IGC PSU problem:

[GrahamnDodder]

I have the PSU built, as well as both channels of the amp, and I fired up the PSU for the first time tonight. First time I ever plugged a DIY project into a wall socket:

Good news: I am still alive.
Bad news: Not getting the right V++ and V-- readings from the bridge (which are discrete '860's)

My transformer is 300 VA Avel, 25v, dual secondaries. My bridge output readings from V+, G and V- are as follows:

V+ to VG: +37v DC (so far so good.)
V- to VG: +37v DC (this should be -37v, right?)
V+ to V-: About 1 volt difference, which is telling me they are equal (within tolerances, I presume.)

I have the primaries hooked up in parallel (115 VAC "live" goes to the 115 VAC inputs, neutral goes to the 0 VAC inputs)

I have the secondaries in series as:

** 0 VAC (1st secondary) goes to the ac input on the "bottom" bridge.

** 25 VAC (1st secondary) ties to the 0 VAC of the other secondary and the node that connects to two bridges (top ac input of the bottom bridge with bottom ac input of the top bridge)

** 25 VAC of the second secondary goes to the "top" AC input of the top bridge.

At least nothing blew up, and my fuse didn't blow, so I got that going for me, which is nice.

Can anyone tell where I screwed up from my description?

Many thanks,

GnD

 

[hacknet]

try putting ur -v tap to ground and let the other wire from that secondary winding be the -v....

 

[AudioFreak]

Sounds like you need to invert the ouputs on the lower bridge.

 

[GrahamnDodder]

Audio-

Do you mean swap them?

GnD

 

[AudioFreak]

Yes, swap the outputs on the lower bridge.

 

[GrahamnDodder]

Not to sound dumb, but I don't wanna screw up an AC power module.

I want to make sure what, exactly, it is that you mean.

Is it to swap the DC outputs coming off of the lower bridge, i.e., what was my lower bridge ground now becomes v- and what was my lower bridge v- becomes gnd, which would also now be connected to the upper bridge output gnd?

This doesn't seem to match the PSU circuit I have seen, but heck, I have obviously screwed up somewhere, so who am I to judge!

Thanks,

GnD

 

[GrahamnDodder]

I think I understand now.

A) My PSU circuit .gif, which I pulled from somewhere on DIYAudio chip amp's forum, was wrong.

B) I looked at the ThorAmp PSU circuit, which now makes sense. The DC output of the bottom bridge feeds into the DC Gnd of the upper bridge, setting up a voltage divider, assuming the amp's power ground comes from this junction, too.

Right?

 

[AudioFreak]

Is it to swap the DC outputs coming off of the lower bridge, i.e., what was my lower bridge ground now becomes v- and what was my lower bridge v- becomes gnd, which would also now be connected to the upper bridge output gnd?

Exactly.

 

[GrahamnDodder]

WooHoo! It works!

I have to find out where I pulled up the screwed-up PSU circuit from on DIYAudio. It had the bridge AC inputs in series, and the DC outputs in parallel. That never made any sense to me, but I chalked it up to my noob status.

I used Thor's PSU circuit as a doublecheck after your advice, which has each AC secondary running each bridge, which are hooked up in series, which gives me a nice DC voltage divider, and makes perfect sense. Even to me.

And you are telling me this realtime from Australia, no less. This board is so effin' cool.

I'd buy you a Foster's, but it'd be warm by the time it got there. Instead, as a thank you, if you ever travel to the USA, you've got a free guest room in which to crash only 20 mins from Washington DC.

How's that?

Now, on to the amp stage testing. But that is for another night.

Thanks again,

GnD