Going through a phase...

[LewKellogg]

OK, I have completed my first two C84s and N72s. I am just beginning to really listen to them and so far I am impressed. I like the character or lack there of both units. I have only done a quick guitar piece with a couple of AT4041s so it is not a through test by any means.

One observation is that the C84s seem to be out of phase with the N72s. Anyone else having this issue? I used the same cables and microphones, recording the same material, one mic with a C84 and one mic with an N72, with the mics so close together that they were almost touching. An N72 with a C84 was out of phase. The N72s together or the C84s together were in phase…

[kudos]

Did you flip the phase switch on one of the pre amps to see if they go back into phase? I have built 18 of these pre amps and never had an issue like that before. I have put them in all combinations also.

[LewKellogg]

I did flip the phase switch and they did go back into phase. What ever I did to come up with this combination was consistent. All combinations are out with each other - If you understand what I mean.

Actually doesn't cause an issue because I listen and watch for phase carefully anyway... I just keep two of them flipped and all is well.

[tele_player]

Tim should comment on this - maybe the wiring on the N72 transformers is incorrect?

[LewKellogg]

It isn't a big deal - I was just curioous in case it was a known thing. Like I said, I just keep the switch flipped...

[tpryan]

I just had a chance to verify this on the bench, and the C84 does invert phase if built as described. This is pretty annoying, since it's on my list of problems with the first proto and I thought I had it corrected. An easy workaround is to cross over L1 and L2, one on top and one on the bottom of the board. This will be corrected in the next revision.

[ohoen]

Quite a few of the resistor band colors listed in the bill of materials don't match the actual resistors. Not a big deal but it probably added 20 minutes to my build. I'll note which ones are off when I build the second one. I don't decode based on the bands so I don't know if the BOM is off or if the resistors are misprinted.

So, Rev. 1.3 needs to have L1 and L2 crossed, correct?
Thanks,
Oliver.

[tpryan]

Are you looking at the on-line BOM? The printed BOM packed with the PCB may be out of date.

[ohoen]

I wasn't but I am on the second one. Orange-Orange-Gold-Gold gives me 5.5ohms when it should be 3.3 according to the online BOM.

I have what looks like Violet-Black-Gold-Gold but might be Brown-Black-Gold-Gold (That's all I can find that's likely to be R5) which gives me 3.3ohms when, I guess, it should be 1. I may be overlooking something obvious but I've gone through everything several times.

Any ideas on what I might have got wrong?
Thanks Tim,
Oliver.

[tpryan]

What does your meter read when you short the probes together? I'm guessing about 2.2 ohms.

[ohoen]

oo, more like 7. DOH! I just checked with another meter and things are as they should be. Whoops, thanks Tim.

[LewKellogg]

So I wasn't dreaming!!! I'll cross over and make them the same. Thanks aain!

By the way - these things still sound awesome

[Ken Schumacher]

Tim,

Has the c84 phase correction been made to the kits yet? If so what revision number does it have? I will be doing a multi-channel recording TOMORROW and would like to have everything in phase. It will be a live recording on location so will be difficult to test on site. I bought my C84 kits about a month ago.

Ken

[tpryan]

This is corrected on rev 1.4.

[Ken Schumacher]

The C84 schematics for the kits I built was 1.3, so I am guessing the phase is reversed. The existing zero ohm resistors have been trimmed and can't be crossed. I assume I can just solder in crossed insulated jumper cables to make the phase right, and don't have to use zero ohm resistors. Correct? I would like the phase switch to report the correct setting. BTW, tonight I use the mic pres for the first time. Recording a jazz band on location, 24 tracks, two of which will use C84s. I'll make sure the phase switch is reversed for this gig.