[Michael G.]

Many of us know that the UHC is a switchable, transformer based impedance-matching device with both speaker connections and a headphone jack. It is inserted between a loudspeaker amp and the loudspeakers and allows one to use a normal amp for both headphones and loudspeakers. My questions pertain to the amount of power that would be available from the headphone jack on the UHC. I ask because I would want to try plugging my AKG K-1000's into a UHC's headphone jack, rather than using the UHC's speaker terminals. Doing this should solve any impedance mismatch between the "high" 120 ohm load of the AKG and the typical loudspeaker amp that is designed for much lower impedance loudspeakers. We know the K-1000's need a lot of power. The speaker terminals on the UHC would'nt restrict power delivery, but what about the headphone jack? In the process of "impedance-matching" would the transformers in the UHC also limit current to the headphone jack output? I don't know enough about how a transformer works (especially when used as a coupling device in the signal path) to answer this question for myself. Any help appreciated, thanks.

 

[Michael G.]

Just for the record: I tried emailing ASL with my question. All they told me was that the UHC device was discontinued. I searched around on other forums and found out how a "step up transformer" works, which is basically what the UHC is. Well, duh! So basically, all the UHC "impedance matching" device does is change the ratio of voltage to current in the amp's output. Overall "power" is not diminished. This may or may not be a good thing with the K-1000's - I'll just have to try it out. My little Decware SE84C may not be manly enough to drive the AKG's. I'll post on the results later...

 

[rickcr42]

No way the Decware amp is up to driving the K-1000 properly.You will get sound but you will not be satisfied with the results.You need to think Power Amplifier and not Headphone Amplifier unless that headphone amp is a powerhouse (pentodes).

AKG has a history of making headphones fully meant to be driven from a studio control amplifier with their "M" Series cans (M for Monitor) that because of the high impedance combined with a very low sensitivity need a lot of voltage to get moving.The reason for this is durability.
This type of headphone design can take a real beatin'.Serious abuse far and above what most "consumer" cans are capable of which in a pro setting is more than just a convenience but is a requirement where time IS money and down time still on the clock (studios charge hourly rates).
So you need to be looking in the 10-30 watt range for a proper amp.Low power SET Amps need not apply unless you want to strap a few of them together in parallel

Quote:

Just for the record: I tried emailing ASL with my question. All they told me was that the UHC device was discontinued.

Mini-Rant :

That is a real shame.Even though not applicable here with the AKG (you really have no need for it since the K1000 connects directly to an amp) it was only a matter of time since it was far too cheap and was not flashy enough.No Fanboy clubs.
My personal opinion is there is not a single amplifier for headphones at the same price point that could compete head-to-head with the UHC and win the test but since there are no fancy knobs,no user controls,no exotic metals or woods and no option to "improve" by upgrading/modifying and no page long ad copy hyping things it does not do no way could it sell to the targewted market.that is us who mostly WANT to be lied to or pay too much for "fluff" over actual sonic substance.A seriously good product that just did what it was supposed to in a low key manner.Kinda like having a great headphone output on a vintage receiver but that is no fun right ?
Would it do if it ever got out that most medium to high impedance headphones are a far better match for power amps with a simple resitor matrix or an impedance matching/signal limiting transformer on the output ?
Ever wonder why wimp opamp headphone amps are a new thing to pro gear ? One that is there because it is an expected feature not because it is a better way.

End Rant....

Anyway......better to look to get a good medium power speaker amp in the 10-30 watt range and whip up an adapter box that allows switching between the K-1000 and loudspeakers.Again not flashy but the right way to go if actual the sound quality is your goal.

At least that is my opinion and I'm sticking to it

 

[jpelg]

Quote:

Originally Posted by Michael G. I would want to try plugging my AKG K-1000's into a UHC's headphone jack, rather than using the UHC's speaker terminals. Doing this should solve any impedance mismatch between the "high" 120 ohm load of the AKG and the typical loudspeaker amp that is designed for much lower impedance loudspeakers.

What is the benefit of using the step-up transformer device with the K1000's rather than straight from the speaker taps directly?

 

[Michael G.]

Quote:

Originally Posted by jpelg What is the benefit of using the step-up transformer device with the K1000's rather than straight from the speaker taps directly?

Obviously, I'm not sure yet about what all of what I'm doing. My thought was that the UHC Signature "impedance matching device" would do just that - match a loudspeaker amp's normal output to the high 120 ohm impedance of the K-1000's. Most amps are designed for loudspeakers that operate within the 2 to 16 ohm range, so it would seem to me that impedance matching, for the sake of both the amp and the AKG's, would be a good idea. But, while using the ASL UHC device would effectively MAKE THE LOAD RESISTANCE EQUAL TO THE INTERNAL RESISTANCE OF THE POWER SOURCE, thus making the K-1000's "feel" like an 8 ohm load to the amp, I'm wondering if in the process the drive capabilites of the amp will be diminished too much (?)... (With the UHC device, voltage output should increase while current output will decrease, if I understand things correctly.) So, I'm not sure what the outcome will be right now. I'm going to try driving my K-1000's with the Decware SE84C - both with and without the UHC device - as soon as I receive them. I'll post on Headfi about the results later...

 

[Michael G.]

Quote:

Originally Posted by rickcr42 ... No way the Decware amp is up to driving the K-1000 properly.You will get sound but you will not be satisfied with the results.You need to think Power Amplifier and not Headphone Amplifier unless that headphone amp is a powerhouse (pentodes)... Anyway......better to look to get a good medium power speaker amp in the 10-30 watt range and whip up an adapter box that allows switching between the K-1000 and loudspeakers.Again not flashy but the right way to go if actual the sound quality is your goal... At least that is my opinion and I'm sticking to it

You might be right. But what I've been hearing lately is that: The K-1000 does not need more than a couple of watts of power. What the K-1000 really needs is a only COUPLE OF WATTS + A LOT OF VOLTAGE! There is no guarantee that a "high powered" loudspeaker amp will drive the K-1000's well if it is not also capable of meeting the demands for very large voltage swings into a high impedance load... What do you think?

 

[cosmopragma]

Rick, the last edition of the UHC looks far better than the shabby prototype you've once reviewed, and it even provides the headphones /speakers switch you've asked for.Nevertheless it was obviously too cheap/low profile for the market.

Back to the original question:
I've never plugged the K1000s into the UHC since I have no XLR to 1/4 " adapter.Derived from my experience with lower sensitive cans (AKG K340, AKG K240 M and DF) this might work, the UHC generally doesn't attenuate the volume that much and was probably originally meant as an "impedancer" for low power tube speaker amps.
However, wouldn't make much sense in my case since I'm utilizing a balanced source and a fully balanced speaker amp, and it seems quite natural to me to drive the cans in balanced mode in this configuration.

 

[rickcr42]

Quote:

There is no guarantee that a "high powered" loudspeaker amp will drive the K-1000's well if it is not also capable of meeting the demands for very large voltage swings into a high impedance load... What do you think

I think you will find the Decware severely underpowered for this particular application,especially in the mid to low bass which will make your cans sound overly bright being mid-high dominant.The real test is to try it and since you already have the amp in hand nothing to lose .Audio gear has a way of breaking hard-and-fast rules more often than not so everything is worth a shot if only to satisfy curiosity.
Pete Millett has an ECC99 SRPP amp on his DIY pages designed specifically for the K-1000 that has a 300mw output but is capable of 12 volts !
DIY Hi-Fi Supply has an EL-34 headphone amp that is about 2 watts and is reported to work well also so anything is possible.

Be aware if you make a "adapter box" to switch between headphone output and speaker output on a transformer output tube amp you want to use a shorting high current rotary switch and provide a load to the amp output at all times.Many transformer coupled output tube amps don't like a no load condition and will let you know this by self destructing

A couple of 10 ohm 10 watt power resistors across the switch contacts on the headphone side should do OK just in case they become unplugged.Too late once the damage is done

 

[nblis]

Hey Rickcr42



Mini-Rant :

That is a real shame.Even though not applicable here with the AKG (you really have no need for it since the K1000 connects directly to an amp) it was only a matter of time since it was far too cheap and was not flashy enough.No Fanboy clubs.
My personal opinion is there is not a single amplifier for headphones at the same price point that could compete head-to-head with the UHC and win the test but since there are no fancy knobs,no user controls,no exotic metals or woods and no option to "improve" by upgrading/modifying and no page long ad copy hyping things it does not do no way could it sell to the targewted market.that is us who mostly WANT to be lied to or pay too much for "fluff" over actual sonic substance.A seriously good product that just did what it was supposed to in a low key manner.Kinda like having a great headphone output on a vintage receiver but that is no fun right ?
Would it do if it ever got out that most medium to high impedance headphones are a far better match for power amps with a simple resitor matrix or an impedance matching/signal limiting transformer on the output ?
Ever wonder why wimp opamp headphone amps are a new thing to pro gear ? One that is there because it is an expected feature not because it is a better way.

End Rant....

Dude I like your attitude. We need more guys like you around here.
Noel

 

[Michael G.]

Be aware if you make a "adapter box" to switch between headphone output and speaker output on a transformer output tube amp you want to use a shorting high current rotary switch and provide a load to the amp output at all times.Many transformer coupled output tube amps don't like a no load condition and will let you know this by self destructing

A couple of 10 ohm 10 watt power resistors across the switch contacts on the headphone side should do OK just in case they become unplugged.Too late once the damage is done

[/QUOTE]
When you mention an "adaptor box", I'll assume that you are talking about something I would make myself, and not the UHC device. Correct? As you must know, the ASL UHC device has a switch that is supposed to let you choose between it's headphone or speaker outputs. My K-1000 cable is equipped with an inline XLR to 1/4" plug that will let me choose between the UHC's headphone jack or speaker terminals. Are you saying that, for example, if I have the UHC's switch set to "headphone" I should still keep the UHC's speaker terminals connected to speakers while I'm using the UHC headphone jack? Or vica-versa? If so, what is the purpose of the UHC's switch?

 

[rickcr42]

Quote:

Rick, the last edition of the UHC looks far better than the shabby prototype you've once reviewed, and it even provides the headphones /speakers switch you've asked for.Nevertheless it was obviously too cheap/low profile for the market.

I actually have the original prototype and made some "mods" to bring it up to speed and address what i considered weak areas.

1-Total mass/hard feet : Way too light so I popped off the hard rubber feet and bolted a 1 inch thick hardwood board to the bottom of the chassis in the holes formerly occupied by the feet screws.To this "pedestal" I attached stick on soft rubber feet.The unit now has some actual "heft" and no longer slides.
2-Replaced the toggle switch with a Mil-spec toggle
3-Replaced the nasty spring clips (only found on my version) with feed-through barrier strips.
total cost about $25.Total satisfaction level priceless.will beat the pants off the average so called headphone amp at the same price point IF the power amp it is attached to also is a quality unit.As i said in the review you pretty much get out what you put in.

Garbage In=Garbage Out


Quote:

When you mention an "adaptor box", I'll assume that you are talking about something I would make myself, and not the UHC device. Correct?

Yes.

Quote:

My K-1000 cable is equipped with an inline XLR to 1/4" plug that will let me choose between the UHC's headphone jack or speaker terminals. Are you saying that, for example, if I have the UHC's switch set to "headphone" I should still keep the UHC's speaker terminals connected to speakers while I'm using the UHC headphone jack? Or vica-versa? If so, what is the purpose of the UHC's switch?

I like the idea of the XLR plug/jack combo because it is impossible to have a dead short condition on the amplifier output when plugging in or unplugging headphones unlike a TRS phone jack which not only can but mostly does have a momentary short of ground to hot.
This is no big deal with tube gear unless it is an OTL design but can be a very real problem with solid state equipment which is not nearly as bullet proof without the addition of protection circuitry that invariably impacts on the sound of the amp in a negative way.Shot out some output stages and you have a blown amplifier unless it has multiple parallel output devices (generally).
I feel even when the amp is protected it does no good to have a loud [size=x-small]POP[/size] in your headphones due to the short circuit (and is the reason i build all my amps with turn on delay muting relays AND a manual muting switch).These pops are actually a zero power to momentary FULL POWER condition that no way are good for something as delicate as a high end consumer level headphone (back to the 600 ohm load of the original studio cans).

Quote:

My K-1000 cable is equipped with an inline XLR to 1/4" plug that will let me choose between the UHC's headphone jack or speaker terminals. Are you saying that, for example, if I have the UHC's switch set to "headphone" I should still keep the UHC's speaker terminals connected to speakers while I'm using the UHC headphone jack? Or vica-versa? If so, what is the purpose of the UHC's switch?

Since your headphones were pretty much designed to connect directly to an amplifier not only is there no need for a device such as the UHC in your case but adding it in can only detract from the signal purity.
ANYTHING added between two devices (in this case the amp and the headphoners) has sonic consequences so it is desireable to eliminate not add to the signal path whenever possible.
Yes the ASL device is fully passive as is any resistor networks but must have some audible consequnces which in this case are easily avoided.

The switch ?

Mine formerly just turned off the loudspeakers while leaving the headphones connected all the time.Something I did not like considering the possible damage that could happen to the cans AND the load always being in parallel with the speaker load.Not wanting to unplug the cans with an active amp (see earlier on shorts) meant either turning off the amp of leaving the headphones connected which could actually be heard as the volume was turned up for the speakers !
Nothing worse than having a "scratchy" upper end,trying to correct it,being baffled then realising it was just the headphones being overdriven enough to be audible !
This condition was fixed in mine by me and in any production models by ASL (as were my other concern areas

).as far as I know i have the only "original" version though my mods mean even mine is not as the prototype.

If I was in your position and wanting to check the AKG K-1000 with various amps I would whip up an adapter box :

Box Description :

I would mount the speaker binding posts on a piece of 3/4 birch plywood on an angle brackets.Either all across the back or amp in on the left side and speaker out on the right side.
On the front of this board another angle bracket would have the XLR and/or TRS jacks plus a heavy duty shorting (make before break) rotary switch.To keep down the cost I would check a surplus dealer of military surplus for the switch.Since I would at this time have a blank canvas I would most likely add a couple of speaker positions so the end device would be a combination speaker selector and speaker/headphone selector though this not essential.
I personally would toss in a couple of "load resistors" just in case the headphones ever came loose from the jack (like from tripping on the cord

).These would do not harm being in parallel with the headphone load and at 10 ohms/10 watts the combination of the 150 ohms & 10 ohms miniscule.

With this type of interface you could listen to any speaker amplifier and still have speaker capability at the flip of a switch.


Quote:

Dude I like your attitude.

 

[mikeg]

My K1000 is connected to the 16 ohm speaker connectors of my ASL AQ-1005DT amp, while my ASL UHC-Signature unit is connected to the 8 ohm speaker connectors of this amp. When powering headphones such as an HD600, HD650, RS-1, and SR225, I got better performance by connecting them to the UHC-Signature unit, that when I powered them with a Grado RA-1 amp. Although this info isn't a direct response to your question, it may still be of interest.

 

[Michael G.]

Quote:

Originally Posted by rickcr42 Since your headphones were pretty much designed to connect directly to an amplifier not only is there no need for a device such as the UHC in your case but adding it in can only detract from the signal purity. ANYTHING added between two devices (in this case the amp and the headphoners) has sonic consequences so it is desireable to eliminate not add to the signal path whenever possible. Yes the ASL device is fully passive as is any resistor networks but must have some audible consequnces which in this case are easily avoided.

Yes, the K-1000's were obviously designed to be connected the speaker outputs of an amp - the RIGHT kind of amp. But, since some amps (like the Decware SE84C) might not like pushing the high impedance (120 ohm) load of the K-1000, the idea occured to me to try something like the ASL UHC device to help smooth the interface between this amp and K-1000 headphones. The "sonic consequences" of inserting the UHC device in the signal path? The sonic consequences would seem to be minimal, by most accounts. By the way, someone in another thread mentioned that 1 watt into 120 ohms is the "max thermal power" rating for the K-1000's. I'm wondering how many watts the Decware SE84C will actually deliver into the K-1000's after it's power output (2 watts into 8 ohms) has been "impedance matched" by the UHC device... In other words, is there any way to calculate how much of the Decware's 2 watts will be available to the K-1000's via the UHC's headphone jack? Your help so far is really appreciated!

 

[rickcr42]

Quote:

The sonic consequences would seem to be minimal, by most accounts. By the way, someone in another thread mentioned that 1 watt into 120 ohms is the "max thermal power" rating for the K-1000's.

A higher load rating just means reduced power.Lower than an amp is rated for is where you run into problems when the amp uns out of steam so an amp rated at 2 watts into 8 ohms may instead of providing 4 watts into 4 ohms clip like mad at 500 milliwatts.All about the output stage and power supply with solid state gear,toss in output transformer performance in single ended tube gear.not all can drive 4 ohms and even some that can work better out of the 8 ohm tap into the four ohm impedance (just like many amps sound best out of the 16 ohm tap).

Reducing signal path clutter is ALWAYS preferable to adding something not needed to do the same thing.


Quote:

In other words, is there any way to calculate how much of the Decware's 2 watts will be available to the K-1000's via the UHC's headphone jack? Your help so far is really appreciated!

Divide the 120 by 8 then the 1 Watt by the resulting number.the final power rating will be that number in milliwatts

 

[Michael G.]

Quote:

Originally Posted by rickcr42 Divide the 120 by 8 then the 1 Watt by the resulting number.the final power rating will be that number in milliwatts

I been "thinking" about this: By your formula (if my calculations are correct), that means I'll only be getting about 130 mW from the headphone jack, while voltage output should increase as current is decreased in the impedance-matching process (because that's how transformers "transform", according to my understanding). But it all may not be that simple for us to figure out. I also think the exact final outcome might have to do with the ratio of primary to secondary windings in the UHC's transformers. Sheeeeeeiiiiiiiiit!!! I guess I'll just have to try the setup and see how it all works out (imagine that)! Anyways, thanks for the math tutorial. The thought of mathematics makes me allergic...