A couple of general C84 questions...

[wertt]

1) what's the expected noise floor on the C84 like? when i turn mine up to the higher gain stages (8 up, say), i start to get some white noise-ish stuff (and one channel has a small amount of ground hum that i've yet to diagnose), even with no mic plugged in. this worried me at first, until i discovered that...

2) these things have a huge amount of gain. i was running a mic through a splitter to compare it with my vintech 1272 (i know...apples and oranges) and the C84 on 5 is about equal with the vintech maxed out. certainly not a complaint...i'm just curious if this has been anyone else's experience.

3) the studio where i sometimes works on the side has an 8 channel millenia pre. we've blown out a channel or 2 on it by hot-plugging mics and apparently millenia recommends that you power the unit down completely before plugging or unplugging a mic in. i'm fairly certain it's due to running mic lines through a tt bay and making a nasty loop with the phantom that the transformerless pre can't handle, but who knows. has anybody had any trouble with this and the C84?

4) also, in step 38 (testing the junction of r8 and r9) i'm measuring 11.7V on both of my channels instead of 13-14 as i should be seeing. is this indicative of a problem somewhere? i'm assuming since it's the same on both that it would be a weird coincidence to make the same mistake twice and i'm ok.


i just finished putting the chassis together and will be using these on a session sunday. so far they sound great and i'm very pleased. i can't imagine the noise i'm hearing is going to be an issue as it would take a really quiet instrument (or mic) to require that kind of level, i was just curious if anyone else has had this experience or if i've got something messed up. thanks!

[wertt]

anybody?

[tpryan]

even with no mic plugged in

The only meaningful way to test noise is with the inputs properly terminated. See this thread: http://seventhcirclestudios.com/SCA/php ... light=#707

these things have a huge amount of gain

If they're built correctly they'll have the amount of gain we claim they have. If you suspect there's a problem, try measuring with a signal generator and meter.

millenia recommends that you power the unit down completely before plugging or unplugging a mic in.

That shouldn't be necessary, but it's certainly a good idea to make sure phantom is off before plugging or unplugging a mic. The C84 has diode clamps to prevent over- and undervoltage on the inputs as well as current limiting components to protect the input transistors. You'll have to try hard to blow it up, but I'm sure it can be done with enough persistence.

in step 38 (testing the junction of r8 and r9) i'm measuring 11.7V

Just make absolutely sure that R25 and R28 are 1K58 and not 1K.

[wertt]

thanks for the response. i did some classical recording this weekend and the pres sounded great and were on for a solid 5 hours with a hiccup. looking forward to getting a couple of more.

[tpryan]

were on for a solid 5 hours with a hiccup

I hope you mean "without a hiccup".

[wertt]

whoops...i certainly do.