alternative for ldr

tip142 · Post by **tip142** » 25 Sep 2012, 13:46

Is possible instead of LDR place a high value resistor?
Look at the schematic below,the Ldr is in series with the Crunch Master pot.
Why because i have not around this LDR.

Liquitone · Post by **Liquitone** » 25 Sep 2012, 20:04

I think substituting the LDR with a resistor should not be a problem at all. I'm not sure, but my guess is that the vactrol's led is connected to a footswitch for boost. led off-boost/led on- normal.
You could put a high value potmeter there to see what resistance you need before soldering in the resistor.

edit; just noticed the vactrol is connected to the relay of the channel selector footswitch. so yeah, you could put in a resistor instead of the ldr, but you will lose the ability to switch between channels.

tip142 · Post by **tip142** » 26 Sep 2012, 15:09

Thank's for reply,i think from viewing the schematic ;that when no led is activated you have Clean channel.
This is confimated from 2.nd schematic ,not that attached
When you engage the selector channel in Crunch position,you leave the Clean and then because is atctivated relay n.1;this have in series the LDr(practiccally a led) so this emits to the receiver and the resistance goes down...
In Clean mode the receiver have a very high resistance,because is non conducting;no relay activated (Number 1 sleep.....)

tip142 · Post by **tip142** » 02 Oct 2012, 22:11

Please,does anybody help???

Liquitone · Post by **Liquitone** » 03 Oct 2012, 10:27

I don't really know if I'm correct cause I'm no expert in these sort of tube pre-amps, but the are my guesses;

1) The Vactrol is connected to Relais 1

2) Relais 1 switches between the clean and crunch volume pot in the Clean channel.

3) When Relais 1 is selected to the crunch setting, the LED in the Vactrol connected to it will light up.

This will lower the resistance of the LDR connected to the Crunch Master potmeter (possibly close to 0 ohms, acting as a connection to Ground).
This will turn the potmeter into a voltage divider so it will work as a volume knob. This way you can tame the crunch volume so it wont be too much louder than your clean sound.

4) since an LDR ís a resistor you should be able to use replace it with a normal resistor without any problems. you will only lose the ability to control the Value of the resistor.

5) when you would use a low value resistor or even jumper wire, the Crunch Master Volume knob will work at the same level in both normal- and crunch-mode.

6) When you would use a high value resistor (a few megaohms) the Crunch Master Volume knob will do nothing, so you can't tame the volume in Crunch-mode.

So basically, I think you can replace The LDR with a high value resistor, you will still be able to switch from clean to crunch, but your crunch sounds will always be louder than your clean sounds.

tip142 · Post by **tip142** » 03 Oct 2012, 22:06

Well,thank your very much for reply ,very appreciated.
Ithink that the best way is experimenting,in bewteen;i'm found these:
ruinwesen.com/blog?id=1325-building and applying Vactrol(diy).
Hope this will be interesting.....

Liquitone · Post by **Liquitone** » 04 Oct 2012, 13:09

your very welcome

nice link, making your own vactrol isn't difficult indeed and can be much cheaper than buying one.
I think a <500 ohm/light to 1 megaohm or higher/dark would be a good choice for your needs.