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Comparison of components for driving an AKG K1000 headphone - Page 6

post #76 of 109
msjjr:

by "biasing" do you mean adjusting to a 120ohm speaker impedance? or did you do further adaptations? if so... please let me know... they're custom making this amp for me, so i might be able to talk them into making some changes.

would you know what the "output impedance" or "Zo" of your amp is? cause i am concerned that mine is too high after reading Millet's article. and i am sure he knows what he's talking about, since his Wheatfield amps are highly regarded.

also... which 300b amp do you have?--i'd like to check it out on the web. did you do the mods yourself, or did the engineers do it custom?

thanks.
post #77 of 109
Mine is the Antique Sound Labs AQ1005 300B DTI. I'll have to check the exact impedance. My AKG's don't connect to the speaker binding posts but through a separate circuit into a balanced output. I have heard them through the same amp at 120 ohms and they don't sound as nice at all. Much improved soundstage and imaging with the correct impedance.
post #78 of 109
is this guy bogus, or is there a kernel of truth in what he says?
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1941714574
post #79 of 109
can anyone that knows what Zo is all about evaluate this response i got from my amp's engineer?:

"Dean,

I don't know whom you have talked with. But he gave you totally wrong idea. Let me explain.

The tube amp and solid-state amp both have two Zo 8 ohms and 4 ohms. And why the tube need output transformer and the solid-state does not need it, because for tube amp without transformer, it Zo is 2400 ohms, so it needs a transformer to make it 8 and 4 ohms, but the solid-state can directly output Zo 4 and 8 ohm. In this point, without output transformer, tube amp Zo
(2400) is much higher than solid-state (4,8). So you are partially right.

But the normal 8 ohms Zo is best for 8 Ohms laud speakers; it can not match the 120 ohms headphones. We need change the output transformer to output Zo 120 ohms to match the 120 ohms headphones. And your headphones need 10W not @8ohms but @120ohms; you know what I mean? 1W@120ohms is far not enough. And even if the 10W@120ohms is more than necessary, just turn down your volume control (when you turn the volume knob to the uppest, it give you the most output, when it turn to somewhere, it can only give you like 0.1 W). I have never heard people complain their amp has too much power before. They just
complain not enough.

The amp 300B SET will have two connections: one for your headphones Zo 120Ohms and one for laud speakers Zo 8 Ohms, "Z" means impedance, 'o' means output; another index is "Zin" - input impedance -. So don't worry any more. The two connections output both 10Watts, best for your headphones, because you headphones need it to be powered, giving out awesome effect. And you still can use it connecting to you speakers, to enjoy music.

Trust us, we are the experts. You will have the best amp you can find for your headphones, and I will have a new type product. :-)"

so, is he correct? about what Zo is?

...and as i understand it, we want an amp with a low Zo... so if he wants to make a Zo of 120ohms, then that's not suitable for the k1000's though it would be good for normal headphones?

...can someone explain before i blow a lot of money? thanks, i appreciate it.
post #80 of 109
msjjr, what do you think of the differences between your modded K1000, hd600 w/equinox, and R10? Which do you prefer and why?
post #81 of 109
I've had a lot of work to do today. So I'm really tired.

Transcendent Sound has a good article on output impedance (Zo). The Z stands for impedance, and the o for output. With this article, you will be able to calculate amplifier output impedance for all 3 types of amps: SET, push-pull and OTL. I suggest that you make some calculations like the ones offered in the article. It sure helps. I also recommend that you read the article slowly a few times.

http://www.transcendentsound.com/amp..._impedance.htm

Orpheus: You should go slow. Do research before you buy!
post #82 of 109
Quote:
Originally posted by Orpheus
can anyone that knows what Zo is all about evaluate this response i got from my amp's engineer?:

"Dean,

I don't know whom you have talked with. But he gave you totally wrong idea. Let me explain.

The tube amp and solid-state amp both have two Zo 8 ohms and 4 ohms. And why the tube need output transformer and the solid-state does not need it, because for tube amp without transformer, it Zo is 2400 ohms, so it needs a transformer to make it 8 and 4 ohms, but the solid-state can directly output Zo 4 and 8 ohm. In this point, without output transformer, tube amp Zo
(2400) is much higher than solid-state (4,8). So you are partially right.

But the normal 8 ohms Zo is best for 8 Ohms laud speakers; it can not match the 120 ohms headphones. We need change the output transformer to output Zo 120 ohms to match the 120 ohms headphones. And your headphones need 10W not @8ohms but @120ohms; you know what I mean? 1W@120ohms is far not enough. And even if the 10W@120ohms is more than necessary, just turn down your volume control (when you turn the volume knob to the uppest, it give you the most output, when it turn to somewhere, it can only give you like 0.1 W). I have never heard people complain their amp has too much power before. They just
complain not enough.

The amp 300B SET will have two connections: one for your headphones Zo 120Ohms and one for laud speakers Zo 8 Ohms, "Z" means impedance, 'o' means output; another index is "Zin" - input impedance -. So don't worry any more. The two connections output both 10Watts, best for your headphones, because you headphones need it to be powered, giving out awesome effect. And you still can use it connecting to you speakers, to enjoy music.

Trust us, we are the experts. You will have the best amp you can find for your headphones, and I will have a new type product. :-)"

so, is he correct? about what Zo is?

...and as i understand it, we want an amp with a low Zo... so if he wants to make a Zo of 120ohms, then that's not suitable for the k1000's though it would be good for normal headphones?

...can someone explain before i blow a lot of money? thanks, i appreciate it.
Your theory seem to be correct but it actually not true on AKG1000 as I know ! AKG1000 actually need much power to feed it. It want very low impedance to source to get good sound.
If you feed it by 120 Ohm amps may be sound thin ! I think it may be only need less than 1W to drive it if impedance low enought. I will have a pair of AKG1000 next week. Will try to design some amplifiers or impedance matcher to drive it.
I never had a AKG1000 . It just read some message on head-fi. I'm not sure it is correct or not ! I had same mind as your before but I think I'm wrong now !
post #83 of 109
Quote:
Originally posted by Orpheus
can anyone that knows what Zo is all about evaluate this response i got from my amp's engineer?:

"Dean,

I don't know whom you have talked with. But he gave you totally wrong idea. Let me explain.

The tube amp and solid-state amp both have two Zo 8 ohms and 4 ohms. And why the tube need output transformer and the solid-state does not need it, because for tube amp without transformer, it Zo is 2400 ohms, so it needs a transformer to make it 8 and 4 ohms, but the solid-state can directly output Zo 4 and 8 ohm. In this point, without output transformer, tube amp Zo
(2400) is much higher than solid-state (4,8). So you are partially right.

But the normal 8 ohms Zo is best for 8 Ohms laud speakers; it can not match the 120 ohms headphones. We need change the output transformer to output Zo 120 ohms to match the 120 ohms headphones. And your headphones need 10W not @8ohms but @120ohms; you know what I mean? 1W@120ohms is far not enough. And even if the 10W@120ohms is more than necessary, just turn down your volume control (when you turn the volume knob to the uppest, it give you the most output, when it turn to somewhere, it can only give you like 0.1 W). I have never heard people complain their amp has too much power before. They just
complain not enough.

The amp 300B SET will have two connections: one for your headphones Zo 120Ohms and one for laud speakers Zo 8 Ohms, "Z" means impedance, 'o' means output; another index is "Zin" - input impedance -. So don't worry any more. The two connections output both 10Watts, best for your headphones, because you headphones need it to be powered, giving out awesome effect. And you still can use it connecting to you speakers, to enjoy music.

Trust us, we are the experts. You will have the best amp you can find for your headphones, and I will have a new type product. :-)"

so, is he correct? about what Zo is?

...and as i understand it, we want an amp with a low Zo... so if he wants to make a Zo of 120ohms, then that's not suitable for the k1000's though it would be good for normal headphones?

...can someone explain before i blow a lot of money? thanks, i appreciate it.
He's correct in his glossary definition of output impedance, but incorrect in so far of his understanding of what is needed to make the K1000s sing their best.

The K1000s are only rated for 1 watt max at 120 ohms by AKG. Look in your manual. To get the best from the K1000s it has been determined that you need to drive them with a high damping factor/low impedance output. This seems to result in better sound than driving them with a 120 ohm source impedance.

So, bottom line, what you want is an amp with an 8 ohm transformer tap output capable of delivering 15 watts into an 8 ohm load. In so doing, you will be able to deliver the requisite 11v max voltage swing to the 120 ohm K1000s and still have them see a relatively high damping factor.

Send this to your engineer friend.

Hope this helps.
post #84 of 109
kwkarth:

What Peter Millett did in his K1000 amp was to pick an SRPP circuit (push-pull) instead of a SET circuit. He also picked a 120 Ohm output (not 8 Ohm) to do his circuit right. I put this info in my previous post. Here's that part AGAIN...

Usually, tube amps have an output impedance of between 30 and 50. This is too high for the K1000s. So Mr Millett made his amp using an SRPP circuit. This type of circuit gives him: Improved linearity, high voltage swing and a very low output impedance of 7 Ohms. Results? He gets a full sounding amp with the necessary bass.

SRPP means Series Regulated Push Pull. Thus, if you are searching for a tube amp for your K1000s, I would go for a push-pull amp over SET amps (single ended triode). The push pull type of circuit insures the very necessary low output impedance. I believe those old Fisher receivers are push-pull. So they work very well with the K1000s.

I am going to try to get Mr Millett to participate in this thread. He should be able to resolve some of the difficulties we are having.
post #85 of 109
Quote:
Originally posted by Gariver
kwkarth:

...SRPP means Series Regulated Push Pull. Thus, if you are searching for a tube amp for your K1000s, I would go for a push-pull amp over SET amps (single ended triode). The push pull type of circuit insures the very necessary low output impedance. I believe those old Fisher receivers are push-pull. So they work very well with the K1000s.
...
The Fisher receivers, unless I'm mistaken are transformer coupled, so output impedance is a function of their output transformer windings.
post #86 of 109
Thread Starter 
In accordance with advice from techical reps at Divergent Technologies Corp., and at HeadRoom Corp., I connected the K1000 headphone to the 16 ohm speaker terminals of my ASL AQ-1005DT amp. The sound is wonderful, but really no better than when connecting this headphone to the 8 ohm speaker terminals of the ASL Wave monoblock amps.
post #87 of 109
Quote:
Originally posted by kwkarth
The Fisher receivers, unless I'm mistaken are transformer coupled, so output impedance is a function of their output transformer windings.
You got it. However, according to the service manual, the 7868 driver tubes are utilized in a push-pull configuration, one pair per channel.
post #88 of 109
Hirsch:

Can you tell us more about the different Fischer receivers? Which ones are good matches for the K1000s, and which to avoid? I imagine that Fisher built some amps with out tuners. Is this correct? TIA
post #89 of 109
Quote:
Originally posted by Hirsch
You got it. However, according to the service manual, the 7868 driver tubes are utilized in a push-pull configuration, one pair per channel.
Thanks Hirsch!
True enough, I wasn't disputing the topology. In this case, the circuit topology has no bearing upon output impedance.

Happy Listening!
post #90 of 109

Driving K1000's

Wow, an interesting thread. Something I think I can contribute a bit to.

First of all, I won't comment on cables - it's a subject I avoid like the plague.

But I do know what it takes to drive K1000's. I have tried a number of different amplifiers - both commercial and home-built - and can tell you what works and what doesn't. So here is a very long-winded discussion...

By far, the most important factor in making K1000's sound good is to drive them with a low impedance source. By this, I mean that the source impedance should be less than, say, 8 ohms. All amps designed to drive speakers meet this criteria, but few headphone amps do.

If you don't, the results are dramatic - at the extreme, the bass goes away completely. I think the K1000's are a little light in the bass anyway, so to me any loss is unacceptable.

If you don't believe this, try a simple experiment: hook up the K1000's to the 8 ohm speaker connections of any amp and listen, then insert a 100-120 ohm resistor in series. You'll have to turn up the volume to get the same level, but the loss of bass is dramatic.

I can hear the difference between a source impedance of 50 and 7 ohms easily, and I think I can hear a difference between 7 and 3. You may hear a difference between 3 and 1. The bottom line is that low is good.

There are many cases in electronics where you want the source impedance to match the load impedance - high-speed signals and RF, for example - but this is often not true in audio.

Part of the confusion here is understanding that source impedance is NOT the same as the rated load impedance. Almost all amplifiers designed to drive speaklers have rated load impedances of 8 ohms (and sometimes 4 or 16 ohms), but that is NOT their output impedance. Their output impedance varies between damn near 0 for many SS amps to 8 ohms or so for some tube amp circuits.

This also relates to the term "damping factor", which is a ratio of the load impedance to the source impedance. A high damping factor, at a given load impedance, means a lower source impedance.

With tube amps, the "impedance" of the secondary of the output transformer is rated at 8 ohms, but again, this is not the source impedance. For a 2A3 tube, for example, you usually use a 2.5k : 8 ohm transformer. But the tube's plate resistance - the source impedance driving the transformer - is about 800 ohms. This is reflected through the transformer to give a source impedance to the speaker of about 2.6 ohms.

Now, if you try and drive K1000's from the typical headphone amplifier, you get really poor results. Why? Mostly because the output impedance of headphone amps are usually 30-100 ohms, but also because the K1000's also need a lot of voltage, and power. They're about 1/10 as effecient as most headphones.

So, let's look at the numbers... If you assume you want to drive 1 watt into the AKG K1000's, you need about 11V RMS delivered into 120 ohms. To get 100dB SPL, you need about 400mW, which is about 7V RMS.

An amplifier designed to drive 15 watts into an 8 ohm load can deliver 11V RMS. If the amp has a very low output impedance, it will deliver vuirtually the same voltage into 120 ohms; a very low damping factor tube amp will deliver more voltage, around 22V RMS if it had a source impedance of 8 ohms (since it is more lightly loaded).

So, any amp designed to drive 8 ohm speakers at 15 watts or more can drive K1000's to 1 watt. To get 100dB SPL, you would need an amp that can do 6 watts into 8 ohms (for 400mW into K1000's).

A typical 2.5W 2A3 SET amp, with an output impedance of a couple of ohms, can deliver around 6V RMS (on an 8 ohm tap), probably enough but a little wimpy. Changing to a 16 ohm tap ups the voltage at the cost of a higher source impedance... louder, but less bass.

As for the solid state vs. tube, single-ended vs. push-pull, and class-A vs. class-AB debate... in theory, it shouldn't matter at all as far as the K1000's go. Of course, different amps will sound different, but no more so than if they were driving speakers.

But in reality, the issue that may make some amps sound good and others bad relates to the fact that most amps capable of driving K1000's are amps that were desigend to drive 8 ohm speakers. They weren't designed to drive, nor tested with, 120 ohm loads. Some can do it well, others fail miserably.

I'm guessing that this is why AKG recommends class-A amps; in general they are less likely to act up into a high impedance load. Some amps - especially class-AB amps with lots of negative feedback - do really nasty things with a high impedance load. They can oscillate, or they can have really high distortion.

Others will do fine. The Crown amp mentioned in a post above is known to be well-behaved into virtually any load - one of Crown's claims to fame - and that may explain why one of the posters found it worked well. (I have a D60 that's been running my TV sound for about 20 years - maybe I should try it!)

Most class A tube amps, both single-ended and push-pull, do OK with higher loads. Distortion is actually lower, but there are possible problems related to the ouput transformer. Class AB tube amps, which almost always have negative feedback, are more likely to misbehave.

One thing you can do to help these potential problems in any amp is to load the amp with a resistor in parallel with the K1000's. Use something between 10 and 50 ohms - enough to present the amp with something closer to it's designed load without dissipating too much power. I'd almost guarantee this will improve things if you're using a class AB amp with lots of feedback. (In fact, if you look at schematics for many classic amps with headphone jacks, they switch in a shunt resistor when you are using headphones).

So, you're in the market for an amp to drive K1000's. What should you buy?

Personally, I think tubes complement the slightly harsh sound of the K1000's. In general I tend to favor class-A circuits with no feedback, which also tend to work well with the K1000's high impedance load.

If you want to do SET with a K1000, I would recommend a 300B as the best power/output impedance choice. About the best sounding driver for the K1000, in my opinion, but expensive. A 2A3 will work, but it's a tad on the wimpy side - probably OK if you don't listen really loud.

A push-pull class-A tube amp might be a less expensive option that would still sound fine, and should do OK into the 120 ohm K1000 load.

As for solid-state amps and clas AB push-pull tube amps, I don't have much direct experience to guess which amps will be well-behaved and which won't. But if you put a shunt resistor in, most should at least do OK.

One SS amp that I would expect would work great is a class-A SE amp like one of Nelson Pass' MOSFET amplifiers. Anybody got one to try?

Well, hope this long explanation is helpful to somebody...

Pete
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