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Post by spendorspain on May 9, 2006 12:11:34 GMT
Hi
I hope you can see the pictures of the modified AD744. The first two links are to the photos and, if they don't work, the third is the Head Fi web page where I've posted them.
With 24 hours burning-in time the AD744 sounds clearly better than LM6171 to my ears, and this even with output caps in place.
I have a technical question: is it impossible with AD744 a DC offset level dangerous for the headphones, so no caps in signal path is always safe? If this works this way in the WNA MkII, it will be the same with the MkIII diamond buffers?
Regards, Jose
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Post by spendorspain on May 9, 2006 12:15:11 GMT
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rickcr42
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Post by rickcr42 on May 9, 2006 12:54:43 GMT
no such thing in anything but ad copy.Straight wire with gain ? even a WIRE imparts sound to whatever passes through ! Tomlinson Holman proved thirty years ago that you can low pass filter an audio signal above 40khz and remove ALL slewing induced distortions.This was pretty much the proof that many needed to prove to them they were not crazy and that yes their "slow" electronics can actually (and did) sound good even though the Mark Levinsons of the world were out to convince everyone they needed electronics on the verge of self destruction or they were not accurate. Nelson Pass actuallu demoed an NS-10 preamp back in the seventies by playing a TV signal through it yet here we are thirty years later and he limits the upper octave response to an F3 @ 100khz www.passlabs.com/downloads/preamp_lit.pdfIt was also once a common practice to measure audio electronics "wide open" for the spec whores then add in filters for production models because while the square wave graphs looked like shit with the filters,and we know how much the reviewers are in love with their O-Scopes showing sharply defined square waves,the fact was they were at the edge of instability AND were as a whole not as good sounding which for some reason many self proclaimed "audiophiles" forget is the ultimate goal. Not the data sheets,not the the scope pics,not the one upmanship to see who can transmit a satellite signal through a gain stage but SQ and that in a natural way,the way music actually sounds rather than "hi fi" which has come to mean "better than real" if what passes for such is an indication. Preferrred by who ? There are "preferred" valves that may not be another persons idea of good sonics and then there are the "edge of oscillation" tubes that without a proper layout,without a grid stopper will go whack job on you but the grid stopper itself has audible consequences.No free rides. The REAL danger is having a front end that slews faster than the succeeding stages.Properly designed a system approach should have each stage be faster than the one preceeding it with the power supplies being faster than the stage it powers or you are pissing on your own leg so rather than try and "speed up" the front end it makes far more sense to slow it down unless your final stage has enough speed to handle what goes before (and why you see all manner of both series,shunt and loop filters in high speed opamp designs). again a broad statement that is not and can not be accurate without using absolute parts identification.some opamps respond to a low impedance feedback loop,some a high impedance loop.Some are unity gain stable,some need to have gains over five to be stable,some can drive a capacitive load,some will go into self destruct mode if the output capacitiance is too high. all about choosing a part to build arond not build the circuit then simply drop in whatever is fashionable that week.Each part has its own requirements which are easily weasled out from the data sheets but that is no gurantee of good sound just as a generic description of a part as being "high speed" has zero to do with how well or how poorly the opamp handles audibly significant frequencies without strain or grain I personally do not like or use the 6171 or 8065,I don't like them no matter how many say they are world beaters.The 843 and 797 yes.These are true "audio grade" parts that are mostly well behaved in circuit as long as they get the voltage required. 5 Volts need not apply for best SQ,12 volts is marginal. Just because. If I ever "lose it" momentarily and list all the "in house" opamps I have at my disposal I hope someone comes over to my house and whacks me upside the head HARD so the next time I conrtemplate a relapse I think back to the head shot and decline the impulse (plus it would take up the whole damn page since i get two or three "eval" packages a week Actually,thinking on it if I ever get the time one of these years I think I should unload a few hundred since I am pretty much locked into the same five or six for all my needs : Op Amps: 1-AD8397 for ALL analog portable opamp duties 2-AD8655 portable digital analog sections using a single +5VDC power supply 3-OP37 with class-A output or "nude" AD797 for mostl line level duty including line drivers/receivers. 4-AD825/AD843/AD826 just because I like to screw with them ;D Buffers: 1-BUF634 portable use in anything not using the AD8397 2-LT1010 run very high into class-A for new designs 3-LH0033/LH0063 personal stash/use and my reference for buffers .
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FritzS
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Post by FritzS on May 9, 2006 14:43:33 GMT
This I found for OP 176/OP 275 and more .... www.zero-distortion.com/tests/opamps/opamps_05.htmOP 176/OP 275 176 is the single version of 275, which is a dual. Unfortunately, it has been replaced by what judging from data sheets, looks like just another me-too op amp of mediocre performance (SSM2275). A pity, as I feel OP275 was an outstanding audio op amp. It uses what is known as a Butler front end, which combines FETs and bipolars for what is claimed to be the best of both worlds. Whatever, it offered a good noise figure of 6 nV/sq.rt.Hz, a slew rate of 22 V/uS, extremely low distortion figures, and a rather good settling time of 200 nS, approximately 10 times faster than usual. It could sink reasonable currents, but don't expect too much of it. In terms of sound, it tends to sound very clean and clear, but a little rich, meaning its bass region is subjectively a little more pronounced than it should be. However, to this day, I have found no better op amp for tuning of Marantz CD players, assuming it is used in the LPF section. Many others can do the job, but none will produce such lovely results as this one; I assume it simply blends in well into Marantz's overall sound scheme, and the end result is really on the wonderful side. However, it can be used only in the standard CD6000 model, because models OSE LE and above use Marantz's HDAM module. This could be blaspheming, but I feel a pair of OP275s in a stock CD6000 model deliver better results than the OSE LE edition. PS: Are the AD845 - Precision, 16 MHz CBFET Op Amp the follower for the OP 176?
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rickcr42
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Post by rickcr42 on May 9, 2006 18:07:57 GMT
The is no single opamp equivelant for the OP275 but there IS the OP2 85 which looks damn near identical except for the availability of a ceramic package www.analog.com/en/prod/0,,759_786_OP285,00.html The SSM parts suck and the reason why I have an entire tube of the bastards hiding out in the dark around here somewhere.I initially picked them up as an OP275 replacement when my at the time source was out of the 275 but had plenty of SSM 2275's. Meant to be used as the balanced driver section on the output of a DIY line mixer I plugged them into the IC sockets,hit the "on" switch and thought something was seriously wrong ! The sound was so rough and indistinct sounding I was thinking I made a wiring mistake,turned the mixer off,discharged the caps and went to wrok tracing the circuit back and found........nothing ! At least nothing wrong so I closed the mixer back up and decided it was maybe a burn in problem,that maybe the parts would "settle in" over time but nope,not happenin' so I waited until my former outlet restocked the OP275,ordered the SSM replacements,plugged them in and all was well in ricksville that day Here is the screwy part.On paper they are the same part with the only difference being the "SSM" designator which denotes "Professional Audio" use yet the sound was worlds apart ! Why this is especially alarming for those who use the chips (and I do,should have added it to the above list ) is RoHs is changing the face of audio electronics with leaded parts being replaced across the board with compliant parts as the stocks deplete plus there is a move to eliminate the DIP package as an option with everything going to SMD. Where this is not true is in the "Pro Audio" parts supply lines where DIP packaging is a must for "fumbly fingered" audio techs who work on the gear (or old blind bastards like me ).Because the pro audio market is a large one it is feasable to carry these specific parts targeted to the intended market (as with the BB OPA627,OPA604,OPA2134,Etc.). Where does NOT make sense is when there are redundant parts as with the OP275/OP285/SSM2275 so obviously something will have to go and my money is on the OP275/285 biting the bullet leaving the sonic butcher SSM part as the butler amp standard bearer.I could be wrong,hopefully I am,but likely I am not. RoHs complaince statutes combined with high density consumer level pc boards means full across the board SMD in combination with "lead free" will at the end of the day rule the supply chain and manufacturing end and if so redundant chips will fall to the side of the road to be passed by the "new and improved" parts which for our purposes are usually anything but.That is the bad news. The good news is pro audio is exempt from RoHs compliance issues and is always a DIP package part with ADI,BB and THAT Corp (full RoHs compliant) still churning full production dual-in-line package parts. We may end up with the OPA604/OP21XX as the "default" pro audio opamps with the SSM line and THAT Corp line for drivers and receivers (though they also have a pretty good preamp chip and have hints more stuff on the way ) My take is if you like the OP275 now would be a good time to stock up and as cheap as they are no real reason not to........ Rickeraptor
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rickcr42
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Post by rickcr42 on May 9, 2006 18:41:48 GMT
The Butler amps : OP176 Single Op Amp: obsolete OP275 Dual: production part OP285 Dual: production part SSM2275 Dual: obsolete (suggested replacement OP275 !) SSM2475 Quad: obsolete blows my theory all to hell....and then some .
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rickcr42
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Post by rickcr42 on May 10, 2006 1:01:10 GMT
more to think about on the "need for speed" front "We try to keep the high frequency below 40K Hz. This minimizes oscillations at supersonic frequencies and adds some protection to the preamp and power circuits that can easily produce supersonic frequencies, if they are not well protected." from the Edcor U.S.A. Tech Notes section- www.audiotransformers.net/tech_notes/tn12.htmI use audio transformers extensively for coupling stages and feel this is the primary reason my system sounds organic rather than "electronic" in nature though I highly doubt my system would pass a very pretty square wave (damn good thing I do not play square waves ! ). I came to the transformer as "filter" about eight years ago when I read somewhere how a person was attempting a hi-res computer based sound system yet no matter how much loot was thrown at it the sound was just "not right" until the person experimented with audio line level coupling/isolation transformers at which time the entire system was transformed into a true music machine. being a skeptic I now only had to reason out how this could possibly be but had to also do my own "el cheapo bastard grande" experiments so I nipped down to my local radio shack and grabbed a couple of auto sound 1:1 600 ohm isolation transformers (meant to remove ignition/RF noise from the audio signal path) for $8 (up to $17 now ;D ) and inserted them between my sound card and line stage/control console and at first I thought something was dead wrong because a more rolled off and lifeless sound i had never heard in my system ! ready to shit can the entire idea as being bogus it came to me that the sound card had crappy output drive and was likely not happy trying to drive a 600 ohm load so I dropped my LH0063 buffer between the two and DAAAAAAAAAMMMNNNN ! The best sound I had ever heard from computer based music ! For the first time ever there was true note separation and a DEAD BLACK background rather than the ever present digital ground noise that is there all the time but never noticed until it is removed and then re-introduced. I was hooked and took out the "el cheapo" Radio Shack transformers and replaced them with a pair scavenged from an old mixer which is how it stayed for years until I decided to add the filtering INSIDE my line stage where everything would pass through instead of just digital signals. I now have a pair of 15K:15K line level trafos permanantly built into my control console .Having control over circuit ground and how/When/if to isolate it is a real advantage I could not live without once used to it and the upper octave natural rolloff has proven to be invaluable because it has saved me from trying to make a "nuetral" RC filter to perform the function of top end cut. as an added bonus I also gained the ability to alter the overall polarity of the signal without adding an active inverter so i can decide which sounds best at the flip of a switch.
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FritzS
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Post by FritzS on May 10, 2006 7:16:54 GMT
more to think about on the "need for speed" front I came to the transformer as "filter" about eight years ago when I read somewhere how a person was attempting a hi-res computer based sound system yet no matter how much loot was thrown at it the sound was just "not right" until the person experimented with audio line level coupling/isolation transformers at which time the entire system was transformed into a true music machine. You have partially right! www.audiodesignguide.com/cdplayer/dac.htmlAndrea Ciuffoli use a Lundahl LL1527XL in his DAC1 www.audiodesignguide.com/cdplayer/dac3.htmland Lundahl LL1636 in other DAC's But coupling transformers add their own "signature" to the sound - i remember more k3 (third harmonic wave). And have an - and more others - interesting headphone amp too ;D www.audiodesignguide.com/Headphone_amp/headphoneamp.html
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rickcr42
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Post by rickcr42 on May 10, 2006 13:44:55 GMT
no worse than changing a single series vishay-dale resistor to a tantalum or carbon and far less than the differences between two capacitors so that dog won't hunt as a deterrent. As a matter of fact you would be hard pressed to say a Jensen trafos had any "sound" other than dead nuetral
Andrea came to it after Stephano Perrigini did a "Glass audio" write up for a transformer output DAC but the article I reference not only predates both efforts,efforts that are more about DAC coupling than general digital ground isolation,but are not universal fixes as in the previous example I used which is closer to the Jensen ISO-Max "ground loop eliminator" products or the now popular tapped transformer volume controls because it is "inline" 100% of the time for all sources so the galavanic isolation of audio ground is available for ALL signals rather than just from a dedicated DAC.
I wish I could find the article that set me on the path but no amount of searching has manged to bring it up so i assume it has gone dinosaur on me (extinct)
When I DO use a dedicated trafos it will be either a 600ohm/600ohm bridging transformer terminating a high current solid state line driver,a 10K/150-600 ohm step-down at the output of a triode stage,a 2:1 step down as the input to my DIY ADC (totally passive front end),all my DACs have an output trafos,my phone stage uses ine for balanced output,etc.
heh,even my "tone control/filter bank" uses all LC (inductor/capacitor) filters with a transformer input and makeup gain stage at the output rather than the less desireable though far cheaper to manufacture "synthesized inductor" topology used in most modern equalisers (and what gives them a bad name even though the "ad copy" SAYS they are better and will even show you the graphs to prove it while your easrs tell you something is dead wrong ! )
Bandwidth is in the 30khz-100khz area depending on the what/where,group delay fine,noise levels non existant,SQ all I could ever want it to be which means "music" flows not Hi-Fi to send the dog scurrying for cover when he hears the upper octave crap many have without even realising it
Nope.My way is wide band active circuits intentionally band limited to audibly significant frequencies and has served me well since my first "ear opening" revelation. Any who I have managed to "con/weasle/cajole/intimidate" into choosing the passive path over active ciruitry and use transformers to interface two items have universally reported back there was a noticeable SQ increase which is good enough for me to know I am not delusional and that i am and have been on the right track. Just had to get my head around the "measurements rule,I must reproduce a perfect square wave" thought process that was beat into my cranium over and over by manufacturers trying to justify circuitry that measured great,sounded OK but in a head to head found to be lacking which was in reality truly meant as a cost saving measure and not an all out assualt on sonic quality which this being DIY is what it is all about-no limits due to manufacturing/assembly line/profit margins
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Post by PinkFloyd on May 10, 2006 18:30:14 GMT
OK Fritz, there's a present on its way to Austria for you I won't be using it so, as you're so keen on the WNA amp, I've sent you the WNA Cascode PSU board along with the construction manual and schematic. This will make your WNA sing and will be something else you can work on (and maybe improve) let me know when the package arrives, it went out yesterday. All the best. Mike.
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xerxes
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Post by xerxes on May 10, 2006 19:11:45 GMT
Never mind all this technobabble, when can we expect the first prototype of the PinkRickyFritz amp?
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rickcr42
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Post by rickcr42 on May 10, 2006 19:38:34 GMT
Retro-Pink with a twist of Fritz anyone ?
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Post by PinkFloyd on May 10, 2006 19:42:57 GMT
Never mind all this technobabble, when can we expect the first prototype of the PinkRickyFritz amp? Well, I for one, am in the process of moving house. Head is really fuzzed up at the moment with interest level in all things (on a scale of one to ten) a "2" at the present time. Just way too much going down and I can't relax and think about anything until I'm settled into my new place and it would help if I knew where the hell I was going! Once settled I think the enthusiasm will come back (I hope it will!) and it would be great (WILL be great) if Rick, Fritz and myself could get together on something cool for all the headphone lovers out there. I, personally, would like it to take the form of a simple "bullet proof" plug and play kit form amp which is guaranteed to work first time and is guaranteed to sound better than anything you can buy in the shops. That doesn't mean a HUGE overly complicated design with bells and whistles and "everything" bar the kitchen sink incorporated into it... No, less is more when it comes to amps (IMO) and "simple" seems the best way to go. Obviously, the other two (Rick and Fritz) will have different ideas so if we do do something it'll be interesting and fun I'm sure
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rickcr42
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Post by rickcr42 on May 10, 2006 19:59:31 GMT
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xerxes
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Post by xerxes on May 10, 2006 20:26:28 GMT
What I want is the best headphone amp in the world, regardless of price, for around £300.00. Tall order?
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rickcr42
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Post by rickcr42 on May 10, 2006 23:11:20 GMT
heh,not at all man we can just build a POS headphone amp for a third of that and TELL YOU it is the bestest gotta have it amp ever conceived by mankind then sit back as the loot piles up.........like most other amp builders
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FritzS
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Post by FritzS on May 11, 2006 6:53:50 GMT
I want to use AD843. I am not surely if the idle current in the output stage in AD843 is great enough to run in Class A when load the diamond buffer. When not a additional current source is needful.
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Post by PinkFloyd on May 12, 2006 22:55:34 GMT
I want to use AD843. I am not surely if the idle current in the output stage in AD843 is great enough to run in Class A when load the diamond buffer. When not a additional current source is needful. AD843 is MUCH better sounding than that horrible LM6171 IMO and you don't have all the associated CRAP that goes along with the LM6171 like output caps, oscillation and all that other grief. White used the LM6171 purely because he could "source" them pretty cheaply and also as they sounded quite good. He wouldn't use the AD843 as they have a long long lead time and are virtually impossible to source in the UK. They are much better sounding in my opinion and, if you can source them, lose those horrible prima donna LM6171's like "now". Offset with AD843 is way low (0.00mV - 5mV) and, thus, you don't need to worry about output caps or trimpots blah blah blah. They "do" get quite warm in operation but drift is negligible (< 1mV either way) they're fuss free and bloody good sounding in the WNA amp
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rickcr42
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Post by rickcr42 on May 13, 2006 5:07:20 GMT
that AD743 has been around so long it is not taken seriously by many and that is really a big problem with much of the DIY crew. For some reason being "old" is reason enough to pass a part up no matter if it actually SOUNDS better than the "new" part or not. Why ? Why in a medium that is all about SQ would a person choose a part based solely on some theoretical of need for speed when that need means running at the edge of instability or overcomplicated circuitry to make it behave with the "fix" being as audible as the initial problem ? when the head to head evals say "choose the other jerky it sounds better" then it is the lesser part that wins I seriously wonder just what the priorities are. Specs ? The data sheet ? Bragging rights to who has the fastest chip ? Surely it is not SQ ! Not saying a person can't make a good sounding amp,it has been and is done though many are not, and this is not surprising considering some of the sources so it is rare. I am saying it makes no more sense the the audio rag reviewers who in print make the ridiculous statements such as "I love the way amp "A" sounds but I would choose amp "B" because it tests better". What a load of horse shit ! Tests better but does not sound better so it is the right choice for music ? And we wonder why there is so much bullshit in high end audio ?Where "pretty" to look at or "check out those graphs folks" means more to a potential buyer than how a thing actually sounds playing music ? Un-fkn-beleivable though not surprising from a group that over and over in open forums will make the ridiculous statement "Looks good,I bet it sounds good too" as if looking good has shit to do with the sound and the main reason why a good part of high end audio is populated with $25 circuits in $500 wrappers which then sell for $2K and the customer line up ! makes me want to fkn puke then kick the cat in frustration because I can not grab that person,shake them and yell " what the fk is wrong with you man ? THINK DAMMIT !" ...anyway,of the handfull of chips I actually use being a discrete/valve type of mad scientist/hobbyist/yankee tinkerer only two are modern devices and those strictly for portables : The AD8397 for split supplies (single stage bufferless portable headphone amps) or the AD8655 for a single supply (portable digital analog section) The rest are old standbys,tried and true that no matter what I try to eval them against seem to win on balance every single time with the absolute fastest of the bunch the AD825-once considered blazing fast but now middle of the road and even IT has special needs or it will misbehave
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FritzS
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Post by FritzS on May 13, 2006 6:49:07 GMT
I want to use AD843. I am not surely if the idle current in the output stage in AD843 is great enough to run in Class A when load the diamond buffer. When not a additional current source is needful. Offset with AD843 is way low (0.00mV - 5mV) and, thus, you don't need to worry about output caps or trimpots blah blah blah. They "do" get quite warm in operation but drift is negligible (< 1mV either way) they're fuss free and bloody good sounding in the WNA amp About AD843 get quite warm - in the WNA MKII output stage - can I change both current source diodes to 3,5 mA? Have the AD843 enough idle current through the output transistors to run in class A *and* drive the BD139/140? To change to "diamond buffer" I will wait till I have the PSU PCB to buy the parts together. If I understand you - with AD843 I did not need the 330k inner loop NFB and the ZOBEL too? Both I don't use with the LM6171.
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FritzS
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Post by FritzS on May 13, 2006 6:54:27 GMT
that AD743 has been around so long it is not taken seriously by many and that is really a big problem with much of the DIY crew. You mean AD743 or AD843? About OP275 - some DIY have the same experience as I
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FritzS
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Post by FritzS on May 13, 2006 7:06:01 GMT
Another question - gives there a CD image with audio test tones? Or a program to *write* this self? All modifications I made by mesurements *by my ears* but not with my old big fat boy - a tektronik dual scope 60 MHz oscilloscope.
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Post by PinkFloyd on May 13, 2006 7:45:12 GMT
From AD843 Spec sheet:
USING A HEAT SINK "The AD843 consumes less quiescent power than most precision high speed amplifiers and is specified to operate without using a heat sink. However, when driving low impedance loads, the current applied to the load can be 4 to 5 times greater than the quiescent current. This will produce a noticeable temperature rise, which will increase input bias currents. The use of a small heat sink, such as the Mouser Electronics #33HS008 is recommended."
From my Head-Fi Notes:
"I've been looking at the AD843 datasheet. Its open loop gain is "only" 30,000 which is low for an opamp. So it qualifies as a low feedback opamp. It also has a very high quiescent current of 12mA which means that the output stage runs in class A. Low feedback class A amps generally have low transient intermodulation distortion ( TIM ) and will sound warm. Quite a few popular power and headphone amp designs are wedded to the low TIM philosophy, which originated with Otala if I'm not mistaken. Given that the AD843 output stage already runs in class A you can reverse the class A mods to the WNA, which were intended to bias the LM6171 output stage into class A, if you intend to stick with the AD843. It doesn't do any harm but will increase the dissipation in the AD843 unnecessarily ( but only by a small amount )"
Hope those notes help Fritz.
Mike.
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FritzS
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Post by FritzS on May 13, 2006 10:09:19 GMT
AnalogDevice recommand: www.analog.com/UploadedFiles/Data_Sheets/565502ad843.pdf ........ Power supply leads should be bypassed to ground as close as possible to the pins of the amplifier. Again, the component leads should be kept very short. As shown in Figure 24, a parallel combination of a 2.2 uF tantalum and a 0.1 uF ceramic disc capacitor is recommended.I think the Evox Rifa PHE 450 0,1 uF close - plus Nichicon FG 100 uF, 25V nearby parallel must fulfill this Basics - I am unsure to use ceramic disc and/or tantalum capacitors in audio design But if it certain need I would solder this an the backside of the PCB www.stockhammer.at/hifi/images2/wna_P1000178_m.JPGPS: I wonder the "diva" LM6171 need them too but the construction engineer ignore this
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Post by PinkFloyd on May 13, 2006 12:43:22 GMT
Done that ages ago Fritz but I used 10uF non polar between pins 3 & 7 to ground with a 200nF polyester paralleled onto each cap as close to the Opamps as possible (so close in fact, soldered direct to the dip8 sockets) Certainly makes thing sound a lot better, I'm not sure of the 10uF non polar but this can be changed @ a later date. Good thing about the NP is its size, can be tacked onto the underside of the board no probs whereas, say, a 2.2uF polster would be VERY large indeed!! I'll go and take some pics of the bypassing and let you see..... be warned, it's messy.. very messy!!
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