Need help pre CMOY build

[Mr Goat]

Hey ho

As long as the DC voltage at the opamp output is zero then its 'safe'. That's measuring as we did in step 10 above.

So duff opamps. Ebay by any chance ?

No it was actually bought via one of the biggest electronic company in sweden. The opamp is created by the company Analog Devices.

 

[Mooly]

Interesting. I wonder if the op amp was oscillating (the OP275 that is). It is a possibility with a high performance device and erm this type of construction where there is a lot of wiring. Oscillation could certainly give a weird 'thin' sort of sound. You would need an oscilloscope to check for that though.

 

[Mooly]

This is what oscillation would look like:
http://www.diyaudio.com/forums/anal...u-have-checked-see-its-stable-havent-you.html

 

[Mr Goat]

This is what oscillation would look like:
http://www.diyaudio.com/forums/anal...u-have-checked-see-its-stable-havent-you.html

i chould check that out, school should own a oscilloscope! not saying i will, but if i have time i sure will.

1 question tho? when i turn the amp on, there was a mild to medium loud pop, is this anything unusual?

Anyways, im off to 3d model a case for this badboy

 

[Mr Goat]

Oh, and i'm looking at buying a odac, maybe even an o2 amp via walter on head n' hifi. On a scale of 1-10 how hard would it be to build compared to this stripboard cmoy? Also, would the o2 apm be a great difference over this simple cmoy so its worth the 70-120 euros i will be spending depending if i diy or not?

 

[Mooly]

The pop is unfortunately normal and due to the circuit needing a fraction of a second to stabilise as the voltages come up.

The 02 headphone amp is a great project and you get the benefit of a proper board layout that ensures its all stable and so on. It still might pop on power on though. I seem to have become one of the unofficial troubleshooters on the 02 build thread but I've never actually heard (or even seen one). As a well thought out design it impresses though.

I've no experience of the odac at all I'm afraid.

 

[Mr Goat]

Hello again. Back at it again with concerns

the amp has been working great till now when i started hearing a odd noice when i turned the amp off. Now when i check the outputs on the amp its delivering around 16mv constantly when turned on. And i remember you that you mentioned that the amp is safe as long as the dc output is at 0.

So im not using the amp atm till im sure it wont destroy the headphones :S

I'm also placing an order for a prebuilt o2/odac later this month, so i just want the cmoy to be useful till i get the new amp/dac combo

 

[Mooly]

16mv won't do harm. We can calculate the current that would flow assuming the headphones were say 8 ohm (DC) resistance. They are probably higher which would improve things however...

0.016/8 is 2 milliamps. That will cause no harm at all. The power dissipated is 0.002*0.016 which is 0.000032 watts.

So no problem. 16mv is very low in the scheme of things. To see why its not zero would need a detailed look at your actual build and perhaps also putting a scope on it as well. Low level HF noise (oscillation) can give the impression of a DC offset.

 

[Mr Goat]

16mv won't do harm. We can calculate the current that would flow assuming the headphones were say 8 ohm (DC) resistance. They are probably higher which would improve things however...

0.016/8 is 2 milliamps. That will cause no harm at all. The power dissipated is 0.002*0.016 which is 0.000032 watts.

So no problem. 16mv is very low in the scheme of things. To see why its not zero would need a detailed look at your actual build and perhaps also putting a scope on it as well. Low level HF noise (oscillation) can give the impression of a DC offset.

So that's a relief but how do i know when i should change my batteries out? atm i switched 2 times, and after the switch the batteries are giving out around 7-8v. i never actually heard a difference in sound. i just switched after about 30h of use

 

[Mooly]

As far as the opamp goes, it will continue to work correctly down to quite low voltages. 7 volts per battery would seem about right (that is measured with the amp on) but because this uses so little current you could well find it audibly OK down to considerably lower voltage.

Typically it will sound distorted when you turn the volume up... if it is OK then keep using the batteries. Get you monies worth from them

 

[Mr Goat]

As far as the opamp goes, it will continue to work correctly down to quite low voltages. 7 volts per battery would seem about right (that is measured with the amp on) but because this uses so little current you could well find it audibly OK down to considerably lower voltage.

Typically it will sound distorted when you turn the volume up... if it is OK then keep using the batteries. Get you monies worth from them

Well i started using it again. i thing i noticed is that when i turn it of there is like a "rumbling sound" like there the amp spikes for a sec when i turn it off. Is this normal? Im not even sure if it was like this all the time since i usaly have my headphones of when u turn the amp off

 

[Mooly]

Noises at power on and power off are to be expected. As the voltage rails collapse there does come a point where the opamp can not maintain its correct operating point, and so it develops a voltage at the output which you hear in the headphones.

To get a silent power on and power off requires a well designed muting circuit (which in the case of the cmoy would be more complex than the amp itself)