[TzeYang]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif so in conclusion...

In summary, know exactly which circuit would produce which results. If the results don't match with the results on paper, then it means something is wrong.

Let's say a PPA V2 for example, if you're using regular opamps like the AD744, i can more or less be sure that the offset is BELOW 1mV. If anything higher, inspect your work again as the offset might be caused by serious instability that will distort your signal.

 

[amphead]

My conclusion from this discussion, is stay away from DC offset larger than 5mv. Especially with K701s = 64 ohms.

 

[d-cee]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif My conclusion from this discussion, is stay away from DC offset larger than 5mv. Especially with K701s = 64 ohms.

but their efficiency is quite low...

 

[Shoewreck]

Quote:

Originally Posted by d-cee /img/forum/go_quote.gif but their efficiency is quite low...

And the coil is big enough to dissipate some extra heat.

 

[dBel84]

Here is my take. Try and prevent dc offset when building an amp

IF you are following a tried and tested design which should not have offset and your amp does, find the problem and fix it. Tubes are often not that predictable and if there is offset in an OCL amp which is not due to some inherent design or tube flaw; either live with it and don't use highly efficient cans with low impedance such as the W5000's , or ......... start again, add a servo, toss it out the window...endless possibilities.

..dB

 

[Paragon]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif My conclusion from this discussion, is stay away from DC offset larger than 5mv. Especially with K701s = 64 ohms.

Grado cans are 32 Ohm.. and they said that they can handle 100mV. handle.. probably not recommeneded that high for long periods.. so below 20mV or so should be peachy. Just don't let it get carried away. Most people seem to get it below 10 and he happy.

 

[Shoewreck]

20mA into 32 Ohms is about 12 mW, that equals pretty loud listening level power (remember, headphone sensitivity is usually rated for 1mW power). Such a DC offset is OK only if you are absolutely careless about your headphones.
20mV into 32 Ohms is about 0.01mW, that is negligible.

 

[Paragon]

That should have been mV.. not mA.. my bad.

 

[Fitz]

Quote:

Originally Posted by Paragon /img/forum/go_quote.gif Grado cans are 32 Ohm.. and they said that they can handle 100mV. handle.. probably not recommeneded that high for long periods.. so below 20mV or so should be peachy. Just don't let it get carried away. Most people seem to get it below 10 and he happy.

I'm a bit obsessive-compulsive about things, so I try to keep DC offset below 1mV, preferably below 0.5mV...

 

[DaKi][er]

20-30mV is what i like to keep it under, if it is anymore than this it is usually something to look into. 100mV is perfectly ok and wont do any damage, and any active overload protection I add to an amplifier I usually set it to trip in the 70-100mV region just so it isn't going to trip in everyday use

 

[regal]

What about this: I forgot to unplug my AKG271s before I turned off my new SOHA. Are these phones compromised now, with one exposure to DC offset?

 

[Fitz]

Do they still sound fine?

 

[regal]

I think so but I have been hearing a little occational distortion, probably in the recording.

 

[majkel]

If the DC offset is below 10mV, you would hardly hear a click on a 32 Ohm Grado headphone while plugging in. This means the diaphragm stress is hardly any at such voltage. Actually, I wouldn't care about offset below 10mV at low volume setting and 30mV at high volume settings. Some DC coupled amps take advantage of via-potentiometer DC offset nulling, so it depends on the volume as well. Using IEMs I would be more restrictive, say 10mV maximum.

 

[Paragon]

It is all in your head, regal.

When you turn an amp on or off, it won't power up/down equally so you will get a pop. You will be fine. The official Grado amp has a bad pop and they tod someone not to worry about that, iirc. Their cans are 32 Ohm.