JSR03 - information

[Keljian]

the regulator is still working

The only thing I've changed in the circuit is the opamp used, I am using a socketed (on a browndog adapter) Ti THS4601 opamp on the regulator.

I find that with this opamp the overall background noise of the amplifier is less than the original AD825 (which is strange).

Overall the regulator is working fine, the sound out of the amp is a bit "thinner" than I am used to. This can be obviously fixed by changing opamps or tweaking the bass boost. So far I like the ths4631D chips in the M3 the most with the SA5000 headphones.

In a few weeks I'll be ordering another board from you, I'll give the design another attempt.

I am concerned about the heatsinks, they do get very hot, but are still within acceptable limits. When I build the next one I think I will drill up another heatsink that will be much larger. May I suggest for the next version that you consider better spacing so one can use some bigger heatsinks for the regulator and power transistor? (T4)  - an example of one is the Aavid-Thermalloy 531102B00000 as used on the mosfets on the M3.

[peranders]

With AD825 you'll get approx. 5 uV noise and with LM317 you'll get a lot more. If you really hear different noise levels, try to switch of you DAC. The DAC may interfere.

When it comes to heat, the LM317 get hottest so there is no need to separate the transistor from the regulator.

[Keljian]

With AD825 you'll get approx. 5 uV noise and with LM317 you'll get a lot more. If you really hear different noise levels, try to switch of you DAC. The DAC may interfere.

When it comes to heat, the LM317 get hottest so there is no need to separate the transistor from the regulator.

I agree.

However the noise issue is there when I use other sources also(I was using another source when I detected it) - so it leads me to believe that it is inherent of the opamp.

[peranders]

Can you actually hear noise coming from the headphone amp when the volume is turned down?

[Keljian]

Can you actually hear noise coming from the headphone amp when the volume is turned down?

Yes, this particular noise I could hear.

Remember I have particularly resolving headphones (sony MDR-SA5000)

[peranders]

The headphone amp of yours has around 117-125 dB in S/N. If noise really bothers you the level in your ears must be 20-30 dB at least. This means that something isn't working properly.

If you have the input of the headphone amp short circuited, do you get any noise then? Is the noise changing if the signal sources are turned on and off?

[Keljian]

problem solved, was a bad connection at one of the inputs