[was ist los?]

I recently built an amp based on an ra-1 and used the same battery grounding scheme. The batteries are at 6Vs each. I know i know i should have bought new ones. Anyway, the negative rail is at like 11.8v while the positive is .22v. There are 2 batteries, wired in series.

 

[stereth]

In the RA-1, isn't the virtual ground referenced from between the two batteries? If so, you're shorting something. Otherwise, how did you set up the power supply?

 

[Squalish]

Was is using the TLE to make a virtual ground. My guess was that he didn't have one of the caps connected correctly, or the RA-1's 0.12uf caps aren't sufficient for the TLE(which has 220uf electrolytics in that part of Tangent's CMOY guide). Here is how I think the whole thing is hooked up for a real ground(minus the pot, which would have screwed up the symmetry of the pic). I've recolored some stuff and revised the pic.

As always, feel free to correct me if I'm wrong.

 

[KTpG]

I don't like the Grado style ground... if one battery is charged more than the other, it seems like it would throw off the ground. Of course, it makes sense to me, but I am probably totally off base as usual.

 

[Squalish]

If one battery is charged more than the other, it will. You will get a big DC offset if you are using one dead battery in here, big enough to fry your cans easily.

Starting with fully-charged batteries, though, an offset will only develop when the batteries have very little juice left in them, long after the music has become unlistenable from undervolting the opamp. There was a thread about it on Headwize a while back, I'll try to find it.

 

[KTpG]

So I was actually right....

Beware, the world me be coming to an end. I was correct. OMG. On that note, perhaps I should go to bed.

 

[was ist los?]

Figured out the problem. I forgot to ground something!

The funny thing about the ground/power of the ra-1 is that when the headphones are plugged in and the amp is off, the led will light slightly, but no sound will be coming through. Then, when the headphones are unplugged, the light goes off.

 

[PeterR]

Quote:

Originally posted by KTpG I don't like the Grado style ground... if one battery is charged more than the other, it seems like it would throw off the ground. Of course, it makes sense to me, but I am probably totally off base as usual.

An opamp would tolerate several volts of difference in battery voltage without any significant change in DC offset. Only when one battery goes really dead, below 1-2V or so, you'll get a lot of DC - goodbye headphones...
So during normal operation, some imbalance will be no problem at all, but when (and probably not if) something goes wrong it may go very wrong.