AMB Laboratories DIY Audio Forums

[DEFL]

We should be aiming 750mV of bias voltage actually not 75mV. I read in some post that says 75mV which is wrong and led me to a wrong path when I started building mine.

Yes, 750mV of course. Typo.

[mloutfie]

not sure if I've posted this before but this looks good as a quad stepped attenuator for the Dynahi http://www.ebay.com/itm/Balance-XLR-23- ... 4197c5f6bf

[amb]

That's the same one we used in the "group build β22". It's good for the price. I wished for more steps and a better feel.

[mloutfie]

hows the sound quality? I've used the valab stereo stepped attenuator for by bottlehead crack and it's pretty good but looks like the design is different to the balanced one. I think I need to change the khozmo stepped attenuator because it's 50k. I head slight floor noise on the right channel. THis mostly caused by the attenuator mismatch right?

[amb]

It "sounded" fine.

I don't know what's causing noise only one one channel without knowing more information.

[mloutfie]

I'll try to borrow a cro to trace where the noise starts but when I start building this the cro shows that the noise shows up on the attenuator output point

[mloutfie]

Still having problem with ground noise. Quick question. Is the signal ground supposed to be connected to both power ground and chassis ground? That's what I have now.

[amb]

There are different grounding schemes. How well it works depends on actual implementation, and what other equipment is used in the audio chain. I prefer the grounding schemes shown at the β22 website, in the "Wiring & ground" section.

[mloutfie]

Thanks for that. That write up for b22 is great. I think I found the issue as per the note in that page. My headphone jack is not isolated from the chassis ground. I will replace it with an isolated headphone jack. The xlr shouldn't matter right? Since there is no ground connection there. Or will I get better noise performance if I use a plastic isolated xlr plug there too?

[amb]

You don't need to use a plastic XLR connector. As balanced headphone jacks, the XLR connector's outer shell isn't used for anything.