120V is correct between the cathode follower and the cap.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.
D-AOC PCBs - the building and help Thread
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Help Support GroupDIY Audio Forum:
Great, thanks will di. I’m using back to back Vactrols. Does that mean the reverse polarity 1N4007 is unnecessary? Would you not recommend using back to back Vactrols?
My unit has been working properly for a long time, but in the past I have destroyed up to 3 vactrols! I never knew the real reason why they were destroyed. I assumed they were poor quality.
Would you be so kind to upload a schematic to make this correction.
In my unit I use two vactrol per channel, kubi mod.
You want to create a full wave rectification so to speak. Smoother discharge of the cap, better response of the vactrol to smaller signal. Even in simulation this is evident.
In the week.
Admiral-dk
Well-known member
LED's usuallly Dies really fast if you expose them to 5Vdc or more in Reverse ...!!!!
So a reverse Diode across is a vary good idea if you expose them to AC or a Series Diode if you have to avoid Clamping (here a Zener + Diode, can work across too).
Per
So a reverse Diode across is a vary good idea if you expose them to AC or a Series Diode if you have to avoid Clamping (here a Zener + Diode, can work across too).
Per
I'm having a problem that has so far stumped me. I have four channels in one chassis. One channel won't compress. I pulled both vactrols from that channel and confirmed they work. First by feeding DCV to the LED and measuring resistance at two voltage levels. Then I drove the LED directly from the AP P1 oscillator (which is floating via a transformer). Both sections of both vactrols work.
When I put a single working vactrol in the non working position I get no gain reduction. I see the tone at the top of the LED on the + pad where the LED side of the vactrol mounts. So there is signal there to drive it. I've confirmed that the - pad is connected to 0V ground. I measured current through the LED when driven from the AC oscillator (1.228VAC produced about 50mA). When I put the vactrol in the non working position and drive the LED through the circuitry I get no current through the LED. I'm stumped. Why would the LED not draw any current when driven on the + side by an AC voltage if the - side is connected to ground? The channels that are working appear to be the same. The non working channel worked before. I have confirmed all component values in the area.
When I put a single working vactrol in the non working position I get no gain reduction. I see the tone at the top of the LED on the + pad where the LED side of the vactrol mounts. So there is signal there to drive it. I've confirmed that the - pad is connected to 0V ground. I measured current through the LED when driven from the AC oscillator (1.228VAC produced about 50mA). When I put the vactrol in the non working position and drive the LED through the circuitry I get no current through the LED. I'm stumped. Why would the LED not draw any current when driven on the + side by an AC voltage if the - side is connected to ground? The channels that are working appear to be the same. The non working channel worked before. I have confirmed all component values in the area.
I have two boards in one chassis. There is no interaction between the boards.
The non working channels will compress when the LED terminals are fed directly from the oscillator. I can pick off the oscillator signal at the relay bypass board before it hits the input transformer. Then drive the LED pins directly from that while still feeding the oscillator to the input transformer. It compresses that way.
Yes, audio common meets chassis at a bolt at the rear of the chassis at the power inlet.
I figured it all out. There were multiple things going on. Although only one channel was dead the others were't behaving the same way. I decided to pull all the vactrols and go through everything. I learned a lot in the process. There were resistive elements that weren't dead but ween't behaving well.
I had back to back vactrols installed. I went through all of them and tested them by feeding them DC and measuring resistance at two voltage levels. Then I did the same thing with the oscillator feeding the LED to see is AC was any different. It was but consistently.
The problem I described above was level related. I was checking with a +4dbu signal. Without the back to back diodes of the two vactrols it needed 6db more to trigger. This got me thinking that the back to back diodes for full rectification were necessary. It also occurred to me that putting the resistive elements in parallel doesn't have any advantage except perhaps noise. In fact having two in parallel makes it harder to match the channels because there are two more resistive elements that are variables.
I'm using 5C2/2 vactrols. The LED's have a 1.6V voltage drop. I measured a few color LED's I had. Orange had a 1.6V drop. So I used orange so they would clip symmetrically. After doing this I was able to get the four channels calibrated more tightly then they had been.
The mod Analag gave for preserving the life of the vactrols also made the metering more stable.
I had back to back vactrols installed. I went through all of them and tested them by feeding them DC and measuring resistance at two voltage levels. Then I did the same thing with the oscillator feeding the LED to see is AC was any different. It was but consistently.
The problem I described above was level related. I was checking with a +4dbu signal. Without the back to back diodes of the two vactrols it needed 6db more to trigger. This got me thinking that the back to back diodes for full rectification were necessary. It also occurred to me that putting the resistive elements in parallel doesn't have any advantage except perhaps noise. In fact having two in parallel makes it harder to match the channels because there are two more resistive elements that are variables.
I'm using 5C2/2 vactrols. The LED's have a 1.6V voltage drop. I measured a few color LED's I had. Orange had a 1.6V drop. So I used orange so they would clip symmetrically. After doing this I was able to get the four channels calibrated more tightly then they had been.
The mod Analag gave for preserving the life of the vactrols also made the metering more stable.
scott2000
Well-known member
wow.... thanks for sharing that..
dagoose
Well-known member
My vactrol search also continues. This week I found out that the left channel, where I recently had a broken vactrol (read back) was working fine, but the right channel needed about 4/5dB more gain to get to the same GR as the left channel. So the vactrol on that channel which I didn't replace still kinda worked, but not as it should. So I replaced that vactrol as well (I still had one spare) and now that channel is also back alive. So it looks like the vactrols could also partly break for some reason. A bit like what Gold also describes I guess.
My D-OAC has 2 'fresh' vactrols now with the mod (which I already did add last time) and fingers crossed that it will continue for many more years now without crushing vactrols because they are gone now.
My D-OAC has 2 'fresh' vactrols now with the mod (which I already did add last time) and fingers crossed that it will continue for many more years now without crushing vactrols because they are gone now.
Knocking on wood here as well.
Maybe, at some point, grab a bag of these (50, 5 values 10 pieces each), just in case.
https://ja.aliexpress.com/item/32833626809.html
Maybe, at some point, grab a bag of these (50, 5 values 10 pieces each), just in case.
https://ja.aliexpress.com/item/32833626809.html
dagoose
Well-known member
I have also removed the anti parallel vactrols. I had to use them to get the unit back running again. I already had leds (2 types) in parallel for years, but now also the bleeding resistor and a 1n4007. Also made the compression a bit more 'solid'.
dagoose
Well-known member
What do you want to use those for? Making your own vactrols?
I put in the 100R and 1M resistors but am using the orange LED instead of the 1n4007. The 1n4007 clips at 0.6V. I wanted symmetrical clipping.
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