Quantcast
Left Side of Bus EQ Dropped 6dB - Gearspace.com
The No.1 Website for Pro Audio
Left Side of Bus EQ Dropped 6dB
Old 23rd January 2013
  #1
Lives for gear
 
BillSimpkins's Avatar
 
1 Review written
🎧 5 years
Left Side of Bus EQ Dropped 6dB

I use a pair of racked ADM 1541 EQ's with UTC OP Amps strapped across the 2 bus in front of a GSSL Comp and one side dropped down about 6dB last night. I double checked the signal path/cabling etc... to verify that it was the EQ. Also hooked up a meter directly on each end to verify this.

I need this fixed ASAP as I am running a business and have mix projects but the nearest tech I trust is about 100 miles away and probably can't get it done for a few days. I live about 100 north of Seattle.

A few questions:
1. Anyone have any idea what the problem may be?
2. I have a little bit of soldering experience. I also have a degree in physics which I studied some electronic theory and took a few labs. Is this something I could troubleshoot PROPERLY? I've fixed bad solders before, just never troubleshooted (I know that is kind of a silly question, but hey! I'm in a pinch here).
3. Anyone know any techs around or north of Seattle that could travel to my studio (I have some other things that need to be looked at)?

Thanks Folks!
Old 23rd January 2013
  #2
Lives for gear
 
Ike Zimbel's Avatar
 
🎧 10 years
Hi Bill,
A 6db drop is almost always a sign that you have lost one side of a balanced output.
I know a guy in Vancouver BC that might be closer to you...he's certainly closer than me!.
Best,
Ike
Old 23rd January 2013
  #3
Lives for gear
 
BillSimpkins's Avatar
 
1 Review written
🎧 5 years
Thanks Ike! Would you mind messaging me that number?
Old 24th January 2013
  #4
Lives for gear
 
Ike Zimbel's Avatar
 
🎧 10 years
Stand by, let me check with the guy 1st.
Best,
Ike
Old 24th January 2013
  #5
Lives for gear
 
Ike Zimbel's Avatar
 
🎧 10 years
Hi Bill,
This didn't pan out. Back to trouble shooting...as I mentioned in an earlier post, the most likely cause of a 6db drop is losing one leg of the balanced signal. I should have said that it can be either an input or an output. So, you should look at the connections, both input and output on your Eq and look for broken solder connections. A picture would be helpful for any further input.
Best,
Ike
Old 24th January 2013
  #6
Lives for gear
 
brianroth's Avatar
 
🎧 15 years
I am quite familiar with the ADM 1540, but have no idea what differences there might be between that and the 1541....and have no 1541 schematics to look at.

The 1540 had optional input and/or output transformers. Otherwise, the in or out is unbalanced. If transformers are used in the 1541, then an "open" of one input or output lead ("hot" or "cold") would cause a FAR greater problem than a -6 dB loss.

Perhaps the 1541 used transformerless in/out circuitry? In that case I could see a -6 dB loss if an input or output leg was open circuit.

Is the 6 dB loss there regardless of whether the EQ switch is in or out? On a 1540, the EQ switch drops out all circuitry besides the input buffer amp and the output line driver.

Bri

PS, I am unsure what "...UTC OP Amps...." mentioned in the original post is referring to. In the 1540, the optional input transformer was a UTC O-8 "Ouncer".
Old 24th January 2013
  #7
Lives for gear
 
BillSimpkins's Avatar
 
1 Review written
🎧 5 years
Thanks Brian! Yeah, it occurs with or without the EQ switch.

Update: I pulled it out of the rack to inspect the solders, looked fine, then put it back in and now the difference is only 0.59 dB (still need to take care of this). Must be a something loose.

I did some frequency analysis and there appears to be no signal degradation on the left side except for the level.
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