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Drip Opto7 LA2A hum
Drip Opto7 LA2A hum
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Old 12th June 2019, 05:47 PM   #1
Jclay85 is offline Jclay85  United States
diyAudio Member
Join Date: May 2012
Default Drip Opto7 LA2A hum

Hi All,
I've been working hard to try and get my Drip Opto 7 (stereo LA2A clone) up and running. Its working for the most part, but I have 4 issues that I would surely appreciate any help with!

1. Hum
Sounds maybe like ground loop hum? Its lower in pitch, like if you grab a guitar cable that's coming from an amp. I hear it even when the gain is all the way down. The volume of the hum doesn't change. Powering the unit off makes the noise disappear. Its not super loud, but definitely noticeable. HAVE TRIED: disconnecting pin 1 of both the XLR outputs. Am I missing something here?

2. Bypass switch not working
I may not have this hooked up right - there isn't much documentation from drip regarding hooking up the bypass. Other than directing that at least one of the GND pads needs to be grounded. I grounded 2.

3. LED lamps
My LED's in my VU meters appear to have burned out. Inside the VU meter there are two LED wired in series. Im getting 6.3 volts across the LED terminals. If I stick an led across the terminals, it lights up, but quickly gets very hot. The LED's were working, but are no longer lighting up. Any Idea what would cause this?

4. Incorrect voltage at R13 resistor.
On both channels, I'm getting around 180v instead of the prescribed 120 at the R13 resistor. Any ideas here? I'll attach a schematic so you can see which one it is.

Thank you in advance for any guidance here! It is GREATLY appreciated.

Photos/diagram/schematic of my unit uploaded here:
Dropbox - GroupDiy LA2A Drip opto 7 photos
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Old 12th June 2019, 09:04 PM   #2
hop.sing is offline hop.sing  Europe
diyAudio Member
Join Date: Feb 2009
Location: Munich
1.Well, many years ago, I built a drip la2a first gen circuit board. Wonderful compressor by the way, but doing it again, I would build it p2p. But anyway, I had hum, too and that was because of the leads to the volume pot, I had to bury them in the corner of the chassis to not pick up hum even though they where screened.
2. No idea...
3. Put an a proper resistor in front of the LEDs to drop a little voltage and do not use ac (6,3v sounds like heater ac) but rectify the 6.3v with a diode and a cap...
4. Check all resistors around the 12ax7. Do you have around 205v above r13?
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Old 13th June 2019, 03:18 PM   #3
Jclay85 is offline Jclay85  United States
diyAudio Member
Join Date: May 2012
Yes, above R13 I have 217v.
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Old 19th June 2019, 05:19 PM   #4
hop.sing is offline hop.sing  Europe
diyAudio Member
Join Date: Feb 2009
Location: Munich
Bad tube or wrong value r14
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