GGG Neovibe/Geofex board question - R.G.???

[DiamondDog]

Hi, all.

Looking at the "Ver J 10/07" Neovibe board obtained from GGG, there are a couple of subtle differences between it, and the layout schematic in the 'vibeupadte' pdf.

1. This board have the option of A or A1 for input. There is an A1 in the layout diagram, but not the schematic. When is A1 (or A for the matter) used? (A1 works for me, it's more curiosity)

2. It looks as as though there is provision for a trim pot between R35 and R36, adjacent to 'N' on the board. It doesn't appear on the layout or the schem.

Anyone (R.G. are you in the house???) with any insight in to these evolutions?

Cheers!

[R.G.]

1. This board have the option of A or A1 for input. There is an A1 in the layout diagram, but not the schematic. When is A1 (or A for the matter) used? (A1 works for me, it's more curiosity)

As I remember - it's been a while since I did that update - I mis-lettered the pads and was in a hurry so I called the second input A1 instead of B. The original Univibe has two inputs, one of which is never used. The purists will insist that without two inputs it's not "original", but even they will never use the second input. A and A1 are identical to the A and B inputs from the PDF.

2. It looks as as though there is provision for a trim pot between R35 and R36, adjacent to 'N' on the board. It doesn't appear on the layout or the schem.

There is, and it doesn't. One of the secrets to a good, deep effect is balancing R35 and R36 so the phase cancellation is as perfect as it can be. That may not be with R35 and R36 exactly equal. The conventional wisdom for doing this is to use a 200K or 250K pot instead of R35 and R36, set the sound by ear, then measure the two legs of the pot and put in the nearest value fixed resistors. I just made that a bit easier for people who don't mind just leaving in a trimpot.

[DiamondDog]

1. This board have the option of A or A1 for input. There is an A1 in the layout diagram, but not the schematic. When is A1 (or A for the matter) used? (A1 works for me, it's more curiosity)

As I remember - it's been a while since I did that update - I mis-lettered the pads and was in a hurry so I called the second input A1 instead of B. The original Univibe has two inputs, one of which is never used. The purists will insist that without two inputs it's not "original", but even they will never use the second input. A and A1 are identical to the A and B inputs from the PDF.

2. It looks as as though there is provision for a trim pot between R35 and R36, adjacent to 'N' on the board. It doesn't appear on the layout or the schem.

There is, and it doesn't. One of the secrets to a good, deep effect is balancing R35 and R36 so the phase cancellation is as perfect as it can be. That may not be with R35 and R36 exactly equal. The conventional wisdom for doing this is to use a 200K or 250K pot instead of R35 and R36, set the sound by ear, then measure the two legs of the pot and put in the nearest value fixed resistors. I just made that a bit easier for people who don't mind just leaving in a trimpot.

Many thanks!

[DiamondDog]

I should have also mentioned- thanks R.G for a great design and layout!   

It had already fired up in a very vibe-like way first go. And it really is a quality board from GGG- kudos to JD (and whoever makes them for him... )

I remember knowing I was 9/10ths the way to a working effect when biasing the lamp, and the lamp responded to moving the pots

I used all 2N3904s. I didn't so much match them as test them to make sure they were roughly in the same hFE range. I did find a couple that were probably best left for another project. Overkill? Probably. But I do try to use similar hFE in all my projects.

For the light (or dark) shield I used the metal from the bottom of a pringles-type  can. It's flat, which was a good start! I lined it with aluminium tape before bending. While it bent very accurately, it didn't solder very well. Instead I wrapped it in two layers of porous tape (with the two solder legs attached) and applied two coats of spray epoxy- I think it looks better and is more solid. Pefect!

Happy with the outcome? Youbetcha!