OD Vibrolux

[Smokebreak]

I opened up my SFVR the other day, in an effort to put that normal channel to use. I also just now came across the clips and pics of that Deluxe Overdrive(s), which I am quite fond of.

I'm wondering about the entrance to the OD. Is that first 5-band resistor to ground, after the new 5n coupler a 36K? Is the extra band(yellow) some sort of temperature marking?

If I'm seeing the rest of the entrance correctly, it would be that 36K to ground, paralleled with a 100K//500(?)p, then a series 1M5, then 33K to ground after that, then the stopper. Does that sound right? Is this what is referred to as "funky"?

Does anyone have an idea about the 3 way rotary labeled "Overdrive"? I'm assuming it changes the values of some part of this network.

I'm assuming the resistor off the 3rd stage is 100K feeding a 100K pot, and off the 4th stage is 180K to ground, then 1M to the OD MV 1M pot?

Any help or input is greatly appreciated.

[jelle]

3.6M

OD entrance as per 2nd gen.

jelle

[martin manning]

The 5-band resistor (orange, blue, orange, gold, yellow) looks like 33.6 ohms and 4% tolerance to me. http://www.eeweb.com/toolbox/5-band-resistor-calculator

[Smokebreak]

And then there's this, second to last paragraph : http://mhuss.com/Resistors/

Good example is PR5 : http://mhuss.com/Resistors/Page3.html .

Plus, it seems like a tweak, in that location, as it parallels the OD entrance 180k//500p to ground. Easier to put it there instead of that tiny little board under the OD rotary
36K puts it at 30K/500p for the first bit of the entrance.
I also fiddled with the presence , and I think 100K/.004 gives useful range.

[martin manning]

33 ohms didn't make much sense either. That's an odd one!

[jelle]

That resistor is after the V1B coupling cap to ground before the OD select rotary switch. The OD entrance appears to be at the rotary switch. 180K to ground (bypassed with a ceramic cap), 1M leading to a 33K to ground.

How could 30-somethin K to ground work between the V1B output cap and the channel select switch?

My take on it is that it is there to prevent noise from switching.

[Smokebreak]

That makes the most sense. I had it in my head that the rotary was more of a voicing switch than a true channel switch, because of the 3 positions

[wjdunham]

That makes the most sense. I had it in my head that the rotary was more of a voicing switch than a true channel switch, because of the 3 positions

Anyone else have an idea as to why three positions on that switch? There's already an OD treble bleed on the back, maybe two different gain option?

Bill

www.sebagosound.com

[Smokebreak]

My guess is that the 33K to ground is on the switch. It appears to be elevated from the tiny board. "N" is clean, "1" is with the 33K to ground, and "2"(obviously the user's fave setting) is with the 33K lifted. This gives a boatload of gain of course, and although it's a different amp, the one in the YT vids has the first stage pot well moderated.

Granted, these observations are with my SFVR, and in the "1" position, it's more like a cranked fender with maybe 1 extra stage, and the treble bleed is much needed. In setting "2", the bleed pot isn't really necessary, but the resistance network needs to change after the 4th stage, because of the massive gain(without the 33K) . I've found that subbing 270K for the 33K on the 3rd stage, and then for 4th stage 100K to ground(instead of usual 180K), 1M to MV gets close. I still need to dump a little gain somewhere.

[wjdunham]

My guess is that the 33K to ground is on the switch. It appears to be elevated from the tiny board. "N" is clean, "1" is with the 33K to ground, and "2"(obviously the user's fave setting) is with the 33K lifted. This gives a boatload of gain of course, and although it's a different amp, the one in the YT vids has the first stage pot well moderated.

Granted, these observations are with my SFVR, and in the "1" position, it's more like a cranked fender with maybe 1 extra stage, and the treble bleed is much needed. In setting "2", the bleed pot isn't really necessary, but the resistance network needs to change after the 4th stage, because of the massive gain(without the 33K) . I've found that subbing 270K for the 33K on the 3rd stage, and then for 4th stage 100K to ground(instead of usual 180K), 1M to MV gets close. I still need to dump a little gain somewhere.

Interesting, thanks for the thoughts. This amp is quite similar to the 70's ODS amps from what one can see from the photos, the slope resistor being a bit lower but otherwise very familiar. In which case, make sure to set the value of that final dropping resistor to get the V1 plate values down around 170V. That resistor is still covered with the black paint but most amps from this generation seem to have a pretty low V1 plate value.

Bill

www.sebagosound.com

[Smokebreak]

So what tonestack is this? The red cap looks to be .047, and slope resistor 82K.
2nd gen with .1 bass cap dropped to .047, and 100K slope to 82K?

Looks like there is what could be a 10K off the bass pot to ground, dating it a bit

[Smokebreak]

That resistor is after the V1B coupling cap to ground before the OD select rotary switch. The OD entrance appears to be at the rotary switch. 180K to ground (bypassed with a ceramic cap), 1M leading to a 33K to ground.

How could 30-somethin K to ground work between the V1B output cap and the channel select switch?

My take on it is that it is there to prevent noise from switching.

The 36K at the explosion entrance only doesn't make sense for a clean channel, as we know it. For the OD, it makes good sense, if you lift the leak on the other side of the 1M2 for the highest gain function. I got these mil-spec resistors the other day and it brought me back here.