crossposted from rtopia.net (my gear building alter ego)
Got this used on Reverb ($35 – couldn’t pass it up)
Most of the reviews on the Vertigo were pretty favorable. The biggest complaints were “range of speeds via the rate control” and “noise”. Once I got it in my signal chain and worked with it for a couple of hours, I thought it’s attempt at the “univibe sound” was adequate and the ramping (gradual change between settings) RATE/FAST switch was a cool feature (The RATE/SWITCH will either go max rate or whatever the RATE control knob is set to. )
MODS PERFORMED:
- added variable control to FAST option on RATE/FAST switch
- extended range of RATE control (wanted a really slow sweep)
- true bypass
- replaced LEDS (red/green = zzzzzz)
Items 1 and 2 are documented below (presuming every modder knows how to do TB and part swaps)
This is the PCB and controls out of the enclosure
The switches are hooked in with connection headers (nice touch). I jumpered the ACTIVE switch so the circuit would always be engaged (rate always evident) on either side of the TRUE BYPASS DPDT switch:
While inspecting the board for circuit clues (couldn’t find a schematic) I noticed this diode installed on an LED pad. I was hoping this might be an indicator for the FAST rate. I installed an LED and it didn’t illuminate. I left the LED in (acting as a diode). It didn’t affect the tone/operation of the circuit. It’s interesting that Q7 is facing the LED pad. I wonder if there’s any chance there may have been an attempt at doing a light sensor configuration?
This is the back of the PCB opposite the RATE/FAST switch header (note: pads for LED to the right of the switch pads are tied into LFO section). I removed R57 (10K) and replaced it with a 25K pot (wired as a variable resistor)
To extend the range of the RATE control I replaced R24 (2K) with a 500R resistor.
(note: excess solder flux on the pads in the comb filter section were already there, perhaps these were post run adjustments made at the factory)
RESULTS: worked! (with some conditions)
The FAST control (small knob between foot switches) and the RATE control knob interact with other. Adjusting one will effect the setting of the other. Starting with FAST control knob and setting an initial speed, then going back and forth between the two until I got a FAST vs SLOW balance that I could use didn’t take very long to dial in. Another benefit was being able to dial in more DEPTH for the FAST setting.
With TRUE BYPASS installed, the LEVEL control will always be set to MAX (I also tweaked the feedback resistor on the output buffer to give it a bit more gain)
I attempted to do some tweaks to the comb filter section (changed C22 from 10uf to 1uf) but it started to sound a little phasery (changed it back). I’m gonna run “stock” for a while, analyze a bunch of different univibe schemos and maybe go back in for some tweaks.
In the meantime – I got a day of “Machine Gun” and “Bridge of Sighs” to get to : )