rickcr42
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Post by rickcr42 on May 28, 2006 18:38:01 GMT
You gotta clear that with me first Mikeraptor 'cause i just happen to be "president for life" of TEAM CHEAP BASTARD being the founding member of
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FritzS
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Post by FritzS on May 29, 2006 8:53:36 GMT
Basically you have right - I know about the SDS amp before I know about the WNA - but it's DIY's kismet to want to get all the best and pay'd a lot of money for it But all of the amps-projects with an OP and a power stage are similar, only odds and ends are different I am a subscriber from audioXpress and seen a similar project here (if you want I can send a private copy to you). PS: Next period I have only little time for my DIY hobby - my daughter want to build a own house so I could only write about, but till autumn I will made a better (cascade, 2x15V) PSU for my WNA MKII But to rebuild a SDS amp with the AD843 is a challenge
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FritzS
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Post by FritzS on May 29, 2006 9:05:30 GMT
* I use a 24V PSU and no heat sinks on transistors and AD843, but I think when I use 30V I should spend them little heat sinks, or? This questions are going under in the last messages ;D Last weekend I heared some of my music CD's, one better than other. But only one test CD with three same pieces of music but other antique guitars - the difference between are greater with LM6171, but more natural with AD843 - I hear this if the guitarists sittig in front of me in the room, great .... and this with an old, modified Philips CD 650 player too .... This countenance me to let the MKII as is with non "Diamond Buffer" and spend my power for better PSU and think about remove the BG 1000uF and DC protection ........
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rickcr42
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Post by rickcr42 on May 29, 2006 16:17:50 GMT
I have a 1000uf elna cerfine sitting on the output of my Szekeres Class-A follower and is my favorite Grado driver bar none but it was a long road to glory and the power section was the make or break ;D Power supplies can be tricky.Too much storage capactiance and you both end up with a "slow" amp (sound-not measurable but easily heard) and possibly an overly stressed rectifier section unless you use a slow turn on profile (thermistors,power resistors between the bridge and first capacitor stage...) but this "fix" can in some instances cause your opamps to lock up ! Some parts just don't like to play nice unless you feed them the right formula and why I sometimes grimmace when i see unimformed hobbyists plugging every opamp known to man into an already optimised design as if they know better what combination works in harmony. They don't understand the reason why some amps that use the same "engine" (the opamp) can sound soooo different from one manufacturer to the next or why certain amps have a good rep until some knucklehead opens one up,identifies the parts then proclaims to the world how cheap it is to make when parts alone are considered and therefore junk. audiophiles being mostly followers will all convince themselves that what they formerly thought to sound great now has issues,issues they actually HEAR because they were told they they were and will at that time go on a years long mission trying to better what they already had in house and enjoyed until someone spoiled the fun (Grado RA-1 is a prime example) There is also the group that like to add up parts cost and then proclaim some sort of theivery is going on because the product costs more than the sum of the parts which would be laughable if not so prevelant.I guess time spent over months trying to get the design to work correctly in the real world and doing the layout and packaging should be free as should be the ad campaign and writing the manuals,setting up the web page,packiaging for shipping,etc The SDS can be built to a high standard at around $250 in parts but if a commercial product fully build and made bullet proof so that it could work in ANY system,as a commercial product must unless from the DIY For Profit crew,would be in the $600 or better range depending on cosmetics (open frame would not work for a consumer product). Mine has AD825 opamps on an adapter board similiar to the Browndog (OK,just a freakin' perf board with Molex Conntectors for pluging it into the IC socket ) and has an "output mode" switch so I can go from Class-A operation for headphone use or Class-AB for speaker driving (see original SDS labs PDF file) www.quadesl.com/pdf/hpart.pdfgotta love Seldon's original layout,at least i find it attractive
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FritzS
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Post by FritzS on May 30, 2006 10:16:46 GMT
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rickcr42
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Post by rickcr42 on May 30, 2006 13:17:50 GMT
meaning ? what is overfast ? When does the harmonic nature of the rectifier need to be addressed with a snubber and when not ? what is a "good" regulator ? Series ? Shunt ? Discrete ? With feedback ? Without ? Split or dual ? And is a regulator even needed in every case (no) ? No matter the rectifier if it is solid state it reacts immediately to the AC input but the filter capacitors must charge up to their potential before they can become functional.That means depending on time to charge (cap size) will be a dead short across the DC output of the bridge and that means over rated rectifiers at least with a huge capacitor bank or you get rectifier failure so the common practice of increasing filter cap size can mean other ptroblems unless it is done smart. That "smart" anything from way over rated rectifiers to a thermistor in the AC primary which has a "cold" resistance that is non existant once it heats up to power resistor (current limiter) from the DC leg to the first stage cap to a smaller first stage cap followed by cascaded stages in a CLC or CRC patter or a combination of the above and all the before considering what regulator to use but this can cause its own set of problems if the opamp used NEEDS full power voltages at turn on or it will lock up,stick to one rail (usually negative) which in turn will send a DC pulse to the output that can cause major problems at the next stage be it a headphone or amp with no input cap. Obviously the fix for that would be a delayed +/- VDC feed similiar to a B+ delay in a tube amp and/or a delayed output muting relay but this adds to complexity and cost. Having those HUGE filter caps may look cool but many times causes more problems than any sonic gains.In fact smaller caps with series resistors form an actual filter that deals with any ripple issues better than capacitors alone with each stage of RC (or LC ) reducing it even further. I suggested this "mod" to mike about a year ago in a WNA MK ll amp build thread at headfi,he tried it and his report was it was mostly a good thing on the SQ merits. When I had 20KuF sitting on my Szekeres amp power supply i had to run 20A rectifiers.Turning it on actually dimmed house lights which at first i thought was kind of cool and which in the end turned out to be a serious mistake because the amp sonic profile was of a slow and ponderous amp (long since corrected) I am not a fan of BG caps even though many are.The Elna is just wrong according to everything i have ever read yet it sounds great and like i said earlier (and often) the Szekeres is my all time favorite amp with Grados and that aginst some very sophisticated ($$$$$$$) designs.Radio Shack IRF510,solens and elnas,a mix of carbon film,wire wound and dale resistors : The amp cost nothing to make,uses no pcb yet kicks ass so conventions be damned and strong voodoo at that...... I have in house eval boards from both TI-BB and ADI and while fine for quicky prototypes are hardly optimised for audio work. First star groundings is not a must with global star grounding being mnany times better.That is where circuit "groups" have their own ground which is then brought to the central star ground point.Aiming for a star for all things many times brings a worse layout than if not. On bypassing the data sheets may give "hints" on what is good electronic layout proceedure but gives you nothing on how it will sound so again goes to self exploration.some chips like bypass caps at both the "+" and "-" pins,some a single cap across the pins (fromV+ to V-) and if the opamp locks up with a slow turn on supply or not is usually extremely hard to decipher from the data sheets if it is even hinted at in the graphs at all and why all the "opamp rolling" where definitive "this part sucks,this rocks" means shit unless the part was used in a circuit actually optimsed to receive it unless it is one of the more well behaved parts. that is the main reason you get reports on sonics all over the map for the same part.It is not just personal preference but proper use of at play and why engineers that take the time to figure all this crap out deserve to be paid for their time while those who "sell" propaganda and have the "I can plug in any part" types are no more than snake oil salesman.NO part is 100% plug and play compatible or they would all sound identical ! the AD825 is not only SOIC only but is a SINGLE not dual opamp so needs an adapter but is a fine sounding chip if you like blues/jazz/female voice due to its mid range "liquidity" (I know,not a word ). The Brown dog adapters cost very little and this works in a pinch www.cimarrontechnology.com/index.asp?PageAction=VIEWPROD&ProdID=9or you can purchase ready plug in modules such as these www.octave-electronics.com/lcaudio/ad825.shtmlwww.soundlabsgroup.com.au/lcaudio/lc_audio_ad825.htm***************************************************** www6.head-fi.org/forums/showthread.php?t=179915i see several areas in that I personally do not like but it is not cool to pick apart another persons design in a public forum so I will not comment other than to say build it and report man ! I beleive the SDS is a better design but maybe you will prefer that over it.Why we have soooo many amp designs-some may be a good fit for you but not for me and one we both may hate could juct be the perfect amp for another person
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rickcr42
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Post by rickcr42 on May 30, 2006 13:25:00 GMT
....and the other examples WAY overly complicated for a headphone amp ! A busy circuit path means more things to impact the SQ so if you do not get everything JUST RIGHT and able to play in harmony you end up with an amp that has no idea what it wants to be which means does a lot well but nothing great and if it does may will not be heard anyway depending on which part of the design has the dominant sonic profile. I like the borbely Headphone Amp designs (both the hybrid and the all FET) and most of his line stages though over the years his designs have gone from relatively simple to very complicated designs.Cloning one of them would lead to a mostly shitty sounding amp unless the clone is damn close to a 1:1 copy (I know this from experience )
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FritzS
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Post by FritzS on May 31, 2006 10:50:49 GMT
Gives non polar Elna 1000uF caps too? I will not remove this DC protection for my headphones yet - but later I want to build a protection with relais. Have you bypassed the output Elna cap? Here in Europe many use Welwyn and Holco resistors - but Dale resistors hard to get. Order in US are expensive in shipping-costs and additional tax - some parts I had purchase from Percyaudio. Gives a PCB from Szekeres? About "Diamond Buffer" - some buffer OP's use this design too, so as BUF634 focus.ti.com/lit/ds/symlink/buf634.pdfOne benefit - the driver transistor between B-E of the power stage transistor make them faster to switch off (if I remember me right!?), the switch on time of a transistor is faster then the switch off time, this obtain too if the transistor running in class A but get an quick impulse. But "Diamond Buffer" is an "hype" seen on all corners I think about to change the true class B rail splitter in WNA to a BUF634T. But surely you will tell me some against that PS: Some other questions: * should I remove the ferrite bead between the OP and the output transistors when I use the AD843 * is the Zobel filter implicit necessary - I dont use them currently * should I use the "inner" NFB 330k resistor when I use the AD843 - I dont use the 330k currently * I use a 24V PSU and no heat sinks on transistors and AD843, but I think when I use 30V I should spend them little heat sinks, or? This questions are going under in the last messages
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rickcr42
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Post by rickcr42 on May 31, 2006 12:53:59 GMT
Nope and never will.I have posted extensively on this at Head-Fi but in short I want one single cohesive path for audio signals not multiple signals mixed together as one at the output,each having a different sonic profile and/or speed plus with an overlap hwere each is producing the same frequencies.Kinda like having two dissimiliar amps in parallel. My personal listening tests conclude better a single imperfect capacitor passing everything as a single coherent sound than multiple caps each having its own path to the output so series capacitors stay unbypassed That is a shame.Dirt cheap here though like most things not a good idea to use them in ALL positions or you lock the amp into a "Dale" sonic signature that will dominate the sonics. Manufacturers of commercial amps mostly have no choice but to use the same generic parts so usually all resistors and all caps will be from a particular vender and be a certain type while we hobbyists can use what is best at each point in the circuit. I also like the Welwyns but like you with the vishay-dale hard to find here.Holco is off my list No need.The entire circuit is a single Mosfet that because I run mine at +24 volts DC @ 200mA per I just bolt them to a back panel mounted heat sink then use terminal strips as passive parts tie points with the gate resistor soldered directly to the mosfet gate and the power supply bypass fixed directly to the mosfet drain pin.The source resistor is a chassis mounted Caddock Finally the power supply external but being a single polarity has the same type layout with the big LM350K bolted to the rear panel heat sink with the parts mounted either ON the TO-3 socket or to a terminal strip bolted to the chassis floor.A LOT easier to do than the description sounds. Every unity gain stage having a balanced topology is called a diamond buffer and why I mostly have a problem with it because it is more catch phrase to rope folks in many times than it is an accurate description as a variant of the classic Jung model. The thing is a one-to-one direct copy would be recognised in an instant as a direct rip off so in order to sell someone elses design it has to be changed and those changes usually mean going away from what is already an optimal design so why bother ? so it can be called a diamond buffer is why. You want to see a nice topology do a search for "LH0033" and check out the internal schematic and if you want a true class A buffer check the LT1010 that can be run almost purely class-a with enough heat sinking but no diamond so not cool actually might be a good idea though from memory the WNA splitter looked pretty good.Monolithics offer convenience and on substrate tracking of the parts over a wide temperature range,hybrid discrete/opamp types can be optimised to the circuit and can offer most of the same benefits if the transistors closely matched then bolted to the same heat sink,all discret would be a bear to match up mike would be the one to answer that being inimate with the design and schemo.I have it somewhere but off hand can not remeber details and have no time right now to check it try without and while playing music feel the transistors.If you can not comfortable keep your finger in place as long as you want to heat sink them.the additional 3 volts should not make too much difference but may
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FritzS
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Post by FritzS on May 31, 2006 13:50:18 GMT
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rickcr42
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Post by rickcr42 on May 31, 2006 22:12:16 GMT
Figure 1 stright up,learn the sound of the amp then decide on an upgrade path if moved to but I have to tell you 99.9% of all builders go back to the original single ended single stage single power supply original on the sonic merits.The amp sounds way better than it has any right to breaking damn near every rule of modern solid state design. critical parts : R1-I used a Beyschlag here but any good "nuetral" low noise precision resistor is good. RG-My choice was carbon film.Because it is meant to eliminate oscillations aboslute precision and/or stability is not real important but being directly in the path sonics are so go for a great sounding part over a tecnically great part.If carbon comps buy ten then measure for the best L/R pair matchup.Carbon comps rock in pulse response but can "wander" so not a real good idea in precision circuits plus use sparingly or the overall circuit sound will be a too soft/slow/dull one.Death with a mosfet in class-a R4-Surprisingly a very audible circuit postion and one that sent me into fits trying every manner of active,passive and hybrid method until I wised up and went back to a simple purely resistive element which again i tried every one i could think of including lightbulbs ala the ZenLite amp.Because of all the experimenting I used a barrier strip to interface whatever screwball idea i had that month to the actual mosfet source and my final conclusion was the Caddoks rule as a source resistor with mosfets ( a good place for personal experiments if you do as I did and use a "screw it in and listen" type connector) C1-Mine is a Solen SCR film and foil,600V rated.Cheap,sounds fine.I even had at one time a 716P "orange drop" at this spot and to be honest it sounded fine.Not as good as the SCR but for the amp build cost at the time which was bare bones just do it and listen not too shabby at all C2-I am quite happy with the Cerfine and even was not displeased having a big purple Radio Shack 2200uf/35VDC Nichicon electrolytic there in my earlier build.another one of those combination junk box/local parts just to get the damn thing built instead of waiting for the UPS guy for a week everything else is fine as is using "anypart" with my personal amp using Dale-vishay for R2/R3 (more on this in a bit),Radio Shack Zeners for the input protection diodes,I raised R5 to a 2.2K/1W wire wound and i am presently using X2 0.1uf/400VDC orange drops for C3 for "color" back to R2/R3.A better method is shown in Fig.9 on this page : headwize.com/projects/showfile.php?file=opamp_prj.htmbut with these changes- 1-no dual supply.the bottom resistor and RS go to circuit ground as in the original 2-use the original R2/R3 values but add a 50K trim pot hooked up as shown in fig.9 so you can dial in the bias point. to keep it simple i would use the original R2/R3 then later when the circuit is operational consider the additional pot. Anything i would maybe change ? I have a suspician transformer coupled may be the bomb and whip the cap coupled version but as of yet have not tried it being too busy actually using the amp in my system.It is that good sounding with the right headphones and a low budget build cheap as it gets
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Post by spendorspain on Jun 1, 2006 22:57:06 GMT
Hi This post is about the WNA MkII (not cap-less yet) using the AD744 op-amp with its own output stage bypassed. I’ve also used AD8610, AD8065 and LM6171(and perhaps I’ll try AD843) but the AD744 is so vastly better that I’m wondering why there is no more enthusiasm about this very easy mod. I urge everyone to try it… I’ve posted some impressions already, so I’m not going to repeat myself, but with more listening I’ve found two more virtues, confirmed every time I hear a new recording, so I believe they belong to the basic character of this op-amp. One is the very high resolution. I can hear clearly more things in very familiar recordings in a natural, not etched or forced, way. Simply I can hear them effortlessly. The other virtue is the soundstage. AD744 has by far the best soundstage because both LM6171 and AD8065 have flat perspectives only improved using some crossfeed (I’ve used the mod Linkwitz circuit seen in Head-Fi, but with a smaller resistance in the main channel to reduce the level of crossfeed and the low-pass filter effect it produces). The AD744 has REAL depth of image and air between the instruments (no crossfeed needed). Without any effort, one can ”see” into the concert hall and “see” the positioning of players, with a clear sensation of front-to-back layering. It’s very easy to relax with the AD744 WNA, what makes listening a very pleasurable experience. I ENJOY to hear my favourite music that way. Regards Jose PS.: I have a more technical question. When using transistors in pairs it is important to match them. Is it enough to match their hFE using a multimeter with a test “b-c-e” socket for this? I have measured these hFE values for the four BD139 used in the output stage of WNA :161, 161, 162, 162; and these for the four BD140: 172, 174, 177, 177. As you can see the hFE is within 1% between the pnp and npn respectively and well within 10% between each npn-pnp pair (e.g.: the worst case is a pair with BD139 hFE=162 and its complementary BD140 hFE=177, about 9% difference). I have read that a mismatch can lead to sonic degradation or more dc offset at output. Is the matching above enough? Thanks for your comments
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FritzS
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Post by FritzS on Jun 2, 2006 15:23:29 GMT
I will order some AD744 - but how is the sound in "normal" (not output-stage less) mode? Gives another way without twist the pin? A resistor between? Have you changed one of the different current sources? Try AD 843 I think it's the similar effect But only one test CD with three same pieces of music but other antique guitars - the difference between are greater with LM6171, but more natural with AD843 - I hear this if the guitarists sittig in front of me in the room, sliding with his fingers over the strings, ... great .... and this with an old, modified Philips CD 650 player too .... to compare www.analog.com/UploadedFiles/Data_Sheets/565502ad843.pdfwww.analog.com/UploadedFiles/Data_Sheets/871938516AD744_c.pdf
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rickcr42
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Post by rickcr42 on Jun 2, 2006 18:57:36 GMT
I prefer the AD743 or AD797 (or even OP275) in a normal opamp but have to say the AD744 from pin 5 is nice being a Class-A front end for whatever output stage you want to add.If you look at Fig.28 of the data sheet you will see a differential jfet front end with active current source to a single ended class-a output stage which will (or should) have better fet matching and tracking over temperature trhan a discrete version so a nice "front end" for a Semi-Discrete-Hybrid Op-amp where you add your own output stage. This can be anything from transistors to a monolithic buffer but cross mosfets off your list.Just not enough drive to overcome gate capacitance which would mean a rolled top end www.analog.com/UploadedFiles/Data_Sheets/871938516AD744_c.pdf
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rickcr42
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Post by rickcr42 on Jun 2, 2006 19:08:06 GMT
BTW-this schematic shows the original Jung AD744/AD811 line stage as an electronic crossover using the pin 5 output connection.lose all the filters and you have the original that for many would be all the amp they would ever need for both preamp and headphone amp duty (output switch and gain select switch @ +6dB/+10dB/+20dB ). Old style chips (pre-cell phone duty),old packaging (through hole DIP) yet will whip many modern designs for way less build cost.As far as I personally am concerned there are only three paths to opamps used as headphone amps unless stricly for portable duty : 1-Op Amp front end to discrete output stage 2-Op Amp fron end to monolithic buffer stage 3-Op Amp front end to CFB Amp output stage with the best being choice #1 if done correctly (WNA MK ll) and not just as a "feature" to sell products-happens way more than most think (diamond buffer ),#2 and especially so if the buffer is run in pure Class-A operation for all levels up to the absolute peaks and finally #3 if used in a multiloop feedback configuration
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Post by PinkFloyd on Jun 3, 2006 9:28:09 GMT
No real need Fritz it was there as a belt and braces protection against RFI which is why it was so close to Mr. LM6171. If you're using AD843 then you can either keep it there or just fit a zero ohm link, totally up to you. Not at all necessary. It was another "thing" designed to keep the amp stable (with LM6171) in the abscence of an output resistor (remember the protection lamp that used to be fitted?) It works by presenting the amp with a low impedance load at very high frequencies, and this tends to kill any tendency towards oscillation with the LM6171. If you're using AD-843 I wouldn't worry about fitting the Zobel. No. This was also for the LM6171.... Adding the 330k resistor reduced the gain of the LM6171 from open loop to 330. This increased the bandwidth of the LM6171 gain block so that the global negative feedback loop was effective out to higher frequencies. The high frequency distortion was thereby reduced. I run mine with 28V and there's no need for heatsinks. The core temp. of the transistors is between 55c - 65c which is perfectly ok to run "naked" If you increase the quiescent current then it may be necessary to fit sinks as the transistors tend to run a bit hotter but, as it is, there really is no need for them. AD-843 runs warm but certainly not hot in the WNA, there is no real drift to speak of and the offset remains within +/- 2mV from cold to warm so, again, no real need to sink it. Having said this, fitting heatsinks is cheap and certainly won't do any harm so if you've got a few spare pennies then go for it Fritz. Get yourself some nice nylon nuts and bolts and a mounting kit comprising bushes and mica spacers and you're good to go
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FritzS
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Post by FritzS on Jun 6, 2006 14:37:53 GMT
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rickcr42
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Post by rickcr42 on Jun 6, 2006 23:38:29 GMT
watch those vishay-dale wattage ratings man they are MIL-Spec so 1/4 watt is actually a 1/2 watt and the 1/8 watt your common 1/4 watt in size
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Post by spendorspain on Jun 14, 2006 20:42:12 GMT
Hi, I’ve at last tried the AD843 in the WNA MkII headphone amplifier. It is the most detailed op-amp of all I’ve tested, with a crystal-clear but not too bright highs (perhaps because my headphones are the very sweet-sounding Grado HP-2) and a good midrange and bass. The dynamic range is also very good, with exciting orchestral climaxes (no hint of congestion or compression). For comparison, I’ve used LM6171, AD8610, AD8065 and AD744 (this with its own output stage bypassed). The only problem I hear with AD843 is an overly upfront and too “in-my-face” sound, a little uncomfortable and not to my taste (I had a similar problem with AD8065 solved in part using a little crossfeed, but I’ve not tried this with AD843 yet). After several days of listening and rolling op-amps, I’ve decided to use the AD744 with its internal output stage bypassed. I’m not going to try it as “normal” op-amp, because it seems unlikely that the use of its own output stage improves its sound (it is just another and unnecessary amplification stage in the music path). The virtue of AD744 I like the most is the way it presents the music, more three-dimensional and finely layered from front to back, with an unforced and natural presentation of detail (it is only a little behind in detail level from AD843). This week I’ll remove, at last, the output capacitors (C4) in the WNA MkII amp and I hope this will make a new and significant improvement in sound quality, as was the case when I removed the C1 input caps. With the AD744 the dc offset at output (before C4, of course) is only 12mV and 10mV in each channel. I think this value is low enough for my 40 Ohm Grados, even if at turn-off there is a very short peak of around 60mV. What do you think about these values? Are they safe? Regarding these C4 output capacitors, the main capacitor is a electrolytic Black Gate Nx 1000uF/25V, bypassed with an Evox Rifa PHE426 4.7uF/250V and a Vishay MKP1841 0.01uF/1000V polypropylene film caps. I’ve already removed these small film bypass caps I was using and I can report my listening impressions. I think that it is easier to evaluate the effects of removing a component rather than those of adding it, because there is no burning-in process to worry about. Although the BG caps are reportedly among the best electrolytic available and are hideously expensive, the film bypasses (rather cheap and non-exotic at all) improve greatly the sound. I know there are opinions against bypassing caps, but to my ears the “composite” cap is definitively better than the BG Nx alone. There is a little more detail and air in general and more agility in the bass, but above all there is much less grain in the highs. They are purer and cleaner and much more realistic. I’ve not heard any congestion or lack of coherence due to the use of the three caps in parallel. (BTW, when I remove these expensive BG caps I’d like to sell/trade them if there is somebody interested. Can I use the “Gear for sale/trade” subforum for this?) Regards Jose
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FritzS
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Post by FritzS on Jun 16, 2006 12:25:45 GMT
I am gladden that the AD843 have enjoy you Now I search for the single OP version of the OP275 - the OP176 is obsolete, the replacement OP184 have a lower slew rate, I contact the AD technical support.
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Post by PinkFloyd on Jun 16, 2006 18:49:17 GMT
What with all this talk of the 744 I unleashed a couple from my underground bunker and socketed them ready for rolling into the MKlll: No shit Sherlock, they certainly are "3 dimensional" with the music coming at you from all angles. When I first had a listen I assumed I must have chopped the wrong leg off as the sound was pretty smoothed out (a bit like LM6171 on valium) however, after prolonged listening, I quite like their airy, "spacy" presentation.... it's certainly a lot more laid back than the 823 but, in a strange way, also "exciting" thanks to the insane 3 dimensionality. I'm not quite sure where the amp is with respect to the LM6171 class A biasing, I may have to reverse that, and the power supply biasing is set up for 843 at the moment so that may have to be tweaked as well but, as it stands, yes.......... AD744 is certainly worth rolling and I shall be stripping the amp back to the board over the weekend and optimise it around the 744 to give it the best opportunity to show what it can do. To sum up, it's like an LM6171 on valium with added 3D. Offset is L/H 0.00mV R/H 0.02mV (744 JNZ)
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Post by PinkFloyd on Jun 16, 2006 19:09:47 GMT
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FritzS
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Post by FritzS on Jun 17, 2006 14:22:19 GMT
But you use them in a wna mkIII PCB - we all have mkII, and I think if we test this we should change the one 5,6 mA current source to 3,5 mA or modify the output stage look as mkIII www.stockhammer.at/hifi/wna.php#Modification1How are the difference in sound between 744 and 823? Where I can get a mkIII (or a mkII) PCB now? I will use a second amp for test! Mike please give me your right address per private mail - I will send you some test music ;D
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rickcr42
Fully Modded
Rest in peace my good friend.
Posts: 4,514
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Post by rickcr42 on Jun 17, 2006 16:20:47 GMT
DAMMIT ! Just lost a very long,very extensive reply that i have no shot at duplicating word for word so will instead do the "revised/condensed" version Do. By eliminating the output stage of the opamp you are only using the differential input stage and output stage driver sections which already operate in class-A. By biasing in the 5-7ma region you run a real risk of burning up the driver section (new output stage) while gaining nothing in SQ. Also.This is one of those opamps that benefits from adding a bypass cap across the chip-from V+ to V-.Why ? No frikkin clue but it does Any good 0.1uf NPO is fine. Mikester.You really need to try the original "Jung Preamplifier" at some point just so you know just how simple a good preamp/headphone amp stage can be.This is the classic AD744 with bypassed output stage to the AD811 CFB amp output driver stage circuit Finally a cool "trick" unique to the AD744/AD811 is thew ability to make the two devices into a single "Super Op Amp" module ! What you do is piggy back the two chips with the driver stage on the bottom and the driver stage on top.Once the two are soldered together you have a drop in module that can replace any pin compatible single opamp stage but with a much higher performance level than any one single opamp can provide if you need a high current output for driving long lines,a low impedance input next stage or even headphones direct. From memory I can't remember the exact pin layout but the data sheets provide the answer.You need to 'clip" the unused AD744 leads and extend the buffer leads ton those now open DIP Socket holes but what you end up with is a "Super Op Amp" usable as a regular DIP pack opamp so a drop in. Where this applies directly to the WNA (untested theory ) could be as a driver stage to mosfet retrofit of the current bipolar transistor output stage.Mosfets like to be run in pure class-A to avoid the soft upper octaves so obviously the biasing scheme would also need an update and the psu would need more grunt but doable . so why the "hybrid" opamp driver ? Gate Capacitance of the MOSFETS ! This is a real problem area rarely addressed in most of the audio circuits I have seen (DIYers wanting mosfets for no reason other than to do it then doing it wrong ) using these devices and the reason again for a rolled off upper register.You combine mosfets in class A/B with improper gate drive and you get a particularly soft sounding amp that over time becomes very boring.You NEED low impedance drive and high current to overcome this gate capacitance just like you NEED low impedance combined with high current drive to drive long interconnects,especially if they have a high capacitance.This is BASIC but even still mostly ignored ;D The close proximity of the two chips is a major plus (lower Z,less stray capacitance,easier byapss scheme) but to really sing you need to add to the mother board a capacitor bank at the V+ and V- pins consisting of a 470uF low ESR electrolytic/10uf Vishay solid Tantalum/) and an 0.1uF NPO.Least important of the three being the local 470uF cap if board space is minimal Finally-it is nice to have a few of the Super Op Amp modules banging around the shop as "reality check" amps.Yes it sucks if after a lot of work you think you have come up with something good only to to find this old and simple amp whips its ass but still,better to know....................... Oh yeah.Makes a nice drop in for many CDPs using opamp output sections if you want to locate the player a distance from the amps or control center and can turn a lot of El Cheapo devices with an opamp engine into serious audio contenders. My first post was WAY better but that is something you will never know,sucks to be you
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Post by PinkFloyd on Jun 17, 2006 17:48:44 GMT
I wish I'd read your reply "before" going under the bonnet earlier on Rick but I will be back under tomorrow so no worries, can all be tried then. Today was spent totally arsing about with power supply bypass capacitors and here's the mess I've made "so far": Fitted AD-744 with pin 5 to 6 mod. Bypassed pins 4 & 7 to ground with a combo of caps in parallel (220nF polyester, 47nF polyprop, 10uF non polar, 10pF ceramic, 4n7 polyprop, 2u2 polyprop) and fired a 3.3pF ceramic across pins 5 & 8 (external frequency compensation) So far so very good. Haven't reversed the 6171 class A biasing yet but from the "sound" of the amp I'm not sure I need to. The 3 dimensionality is now even more pronounced and the mid / treble detail just phenomenal (especially the treble, it sparkles!) Bass is tight, fast and light footed and, overall, the sound is engaging and very musical indeed. I will try a few other bits and bobs but run out of steam today as I had other things to do. the 811 / 744 combo is something I did with the MKll but wasn't too keen on the sound but will try it with the MKlll for sure I seem to have got a bit carried away with the bypassing and have paralled big polyprops onto the rail splitter caps but it all sounds good so far so I won't complain or ask questions! No noise "at all" you can turn the volco up to max and not even a hiss with the CDP on pause, total inky black silence! Here's a few pics of it, it's getting hard to figure out "just" what I've done with all these caps stitched onto the PCB
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