DACT stepped attenuator vs. Alps Blue Velvet: My observations - Page 2

For me the biggest difference between an SA and a pot is channel balance, and the SA does not have the "sweet spot" (sounds the best at a certain volume) problem present on most pots.

I do the same thing, but the darned thing barely gets north of dead cold. I certainly wouldn't call it warm to the touch.... my M^3 gets a little warm, but not the GS-1 ???? I wonder why??

Hi 003

Good to see you.

I just re-tubed the Woo with a new Cetron and jan philips 6922s. What a surprise - even better than before, more air, sparkle and nice deep articulated bass.....

What are you into these days?

Take Care

USG

If I were to hazard a guess, it probably has something to do with Kontai's Alessandro MS-Pros being 32 ohms and your HD650's being 300 ohms/DT880's being 250 ohms. Reduced resistance means increased current means more heat.

Hummm, makes sense, but I thought resistance = heat?

No, resistance doesn't necessarily mean heat. Heat is produced when there is power being dissipated from a device. The amount of power dissipated is the voltage across that device multiplied by the current through it. When there is little or no current, there won't be heat.

In an amplifier, given a particular output voltage, the amount of current delivered by the amp through the load is dependent on the impedance of the load. To simplify matters, think of impedance = resistance in this case. Via Ohm's Law, I = V / R, where I is the current, V is the voltage across the load, and R is the resistance. Hence, as you can see, when all else is equal, reducing the load resistance (headphone impedance) results in an increase in current. Since the current is directly proportional to the voltage, the louder you set the volume, the higher the current too.

Now, assuming that the amp is class B or AB, then the output transistors are going to dissipate approximately the power supply voltage across them multiplied by the load current as heat. Hence, assuming a certain and continuous output voltage, connecting a lower impedance load will cause the output transistor(s) to run hotter than a high impedance load.

In a pure class A amp, the output transistors are biased such that the quiescent current flowing through them is high, so high that under any reasonable output voltage and load conditions, the quiescent current will be higher than the load current. In this event, the output transistors will run hot constantly, and the temperature will not change with the load impedance. That is, unless the output stage is push-pull and the peak load current exceeds the quiescent current, then the amp drops out of class A and goes into class AB, and the output transistors will heat up further. In a single-ended class A amp, if you try to make the amp deliver more than its quiescent current, it will simply result in clipping.

Now, not all "class A" amps are biased the same. Some are set up to have much higher quiescent current than others, and those will run hotter. The higher quiescent current allows the amp to deliver more current before it drops out of class A (or clip, depending on the output stage design).

Hi amb....

My DT880s are harder to drive at a given volume than my HD650s.... but neither produces any warmth to speak of at usual, customary, regular volume levels....

Do you think the Alessandro MS-Pros are drawing more current and therefore causes the GS-1 to run warm?

USG

It's likely but it also depends on their efficiency. I've seldom seen those published for headphones but I would be very, very surprised if they weren't. Generally Grados are considered low impedence for headphones while Beyers and Senns are considered high impedence.