I’d like to know why they fail too. I’ve looked at C104/204 with suspicion before. On one channel I have mystery DC at the inside (as opposed to outside board edge) LED pad. No DC on either side of C104 when measured at the cap. A head scratcher for me.
D-AOC PCBs - the building and help Thread
- Thread starter [silent:arts]
- Start date
Help Support GroupDIY Audio Forum:
scott2000
Well-known member
Both of you have the ME thing going on. Wonder if it has anything to do with that type of usage? Just an observation of course. Nothing beyond that.
It would have to be a very clever Vactrol to figure that out. Mine are built pretty much by the numbers. I wonder if it’s the back to back LED’s of the Vactrols?
dagoose
Well-known member
Good to see i'm not the only one wondering about this. My guts say that C104/204 might be a good starting point to look at. maybe a better, highly spec'd (better DC blocking) cap might do better? Or maybe we can add a zener that grabs the peaks, but I suspect that this would interfere with the vactrol and curves in a negative way.
dagoose
Well-known member
I think that in a mastering context the only big difference is that the GR is less then when used on let's say, vocals. In practice I hardly use more GR then let's say 1dB on the DAO-C. But I can't imagine that this is the case. I was also thinking, i'm using it/have it turned on 5 days a week since the start, which means 2008. That's 14 years. Lifespan of the vactrols?Ah, so not 'mysterious electronics', hmm.
Maybe it has to do with the optocell(s) constantly being hit by AC, as opposed to a rectified signal...
Mine have only been in daily use for about a year. I have four channels in 3RU cases. I wonder if it could be heat related? I don’t remember a temperature spec but I’ll look again. I plan on replacing the top and bottom of the cases with wire cloth to increase air flow. The PCB’s are mounted on PVC bar stock to the sides of the cases.
5v333
Well-known member
Wattage missmatch?
Datasheet says LED current derates 0.9mA per degree Celsius above 30C.
Heat shortens lifespan of LEDs, they age by dimming.
While at it, mounting new optos somewhere away from the tube/valve (and heat-dissipating high-wattage resistors) is maybe not too bad an idea?
Heat shortens lifespan of LEDs, they age by dimming.
While at it, mounting new optos somewhere away from the tube/valve (and heat-dissipating high-wattage resistors) is maybe not too bad an idea?
Put a bleeder resistor (470K) between C104/ VTL5C4 and ground. Also strap a 1N4007 across the LED in the opposite polarity. In mine I insert a 100 ohm resistor in the ground leg back to C104. Nothing has failed on the prototype to this day. I can upload a diagram to make things clearer.
Last edited:
dagoose
Well-known member
That's a good idea indeed! I was also thinking of something like this, but way more complex. Schematic is not really needed, at least not for me.
dagoose
Well-known member
I have mine with a basically open topcover. It runs hot, but not over the top hot.
dagoose
Well-known member
I can 100% confirm it's a broken vactrol..
I have 2 vactrol compressors going strong since 2005. I don't know how I didn't see the missing bleeder resistor in this schematic. Do the mods I suggested and you will notice a difference in the compressor action.
Last edited:
dagoose
Well-known member
So your saying the 470k bleeding resistor is a must?
The drive signal is developed across the resistor. This is why I suspect the vactrol is getting killed.
dagoose
Well-known member
Exactly, that's my thought as well, especially since on the other side of C104/204 there is something like (out of my mind) 120v.
I added the 470k bleeders, that should do the job.
Similar threads
![[silent:arts]](https://cdn.imagearchive.com/groupdiy/data/avatars/s/0/172.jpg?1620371656){kind=avatar}
