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The Stax Thread III

Discussion in 'High-end Audio Forum' started by currawong, Aug 20, 2013.
  1. tigon_ridge
    The TKD cp-2500 is at least priced reasonably. I don't care if the T2 is worthy $100k; if a $900 part adds nothing discernible upon a $100 part, it's just a waste of money. Of course it's also important to consider the durability of components.
    Thenewguy007 likes this.
  2. SeaWo|f
    I have heard all three, unfortunately in amps form different builders. Each individual amp sounded superb FWIW.

    The RK50 definitely feels the part if you ever get to handle it. Just from a physical presence stand point I have no problem dealing out the cash for it.

    I have heard that the dact steppers can get noisy as they age, but I have never experienced this as i have never had an amp with one.

    khozmo has some interesting products too, I have talked to a few people who were really happy with their steppers. I have never heard one though.
    Jones Bob and alota like this.
  3. georgep
    Sure, but you don't know if it adds (or more importantly) or doesn't subtract. And with the rk50, that is beyond build quality, balance, proper log, etc.

    Khozmo does have some interesting products, but I don't know anyone who has remains happy with their products for very long.
    Jones Bob likes this.
  4. statfi
    Thanks for these details. Could you give more details as to why you "preferred" the TKD 2500 and how it "bests" the Slagle?
  5. statfi
    https://khozmo.com is interesting. They offer three different topologies and show the circuit diagrams if you cruise around their pages. For many years I worked at radio frequencies, where the practice is to take great care in operating at 50 ohms everywhere there is a connection. So an attenuator ("volume control") has 50 ohm input and output impedances if it is properly fed and loaded by 50 ohm lines. Has anyone (e.g., Kevin, Justin, ... !-) tried this in audio, or is it obviously over kill. Attenuators use either a "pi" or a "T" topology, with 3 resistors: 3 equations for attenuation, input and output impedance, with three resistance values as unknowns. So, a down side is that either requires 2 switch contacts.
  6. alota
    I had first version of khozmo. Sold immediately due to poor manufacturing. I don't know the actual series
    Jones Bob likes this.
  7. Jones Bob
    Both are damn good. I preferred the TKD 4CP 2500 10K to the ALPS RK50 50K in direct comparison in the same Gilmore designed Grounded Grid amp listening to STAX SR-009. The TKD was slightly more transparent with a more defined and deeper bass presentation. The ALPS was slightly more veiled. The difference could be attributed to the different impedance load between the two I guess, but IDK for sure. Costs aside, I just liked this TDK a little better.

    Earlier when I was running just the RK50, for the hell of it I tried using it as the shunt element with a Vishay RN60 load resistor. After a short audition, I rewired the RK50 back conventionally. The single RN60 was just too dirty sounding.

    Over 25 years ago when the Oregon Triode Society was active, I was involved in many listening sessions when writer Ian Joel was resurrecting the idea of a series shunt passive attenuator for audio. Lots, and I mean LOTS, of potentiometers and resistor combinations were assembled with listening evaluations by all over many months. As these were passive boxes with inputs and output cables to drive there are impedance mismatch issues. The best consistently sounding units were made by Ian. He would not tell us the load resistor, make or value, but he did share he used a common Radio Shack $2 ALPs 10K pot. Those were actually really sounding good stand alone pots. Too bad Radio Shack is kaput. I played around with these for many years, mostly using a Riken in my tube based system in those days. Later used Caddock metal foil for some SS amps.

    Over the years I also bought and tried many other pots, Noble, ALPS RK27 and RK40, PEC. All OK but each a different flavor -none seemed really transparent to the signal as the series shunt attenuators were. Also tried an early DACT 10K stepped attenuator. Meh sounding..... and I did not like the rough step resolution either.

    Later I bought and tried one of Dave Slagle’s basic Intact Audio AVCs. That elevated the SQ a level or two higher than what I had used to up to that point. But it with courser steps and the wiring was a spaghetti monstrosity. Ended up deciding it was not practical for me. His designs have evolved, especially his work with Chapman Audio, but the really good stuff is really expensive these days. Especially for a balanced signal.

    So, back to the GG. From my experience of what the single RN60 load resistor sounded like (with the RK50 used as s shunt), I figured to play around with resistors. The most revealing place would be in the NFB loop of the amp, so I replaced the RN60s I originally used there with mucho expensive TX2575 Z Foil Vishays. I had tried S102 Vishays years earlier as a series resistor in an attenuator and came to really hate them. They stripped the harmonics from the music and bleached out the sound. Even after a long run in, they gave me an instant headache. But these TX2575 were getting great press. Soldering then into the amp, they made an instant positive improvement. Seemed like the noise floor dropped along with grit and grain with more natural detail retrieval and body to the music. So I decided to try them in a series shunt attenuator. I would have liked to used the TKD 2500, but the way it is internally configured, it cannot be used as a shunt element. So I bought the cheaper TKD 601 to use. Soldered up with a TX2575 as the series. I did not directly compare to my Slagle AVC in this amp, but from memory they both share a similar effortless, grainless, and full scale dynamic that I have not heard in any other attenuators. The TX2575/TKD 601 series shunt attenuator is IMO at least the equal in SQ to the Slagle AVC and the clear winner on cost, infinitely variable, and package size. Best I’ve found and used so far.
    Last edited: Nov 18, 2018
    zolkis, rumina and alota like this.
  8. staticdynamo
    This is STAX thread, so I can't understand talking about third party amplifier. If one use non-STAX amplifiers, the warranty of STAX headphones will be void.
    If I were a man working for STAX, I don't want to repair STAX headphones which had been driven by non-STAX amplifiers.
    Anyway, about low-costed,small STAX, good news will come out before the end of this year. Long-waited things will be released.
    They are in production.
  9. raband
    You must be fun at parties :wink:

    What sort of performance will the new, low cost offering provide?
  10. JimL11
    As a matter of fact, the SRX-Plus is a Stax circuit, upgraded with current technology, and all the designed-in Stax safety features. All the Gilmore designs also have all the designed-in Stax safety features to prevent damage to the headphones. These consist primarily of specific safety resistors in the bias supply and outputs, and limited power capability in the bias supply. This is NOT true of other third party designs. Also, the amp which has the most drive current and voltage potential is the original Stax T2. This is matched by the DIY T2 that Kevin Gilmore was authorized by Stax to clone. AFAIK, none of the other third party amps can match the T2 in voltage and current drive.

    The reason for discussing third party amps is that some are interested in achieving the best possible sound from their Stax headphones. Stax amplifiers generally have well-designed circuits, but are limited by their size, weight, and cost by commercial considerations. For example, the size and weight limits how much heat sink they can fit in, which in turn limits the amount of standing current - in some cases that can prevent the circuit devices from running at their most linear operating point. Cost limits the Stax amps to using unregulated high voltage supplies, whereas the DIY T2, Gilmore designs and SRX-Plus use regulated power supplies, which improves the sound. And so on.
    Last edited: Nov 19, 2018
    Ali-Pacha, arnaud, joseph69 and 5 others like this.
  11. PointyFox
    Regarding all this talk about regulated power supplies improving sound and Stax amps being junk because they use unregulated power supplies, check this out:


    What I got from it is that unregulated has generally better audio quality (less interference, better power delivery on transient peaks) except in the cases of running the amplifier into clipping or when you have wildly-fluctuating mains voltage, neither of which should be happening and can be corrected in other ways.

    (Unregulated power supplies are also cheaper, more reliable, produce less heat, and use less electricity).
    Last edited: Nov 19, 2018
    greggf likes this.
  12. JimL11
    Um, no. An unregulated supply that has the same output voltage as a regulated supply will ALWAYS put out LESS power on peaks, because the peaks will cause the power supply to drop its voltage to some extent - the longer the peak lasts, the more the power supply voltage will drop. This is why a popular modification to a commercial amp is to put in more power supply capacitors - it doesn't increase the power supply voltage, but it does increase the power supply reserve so that the voltage drops less with power demands.

    Second, fluctuations in the power supply can also cause spurious signals in the amplifier - the degree to which this happens depends on the ability of the amplifier circuit to reject noise and crap from the power supply. In fact, if you look at the specifications for any op amp, one of them will be the "power supply rejection ratio", which is actually frequency dependent. This is not limited to op amps - any amp will have a similar profile, it's just that most audio amps don't have a specification listed. But rest assured, it does exist.

    A perfectly regulated supply produces no noise and no spurious signals. Also, while mains voltages can vary when there is a transient load - for example, if you are listening and the air conditioning turns on, this can cause a drop in the AC voltage which can sometimes cause a thumping sound in the amplifier. This can easily be measured or seen if you look at the AC voltage with an oscilloscope. It will also show transients from air conditioners, refrigerators, etc. turning on and off anywhere your AC power shares wiring with any other houses on your block.

    It is true that a regulated power supply has more elements than a simple unregulated supply, but a well designed one is no less reliable than the amplifier it is supplying. If you were that concerned about reliability you wouldn't listen to recorded music at all because any amplifier could fail.

    I never said Stax amps are junk. To the contrary, I said "Stax amps generally have well-designed circuits, but are limited in size, weight and cost..." Don't misquote me in order to set up a straw-man argument. Commercial considerations are important for a company which wishes to continue to exist. On the other hand, DIY designs can be more free of cost, size and weight considerations and thus more closely approach ideal solutions. There is a place for both - just don't mistake the priorities of one for those of the other.
    Last edited: Nov 19, 2018
    arnaud, joseph69, GarageBoy and 4 others like this.
  13. PointyFox
    Don't misquote me either. I didn't say it was you who said they were junk. It's something I've seen a few times in this thread. Accusing me of setting up a strawman argument is setting one up of your own.

    Why would that article list a disadvantage of regulated power supplies as "The amplifier can no longer deliver higher power on transient peaks."?
    Last edited: Nov 19, 2018
  14. JimL11
    The reason is as follows: as I stated, an unregulated power supply's voltage will drop to some degree as the amp draws more power from it. So, for example, suppose we have an amplifier with unregulated power supply which is rated at 100 watts into 8 ohms, and another amplifier with regulated power supply which is rated the same.

    For the unregulated amp, the power supply is +50/-50 volts, which decreases to +/-42 volts at full power. For the regulated amp, the power supply is +42/-42 volts all the time.

    Now, since music usually does not play at full power, normally the unregulated amp's power supply sits at close to its quiescent level, which is +50/-50 volts. Along comes a transient. Initially, the unregulated amp is able to put out more than 100 watts - say 130 watts - because it has higher power supply voltages - however, as time goes on (we are talking 10s of milliseconds here), the power supply voltage sags down to +42/-42 volts and the amplifier can only put out 100 watts after a short interval. Thus, the unregulated amplifier is able to put out a higher power for a short period of time, but eventually physics catches up with it and it can only supply 100 watts on a continuous basis. Once the transient has passed, the power supply can build itself up to +50/-50 volts again for the next transient. Note that this change in power supply voltage with the transient will affect, to some degree, the ability of the unregulated amp's ability to faithfully amplify the signal. An obvious way this happens is if the transient continues at the same level, it's initial peak will be reproduced at 130 watts but its continuation will only be reproduced at 100 watts as the amp will clip during the latter part of the continuation.

    On the other hand, the amp with regulated power supply, because it starts with lower power supply voltages, can only put out 100 watts - but, it can put it out on a short term basis, or continuously. That is why an unregulated power supply allows an amp to put out more power than its continuous rating. So the regulated amp will clip on the first part of a transient at a slightly lower level than the unregulated amp, but as long as you play it below clipping, it will reproduce a prolonged transient more faithfully.

    A classic example of this behavior is the original NAD 3020, which was rated at 20 watts/channel continuous into 8 ohms, but could put out 40 watts into transients for a short period of time. However, if you were to take the exact same circuit but run it with a regulated power supply set at the same quiescent voltages as the original design, it could have been rated at 40 watts continuous power. It would also have cost much more for the regulated power supply, and also probably for larger heatsinks to tolerate it being run at 40 watts. The original 3020 is an example of cost-effective design using a "soft" unregulated power supply, and takes advantage of two facts: first, that transients are brief and relatively rare occurrences and second, that the ear is relatively tolerant of distortion on peaks. The significant words here are "cost-effective." For example, the Mark Levinson ML-2 was also rated at 25 watts/channel, however, it had a regulated power supply, ran in class A, weighed 65 lbs for each mono amp, could put 100 watts/channel into 2 ohms, and cost a lot more. Consensus opinion is that the NAD sounds very good for the price. The ML2 sounds better.
  15. tigon_ridge
    If you take the regulator out of the circuit, you can supply more power; because the regulator itself is dissipating heat at a constant rate. All that means is that you need a bigger PS, if you want to more cleanly render the same transient with a regulated signal. In the context of headphone amplification, here is nothing in a regulated design itself that makes it inherently less capable of producing transients; you just pay more for the bigger, bulkier PS.
    mulveling likes this.

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