[Madcat05]

Looks like a very nice build Mike.

I've been following the MKII thread for awhile and it'll be interesting to hear your impressions of your latest build.

Cheers.

 

[BrokenEnglish]

btw.. i'm thinking about tantalums as replacements for c5/c6. in theory they should be a better solution than the best electrolytics there. has anybody actually tried this?

 

[bludragon]

Well, before trying any of the recommended tweaks, I decided to take some measurements using RMAA and an e-mu 0404 sound card.
Going by these it would seem that the 1st thing to change is to add a zobel, and remove the output lamp (R11).

Without a load the performance didn't degrade much from the sound card looped back to itself without the amp in place.

With a load however (a pair of HD650's), there was significan distortion at lower frequencies, and some small amount of IMD. As an aside a resistive load had a much lower 2nd order harmonic than the headphones.

Adding the 330K feedback resistor didn't change things.

Adding the zobel, and removing R11 (the incandesant bulb) helped significantly.

The 2nd harmonic at 60Hz dropped from -60dB to -85dB, the 3rd from -74dB to -101dB.
IMD dropped from having distortion products at -91dB and -110dB to -126dB and -120dB.

So there you have it. Bear in mind that these measurements could be affected by a bunch of things, not least my neck around which the hd650's were hanging

 

[PinkFloyd]

Quote:

Originally Posted by BrokenEnglish i guess, you've fitted most of the tweaks (330k, qc up)? but i couldn't find the zobel net. i'm sure, you'll spend some coolers to the transistors.

Hi Udo,

Yep, fitted the 330K but have not upped the QC (hence no heatsinks) I'm going to live with standard QC for a while and then up the QC at a later date... this will give me a better idea of what it does to the sound.

Zobel is fitted on the underside of the board.... it's basically just a 100nF cap and 10R resistor in series connected across the amp side of the output cap and ground....... it makes a big difference to the sound quality / measurements Udo.

Mike.

 

[BrokenEnglish]

hey... nice layout, mike... lots of bypassing there - i like it. just forgot to send you a pack full of small-value fkps... they'll round up the colours there nicely...

. give me another 2 weeks...
what are those extra-cables from the pot to somewhere for?
/edit: or is it the headphone jack? extra wiring from out to jack? thought, that wouldn't be necessary with those onboard-pcbs...

hope you're back on stage, mike. all the best to YOU and your tooth!
udo

 

[PinkFloyd]

Quote:

Originally Posted by BrokenEnglish hey... nice layout, mike... lots of bypassing there - i like it. just forgot to send you a pack full of small-value fkps... they'll round up the colours there nicely... . give me another 2 weeks... what are those extra-cables from the pot to somewhere for? /edit: or is it the headphone jack? extra wiring from out to jack? thought, that wouldn't be necessary with those onboard-pcbs... hope you're back on stage, mike. all the best to YOU and your tooth! udo

All that wiring is necessary and is the "wiring" I've been going on about for the past year......... the sooner that wiring can be dispensed with, the easier the amp will be to build and that's good news for everybody.

Mike.

 

[FritzS]

Quote:

Originally Posted by PinkFloyd Zobel is fitted on the underside of the board.... it's basically just a 100nF cap and 10R resistor in series connected across the amp side of the output cap and ground....... it makes a big difference to the sound quality / measurements Udo.

Hi PinkFloyd
what type's are the other blue an red caps?
what value they have?

 

[PinkFloyd]

Quote:

Originally Posted by FritzS Hi PinkFloyd what type's are the other blue an red caps? what value they have?

Hi Fritz,

The little blue bypass caps are 220pF EVOX Rifa polyprops and the red ones are WIMA MKS4 (100nF for the zobel network)

The one small red cap in the rail splitter is a WIMA 200nF K5. There's no rhyme or reason for this and I am just experimenting with bypass caps....... I'll probaly end up bypassing the 100uF electrolytics with a 220pF silver Mica and a 1uF polyprop.

I'm slowly building up a picture (and taking notes) of the differences (not necessarily improvements) with the bypass caps in situ and will experiment with a few more combinations before posting.

One thing I have noticed......... I can't listen to the HD-600's with polyprop caps..... they sound way too chocolaty and distant....... the Grado SR325i sounds excellent with the polyprops.. sharp, attacking, hyper detailed yet comfortably listenable. It could be that I prefer the SR325i to the HD-600 but I can't remember the HD-600 sounding so mushy and syrupy through any of my many previous WNA amps .... they just sound plain boring and lifeless driven by the polyprop WNA (nice sound but a jack of all trades and master of none sound)...... as I say, It could be the case that the SR325i is better suited to my ears but I suspect it's due to the polyprop caps........... polyprop has always sounded rubbery and artificial to me, I understand why people like them in audio circuits...... they have a tendancy to warm the sound down a tad and present you with a "comfortable" inoffensive listen.

I may be barking up the wrong tree here but, at the time of writing, I don't like the sound of the WNA with the polyprops in circuit........ it's as if someone has coated my eardrums with rubber........ sounds way too quacky, honky and smeared with the HD-600 yet, strangely, the sound is inch perfect through the SR325i.

I've got a cartload of polyester caps and will try them out and compare them to the polyprops....... at the present time it's the case that either the SR-325i sounds miles better than the HD-600 or the polyprops don't sound as good as the polyester....... it could be a headphone thing but the fact the HD-600 sounds so lifeless and unexciting driven by the polyprop WNA has me pointing my finger at the polyprop caps.

I'll report back once I've experimented with a few different caps and once my tooth has been fixed.

Mike.

 

[spendorspain]

Hi

I’d like to post my opinion on 330k mod because it’s different. My modded WNA hp amp sounded great, as I said in my previous post, but as listening hours passed I began to feel a certain loss of extreme highs, like a subtle but noticeable filtering of the “air” of the recordings. It appeared only after a long (two months!) break-in period when, I guess, the sonic personality of the new components fully developed. Perhaps there was simply a mismatch between the modded amp and my very mellow-sounding audio system (Meridian 206DS CD, Van den Hul “The First” carbon cable and Grado HP-2 with flat earpads, which reportedly sound a little dark and very different to the brighter RS-1 or SR-325). Looking for an explanation, I searched the Web and read a lot of posts in this and other forums. All info pointed to the 330k resistors because several head-fiers described this mod as “smooth sounding” or giving more “soul and warmth” to 6171 IC (perhaps the Grado HP-2 have “soul” enough on their own

). Moreover, I’d used AudioNote tantalum resistors, also said to have a sweet sound. So, I decide to open the case and unsolder them, with amazing results. The highs went back and the missing air and space are there again without any audible side-effects in the rest of frequency range. I’d like to know if somebody have similar experiences with the 330k mod, although perhaps it’s only a mismatch with my own system.

Regarding the last post of Mike and others from Udo, and my own preference for a very open and transparent sound, I’m thinking about removing the polypropylene input caps to see (hear?) if this improves the sound, but I’d like to do that in a safe way. Could you explain how to measure DC offset at output of CD player with a voltmeter? I suppose I have to touch the inner tube ("live") of RCA socket with the red probe and the outer ring ("ground") of socket with the black probe, in both channels and with my multimeter set to measure mV DC (in my case in its "< 2V DC" setting ). Is this correct? Is the measurement made with music playing or perhaps in "pause"?.
What would be a safe value of DC offset, if present, in order to connect the CD player to the WNA hp amp with no input capacitors? Can this value drift in certain circumstances (e.g.: be a safe value today but larger and dangerous in other moment)?

I’d also like to comment the musical results of using a WNA Cascode PSU instead of the switching-mode “wallwart” supplied as standard. As “1up” and “Captain” have said before, it is worthwhile. It improves dynamics and detail, lowers the noise almost to inaudibility and makes big orchestral climaxes clearer and effortless. The sound is more natural, realistic and “free”. Now, without the 330k resistors and with Black Gates output caps and the Cascode PSU, the WNA amp sounds better than ever… until the next upgrade arrives (perhaps the removal of input caps or the increase of quiescent current of output transistors).

As always, I’m afraid this post is too long, but I hope you can explain the doubts I have.

Regards,
Jose

 

[PinkFloyd]

Quote:

Originally Posted by spendorspain Hi I’d like to post my opinion on 330k mod because it’s different. My modded WNA hp amp sounded great, as I said in my previous post, but as listening hours passed I began to feel a certain loss of extreme highs, like a subtle but noticeable filtering of the “air” of the recordings. It appeared only after a long (two months!) break-in period when, I guess, the sonic personality of the new components fully developed. Perhaps there was simply a mismatch between the modded amp and my very mellow-sounding audio system (Meridian 206DS CD, Van den Hul “The First” carbon cable and Grado HP-2 with flat earpads, which reportedly sound a little dark and very different to the brighter RS-1 or SR-325). Looking for an explanation, I searched the Web and read a lot of posts in this and other forums. All info pointed to the 330k resistors because several head-fiers described this mod as “smooth sounding” or giving more “soul and warmth” to 6171 IC (perhaps the Grado HP-2 have “soul” enough on their own ). Moreover, I’d used AudioNote tantalum resistors, also said to have a sweet sound. So, I decide to open the case and unsolder them, with amazing results. The highs went back and the missing air and space are there again without any audible side-effects in the rest of frequency range. I’d like to know if somebody have similar experiences with the 330k mod, although perhaps it’s only a mismatch with my own system.

The 330K certainly does "warm" the sound up a tad giving the impression of a smoother overall sound with deeper bass and more musicality overall. Yes, you do trade off a bit of air (everything in audio is unfortunately compromised by one thing or another, you generally can't have your cake and eat it) but you benefit as the LM6171 becomes less sterile, clinical and analytical. I liked the 330K mod when I was using polyester caps in my last amp (the 100nF ones) but, as I say in the post above, the sound with the 330K and polypropylene caps in place doesn't have the same bite and grunt as the amp with polyester caps and 330K did.

My newly acquired SR-325i may be throwing me off course a little here but I distinctly remember them as sounding pretty forward and aggressive with my last (WNA fitted with polyester caps and 330K) with the new WNA (polypropylene and 330K) they sound beautiful.... a match made in heaven.

However my HD-600's, which sounded perfect driven by the polyester / 330K WNA now sound slightly rolled off and positively syrupy driven by the polypropylene / 330K latest WNA..... so, yes, I totally agree that the 330K plays quite a big part in the sonic signature of the amp but so do the 100nF capacitors! 330K and polyester gave perfect synergy with the HD-600 whereas 330K and polypropylene makes them sound too chocolaty. 330K and polyester made the 325i's sound forward, aggressive and "toppy" whereas 330K and polypropylene make them sound absolutely heavenly.

It's a weird old game but the beauty of DIY is that you can tune the amp to your own requirements....... I'll be trying the WNA without the 330K but with the polyprops in place this weekend..... I've got a feeling the combo of polyprop and 330K may account for the "smoothness" with the HD-600 but I don't wan't the SR 325I's reverting back to sounding "in yer face" at the same time, I love the WNA / HD 6** combo and would like to get good synergy with both the Grado and Sennheiser 'phones........ a good challenge for the weekend!



Quote:

Originally Posted by spendorspain Regarding the last post of Mike and others from Udo, and my own preference for a very open and transparent sound, I’m thinking about removing the polypropylene input caps to see (hear?) if this improves the sound, but I’d like to do that in a safe way. Could you explain how to measure DC offset at output of CD player with a voltmeter? I suppose I have to touch the inner tube ("live") of RCA socket with the red probe and the outer ring ("ground") of socket with the black probe, in both channels and with my multimeter set to measure mV DC (in my case in its "< 2V DC" setting ). Is this correct? Is the measurement made with music playing or perhaps in "pause"?. What would be a safe value of DC offset, if present, in order to connect the CD player to the WNA hp amp with no input capacitors? Can this value drift in certain circumstances (e.g.: be a safe value today but larger and dangerous in other moment)?

I always check DC offset from the source at the input of the amp with a CD in the CDP on pause. Set your voltmeter to DC and onto the 200mV range. Probe the phono socket (inside your amp) thus:

Black probe (com) to phono socket ground and red probe (V) to phono socket signal...... IMO anything under 25mV is acceptable and you're safe to dispense with input caps (jumper over C1) My CD17 measures 0.00mV on both channels though my Denon CDP measures 4.1mV L/H & - 2.1mV R/H both are ok to use the amp without input caps (as are the vast majority of CD sources)

The WNA kit only employs input caps to make it bullet proof for use with every source under the sun..... there may be 2% of sources that output DC so the caps are fitted as a "better safe than sorry" measure..... a bullet proof safety net if you like. Sure the amp will sound a lot better without them in the circuit but check your sources offset before binning them.

Another thing you may want to try is replacing the 47K input resistor with a 10K resistor. Dr. White commented on this on the MKl and I quote:

"Lowering the input impedance to 10k will give ( theoretically ) lower noise and will also reduce the output offset with the LM6171, but not enough so you can dispense with the output caps. The component values that I choose for my designs are a compromise which will work satisfactorily with the widest range of attached equipment. I generally use 47k input impedance because that'll pretty much work with anything. For my personal stuff I always use 10k. That's the beauty of DIY you can tweak your gear to suit yourself."

You'll note Dr. white also says " The component values that I choose for my designs are a compromise which will work satisfactorily with the widest range of attached equipment" in 99% of cases it's probably perfectly OK to dispense with input caps and use 10K input resistors etc. He's providing a kit which has to work first time every time with all equipment.......

It's not for me to suggest you remove these safety barriers but the performance of the amp is certainly a lot better with them removed but, if you do decide to remove them, ensure your source has minimal DC (only really crap / obsolete / faulty gear will have a massive DC output.... 99% of it should be fine

)

As to the Output caps..... I'd recommend leaving them in........ I tried the 10M resistor and trimpot and couldn't hear a lot of difference but the input caps are well worth removing

Quote:

Originally Posted by spendorspain I’d also like to comment the musical results of using a WNA Cascode PSU instead of the switching-mode “wallwart” supplied as standard. As “1up” and “Captain” have said before, it is worthwhile. It improves dynamics and detail, lowers the noise almost to inaudibility and makes big orchestral climaxes clearer and effortless. The sound is more natural, realistic and “free”. Now, without the 330k resistors and with Black Gates output caps and the Cascode PSU, the WNA amp sounds better than ever… until the next upgrade arrives (perhaps the removal of input caps or the increase of quiescent current of output transistors).

I must get round to auditioning a cascode PSU, sounds good, I'm still using the linear open frame calex PSU and it rocks my boat

Quote:

Originally Posted by spendorspain As always, I’m afraid this post is too long, but I hope you can explain the doubts I have.

No post is too long when It's interesting Jose and your first three posts have been very interesting and informative.... please keep them coming

All the best.

Mike.

 

[spendorspain]

Hi

As you’ve said, one of the beauties of "DIY" is the posibility of fine tuning the equipment to the rest of system and to personal tastes. More fun!

I have just received the schematic of my 206DS CD player from Meridian Audio (see image attached to this post) and I've measured the DC offset at RCA outputs. I have read in my multimeter a DC voltage between 0.000 and 0.001 volts in both channels but I can't see an output capacitor in series with the RCA socket to blocking DC. In other forum I've been told that the resistors between the 5534 op-amp and the output transistors are precisely for nulling any offset but I'm still concerned about the possibility of drifting in these values (although 1mV is very low). What do you think about this? Is there any situation that can induce an anormally increased DC offset?

However, as I'm going to keep the output caps (very high quality Black Gates) in the amp, I guess the headphones are always protected from DC in any circumstance (am I right?)... So, I have removed the input caps

and fitted a silver wire jumper in their place. A great advantage of evaluating the removal of components (instead of the adding) is that there is no "burn-in" time and the effects can be heard inmediately (and no week or even months later). From the minute one, the input capacitor-less WNA amp sounds vastly better. To put it shortly (and at risk of falling in a commonplace) this mod takes away a veil that previously was between the musicians and me, although I wasn't aware of it before its removal. It is, by far, the biggest improvement to date in my WNA amp (and the cheaper!)

Drawbacks? Only a very minor and I hope not worrying: when I rotate the volume control fully counterclockwise (I always do that before turning the amp off or when changing interconnects) there is a faint crackling, but only at the very end, never in the useful range of pot. I now simply stop their rotation a little before it ends (anyway, at this point the sound level can be -60/70 dB, I guess).

I'm afraid the WNA amp is becoming addictive...

Regards
Jose

 

[PinkFloyd]

Quote:

Originally Posted by spendorspain Hi I have just received the schematic of my 206DS CD player from Meridian Audio (see image attached to this post) and I've measured the DC offset at RCA outputs. I have read in my multimeter a DC voltage between 0.000 and 0.001 volts in both channels but I can't see an output capacitor in series with the RCA socket to blocking DC. In other forum I've been told that the resistors between the 5534 op-amp and the output transistors are precisely for nulling any offset but I'm still concerned about the possibility of drifting in these values (although 1mV is very low). What do you think about this? Is there any situation that can induce an anormally increased DC offset?

You're fine using the Meridian without input caps, I believe the 206 uses an LF353 op-amp somewhere in the circuit which provides a DC-servo action so you're ok

Quote:

Originally Posted by spendorspain However, as I'm going to keep the output caps (very high quality Black Gates) in the amp, I guess the headphones are always protected from DC in any circumstance (am I right?)...

You are correct

Quote:

Originally Posted by spendorspain So, I have removed the input caps and fitted a silver wire jumper in their place. A great advantage of evaluating the removal of components (instead of the adding) is that there is no "burn-in" time and the effects can be heard inmediately (and no week or even months later). From the minute one, the input capacitor-less WNA amp sounds vastly better. To put it shortly (and at risk of falling in a commonplace) this mod takes away a veil that previously was between the musicians and me, although I wasn't aware of it before its removal. It is, by far, the biggest improvement to date in my WNA amp (and the cheaper!)

I too removed my input caps earlier on and replaced them with axial lead ferrite bead inductors and all I can say is [size=large]WOW!!! [/size] I didn't have input caps in place with the MKl and don't know why I fitted them in the MKll but removing them brings about a vast improvement to everything across the spectrum.

The input caps were certainly muffling the music, with them removed not only is there a lot more clarity and detail but the timing has improved as well..... not subtley but very noticeably.... this has to be the best WNA I have ever heard and I can see me hauling out all of my CD's to rediscover them through the input cap free WNA this weekend....

It's a revelation with the caps removed and my jaw dropped to the floor when I listened to a couple of my very well known test tracks (I know them like the back of my hand) My god "planet dada" (from YELLO "the eye" album) sounded completely different I really was / am shocked! The rhythm, the timing and the entire "tune" is now presented totally differently.... where before the bass line sounded as though it was bam bam bong It's now de bap a boo bam de bap a boo bam..... "everything" is now perfectly syncopated and this particular tune now makes a lot more sense both rhythmically and musically.... with the input caps in place this same track sounded to me as if YELLO had lost the plot with this album but with them removed this track makes a lot more sense musically and every element of the sound comes together perfectly...... total magic!

As I type this I've got Mike Oldfield's Tubular Bells playing and (jesus H christ) I can't remember it sounding as exciting as this and I have been listening to it through a variety of equipment since the first day it was released back in the 1970's..... there are elements in the mix that I have never before heard and they are being delivered to my ears in copius amounts.... I don't usually over enthuse when it comes to audio but (excuse my p's and q's) this is ******* incredible stuff!!

What Hell of a swamp has my brain been drowning in this past year that it didn't receive the oxygen to make me think "remove the input caps" ??? I never used them with the MKl (which is why I probably remember the MKl with fondness) When I first tried the MKll I built the kit "as per the manual" and, quite honestly, rested on my laurels and couldn't be arsed messing about with it... it sounded "good" and that was good enough for me.... sure I tried Dr. White's 330K mod etc. but my enthusiam for anything Hi-Fi was at a life time low as was my enthusiasm toward life in general.... what with severe bouts of toothache, cluster headaches and a general accompanying feeling of doom and gloom It's no wonder I'd lost my enthusiasm and, at times, the will to live.......

Well, enough of that.... the birds are singing and the sun is shining and the input caps are removed

I was honestly not expecting too much of a gain in quality by removing them but am pleased to report that, yes, the improvement is enormous...... It's like listening to a new amp...... The HD-600's have perked up and the SR-325i still sound glorious so It's a win win situation all around.

If the sound should get so much better with the removal of the input caps then the same should hold true for the output caps.... I'll remove the output caps tomorrow and report back with my findings.......... I can mount the 100K trimpots where the input caps used to sit so I don't have the excuse of "there's no room on the board" anymore....... the output caps will be removed tomorrow.

This input capless amp is exciting my ears so much that I'm off to re - explore my CD collection..... I'll be back.

Mike.

EDIT: I'd written 10 times more than the above

and Head-Fi had one of its moments and I lost the entire post

I must remember to do my write ups "offline" and then copy and paste them in........ It's tragic when you spend an hour typing and the entire post disappears before your eyes

Mike.

 

[PinkFloyd]

Quote:

Originally Posted by spendorspain Drawbacks? Only a very minor and I hope not worrying: when I rotate the volume control fully counterclockwise (I always do that before turning the amp off or when changing interconnects) there is a faint crackling, but only at the very end, never in the useful range of pot. I now simply stop their rotation a little before it ends (anyway, at this point the sound level can be -60/70 dB, I guess).

I've had the same thing with a couple of WNA amps It's not a problem but annoying nonetheless.

Try the following:

Wear a pair of rubber gloves and rotate the Volco to zero end stop....... if the crackling disappears either fit a plastic volume knob or ground the aluminium potentiometer housing to 0V......... It "only" happens if you are using a metal volume knob and touching the knob at the time?

There are a few workarounds for this scenario but I need to know whether the crackling disappears with rubber glove first...... If not then I know what's causing it.

Mike.

 

[Alick]

Like you Mike, I fitted input cap's to my Mk II although I had omitted them from the Mk 1. After reading your post, I'm planning to short them out tomorrow. I'll report back.

 

[PinkFloyd]

Phew! What a weekend that was, almost all of it spent trying to get the LM6171 to work without input / output caps.... to cut it short you can use the LM6171 with 10M resistor and trimpot only if you leave the input caps in place.... Dr. White explained what was going down but I'm too tired to type it all out but basically with the input "and" output caps removed the LM6171 measured a very low 4mV offset (without the 10M resistor and trimpot fitted) I thought this was excellent and thought I must have got a couple of really closely matched LM6171's with very low offset..... nope, not as simple as that... as soon as I turned the volco clockwise the DC offset started to rise and at fully clockwise position the offset was very high... as I say, something to do with the input caps being removed and once I get the explanation / reason I'll post it.

It turned out to be a blessing in disguise, however, as the amp was input / output cap free I thought I'd roll in a few other opamps as I've never heard other opamps in a totally cap free WNA.

OPA627..... in a word "awful"..... to give it the benefit of the doubt I removed the 330K between 2&6 of IC1...... still awful.... bland, dark, mushy and tuneless.

So it was out with the OPA627 and in with the AD843...... Ladies and Gentlemen, allow me to present to you my new favourite opamp..... please give a hand for the AD843!

I enthused about this chip a while ago, before the LM6171 330K mod, and it sounded pretty good then but with the input and output caps removed and a 32V supply it sounds exceptional.... far better than the input cap free LM6171 IMO...... gorgeous deep bass, better definition (instruments better defined than with LM6171) in fact it does everything better and no need for input / output caps or DC trimming resistors.

Just read my original impressions of the AD-843 and then add 40% improvement onto that and you'll get the idea of just how perfect this opamp sounds to my ears.... there's no doubt that the LM6171 is a very fine sounding opamp but it's not in the same class as the 843 running without input / output caps... the detail of the 843 at the lowest volume setting is amazing..... you get the impression that the headphone drivers are really shifting tons of oxygen and that's with the volco just off the 7 o' clock position...... no need to notch the volco up to mid / loud levels to hear every last detail with the 843 but when you do crank the level up a few notches you're in for something pretty special. I always classed a pair of loudspeakers as "good" if they could convey the same detail at very low volume levels as they could at medium levels... why should headphones be different..... the 843 can deliver the goods at the lowest of volco settings.

It certainly likes voltage and upping my calex PSU from 24V to 32V reaped rewards (more of everything!) so if anyone is considering trying it with the WNA then 24V is gooood but 30V is optimal (my PSU adjusted to 32V)

At last! a cap free WNA and an opamp that makes seriously good music.... there's no way I'll be mucking about with the LM6171 from here on in..... no way........ It's got too many limitations for my liking and I don't like its prima donna nature...... if it sounded fantastic then maybe I could live with its erratic behaviour patterns but, as it stands, it has served its time in my amp and has now been replaced with an AD843 which IMO sounds truckloads better than the LM6171 ever did..... and that's a directly rolled in 843 (circuit not optimised for it) with no input / output caps in sight...... It can only get better!

LM6171 is out the window but I am interested by a recent entry in my website guestbook:

" Have you tried the composite configuration of the AD744 and the AD811 as described in Audio Amateur/Audio Electronics and designed by Walt Jung of Analog Devices? The best I've ever used as a pre amp line driver or a head phone driver. Other op amps can be used with the AD811 if you prefer and use caution to make sure the phase margin and bandwidth is compatible."

I haven't tried it but sure want to try it! I contacted Dr. White regarding this question and got the following reply:

"I designed a little adaptor pcb to implement this idea a few weeks ago. You use surface mount opamps, one on top of the pcb and one on the bottom. Then you just plug it into the WNA in place of the LM6171."

I'm not sure if he has got any adaptor PCB's for sale but will ask.... would anyone be interested?

Right, enough typing, I'm off to have a long session with the 843WNA......... I could be gone a long time

All the best.

Mike.

Cap Free at last!!!

Free at last.