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honkyjonk
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Check out this ribbon

Post by honkyjonk » Tue Jan 08, 2008 11:16 am

http://img156.imageshack.us/my.php?image=ribbonac9.jpg

This is an Apex 210.

What the hell happened? I was using it to record a bass being played through a guitar amp, so the volume was not very loud, and it was about 1.5 to 2 feet back off the grill. Awesome sound one day. The next I start recording with the exact same settings and immediately I hear distortion.

Does this look like a ribbon that has had phantom applied?
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Post by Randy » Tue Jan 08, 2008 11:23 am

If that black stuff is carbon, it sure looks like it was fried somehow. I have seen ribbons that got stretched and ones that were just broken from a blow, none of them were damaged like that. They just were less corrugated or simply bent and up against one of the magnets.

Depending on the transformer in the mic (i figure a 1:10 ratio?), a 48v spike from the phantom power could be stepped up to 480v, right? That would be enough to melt metal a couple microns thick.
not to worry, just keep tracking....

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Post by honkyjonk » Tue Jan 08, 2008 11:58 am

Thanks Randy.

This is pretty much what I thought. So this leads to a couple more questions I have.

The first: Is there any hope for this mic at all? I imagine not. It's cheap enough that I'm definitely not paying for a re-ribbon job. Maybe if there was some source for this ribbon I could do it myself, but who knows. The material that's covering the
(magnet?) on either side of the ribbon is pulling up, and yeah, some sort of carbon or charred something underneath, or it could just be particles that have attatched themselves to the magnet.

The second. THis is the scary one. Is there a possibility that my seventh circle preamp is kicking phantom power up the cable when no phantom is applied? And also kicking WAY too much phantom power when it is applied?

The reason I ask this is that I had 2 brand new AT 4047's take a crap. Remember the "help! my 4047's are popping thread?" Anyway, AT had to replace the capsule in both of them. Very wierd. They didn't know why the capsules were popping, couldn't figure it out. Didn't make sense that it would happen to both mics. So they replaced the capsules on both of them, and sent them back. Well, they've worked fine until just the other day one of them started emitting a really distorted ocean sound.

This has me freaked and a little pissed off. All these instances have occured when using my Seventh Circle preamps. It was an N72 the first time, and an A12 w/ the ribbon and the last 4047.

Ideas? Just coincidence? What could be frying my mics? Damn.
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Post by Randy » Tue Jan 08, 2008 12:19 pm

Since the SC preamp is a common factor in the blown mics, I'd start my troubleshooting there. If you have a multimeter, you could turn the unit on (no mic attached) and check for DC current with the phantom power off, then on. You might also want to check to see if there is any AC coming through.

I'd make sure the unit is running to spec before hooking anything up to it again.

If there is nothing wrong with the unit, it could be a short or an intermittent connection in one of your mic cables. When phantom power is going through a cable with a broken wire that closes and opens the circuit, the phantom power circuit could be sending some large spikes through to the mic. Phantom power is usually not a problem for ribbon mics unless there is a huge difference in current on either side of the ribbon. If one side cuts out, all of a sudden the electrons on one magnet want to jump across to the other magnet, and they do it through the ribbon, frying it.
not to worry, just keep tracking....

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Post by honkyjonk » Tue Jan 08, 2008 12:33 pm

I'm pretty sure I can rule out the cables as they were different in every case. The latest AT instance was with a cable I just made recently making it too young for the first AT incident. And the ribbon has it's own cable that's attatched to it.

Anyway, yeah, I'll definitely apply a multimeter to the outputs of the SC. I did this once before and found the 48V to be pretty consistent across all the channels. But I didn't check for AC and I didn't check when phantom was off.

Thanks Randy.
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Post by SeventhCircle » Tue Jan 08, 2008 2:15 pm

it could be a short or an intermittent connection in one of your mic cables
Or it could be an intermittent solder joint at one of the 6K65 resistors in the phantom circuit or a miswired input transformer. You should measure 0V between pins 2 and 3 no matter what, even (especially) when phantom is turned on. Clip your voltmeter leads across the pins and flip the phantom switch and also cycle power on the whole chassis. If you see a voltage difference between the pins in any situation, there's a problem.

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Post by UnlikeKurt » Tue Jan 08, 2008 2:18 pm

Just sliding in a curiosity question here on the same general topic.

Even with phantom off, my sytek measures something like 2v dc across all 4 channels. And I have another preamp in the rack that I have taken measurements of up to 40v with phantom off, yet it doesn't power any mics until you engage the switch. Lastly, again with the sytek, after disengaging phantom it takes a heck of a while as it slowly ramps down whereas other preamps I have immediately go from a reading of say 46v to 0.

I'm just looking for general knowledge type info here i guess.
Thanks

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Post by SeventhCircle » Tue Jan 08, 2008 2:59 pm

Even with phantom off, my sytek measures something like 2v dc across all 4 channels.
How exactly are you making this measurement? It could be the Sytek doesn't pull the phantom voltage all the way to 0V, which isn't necessarily a problem, or there's a 2V difference between pin 1 and your measurement ground. That 2V difference could also disappear if you measured across a realistic load instead of an open circuit.

A similar situation could exist with the "40V with phantom off" unit. Try making the measurement with a load connected. It's also possible that they're switching the phantom on the "low side", opening the DC path between pin 1 and the supply ground to turn phantom off.

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Post by RodC » Tue Jan 08, 2008 4:03 pm

I wonder if there are filter caps in the phantom supply that were not drained, you plugged in the mic and zap. You would think that if this was the case they would be on the other side of the switch.

I cant make out the pic very well, but is the motor damaged on each side as well as the ribbon? If so, I would think that would take a lot of amps, something that a phantom supply dont have. I dont think it would even give you enough juice do do this through the transformer??
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Post by UnlikeKurt » Tue Jan 08, 2008 4:58 pm

Multimeter. XLR cable. Pin 2 + Pin 3

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Post by SeventhCircle » Tue Jan 08, 2008 5:02 pm

I wonder if there are filter caps in the phantom supply that were not drained
If you turn phantom off at the module, the supply side of the phantom power resistors is held at ground and the local filter caps discharge in a few seconds. If you leave phantom turned on at the module and switch the supply off, the +48V does take several minutes to bleed off with no load. Even so, hot plugging a mic, even a ribbon mic, won't do damage like that unless pin 2 or pin 3 is inadvertently grounded. There's no way for substantial differential current to flow otherwise.
Last edited by SeventhCircle on Tue Jan 08, 2008 5:13 pm, edited 1 time in total.

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Post by SeventhCircle » Tue Jan 08, 2008 5:04 pm

Multimeter. XLR cable. Pin 2 + Pin 3
Yes, but where is the black probe? Pin 1, the chassis, or somewhere else? If you're measuring 40V across pins 2 and 3 you've got big problems.

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Post by honkyjonk » Wed Jan 09, 2008 10:01 am

Okay guys,

I took some measurements and this is what I got.
These measurements are true with all 4 channels of the SC, and with 2 different cables. I used a Fluke multimeter, with the setting at "200" unless otherwise noted. This setting yields the 48.0 V in the appropriate decimal spot.

Black probe on 1 and red on 2:
DC-Fluctuates between 47.9 and 48V.
AC-Eventually it is 0V, but switching the phantom either on OR off results in a quick spike of up to 28V! (Is this normal?)

Cycling the main power has no effect other than the effect of the phantom also being cycled (if it is on) as described above.

Black and Red probes between 2 and 3:
DC- I'm getting -0.00. When I switch the Fluke to the "20" setting, the reading jumps as high as +.07 when the main power is cycled. This voltage reading is pretty low (considering the "20" setting), but not zero.

AC- 0.00V on "200" setting no matter what I do. It does have a consistent reading of .02 when the meter is set to "20" but I'm guessing that this reflects the amount that the Fluke is out of bias in AC mode.

Anyway, the reading I'm wondering about is the jump in the AC voltage measured between pins 1 and 2. ????

(BTW, just to be clear, with all these measurements, there was never a mic attached to the cable)
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Post by SeventhCircle » Wed Jan 09, 2008 12:05 pm

AC-Eventually it is 0V, but switching the phantom either on OR off results in a quick spike of up to 28V! (Is this normal?)
Yes. The "spike" is the transition from 0V to +48V (or vice versa) which takes about 30 milliseconds. Since the meter is set to measure AC volts, it shows the fast transition as a slowly changing voltage averaged over time.
Black probe on 1 and red on 2:
Do you get the same results with the black probe on 1 and the red on 3? I suspect you will, but it's good to be thorough.
(BTW, just to be clear, with all these measurements, there was never a mic attached to the cable)
Your measurements look OK to me, but you might want to test with a load as well. Get a spare male XLR plug and tack a 3K resistor between pin 2 and pin 1 and between pin 3 and pin 1. For the most accurate measurements, use 1% parts or hand match a pair. The 3K value isn't critical, just find a pair somewhere in the ballpark.

When phantom is on, each resistor will draw about 5mA out of the module. If you have mismatched resistors, bad solder joints, a miswired input transformer, or some other problem on the module, you'll see it as a difference in voltage between pins 2 and 3. Some small voltage difference is normal since the matching is never perfect, but a few millivolts is nothing to worry about.

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Post by nclayton » Thu Jan 10, 2008 10:21 am

Wow, that's mysterious.
Randy wrote: Depending on the transformer in the mic (i figure a 1:10 ratio?), a 48v spike from the phantom power could be stepped up to 480v, right? That would be enough to melt metal a couple microns thick.
except that going from the phantom side to the ribbon side you get a step down so that (if 1:10) you'd actually have a 4.8 volt spike at about 34 ohms impedance (2 6.8k resistors in parallel /100 because of the transformer), so you'd get at most a little over 140mA through the ribbon. Plenty to whip the ribbon around, but not anywhere near enough to cause damage to the magnets. Had you ever opened this ribbon up before now? That looks almost like physical damage, it's so locallized.

I'd suggest using an ohmeter to see if there's a short from the primary to the secondary of the microphone's transformer. I'll bet there is.

Ned
Last edited by nclayton on Thu Jan 10, 2008 10:29 am, edited 1 time in total.

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