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Post by minivan on Feb 24, 2008 3:08:02 GMT
saw a thread somewhere about some1 raving about how good their hd600 sound driven by his speaker amp in balanced mode in compare to being driven by headamp in single end. this had me intrigued, since i already have a speaker amp and a k340 headphone i dont really like, this would be a cheap way to experience what's balanced mode like. for the connection, i assume it would be R+ and R- from the speaker terminal going to the + terminal and ground terminal on the right hand side of the headphone respectively, same goes for the left side. my question is: if my speaker amp is rate 68w at 8 ohm, and my headphone is 400 ohm. how can i ensure the safety of operation without blow up the amp or damage the headphone? do i put a resistor across the R+ and R- of the speaker output, and using this ormula : with R total as 8 ohm, R1 = impedance of headphone= 400 ohm. this give me R2 = 8.16?
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rickcr42
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Post by rickcr42 on Feb 25, 2008 3:26:03 GMT
In a Balanced Bridge hookup the amp has no "common ground" but rather two independant "hots" per channel with one providing the "+" signal and the other the "-".This means you now have four distinct "HOT" lines while headphones have only the two : 1-Left Hot 2-Right Hot 3-LR Common (normally amp ground) The proper way is to modify the headphones to have FOUR lines then make an interface box having the gain reduction resistors (depending on amp power a 1K resistor for Grados,120 Ohms for senn and the like in EACH feed ),the binding post amp in/binding post speaker out/Left TRS jack headphone out/rightTRS jack headphone out and a BALANCED (four poles ) speaker/headphone selector switch of enough current to pass the amps power to the speakers. the wiring for the headphones looks like this : remeber to NEVER let the left and right "-" amp outputs touch either each other OR any common ground (speaker switchers and the like) or you will blow the amp good luck rickmonster
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Post by minivan on Mar 10, 2008 0:52:42 GMT
i finally recabled my k340 , terminated onto a 4 pin male xlr, also made a 4pin female xlr to trs adaptor , as well as a 4 pin female xlr to speaker spade connectors. this allow me to use the headphone on a headamp as well as a speaker amp. to be one the safe side , i will put a 10 ohm 5 watt rating resistor across the output of the speaker amp. here's some pics. i have not try it yet, worry i might blow up stuff. rickmonster:is everything safe to go?
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rickcr42
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Post by rickcr42 on Mar 10, 2008 3:34:36 GMT
you need another resistor in the "-" leg of the feed (active drive rather than a ground remember ) plus a means to switch between speakers and headphones would be a plus.Something like this : www.avahifi.com/root/audio_basics/ab_pdf/ab1993-07.pdfBut with NO COMMON GROUND CONNECTIONS !any common ground would be a short to one side of the amp and would blow the output stage so the above is just a basic guide. To make one usable for a balanced amp you need to snip ALL common ground connections then double up on the resistors and toggle switches (two per channel ).The resistors shown are for Grado cans so either use 120 ohms (the standard) or your current 180 ohms X4 Also,to be on the safe side start with the volume control at full mute and bring it up gradually until you know the power curve with your headphones AND at full mute when switching between headphones and speakers.At that power level a simple "pop" can mean a full peak power pulse hitting your headphones and that can't be a good thing Good luck rickmonster
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Deleted
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Post by Deleted on Mar 10, 2008 4:14:25 GMT
Rick Do the benefits REALLY outweigh the disadvantages ? (A serious question !) Alex
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rickcr42
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Post by rickcr42 on Mar 10, 2008 5:39:16 GMT
Rick Do the benefits REALLY outweigh the disadvantages ? (A serious question !) Alex No easy answer on that man.In a strictly headphones only amp my personal opinion says no,there is no real advantage,at least not one that outways the disadvantages with the foremost being added complexity followed by increased cost (that last no hurdle to an audiophile who seems to delight in spending large then bragging about it),but others do not agree with that position and claim all manner of improvements. what "improvements" ? Better drive for one,something just as easily provided by a more powerful traditional amp.Another is increased clarity though I have yet to hear that in any of my experiments in the area so the "double amps" to me is no more than double the price,double the desk space,double the amnount of things that can go wrong with at best maybe an apparent increase in dynamics,again just as easily acheived with a more powerful amp. again this is just one persons opinion and there must be something going on I miss because balanced amps seem to be "the next big thing" and all the rage with just about every manufacturer jumping on the bandwagon (or could just be an excuse to sell more amps at a much higher price ) In this particular case (originally posted question) it seems this person is looking to use an amp already in house,an amp he/she is very pleased with in the sonic sense,to drive headphones so a simple matter to create the proper "interface" for the cans which is way different than actually going out and purchasing a balanced amp. For speaker amps I often have used balanced bridge class-A amps and yes,there was a definate benefit in woofer drive which in a class-A speaker amp is many times the achilles heel unless the system is a relatively simple one with no crossovers or if there are,simple rather than complex ones which can be a real bitch to drive
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Post by minivan on Mar 10, 2008 7:05:11 GMT
this is my experiencement to find out what's all the craze of balanced amp about, as rick pointed out, i already have a speaker amp, so i figure this will be a cheap way to drive the headphone in balance mode without buying a balanced headamp. that audio switch box is very nice, but way complicated for my capability to do it. for my setup ,the pic below how how my xlr connection is like. i believe there should be no common ground in this connection?
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Deleted
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Post by Deleted on Mar 10, 2008 7:21:03 GMT
Rick That was my gut feeling, as I would imagine that balanced mode,in general, is usually the province of sound studios/ distribution where relatively long cabling is involved ? Thanks for the reply. Alex
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rickcr42
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Post by rickcr42 on Mar 10, 2008 15:42:26 GMT
actually it is a rare piece of studio gear that has actual balanced stages so are more balanced at the input and output but single ended in the middle.The reason is cancellation of common mode signals with any noise picked up in the long lines being "common" while the signal is bipolar. BAL-to-SE transformer at the input/actual electronic circuit/SE-to-BAL output trafos read this for a more detailed explaination www.jensen-transformers.com/an/Audio%20Transformers%20Chapter.pdf
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rickcr42
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Post by rickcr42 on Mar 10, 2008 15:50:55 GMT
Makes perfect sense to me.Relatively painless way to see (hear sic) for yourself rather than listen to the opinion of self appointed experts (won't say i am in that category ) As a sidebar I should say the VERY FIRST headphone amp i ever in my life built was a balanced bridge design using the LM380 from an article in Popular electronics.The year ? Sometime in the mid seventies.It worked but high defination audio is not exactly the word i would use looks complicated the way it is layed out in the article but the reality is the "box" is no more than one DPDT switch to select between speaker A and speaker B and the second to select between speakers or headphones with series resistors on the headphone output.All in one bite-complicated.Break it down into the basic blocks and it becomes a tad more clear. correct
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cosmopragma
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Post by cosmopragma on Mar 11, 2008 15:09:37 GMT
To make one usable for a balanced amp you need to snip ALL common ground connections then double up on the resistors and toggle switches (two per channel ).The resistors shown are for Grado cans so either use 120 ohms (the standard) or your current 180 ohms X4 At least for a proof of concept there's no need for resistors inline at all. The K340 are high impedance (~400 Ohm) and really low sensitivity cans (about 13 dB less than a Senn HD 600 or so). Naturally you'd still have to be careful with the volume pot, but I do get usable adjustability with a 2x60W RMS balanced speaker amp.
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rickcr42
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Post by rickcr42 on Mar 11, 2008 16:54:19 GMT
I think there is a real benefit to adding some inline attenuation because it gets your volume control adjustment range away from the bottom of the rotation where interchannel tracking is at its worst and more into the range where you would adjust for your speakers so in theory at least going from the one to the other should not be a drastic change in operation. there is also the "IHF Standard Load" thing where the 120 ohms is already accounted for in the actual design of the headphones and as such means where you should get the flattest frequency response with headphones which may or may not be a plus depending on how they were voiced at the factory. bottom line,yes you can go resistorless and yes you would probably not suffer any dire consequences (unless the volume ramps up so fast you go from nothing to overload) but for the piddling $5 or so max cost it is probably a good idea to add them all things considered
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Post by Deleted on Mar 11, 2008 20:09:32 GMT
Please consider resistors as stated, even if a little lower in value. It will give peace of mind, and the other benefits Rick described.
SandyK
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