono headamp and preamp now. I just couldnt get on with the lm6171. Something just seemed to be missing and the ad843 has it.

I have tried ad818 and ad817 now as well - good but no threat to lm6171 / ad8065 / ad843.

Will keep you posted about the BG / vishay upgrade.

 

[PinkFloyd]

This one is courtesy of Rickcr42 and it most definitely is worth implementing! I originally tried it with 100R resistors but that was a misprint from Rick and should have read 10R..... I replaced the 100R's with 10R and, yes, I can detect a noticeable (not humungous) improvement in the sound...... business as usual but "cleaner" overall presentation... this is well worth a go and thanks Rick!

Rick explains the mod:

"Capacitor ideally should never "see" another capacitor like the way C11 and C12 "look" directly at C5 and C6. Instead the two series connected caps should be either resistor or inductor isolated to form a high pass filter / isolation network.

Try adding a 10 ohm 1 watt resistor series connected from C11 to C5 and from C12 to C6 and see if you hear an improvement."

Thanks Rick, a very cost effective and extremely easy and worthwhile mod to put into the circuit

 

[12796]

Hi,

I am having problems with stability using the ad843 - any advice?

Regards,

Nick.

 

[PinkFloyd]

Quote:

Originally Posted by biovizier Hi, I am having problems with stability using the ad843 - any advice? Regards, Nick.

What kind of instability are you experiencing Nick and in what piece of equipment... the headamp?

 

[12796]

PF,

I have experimented with various sources and with both the headphones and the speakers. Your headamp is fine with the ad843 but the volco buffer mk 3 and phono both oscilate. The phono is worse than the volco and the osciallation isnt that severe. Consequently its nothing really to do with this thread - sorry for wasting your time! The ad843 data sheet seems to state what the problem is quite explicitly and how to solve it.

Regards,

Nick.

 

[PinkFloyd]

Quote:

Originally Posted by biovizier The ad843 data sheet seems to state what the problem is quite explicitly and how to solve it.

What was the problemo Nick? BTW, on the subject of AD843, what do you think of it?

Mike.

 

[12796]

PF,

On the phono I got what I thought was hum but when you play music it starts to impose a modulation on the hum at much greater amplitude - or even if you tap the tonearm. Looking at the ad843 datasheet it needs to be tweaked to drive any capacitive load above 100 pF - and the interconnects alone I guess would be more than that, let alone the switch. There are also dc coupling caps inbetween stages 2 and 3 in the phono (both of which use ad843). Perhaps these could be cut out now I have switched away from LM6171 in the phono. I am also getting oscillation in the preamp but of a much less degree as the mk 3 has a transisitor output buffer like the mk 2 so I guess its not seeing as much capacitance. Its mainly manifesting itself as high frequency twittering and high levels of hiss as well as humming oscialltion past a certain point on the volume control. The buffer drives three balanced outputs in paralell for my triamped PMC-Bryston configuration.

In the phono the ad843 comprehensively trashes the lm6171 - I got that far with the cmoy (which doesnt make the phono oscilallate as badly, I just get a high level hum). Replacing the LM6171 with ad843 in the pre also made a big difference - the wiriness and sterility have gone. I havent tried the lm6171 in your headamp as I decided to go straight to the ad843 on this basis. Your headamp is clean as a whistle with no problems! No hum, inaudible hiss and no hint of oscilalation. After 2 years I have finally got the sound exactly as I want it - which obviously offends the the oscillation gods!

http://www.analog.com/UploadedFiles/...65502ad843.pdf

This link has info about the capacitance issues and also about tweaking the circuit for the ad843 - it seems the chip might have a bit more to give in the same way that the LM6171 tweaks evolved over time. There were no problems with the ad843 in the cmoy - indeed it seemed to have a little more attack if anything and some of the notes on the link seem to pertain to rise times and pulse response - which might be relevent.

All of my electronics experience is far enough in the past that just thinking about this makes my head hurt. I dont really want to go back to the lm6171 - theres something about it that just doesnt agree with me. Perhpas you will have a better idea of how much mileage there is in the ideas in the notes? I was hoping everything would be uncomplicated when I got the kit back - I have been without music too long already!

Thanks for your time and understanding!

Regards,

Nick.