What is the Effect On Headphone Amplifier Output Transistors [Last Stage] When Repeatedly Subjected to Brief (5-40ms) Short Circuits

[mike7877]

With Topping's A70 Pro headphone amplifier + preamp, when you disconnect headphones (by removing the eg. 1/4" male connector), a relay quickly cuts power to the jack. I assume this is to prevent the brief short-circuits which occur on insertion/removal from reaching the transistors (to prevent too much current from flowing, and to maintain amplifier stability, correct?)

In the 1/4" female receptacle on the face of my A70 Pro, I have semi-permanently installed a Y-adaptor (installation was nothing special, I just don't unplug it...)
It's a 1/4" male to two 1/8" female. Reason being, sometimes two are listening. Otherwise, I've got many different headphones accumulated over the years, and I prefer some of them for for some things, others for others. As you can imagine, the y-adaptor gets a good amount of use because of this. My estimate for the average number of insertions/removals per day over the last 6 months, is 12-15. Twelve to fifteen!

I do mostly switch between two pairs of headphones, but due to chance, one is 250 ohms and the other is 34. The impedance isn't a huge issue itself (amp stable down to 8 ohms), but in addition to the 250s' low sensitivity, they're also quite inefficient -a stark contrast with the 34s which... I wouldn't say are extremely efficient, but... they're efficient! So even if I couldn't hear the 34s on my desk through the 250s on my head (I do...), there's still another problem: even if I soundproofed my desk drawer to toss the 34s in while listening to the 250s, the 34s will still be being subjected to that [heavy] use. After some months, the sound quality of the 34s will undoubtedly be, well.. degraded.. Before this has a chance to happen, though, I'm pretty sure that a low frequency event will occur, something too hot for the 34s to handle, and they'll just asplode.


Now, obviously I don't want my headphones to break, but also, I don't want my A70 Pro to break!!
Most of my headphones cost less than the A70 Pro, so he is priority 1. Am I putting him in danger by not allowing the protection circuit to temporarily cut the 1/4" jack when I'm swapping headphones? Or is it OK?

 

[AnalogSteph]

If you're worried about this, just briefly turn off the amp before swapping cans. Problem solved.

 

[mike7877]

If you're worried about this, just briefly turn off the amp before swapping cans. Problem solved.

I guess... But since it happens so often I'm trying to reduce wear. Whenever you plug in, the signal then gets sent to that jack (there's nothing there until you connect something).

So there's the sense ability and the relay... I think this would negate the purpose of reducing wear - it would add wear, actually, because there are many more relays inside and some that click on/off with power (obv lol). This is a somewhat longer OP, so maybe you didn't read the part where I connect/disconnect 12-15 times per day

I do usually make sure nothing's playing, and if there is something, the level is WAY down, I'm talking 5mV

 

[little-endian]

I'm aware that this isn't a direct answer to your question whether your usage will shorten the lifespan of your A70 Pro and probably is something only the manufacturer Topping can really answer, but just as a thought - wouldn't a RME ADI-2 Pro or 2/4 SE suit your special needs a lot better?

Not only do they come with several headphone jacks, but also feature the "fading in" protection which might come in handy when reconnecting headphones without risking to high output levels right away.

After all, the DAC quality is irrelevant in terms of being beyond human hearing capabilities anyway so it breaks down to pure usability.

 

[mike7877]

I'm aware that this isn't a direct answer to your question whether your usage will shorten the lifespan of your A70 Pro and probably is something only the manufacturer Topping can really answer, but just as a thought - wouldn't a RME ADI-2 Pro or 2/4 SE suit your special needs a lot better?

Not only do they come with several headphone jacks, but also feature the "fading in" protection which might come in handy when reconnecting headphones without risking to high output levels right away.

After all, the DAC quality is irrelevant in terms of being beyond human hearing capabilities anyway so it breaks down to pure usability.

Fair question. I've had my A70 Pro for a good 6 months now. I guess I could sell it, but then I'd have to sell my D90 III which I've really come to like. Not only that, but I'd have to take a 20-30% loss on them, probably plus shipping. Also, I do intend, in the semi-distant future, to get some low-impedance, low efficiency headphones (planar-magnetic). They could end up being 14 ohms or something (one of the reasons I went with the A70 Pro is its 17,000mW into 16 ohms lol)

edit: also, I've had both long enough to have pretty high confidence they're going to last me a decade or more. If I get something new, it could end up breaking which is a hassle. Not a big point, this last one, but.

edit2: checked the power output measurement of the ADI-2 (which is probably the same as the four), and its 32 ohm measured output power is only 1.042W. I think this is current limited, so dropping to 16 ohms would mean 0.5W (+/- 20%) : not enough. When spending a few thou on cans, I'd like to be able to get the most out of them