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Post by Deleted on Aug 13, 2013 4:01:53 GMT -6
I know there is a specific thread for this on the GroupDiy forum, but I am having trouble getting through to somebody who can help me. I totally appreciate that Mike at Hairball sells his kits without support and that it is very gracious of him to spend the amount of time he does on that forum helping people out but, at the moment, it seems as though he is the lone voice dealing with a lot of questions!
I am posting here with the hope of hooking up with some kind soul who might be able to help me trouble shoot a MNATS/HAIRBALL 1176 REV D. I have spent a lot of time reading the above thread (and others) and trying to deduce my problem but I have reached a brick wall. I am willing to buy a lot of beer! I will post a summary of the problem/solution in the groupdiy thread to help others.
A little background: I have successfully built in the past: CAPI VP26, CAPI LC53A, DRIP PULTEC EQP 1A. These units worked first time. I am methodical and solder well. My electronics theory is very basic, I have an "elementary" understanding of the schematic. The unit passes clean audio and is compressing. It is "calibrated" but has an issue which I can elaborate further.
many best wishes,
Pace
(hope this thread is appropriate tonycamphd and Johnkenn, please delete if not!)
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Post by Gustav on Aug 13, 2013 5:59:54 GMT -6
Someone might be able to help you if you post the problem/link to a post on groupdiy describing your problem. Located in Spain? I need Help - I have a list of people willing to help with DIY stuff (at a price) on my site. Still need to fill a lot of holes on the list, but you might find someone suitable. Gustav |
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Post by Deleted on Aug 13, 2013 7:26:55 GMT -6
Gustav, thanks so much for getting back to me. Yes, I am located in Soller, Mallorca. My problem is outlined in post #3920 here: www.groupdiy.com/index.php?topic=20058.3920I post as fluxofpinkindians. Mike has been so kind to help, but as I said, I am getting lost amongst the noise and I don't want to further burden him with potential newb errors. I will, of course, supply and solution to the thread for others. best wishes David / Pace / Fluxofpinkindians! |
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Post by tonycamphd on Aug 13, 2013 15:33:30 GMT -6
Hi Pace, sorry your having issues, if you've shot all those suggested possibilities down, a simple and surprisingly effective thing I've done in the past is...
go through, and reflow all your solder connections! I know it seems silly, but i've had 3 or so different undetectable issues solved like this in my DIY life?? ya never know? let us know how you make out.
T
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Post by paulhunt on Aug 14, 2013 1:05:13 GMT -6
I get a good magnifying glass and check all solder joins for little bridges or blobs that might be causing a short, especially when the PCB is a bit crowded. I do that after cleaning the board with isopropyl alcohol.
I also check/measure twice, solder once!
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Post by Deleted on Aug 14, 2013 2:38:38 GMT -6
Thanks for the input guys. The weird thing is, I am getting correct voltages as per the schematic. The unit is passing audio and is compressing - just too much! All resistors and transistors were checked before installation, I have checked for bridges etc... and re checked the wiring many times! I am at a loss as to what to do next bar desoldering everything and starting again!
I wonder if I have a faulty t-pad / input transformer.
It would be a great help if someone with a functioning 1176 rev d could do a couple of voltage checks for me for comparison? Specifically, with 0.775VAC applied at input (between xlr pins 2 and 3) what voltages do you get at the input and output of the input transformer with the input control fully CW and fully CCW ?
all the best,
David
p.s see post 1 for a link to a detailed description of the problem
Would love to change the title of this thread as it is a little histrionic, but I am going crazy here!
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Post by svart on Aug 14, 2013 7:31:33 GMT -6
Are you taking out that resistor that you are supposed to remove for calibration?
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Post by sll on Aug 14, 2013 7:37:58 GMT -6
I have not read through the Group DIY thread, nor will I. Forgive me if this has been addressed. You could have a bad FET. Are you able to change the amount of compression at all, or does it just sit at one level?
Additionally, you could have contamination from solder flux around the FET. That area and part of the circuit is of very high impedance. Any flux or foreign material can drain voltage away from the FET causing weird symptoms.
I don't have the Hairball kit, but I've built many 1176 style compressors of my own.
It's also very easy to overlook a wrong value resistor many times. For instance, my 1176 used 4K75, and 47K5 resistors all over. It was very easy to mix those up and think they were right at a glance.
Keep us posted on your findings. Hopefully one of us can steer you in the right direction.
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Post by Deleted on Aug 14, 2013 11:45:33 GMT -6
Are you taking out that resistor that you are supposed to remove for calibration? I am but thanks for thinking of me! I have not read through the Group DIY thread, nor will I. Forgive me if this has been addressed. You could have a bad FET. Are you able to change the amount of compression at all, or does it just sit at one level? Additionally, you could have contamination from solder flux around the FET. That area and part of the circuit is of very high impedance. Any flux or foreign material can drain voltage away from the FET causing weird symptoms. I don't have the Hairball kit, but I've built many 1176 style compressors of my own. It's also very easy to overlook a wrong value resistor many times. For instance, my 1176 used 4K75, and 47K5 resistors all over. It was very easy to mix those up and think they were right at a glance. Keep us posted on your findings. Hopefully one of us can steer you in the right direction. I am able to change the amount of compression but not by very much as the input attenuator only attenuates by about 6db. In a nutshell, my problem is: In +4VU mode, IN BYPASS, If I apply 0.775VAC to the input, to get 0.775VAC at the output, I need to fully rotate the input CCW (full attenuation) and rotate the OUTPUT CCW to -50 (huge attenuation). It is as though the signal preamp is amplifying too much or the t-pad / input transformer is not functioning correctly. This means that I always have lots of level 'going in to the compressor'. Even with the Input fully CCW I always am compressing too much (tracks recorded at -18dbfs rms / -10dbfs max) |
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Post by svart on Aug 14, 2013 11:49:59 GMT -6
Sounds like you have a stage that has too much gain or the input transformer is connected incorrectly. I'd second that maybe you have a wrong value resistor around one of the gain stages, maybe the input stage. I seem to remember having a similar problem with one of my builds and it being a resistor value issue or something like that.
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Post by Deleted on Aug 14, 2013 11:56:16 GMT -6
Sounds like you have a stage that has too much gain or the input transformer is connected incorrectly. I'd second that maybe you have a wrong value resistor around one of the gain stages, maybe the input stage. I seem to remember having a similar problem with one of my builds and it being a resistor value issue or something like that. Thanks svart. I was editing my post whilst you replied! I'm almost certain that I wired the input transformer correctly with the dot aligned to the correct pad. However, I got the polarity of the wiring from the output of the input transformer wrong and had to re-solder. When desoldering part of the pad of the output of the input tranny pcb came off but enough remained to solder. The unit passed audio so I assumed that it was making a good connectiion. I will check for continuity. I will check the resistors around the signal preamp. David |
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