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DIY HE Adapter - Page 3

post #31 of 39

I have no capacity/time to DIY; however I am considering the Can Opener which I am sure some of you are familiar with. I know I am asking a lot so please accept my sincere thanks for bothering if you do. I have a NAD M3 integrated amplifier and I want to use the speaker B channel (currently unused) to hook the Can Opener into for use with my HE 560. My concern is whether or not these various components match well or not. I have inbound a nice Yulong A18 headphone amplifier, but I always thought that the NAD M3 is a very good amplifier and if I could just get a headphone adapter with it my thinking was that it should be better than all but very expensive headphone amps. That said, I am not knowledgeable enough about dampening factor and how a device such as the Can Opener would work. If anybody has some thoughts to share about my scenario I would be very appreciative. Cheers.

post #32 of 39

Ahh...finally....diagrams....that I can understand...lol 


THANK YOU robrob.


I hope this thread isnt too dead to get some info, or at least be pointed in the right direction. 


I was primarily interested in why you put the series resistor "in-front" of the parallel resistor?  I really only ask because I plan to use a tube amp and run the headphones "balanced" with custom cables as I have some "amp" rolling to do....some quite literally...oh wheels...lol. 


I have posted in another related speaker amp/headphone thread, so dunno if I will get in trouble, but I didnt find any "current" info....really.  If there ever was a final word about the best route to use to run headphones off of just about any kind of amp.  

post #33 of 39
 I was primarily interested in why you put the series resistor "in-front" of the parallel resistor?


If you put the series resistor 'behind' the parallel resistor the parallel resistor becomes a load resistor and causes no attenuation. With it 'in front' the two resistors form an L-pad attenuator and do both--bring the speaker load down to desired levels and add attenuation.

post #34 of 39

YES!  For once I "guessed" something right!  I have some experience in passive crossover design and build for custom speakers of all types.  I recognized the "L-pad" early in my research, but only seen it called out by that name a handful of times in the few threads I am still reading.  I hate to crosspost, but you seem like you might be able to help me some. And I am itching to buy a bunch of resistors and parts to add to my “pile”. How important is matching the resistors? I will be ordering in bulk anyway, doesnt everyone LOVE sitting around with a DMM and a pile of resistors trying to pair or quad a set of exactly matching resistors??? I will probably do it regardless... 'cause of my pseudo-OCD self. Lol....


I have noticed some people are inserting a third resistor, essentially creating a "center tap" from two resistors in series(instead of the one in parallel across pos and neg), and then running the "series" resistor from that "center tap" where the first two resistors connect to each other.  Does this have any benefit you could think of?  I'm a bit confused about this, it seems as if they might be able to better control impedance matching.  They usually halve the impedance of the parallel for the two, but I thought that staggering it might have some effect, desired or not as long as they added up to the original value of the single parallel resistor.  I realize that this puts the series resistor "behind" the parallel though.  Any thoughts? I just found it curious.


I was also wondering about using a stereo stepped attenuator for different headphones.  I have 80 Ohm for now, but plan on 600Ohm in the future, plus the flexibility to play ANY headphone is nice.  I am going to build a Headphone switcher out of a Parasound 1U/"half rack width" speaker selector(once I make sure it is balanced and not common ground, or MAKE it balanced as it is just a passive switch), and an "empty" Parasound Zamp case(same dimensions as speaker selector, and I can “link” them into a “full rack width” 1U unit) to hold both front and back panel inputs and outputs.  Obviously everything will be "balanced", and I hope to have a digital display(for each resistor) indicating what impedance is being introduced into the audio circuit, both to attenuate and to match impedance.  Do you think that is possible, any suggestions?  I am not completely helpless with a soldering iron, but far from a circuit design guru, but I think I already know of a circuit I can use to display the values....ironically it uses different value resistors to change numbers(old school "alarm clock" like LED), just for basic functionality.  I am worried that the readings would be skewed by being “in circuit”. So I even thought of using a “bank” of reference resistors to display the value that is being used in the circuit.


I figured if anything I could build a box like that and use it to easily and quickly get the right value components and then switch it out with "hard wired" replacements; much like I use active crossovers to determine the best roll off frequencies, and then go back and fine tune with passive components. 


So Mr. robrob, if you are still reading....What are you resistor value suggestions for the following amps?  I plan to use an LPad regardless, and was going to use my Beyer 80ohm cans for now and will modify the cord to run true balanced with 4pin mini xlr, but like I said...will jump on the next set of high impedance cans I can find.  Even just the drivers would work...I have a few pair of junk headphones that I would love to mod.  People are less likely to steal what looks like a cheap pair of "no name" headphones. 


Anyway, here is my “other post”....really dont know if I should post a link or the whole thing, but to make things easier on the “reader” I will just post the whole thing....


Basically, I have GAS(Gear Acquisition Syndrome)....sadly no dedicated headphone amps.  Just a few pre and int. amps with "ok" sounding HP outs.  Right now I have some stock Beyerdynamic Dt770/80, though I plan to get the 250 ohm version as well for doing mods.  I do have several home amplifiers that I wouldnt mind trying.  I have read about the parallel and series resistors and suggested values.  Strange I always called that resistor configuration an L-pad and used it as a standard part of passive crossover design for speakers.  Usually one was a variable resistor to adjust the attenuation.  Now I realize that the resistors are more about impedance matching, but couldnt we use vari resistors to fine tune an amp to a pair of head pho9to figure out the right valuesnes?  I am picturing a neat little case with a couple of knobs and some sort of digital readout of what values are currently being used.  At the very least use the device to setup level for hard wiring; much like using active crossovers to determined the best crossover point to build in passive in speaker building. 


Am I asking too much, is there already a product like this out there?  If so, I cant afford it and still want to build one myself.


Some amps I am considering. The specs I think I need for the 80 Ohm cans (16 Ohm/20W “parallel”, and a 550 Ohm/ 0.25W “series”) What do you think of the higher impedance for the parallel(most have called for 8 ohms/10W, I have always thought that higher impedance speakers sounded better, and this would get the amp a bit further into its “sweet spot” if I understand this all correctly. Finally on resistors...do you really think there is much sonic difference between the “cheap” and the “megabuck”? Including my “matching” of resistors, I figured that the mid priced parts should do alright.


Amp 1 Conrad-Johnson MV-50 tube


Amp 2 Crown PSA2  SS (actually have two...talk about silliness:), but would just use one...for a while...lol then I would HAVE to try both) If I pop my cans its a good excuse to get the 600ohms....;)(actually I would cry...I have big plans for the modest BD-DT770.


Amp 3 Parasound 855a SS five channel but I will only use two.


Amp 4 Crown D-150(I can hear the cringing from here...lol) VERY “SS” ssssssounding...lol, but certainly a powerhouse...


Amp 5.  Some sort of Chip amp like the lm3887(or whatever it is, cant remember off hand)....SS, and I would still need to build it...lol


AMP 6  Even more out there...I have some VERY NICE car audio amplifiers, as well as a very powerful 12v supply (70A) that I use on my test bench for repairs and what not.  In the past I used it to drive a pair of Soundstream 10.0 "Class A" amps to a pair of Magnepan MgIIbs.  Sounded pretty good, also used some Denon car amps...and a slew of others(classics from the 1990's)...  Some of the high current amps have me curious.  The "cheater" amps rated at 50watts at 4 ohms, but would do 800watts if the impedance was driven low enough..usually 1ohm stable, 1/4ohm if actively cooled.  More silliness I know, just would like to get some ideas before I start liquidating the majority of my collection.....car, home, HT, and pro sound(mostly amps and speakers).....baaaad gas.  I know that a car amp seems silly but it could be battery powered, and some really do sound good, especially in the first watt, where I expect my headphones to stay.  I have other "outlets" for LOUD.....;).  


FWIW I also have Parasound Speaker Switch that I plan to incorporate, eventually.  My custom speaker build has been put on hold. 


Thanks for any productive replies, your time is very much appreciated.  Obviously most concerned about the MV-50 tube amp, and was hoping someone had already successfully done one.  I am under the impression that the both the parallel and the series need to be used for tube amps.  It is el34 based, pretty sure common ground but will check when I unbox it...guess I could look at the schematics...heh.  But pretty sure it will be fine, I was thinking of going a little higher that 10 ohms, maybe 16 or so, depending on what is available.  Not really sure what to use for the "series" leg resistor though.  Help!?!



Thanks again robrob, and anyone else who can help me out here. Nathan

post #35 of 39



Recommendation: Try the amp connected directly to your balanced headphones first. Most amps, even tube amps will work fine with headphones. Do you have enough control with the volume control for comfortable listening? If the knob is too sensitive to movement then adding attenuation should help. Do you hear hiss? If yes then attenuation may help lower the noise floor and reduce the audible hiss. If you don't need attenuation you can run a 10 ohm 5 watt 1% resistor across the + and - terminals (one resistor for each channel) to give the amp close to 8 ohms of load with headphones from 30 to 600 ohms.


Matching the resistors isn't needed because small differences between them will have miniscule effects. You could design a stepped attenuation circuit but it really isn't needed. An L-pad will match headphones from 30 to 600 ohms with no problems. Play around with my headphone resistor network calculator and you'll see what I mean. If you do need attenuation I recommend you start with an L-pad that gives you around 18dB of attenuation.


I'm not familiar with the amps you mention so I can't help you there.

post #36 of 39

No problem on the amp suggestions.  Some of my amps have "volume" knobs but I will be using either a Parasound Zpre(SS) or a Conrad Johnson PV-1 (tube) for a preamp.  Most likely will use the CJ-MV50 in the end, but want to try some of the other "monsterMay use both as the PV-1 has a phono section, right now the Zpre is setup as a "zone" from my HT preamp (Parasound AVC-2500).  I more or less know what I need to do to protect the amps.  Stay balanced, tube amps need that extra dummy load regardless IMO(not willing to take that chance); I have seen a "runaway" tube in an amp where the speaker wire came off, pretty light show....but releases the "magic" smoke stored inside of amps.  Many dollars to put that "smoke" back in the amp too.  I think the MV-50 has a 16ohm speaker tap, I know my old Dynaco St-70s did, would it be best match the tap with a 16 ohm parallel resistor?  I used to run the 4 ohm taps because my Infinity Q5 would drop impedance dangerously low at certain frequencies(mainly due to the odd Watkins dual VC 12" woofer: different Nominal Impedances on each coil, along with different crossover points[bandpass; I think], made for an "interesting" curve.  I used the 16 ohm taps when I switched to some very efficient Altec VOTT A7 "pseudo-clones"(511 horns and 15" Altec woofers in vented boxes).  I tried the 4 ohm tap first, but the 16 sounded better....I know much less about headphones than speakers, but know the "basics" are the same.  Just with some radically different impedances. 



Admittedly rusty on my Lpad design(beyond a simple parallel and series setup), could you suggest R values for your 18db of attenuation?  You have already helped me enough that I could happily go look it up myself, but I am always looking for someone that knows more than me, and that is quite obvious here.  What do you think would be optimal for the tube amp?  I still am interested in that 16 ohm dummy load and your thoughts.  I will read your calc page, probably more than a few times. 


Thanks again...Need to make that Calculator a sticky...though I hear that is quite difficult.  I doubt I would of asked a single question if I had found that earlier.  But again....always looking for new/fresh info/opinions/options..... You da man robrob!!!  Anything I can do for you?  Within reason of course....lol....I do know a few things about *gasp* speakers....among otherthings...always happy to return a favor!

post #37 of 39

R2 of 14 ohms 5 watts 1%


R3 of 2 ohms 5 watts 1%


With headphones from 30 to 600 ohms of impedance will show your amp a speaker load of 16 ohms with 18dB of attenuation at the headphones.



If you don't need attenuation then an 18 ohm 10 watt 1% resistor across the + and - terminals will give your amp approximately 16 ohms of speaker load.

Edited by robrob - 10/8/14 at 6:25pm
post #38 of 39

Very Nice! Thank You very much!  But.... D'OH!!  I gotta admit I was a bit impatient and went ahead and ordered some resistors earlier today.  16ohm 10w x (6) and 523ohm 1/2watt  x (10).  I was thinking(could be a problem, I know:)) if I needed to get to 8ohms for the parallel resistor, I could just parallel two of the 16ohm to bring it to 8ohm and use that.  Not sure if the dual resistors would have any ill effects or if I just "flunked" impedance calc 101....lol, but I got a few extra just in case they become permanent fixtures on certain amps.  For the series resistor, I was under the impression that it did not have to have that high of a wattage rating, though it does make sense that it should be the same.  I think I picked up that idea from somewhere else?  Not a big deal at ten cents each...:).   


I will be placing a second order with suggested parts, and a few other odds and ends after I get a bit further on some other projects I am working on and also get a chance to play with your resistor calc some.  Could post results for this if anyone is interested.  I have modest test equipment; a "vintage" hand held battery powered RTA with built in microphone.  Still very useful despite its age(it even comes with its own battery powered pink noise generator...lol)...just a little time consuming...lol...good for "tuning" a listening room.  I havent had much success, or tried very hard either, to use it to measure either of my own headphones.  I think I need to "seal" the mic to the ear pad(some sort of adapter), much the way the ear pad seals the can to your head; to create the same airspace and sound pressures that are actually present when using a headphone, "on your head".  All this in mono with just one speaker of course....cross talk and other stereo stuff is a bit more complicated....I do have an oscope and a "few" other pieces of test gear too.....:D  Have to see what I can cobble together.


Results could be interesting, but I'm not sure how useful they would be for others unless they have the same rig as I do....  never know though.... 


Thanks again and again robrob...."If ya ever need a favor..."...just ask.  :ksc75smile:

post #39 of 39

The 16 ohm resistors would work just fine as load resistors (no series resistor). Your amp would see around 14 to 15 ohms of speaker load and that wouldn't be a problem at all.

Edited by robrob - 10/9/14 at 5:12am
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