[Oregonian]

  Both of what you mentioned is correct.
 
The biggest issue with headphones I have is the *sigh* TRS jack(s).  Any headphone should have 4 terminals - each channel  separately, no possibility of short circuiting the output of the amp when plugging or unplugging the headphones in or out.
 
No one would believe the sound something as lowly as Grado SR-60 can produce if driven right.  I have modified the output of the Perreaux SM2 preamp in order to be able to drive headphones - and after a couple of months of use, phone rang and I accidentally pulled out the TRS plug and one channel output went up in smoke - what else ?
 
I will repair it ( 300V output MOSFET by now rare as hell gave up the ghost  ) and re-terminate the thing with 4 pole XLR connector - to avoid that dreaded TRS short circuit.  I might even put a fuse(s) in series - but I try to avoid them whenever not absolutely required. SM2 has +-45 VDC power supply, so approx 30 VRMS output capability, is pure class A, has power supply bank greater than most power amps - and should be the dream amp for the AKG K-1000.
 
Sorry, no receiver will ever even dare to dream about this kind of performance...

Sounds like this is a good "public service message" opportunity.   Seems we should never unplug a headphone from the jack while music is playing, correct?   Good to know (seriously). 

 

[Mechans1]

What are TRS jacks.  I have to assume they are the common terminals on better headphones, but never heard them referred to that way?    Are you using the XLR type jacks used for balanced operation?  Just trying to understand your post. Thanks

 

[analogsurviver]

 
Sounds like this is a good "public service message" opportunity.   Seems we should never unplug a headphone from the jack while music is playing, correct?   Good to know (seriously). 

In effect - yes.
 
The usual action on the part of the amplifier manufacturers is to insert some resistance in series with the output - so that unplugging or plugging the TRS, which WILL and DOES mean short circuit for a moment, can not destroy the output circuitry. This can lead to deleterious effects with some headphones ( see Meier/Tyl link a few posts above ).
Alternatively, some output short circuit protection is required - which again can mean adverse effect on sound, IF it is fast enough in the first place. It also means increased power consumption, which can be problem in portable devices.
 
There is no problem of this nature with receivers with relatively large output resistors - anything above say 30 ohms is quite safe. But so high output resistance( or low damping factor ) can, with some headphones, again lead to decreased performance. And at the same time, so high resistance may be required for some headphones. The point that adding the required resistor in series is relatively easy ( it can be inserted into say extension cord for the use with headphones requiring such high value output impedance ) , whereas lowering too high output impedance of an amp for those headphones requiring as low output impedance of the amp is generally impossible for the average user.
 
4 pin non TRRS type connector ( XLR or mini DIN or whatever small enough to be considered OK for headphones, little IEMs included ) would solve this unnecessary issue. But I am afraid we will be stuck with this TRS(S) nonsense for quite some time - similar as with loudspeaker binding posts, which means audiophile nightmare whatever vs Neutrik Speakon - which is professional and good and foolproof, but extremely unfriendly for those who wish to experiment with cables.
 
So, tradition can be a considerable hindrance to the actual performance of audio gear. 

 

[buson160man]

  Don't wish to derail the thread, but having read a lot of it in the past few weeks I thought I'd post my comparisons of an SA-9100 with a Master 9.
 
Firstly, I'll thank Oregonian who took the time to answer some questions I had on vintage gear and nudged me over the edge into buying the SA-9100.  This was sold to me by someone who has refurbished 6 of these already, and I understand is known on AudioKarma for his work.  So I'm confident that all the recapping and whatnot has been done well.  
 
In its own right I've been very pleased with it as a headphone amp, but in the past couple of weeks I've had a few listening sessions to try and tease out the differences between the 9100 and my Master 9.  This has largely been done with TH900s, although this evening I tried my LCD XCs as well. For information, my general tastes are rock: Royal Blood, Rival Sons, Band of Skulls, Arctic Monkeys, etc etc.  
 
And quite honestly the differences between the two amps aren't very obvious: it takes a lot of back and forth between the two to work out what they are.  With the TH900s the 9100 hits a little harder in the bass and the lower end of the mid range, but not overwhelmingly so.  The Master 9 is a touch crisper, probably because I detect a little more presence in the treble.  The soundstage is possibly very slightly wider on the M9 on some tracks: difficult to be certain.  
 
But what the 9100 does have is a sort of propulsion to the music: it gets my toes tapping, there's a bit more meat on the bones of the music.  I don't know whether this is anything to do with the output impedance of the 9100 which I assume is somewhere in the 100-300 ohm range which I've been told that many of these vintage amps have, versus the 1 ohm or so of the M9.  The TH900s aren't insensitive 'phones.  
 
So, I'm very impressed.  Much as I've enjoyed the M9, and had regarded it as my endgame amp, it may be appearing in the for sale forum at some point.
 
Then finally, the TH900s versus the XCs out of the 9100..................... I prefer the TH900s.  I find the XCs to be warmer phones (certainly compared to the LCD3s which I had until recently), and it's too much for me when added to the slight warmth of the 9100.  The XCs sound almost a bit sluggish, whereas the TH900s retain a crispness and attack which works for the type of music I like.  
 
Anyway, hopefully this'll be of interest to a couple of people.  

 Does your audeze have the stock cable . I have a pair of LCD v2s and with the stock leash they were disappointing sounding. I replaced the stock cable on mine and they sound much better But the replacement was not cheap costing me 600 dollars which  is two thirds the cost of the phone(ouch!!!!!) but I am much happier with my lcd-2s . Changing the stock leash  made a huge difference .  I use a recapped concept 16.5 and it drives the hell out of all my phones .

 

[henree]

Hi,
I was wondering is there is a definitive list on which vintage Receiver Brands use cheaper op-amps for the hedphone jack. And which ones  drop the speaker outputs through a 120 to 300 ohm resistor to limit the current? Is there a way to tell by opening up the unit? Would is be possible to obtain this from schematics? I  have a 1979 marantz 2500 & Nad integrated from 1984. 

 

[Skylab]

You have a Marantz 2500??? THE 2500, the one Marantz monster receiver? Doesn't get better than that.

 

[jnorris]

  Hi,
I was wondering is there is a definitive list on which vintage Receiver Brands use cheaper op-amps for the hedphone jack. And which ones  drop the speaker outputs through a 120 to 300 ohm resistor to limit the current? Is there a way to tell by opening up the unit? Would is be possible to obtain this from schematics? I  have a 1979 marantz 2500 & Nad integrated from 1984. 

I've never seen a definitive list.  However if you're even haltingly familiar with reading schematics, create an account for you at hifiengine.com.  They have schematics there for a large number of vintage and some current components.  I go there every time I see something of interest on Craigslist.
 
Most receivers and integrateds tap off the speakers through a 120-300 ohm resistor to the headphones.  Many preamps that offer headphone jacks drive them either with an NJM4556 IC or directly from the preamp output.  One supposedly "high-end" preamp used a crap LM386 IC amp for a headphone driver. 

 

[analogsurviver]

  Hi,
I was wondering is there is a definitive list on which vintage Receiver Brands use cheaper op-amps for the hedphone jack. And which ones  drop the speaker outputs through a 120 to 300 ohm resistor to limit the current? Is there a way to tell by opening up the unit? Would is be possible to obtain this from schematics? I  have a 1979 marantz 2500 & Nad integrated from 1984. 

http://www.hifiengine.com/manual_library/marantz/2500.shtml

 

[jnorris]

  http://www.hifiengine.com/manual_library/marantz/2500.shtml

You'll need to create an account for yourself if you want to download service manuals which is where the schematics are usually shown.

 

[analogsurviver]

 
You'll need to create an account for yourself if you want to download service manuals which is where the schematics are usually shown.

Correct.

 

[KeithEmo]

If you're trying to tell BEFORE you buy it, and you can't find the schematic from more "formal sources", then often you can find a schematic by simply Googling "company model XXX schematic"; you'd be surprised how many schematics for vintage equipment have been scanned and posted over the years. (In general, older models used the dropping resistor, while newer models didn't - because, in modern terms, a separate low-level headphone amp is considered to do a  better job. While there isn't some specific date where everyone switched over, you'll probably find that most manufacturers did switch over, so most models from each changed from one to the other at a certain date - while, possibly, higher end models switched a little sooner - since a separate headphone amp would normally be considered a more premium design.)
 
You can tell easily enough from the schematic. You should also differentiate between a simple series dropping resistor and a true voltage divider. A dropping resistor is a simple single resistor in series with the headphones. With a single resistor, you will get a higher output impedance, and so more interaction between the output and the headphones. (But the level will be more consistent between lower efficiency high impedance phones and high impedance phones of lower efficiency.) With a true voltage divider, depending on the values chosen, you should have a more consistent frequency response, and less interaction between the headphones and the output... and so a more consistent frequency response.
 
You also need to beware of making foolish generalizations....
 
Some units with simple-resistor outputs sound very good, but units with noisy amplifiers, and some older designs with amps that distort heavily at very low power levels, may sound awful. Also, of the units which have separate headphone amplifiers, some with discrete transistors sound very good, while some are really bad, and likewise for op amps. In other words, unless you know a LOT about circuit design, don't assume that "a cheap op amp" will sound bad, or that "an expensive op amp" will sound good, or that "a discrete transistor amplifier" will sound good. There's a lot more involved than which op amp someone chose to use.....    (there are very few op amps that I would automatically assume would sound bad, and none that I would assume would sound good).
 
Another thing is that the output of units with output resistors will interact heavily with your particular headphones. All of this suggests that, if at all possible, you should try to get a chance to hear how a particular unit will sound with the headphones you're hoping to use it with...
 
 
Quote:

  Hi,
I was wondering is there is a definitive list on which vintage Receiver Brands use cheaper op-amps for the hedphone jack. And which ones  drop the speaker outputs through a 120 to 300 ohm resistor to limit the current? Is there a way to tell by opening up the unit? Would is be possible to obtain this from schematics? I  have a 1979 marantz 2500 & Nad integrated from 1984. 

 

[jnorris]

Which receivers/integrateds that you know of have a built in headphone amp?  I have only seen that in preamps - and for the most part they are of less-than-stellar quality.  I'm thinking that manufacturers would rather provide a minimalist headphone solution on their mainstream product in order to keep prices reasonable, and sell a ridiculously expensive separate headphone amp to us headphone weirdos.

 

[buson160man]

  Which receivers/integrateds that you know of have a built in headphone amp?  I have only seen that in preamps - and for the most part they are of less-than-stellar quality.  I'm thinking that manufacturers would rather provide a minimalist headphone solution on their mainstream product in order to keep prices reasonable, and sell a ridiculously expensive separate headphone amp to us headphone weirdos.

I agree a lot of the headphone outputs on components really suck .While there are some pretty nice sounding dedicated  headphone amps out there. The concept of high end headphone amps is really not that old and it has not been that long since they have seen the light of day. I get the feeling that they will get a lot better as time goes on and as they develop more high end headphone designs. The high end headphone rage that is going on  itself  really did not start that that long ago.  When you think of it the only really long standing high end headphone designs where the stax and the sennheiser Orpheus and the jecklin float when they were made.
  Before I purchased my old vintage monster receiver I had been following this thread for awhile. I decides to take the plunge. I am loving it too. Some of them really do make excellent headphone amps that can more than hold their own against the high end headphone amps of today.

 

[Bob Cancel]

Hi were can i purchase the led bulbs for the same receiver you have Thank You

 

[buson160man]

  Hi were can i purchase the led bulbs for the same receiver you have Thank You

I purchased my concept 16.5 from decibel audio used of course so I can not say. But you may want to contact pacific stereo which is a repair shop in California. Just google pacific stereo. That shop specializes in rebuilding components. They have some pictures of rebuilds they have done on a concept 16.5. I am sure you can buy some replacement  leds from him. I am loving my 16.5 more and more each time I use it. Lately I have been experimenting with tweaks. I have been pleased by the results so far . I upgraded the fuses to isoclean 7.5 amp fuses on the back panel . That was a rewarding tweak things got a lot quieter with more low level info and things tightened up a bit as well  I just purchased a cable pro interconnect to upgrade the jumper plug between the pre out and main in . So far it is already sounding a lot better . There is much more space  to the sound and things in general are improving  nicely . Once they break in with about 40 hours of use per the cable pro person . It should be interesting. I wished I lived in California pacific stereos rebuilds look awesome and they probably sound awesome too . Though they are not cheap a top level rebuild will set you back around 1800 usd .But  transporting something this heavy could be catastrophic the way they deliver things these days.
   I am glad to meet a fellow 16.5 owner . They are great and getting greater right along with my tweaks.