PaulS
05-30-2007, 10:29 PM
A while ago I had posted my vox 847 up for sale. There was some interest but no cash showed up... The vox had been modified in large way, I have been expiermenting with it for the last two years. It sounded good but not what I really wanted. The pedals has been true bypassed, Fulltone Halo inductor and Fulltone Icar Pot. I had changed out all the caps for a higher grade and changed all the resistors to the brown carbon comp type and changed a few values. Here is a pic of the board..
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF0936.jpg
Well since it was sitting on the shelf I thought I'd give it another look. I googled the 847 for mods and found one by a gent who had went through all the trouble converting his back to the specs of the Italian 846. I read his thread and thought what's to lose.. Anyway Changed out a C1 and C5 with mallory .01 uF caps, left the .22 uF orange drops . C1 is the input cap and C5 is the sweep cap and the type of cap used here does change the character of the pedal. Next I replaced all the resistors with 1% Metal film resistors with the exception of the input resistor because I had changed the value and didn't have the right metal film value. Basically most of the values stayed the same with the resistor across the inductor changing to 27K and the input resistor to 47K. The last change was the transistors, in his article he suggested that the 2N5172 type were far better than the MPSA18 type that were used in the 847's. To try this I hooke up a couple temp sockets and A/B'ed the two pairs. The 2N5172's were actually a lot nicer than the original so I soldered them in permanently. That was a trick because the pin out differs between the two. Finally I have the wah that was hiding inside that pedal. A very expressive sweep sort of vocalish and just the right range. That is another trick, finding the sweet spot on the pot.... many moves of the pot until it was finally there.... now some pics....
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF1236.jpg
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF1237.jpg
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF1232.jpg
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF0936.jpg
Well since it was sitting on the shelf I thought I'd give it another look. I googled the 847 for mods and found one by a gent who had went through all the trouble converting his back to the specs of the Italian 846. I read his thread and thought what's to lose.. Anyway Changed out a C1 and C5 with mallory .01 uF caps, left the .22 uF orange drops . C1 is the input cap and C5 is the sweep cap and the type of cap used here does change the character of the pedal. Next I replaced all the resistors with 1% Metal film resistors with the exception of the input resistor because I had changed the value and didn't have the right metal film value. Basically most of the values stayed the same with the resistor across the inductor changing to 27K and the input resistor to 47K. The last change was the transistors, in his article he suggested that the 2N5172 type were far better than the MPSA18 type that were used in the 847's. To try this I hooke up a couple temp sockets and A/B'ed the two pairs. The 2N5172's were actually a lot nicer than the original so I soldered them in permanently. That was a trick because the pin out differs between the two. Finally I have the wah that was hiding inside that pedal. A very expressive sweep sort of vocalish and just the right range. That is another trick, finding the sweet spot on the pot.... many moves of the pot until it was finally there.... now some pics....
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF1236.jpg
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF1237.jpg
http://i72.photobucket.com/albums/i183/sarg_2006/DSCF1232.jpg