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Sonic Impact Tripath amp-->AkG K1000? - Page 3

post #31 of 86
Quote:
Originally Posted by mikeg
It was an ASL AQ-1005DT power amp., with a SinglePower SDS amp. serving as preamp. The K1000 was connected to the 16 ohm speaker posts.
By putting a 120 ohm load on the 16 ohm tap, you've increased the impedance seen by each 300B tube by 7.5 times and decreased the signal current running through each tube by 7.5 times. This is what output transformers (OPT) do: convert a low speaker impedance to a high plate load impedance. Running a 120 ohm load on the 16 ohm tap reduces the output power by a factor of 7.5 as well, so the amp runs out of steam at 1 watt instead of the rated 8 watts.

Even if 1 watt is enough to drive the phones, the mismatched load changes the operating conditions (bias point and load line) of the 300B. This will probably cause clipping even at this low power level, or add large amounts of THD, or both. This may explain why the amp doesn't sound too good driving the phones.

There is one advantage. By lowering the signal current swings, the OPT is less likely to saturate. But the other two factors will outweigh this advantage.

Here's a little tutorial on mismatching loads with tubes and OPTs: http://www.diyguitarist.com/GuitarAm...lectedLoad.htm.

There's no info on the relationship between power and load for the tripath chip in the datasheet. The main issue is filtering out the ultrasonic noise. I really think that you guys running headphones off the SI amp without changing the lowpass filter are looking for trouble.

- Eric
post #32 of 86
Sorry Eric, but your explanation is way over my head. All that I know, or care about, is that the music sounds great.


Quote:
Originally Posted by eweitzman
By putting a 120 ohm load on the 16 ohm tap, you've increased the impedance seen by each 300B tube by 7.5 times and decreased the signal current running through each tube by 7.5 times. This is what output transformers (OPT) do: convert a low speaker impedance to a high plate load impedance. Running a 120 ohm load on the 16 ohm tap reduces the output power by a factor of 7.5 as well, so the amp runs out of steam at 1 watt instead of the rated 8 watts.

Even if 1 watt is enough to drive the phones, the mismatched load changes the operating conditions (bias point and load line) of the 300B. This will probably cause clipping even at this low power level, or add large amounts of THD, or both. This may explain why the amp doesn't sound too good driving the phones.

There is one advantage. By lowering the signal current swings, the OPT is less likely to saturate. But the other two factors will outweigh this advantage.

Here's a little tutorial on mismatching loads with tubes and OPTs: http://www.diyguitarist.com/GuitarAm...lectedLoad.htm.

There's no info on the relationship between power and load for the tripath chip in the datasheet. The main issue is filtering out the ultrasonic noise. I really think that you guys running headphones off the SI amp without changing the lowpass filter are looking for trouble.

- Eric
post #33 of 86

K1000+T-amp Is Great!

I love my K1000/T-amp combo - its detail and bass response is better than I can ever remember with the RKV MkII, and it's $20 (used)! I found the RS PS for $30! This is $50 for an amp that approaches (if not exceeds in some areas) the ASL AQ-1005DT, RKV MkII and nOrh! Here is my plastic amp (look at that massic 3A PSU):


I'm gonna spend the $75 for the chassis and parts and my T-amp will look like this:


This way I can use my Stefan AudioArt upgrade cable and finish off the AKG system.

K1000: ~ $400
Cable: ~ $ 75
T-amp: ~ $ 20
Upgrade:~$ 75
PSU: ~ $ 30
Total: ~ $600

That's $600 for one of the best headphone combos around! That's still cheaper than even a used RKV alone!
post #34 of 86
Quote:
Originally Posted by mikeg
Sorry Eric, but your explanation is way over my head. All that I know, or care about, is that the music sounds great.
Let's try this: when the speaker load doesn't match what the amp is designed for, the amp doesn't work right. So you're not hearing the amp as it's intended to sound.

It's the same as what happens when you start riding your bike from a stop in 18th gear, or when moving at 20 mph, you shift into 1st: your legs (amp) don't perform very well into the bike under current conditions (load). That's an impedance mismatch. The gears (like a transformer) are used to adjust the load seen by your legs to match the work demands of the bike.

With the 300B amp driving the phones on the 16 ohm tap, the output power is too low, distortion is very high, and there's probably a lot of clipping going on.
post #35 of 86
Quote:
Originally Posted by NeilPeart
I love my K1000/T-amp combo - its detail and bass response is better than I can ever remember with the RKV MkII ... this is $50 for an amp that approaches (if not exceeds in some areas) the ASL AQ-1005DT, RKV MkII and nOrh!
Look, it may "sound" like a great combo, but

1) Saying the tripath amp is better than the others is like saying that your Ford pickup is better than a Porsche because you couldn't get 1000 lbs of bricks in the Porsche's trunk; and

2) Watch those ultrasonic frequencies, you may be buying new phones soon.

- Eric
post #36 of 86

...

Why can it not be better in other ways too? A well-designed amp can sound better than old-school amp, be well engineered and very easy on the wallet. Affordability and quality aren't mutually exclusive all the time. Since you're in my neighborhood, drop by and bring the RKV over for comparison. This little amp proves that a digital amp may have a place in many homes. In fact, Bel Canto has a $3000+ integrated amp with the same Tripath chip found in the T-amp. With a good power supply like the 3Amp RS and the quality components shown in the second photo I posted, I'm sure the T-amp can approach the quality of the highly praised Bel Canto amp. Just because an amp isn't expensive and doesn't feature expensive tube outputs doesn't mean it's a poor-quality amp. Who cares though - enjoy your ignorance, Sir.
post #37 of 86
Thread Starter 
Quote:
Originally Posted by eweitzman
Look, it may "sound" like a great combo, but

1) Saying the tripath amp is better than the others is like saying that your Ford pickup is better than a Porsche because you couldn't get 1000 lbs of bricks in the Porsche's trunk; and

2) Watch those ultrasonic frequencies, you may be buying new phones soon.

- Eric
There's been no problems of any kind running the SI/K1000 for weeks, ultrasonic or otherwise. Believe me, I've cranked it with every music genre possible. If you own K1000, it would almost be a crime not to try the SI with good PS.

The Ford/Porsche analogy reminds me of what my English professor used to say, though: "Just because you can make an analogy, it doesn't mean you should." Cheers and happy listening to all
post #38 of 86
Hirsch: Thanks for the prompt reply - and confirmation of my strategy. You're at the top of the informal "credibility metric" I've developed in reading Head-Fi so your opinion means a lot to me. I very much look forward to your continuing evaluation of the K1000/Sonic Impact combination!

And my appreciation to the rest of you who took the time to chime in with your opinions and suggestions about a power supply.

A couple of niggling follow-up questions...

AM I REALLY GONNA FRY MY NEW PHONES WITH THIS AMP????

Eric: You sound like you have the technical expertise to know whereof you speak (which I ain't got). What's the risk to the phones that you're describing? A major melt-down in the voice coil or some such? Or more subtle deterioration as electrical/mechanical parts are stressed beyond their design limits over time?

Also, from your statements about the ASL, I'm not clear if the risk from ultrasonic overload you describe is unique to the digital amp or is possible from any amp designed for 4-8 ohm speakers. Am I correct that you're implying that most any tube amp intended for speakers will have some sort of difficulty in properly amplifying a signal accurately into a 120 ohm transducer - though perhaps without the potential for damage? Does this apply to traditional solid-state devices also?

Coming at the design business from the other direction - while speaker amps may not be designed for use with 120 ohm loads, the folks at AKG obviously designed the K1000 to work with speaker amps. Perhaps there is something in the K1000 electrics that accommodates your concerns? I don't have an iota of technical knowledge so I'd appreciate your opinion and those of other techies on the board.

Power supply follow-up: I assume this is the 13.8V RS PS that you folks are recommending. It looks different than the metal-bodied one in NeilPeart's picture - newer model, maybe? Radio Shack doesn't describe this as a regulated supply as it does with its regulated wallwarts. Is that a problem?

Also, I saw an Astron supply recommended (forget by whom) in another thread. These are not only regulated but also linear, which is supposed to be in its favor. It also looked darn good with the SI in the pic that was posted. Comments, anyone?

That's it for now. Thanks again for all the help! Will look forward to your replies...

Best,
Beau
post #39 of 86

Beau,

The RS 3Amp PSU that you linked to isn't as good as the one I have. I saw that one at the store too, but it was far less substantial (in dimension and weight), and was not as well built (compare the banana plugs and transformers of the two). Also, the lesser PSU cost more than the better-built one! Perhaps they were selling off the older (though better) model in favor of the cheaper-to-produce version (mine was the last one left in the store)? My PSU is clearly regulated, as this is posted on the box itself. I'm still researching better power options, and will probably purchase the linear PSU from Astron; I just picked up the RatShack PSU as a temporary measure, and it sounds far better than the stock wall-wart and battery operation (standard batts, not lead-acid or any exotic battery configuration).
post #40 of 86
Why not get a 19Ah car battery booster from Target (~$50), like what I use?
It is a portable lead battery in a nicely sealed package with a handle and a pretty casing.
Powers air compressors and other 12V devices nicely when you don't use it in the audio chain.
As for convenience, it can feed a T-amp for a month (>150 h).
It would be very hard to convince me that any PSU below $500 or even higher can provide cleaner DC than a battery.
This battery can output hundreds of amperes of instaneous current, which should be great for audio transients.
post #41 of 86
I was going to start a new thread on this with the text below but it seems appropriate to include it here:

It has been a few years since I have posted in this forum. During this time, I have been enjoying a K1000 driven by a 300B SET.

Last fall, I was “6-mooned” into trying the SI T-amp with the K1000s. I found it to be a little bright but surprisingly good. On balance, I preferred my SET (a tweaked Audio Note) but was more than a little intrigued by the T.

BTW, I also tried the T-amp on a pair of Stax Lambda Pros (with the transformer) and found it to be a great match. It had none of the brightness that I heard with the K1000s.

Attracted by the size, cost and battery power, and impressed enough with the sound of “the little-Tripath-that-could”, I bought Vinnie Rossi’s modded version of the T-amp, aka the Clari-T. The combination of the mods, battery power and the “real” connectors permitting the use of better cables all improved the basic sound noticeably. I could have lived quite happily with this as is.

If pressed (and having a touch of the audiophile syndrome), I still thought it somewhat bright. I mentioned this to Vinnie Rossi and he suggested I try putting a 4 ohm resistor in parallel with the K1000s (essentially across the speaker connectors).

I have been listening to it this way for a couple of days and find that this improves the sound significantly. To my ear, it adds more body and reduces some (all?) of the HF emphasis. Has anyone else tried this?

I will continue to listen to this setup to make sure that it stands the test of time but at the moment my feeling is that this easily surpasses the sound of the 300B. I am amazed!
post #42 of 86
Thanks for the simplified explanation. There is absolutely no clipping, even when I increase the K1000 volume to ear shattering levels. The sound is absolutly clean and clear. I use lots of other headphones, with other amps., so I know what great sound should sound like. There is absolutely no audible distortion when connecting the K1000 to either amp.

Quote:
Originally Posted by eweitzman
Let's try this: when the speaker load doesn't match what the amp is designed for, the amp doesn't work right. So you're not hearing the amp as it's intended to sound.

It's the same as what happens when you start riding your bike from a stop in 18th gear, or when moving at 20 mph, you shift into 1st: your legs (amp) don't perform very well into the bike under current conditions (load). That's an impedance mismatch. The gears (like a transformer) are used to adjust the load seen by your legs to match the work demands of the bike.

With the 300B amp driving the phones on the 16 ohm tap, the output power is too low, distortion is very high, and there's probably a lot of clipping going on.
post #43 of 86

Tripath simulation with 120 ohm load

This image shows the results of simulating the output circuity of the tripath chip while driving three different loads.

The top of this image shows three versions of the tripath reference circuit from the chip amp to the speaker. Each circuit has a different speaker load on it: 4 ohms, 8 ohms, and 120 ohms (AKG-K1000). The circuit values are for the 4 ohm configuration, which may or may not be exactly how Sonic Impact supplies their amps. (If they used values for 8 ohm loads, it wouldn't make a big difference to the simulation anyways.)



The frequency response for each load is shown on the bottom. Cyan = 4 ohms, yellow = 8 ohm, green = 120 ohms. Notice the huge peak at 53kHz at 1.5 volts on the 120 ohm load. It's three times "louder" than the volume from 20-20kHz at about 0.5 volts. It's about 10db higher than flat. You can't hear it, but this ultrasonic signal is going to the phones. Now, the phones may not have a frequency response that extends that high, but even at 40kHz (which many phones will play), the output level is close to double what it is in the audible band.

I also ran the simulation with a 300 ohm load (HD-650). The peaking was about 20% higher. Everything else applies.

Beauregard#1: Whether your phones will survive these high levels at ultrasonic frequencies is not something I can tell you: it will depend on the phones. Your risk tolerance is another factor. Personally, I wouldn't drive my HD-650s with this amp. But I am trying to redesign the filter for headphone use.

Beauregard#2: The ASL won't put out ultrasonics, just more THD than you'd like. Only the best output transformers extend far above the audio band, perhaps up to 60kHz or 80kHz.

Jon L#1: Maybe you could hook up your phones to the amp and then put a scope on them. Tell us if you see any ultrasonics. The simulation may not be 100% accurate, but this is what tech support at tripath suggested I do.

Jon L#2: The analogy is apt: you're asking a class D amp to drive something it's not intended to drive, just as a Porche isn't designed to hold 1000 lbs of bricks.

NeilPeart#1: I'm not saying the tripath is better or worse than a $3000 SET, just that the reports comparing them for headphone use are not appropriate. You can't drive a 120 ohm load from a SET amp and expect it to sound right.

NeilPeart#2: Tripath makes about a dozen chips. The Bel Canto may not be using the lowest-powered (and highest THD?) chip like the SI does. No doubt better parts DRIVING AN 8 OHM LOAD would make the SI sound even better. You still have the ultrasonics to worry about if you're driving a 120 ohm (or 300 ohm) headphone load.

NeilPeart#3
Quote:
Originally Posted by NeilPeart
Just because an amp isn't expensive and doesn't feature expensive tube outputs doesn't mean it's a poor-quality amp. Who cares though - enjoy your ignorance, Sir.
That's totally uncalled for I'll forgive you when you invite me over to listen to your amp Maybe I'll bring over a high quality power supply and we'll see just how far this thing can be pushed But with your phones, not mine...

RonD2: Putting a 4 ohm load in parallel with the headphones is one possibility: the amp will see an approx. 4 ohm load and should behave properly. The problem with this is that most of the power will be delivered to the resistor, not the phones, so you'll have to run the amp full out to get enough power to the phones. If you try this, make sure you use a high power resistor rated for the amp's maximum power output.

Ferbose: I've looked at the charging circuit in one Chinese battery booster at Walmart. The charger did not use the charge controller chip from Unitrode (U????) that most good chargers use, so the battery's life would be reduced from the ideal of 100-200 charge/discharge cycles. Perhaps not a problem if you can get a month of listening per charge. Of course, other boosters may use the magic charging chip.

mikeg: I'm glad that neither amp was clipping with the K1000. I'd have to look at the circuit for the ASL amp (and spend more time than I'm willing) to figure out if/when it would clip and the amount of THD you'd get at the new operating point with a 120 ohm load.

- Eric
post #44 of 86
Quote:
Originally Posted by eweitzman
Notice the huge peak at 53kHz at 1.5 volts on the 120 ohm load. It's three times "louder" than the volume from 20-20kHz at about 0.5 volts. It's about 10db higher than flat. You can't hear it, but this ultrasonic signal is going to the phones. Now, the phones may not have a frequency response that extends that high, but even at 40kHz (which many phones will play), the output level is close to double what it is in the audible band. I also ran the simulation with a 300 ohm load (HD-650). The peaking was about 20% higher. Everything else applies.
Thanks a lot Eric.

It seems that it is flat within the audible band. If I don't worry about the ultrasonic, I can use the amp without changing the filter.

Does anyone make a cheap cable for Sennheiser HD580 without a common ground? Balanced?
post #45 of 86
Eric - Your knowledge is amazing, and the information that you provide is unfortunately way beyond my understanding. But, I'll simply enjoy for now the excellent sound that I get from my K1000, when connected to my expensive and inexpensive amps., and I'll have faith that the K1000 will continue to work, just as it has for the past two years. If the unfortunate happens, and it fries itself in 10 or 20 years, I'll just buy a replacement to use for another 20 years.
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