The No.1 Website for Pro Audio
RME FireFace 800 Preamp Distortion
Old 10th August 2013
  #1
Gear Maniac
 
🎧 10 years
RME FireFace 800 Preamp Distortion

Hi All,

One of the preamps on my Fireface 800 has failed. It's making a loud, low-level noise. Before I send it off to get it fixed, I was curious if anyone else has had this issue and knows of a solution. It's wishful thinking on my part, but perhaps this is a simple fix that I can do myself.

I've attached a recording of the noise it's making. Be careful playing it back.

Thanks!
Attached Files

Untitled_3#01.wav (1.86 MB, 1984 views)

Old 10th August 2013
  #2
Lives for gear
 
Lotus 7's Avatar
Whew! Negative 10 mS pulses every 100 mS or so with a lot of higher frequency random noise superimposed.

A few DC voltage measurements would help, but some guesses might be a defective op amp, shorted or leaky input coupling cap, a shorted input clamp diode on one of the inputs, open bypass cap, or a open circuit ground or even a leaky output coupling cap. The mic pre sounds like it's "motorboating" (oscillating at a low frequency) and that's what the waveform looks like. Since you have other channels that are presumably working correctly, if you have a simple DC voltmeter you could compare comparable circuit points, like the op amp output terminal, each power supply pin, and the voltages on each side of the input coupling caps. I'd first check the clamp diodes (there are probably four of them) and the coupling caps. If a clamp diode shorts, it will couple one side of the high-gain mic input to a power supply rail and you will hear any power supply noise at the mic pre output.

Does switching phantom power on/off make any difference?

Is the noise constant, or does it change with the gain setting of the mic pre?

If you connect a mic to that channel do you hear the mic signal, and if so, does the channel seem to have the same gain as the good channels?

If you short the input (plug in a mic cable with a bare jumper wire connecting pins 2 & 3 at the female XLR connector) does the noise go away or change?

Without a schematic and a few voltage measurements the above are just guesses. It could be anything.
Old 10th August 2013 | Show parent
  #3
Gear Maniac
 
🎧 10 years
Thank you!

Quote:
Originally Posted by Lotus 7 ➑️
Does switching phantom power on/off make any difference?
No difference.

Quote:
Originally Posted by Lotus 7 ➑️
Is the noise constant, or does it change with the gain setting of the mic pre?
The noise level changes with the gain setting.

Quote:
Originally Posted by Lotus 7 ➑️
If you connect a mic to that channel do you hear the mic signal, and if so, does the channel seem to have the same gain as the good channels?
Yes and yes.

Quote:
Originally Posted by Lotus 7 ➑️
If you short the input (plug in a mic cable with a bare jumper wire connecting pins 2 & 3 at the female XLR connector) does the noise go away or change?
The noise becomes significantly louder when any combination of pins are shorted together.

Quote:
Originally Posted by Lotus 7 ➑️
Whew! Negative 10 mS pulses every 100 mS or so with a lot of higher frequency random noise superimposed.

A few DC voltage measurements would help, but some guesses might be a defective op amp, shorted or leaky input coupling cap, a shorted input clamp diode on one of the inputs, open bypass cap, or a open circuit ground or even a leaky output coupling cap. The mic pre sounds like it's "motorboating" (oscillating at a low frequency) and that's what the waveform looks like. Since you have other channels that are presumably working correctly, if you have a simple DC voltmeter you could compare comparable circuit points, like the op amp output terminal, each power supply pin, and the voltages on each side of the input coupling caps. I'd first check the clamp diodes (there are probably four of them) and the coupling caps. If a clamp diode shorts, it will couple one side of the high-gain mic input to a power supply rail and you will hear any power supply noise at the mic pre output.
The solder points are all on the bottom of the board, and getting to them would require completely disassembling the unit. You've been incredibly helpful but I'm thinking this is beyond my ability to fix. Unfortunately I'm recording a festival this week and I have no choice but to use the Fireface. I guess I'll just have to do without one preamp for a few days.

Thank you!
Old 10th August 2013
  #4
Lives for gear
 
Lotus 7's Avatar
No difference with PP on or off indicates it's probably not a bad input coupling cap.

Noise changing with gain setting and having a signal that's about the same level as the good channels means the op amp is at least functioning. It may still be the problem, or it may be something like a cold solder joint on a ground connection causing the noise and "motorboating".

Since the other channels are functioning properly, it's not a power supply problem.

If the noise is coming from the input stages of the op amp, It should not increase significantly with the balanced inputs shorted (pins 2 & 3). It should actually be reduced with the inputs shorted. It could be one of the clamp diodes. Those are a network of diodes that are connected from the amp inputs to the + & - power supply rails to prevent overvoltage surges from damaging the op amp inputs when phantom power is turned on or off, or a mic is plugged in when PP is already on, as the input coupling caps charge/discharge.

It still could be a shorted or leaky output coupling cap.

Its going to take someone with a schematic, meter and possible a scope to pinpoint the problem, so sending it to a qualified tech is probably the way to go.

Sorry it's not an obvious component.
Old 10th August 2013
  #5
Gear Maniac
 
🎧 10 years
Thanks for your help!
Old 22nd August 2013
  #6
Here for the gear
 
🎧 5 years
This has happened to 3 of the preamps on the front of my fireface. Probably something to do with phantom power, i am unsure... Mine was out of warranty when it happened and ive needed my fireface constantly since, so ive had no time to send off for repairs. Bums me out that such a respected company/product has such a huge flaw that seems to be so common.
Old 22nd August 2013
  #7
Gear Maniac
 
🎧 10 years
Yikes. Sorry to hear about that. I had no idea this was a common issue.

I just finished recording a festival, and I have a few weeks until my next project, so I'll be sending mine off any day now. I'll let you know how much it costs to fix it.
Old 22nd August 2013 | Show parent
  #8
Lives for gear
 
Lotus 7's Avatar
Quote:
Originally Posted by JustAnotherUser ➑️
Yikes. Sorry to hear about that. I had no idea this was a common issue.

I just finished recording a festival, and I have a few weeks until my next project, so I'll be sending mine off any day now. I'll let you know how much it costs to fix it.
Although RME may be reluctant to tell you exactly what the problem is/was, if you can, please try to get that info from them. It's a "strange" sort of fault. I'm still leaning toward the phantom power clamp diodes, but who knows?

There have been other well known mic pres with clamp diode issues including some [quite costly] Millennias. Their early mic pres had a problem with "hot" connects/dis-connects and the manual said not to do it because the protection diodes were chosen for sound quality and were not capable of withstanding hot patching mics with the phantom on. Apparently. hot swapping mics or patching the mic inputs through a TRS or Bantam patch panel would also "blow" the diodes.
Old 5th September 2013
  #9
Gear Maniac
 
🎧 10 years
Welp, I couldn't get them to tell me anything beyond "circuit repair." I might get an itemized receipt when it comes back, but for now, all I know is $200 for "shipping, parts, labor, and insurance." Shipping to get it there was about $60 for UPS ground, I'm assuming their return shipping cost is about the same, so $140 for the actual repair. It took them about 2 days to turn it around. Sorry I couldn't be more helpful.
Old 5th September 2013
  #10
Lives for gear
 
Lotus 7's Avatar
Glad they were able to fix it relatively quickly.

Yes, not relating details of any component failure seems to be the norm for most manufacturers these days. I suspect that with our world of instant communications, if 4 customers out of 1000 have the same problem, they will be accused of having a chronic defect and the other 996 customers will be demanding a recall and "fix" for the "problem", even if their gear is working perfectly.

At least they were able to repair it at a component level.

Some manufacturers, especially auto makers will only make repairs at the replacement circuit board level. I've heard of BMW owners being quoted $900 parts plus $250 labor for replacement of burned out dashboard LEDs on late model BMW's because they require a swap of the whole dashboard display printed circuit board.
Old 17th January 2014
  #11
Here for the gear
 
🎧 5 years
Sorry for the bump, (i dont check here often) this actually happened to a friend of mine recently too! also, where did you ship the fireface to and from? was it to germany or something like that? cheers

also Lotus 7, when i asked about repairing long ago, they quoted me for a new board. was like $800 or something. not sure why Justanotheruser got a different response
Old 18th January 2014
  #12
Gear Maniac
 
🎧 10 years
I contacted RME's US distributor, Synthax, who told me to send it to:

Doc’s Radio & TV
6607 Market St
Youngstown OH 44512
Old 15th May 2017
  #13
Here for the gear
 
🎧 5 years
I realize this is an older thread but I figured I would post in case anyone has the same issue. The problem is a preamp circuit. I'm sending mine in for the third time.
This time it is channels 9 & 10. The first one went just a month past the 12 month warrenty.
πŸ“ Reply
Topic:
Post Reply

Welcome to the Gearspace Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…

Forum Jump
Forum Jump