Build Your Own Clone Message Board

I'm gonna need you to do that over using only one shade of yellow Post-it notes please.

I didn't keep track but it I am sure it was at least a couple of hours for each of the two halves. It was a fun puzzle. I wish I had learned more about how the circuit works while doing it, but, oh well. I reckon I will learn something when I actually build it.

So far, I've attempted to trace the part of the PCB that corresponds to the upper half of the schematic, and therefore the part that has to do with the chorus mod and the proposed flanger mod. I'll describe in words what I found, and then go read the primer that I know is here somewhere about how to post images and come back to try that.

(1) There is a 200pF cap in the parts list and it has a spot on the PCB (right next to the six-pack of 10k resistors near the 6110, and which seem to be R14 through R19 inclusive and in order, right-to-left when looking at the component side of the PCB with the writing right-side up). But it isn't on the schematic, so it doesn't have a label of the sort "Rn". It ties the base of Q4 to ground, in a fashion analogous to the way C11 (220pF) ties the base of Q3 to ground, and presumably for the same purpose. (To suppress high-frequency noise?)

It's just missing from the schematic. If you find an original BOSS VB-2 schematic, it's off the base of Q3 (or Q4 on the BYOC schematic). It's just part of the low pass filtering. On the original, BOSS used a 47pF and 150pF in parallel. It's been consolidated to a single 200pF in the BYOC version.

(2) C7 on the schematic is 10uF electrolytic, but on the PCB it is labeled as 1uF (it is right next to the 25k bias trim pot). This makes two electrolytics of 1uF on the PCB, which matches the number in the parts list, and I'm guessing it will match what I will find in the parts bag, given that I have found no commentary on this point in the threads I have read. It connects to pin 4 of the 3207 and I can't even guess what is an appropriate value for a cap that goes there.

C7 is a 1uF. That's a typo on the schematic.

(3) One of the access points for the suggested flanger mod is the junction of C12 and R19. Those two components are right next to each other on the PCB and a continuity checker is probably all you need to find out which two of the four pads connect (the "lower" two); they also connect to the emitter of Q4.

They are all connected as well as C13, so you could connect that to any of those solder pads.

(4) Here's a slightly trickier part. The proposed flanger mod also shows, on the schematic, an access point at the junction of C2 and C3, also connecting to one end of R5. These components, along with R4, are the four that occupy the space just above and to the right of the 4558, on the way over toward the 6110. C2 is the one just above the 4558. However:

--(a) C2 and C3 don't actually connect to each other. They don't have a junction. This is because the actual topology implemented on the PCB I have has C3 and R4 swapped, w/r to what the schematic shows. From the point of view of how the vibrato circuit works, I don't think it makes a difference. The series connection of C3 and R4 should have the same kind of contribution to the frequency dependence of the gain of 4558 IC1b no matter which order they are in. If what I just wrote is not correct, I would love to be corrected about it! However, it raises the question of where the connection should be made for the flanger mod. I suspect it should be at the mutual C2/R4/R5 connection, but I'm not sure.

You are correct. C3 and R4 are flipped on the PCB. Here, the error is not on the schematic, but on the PCB if you are looking at it in terms of making it exactly like the original VB-2. However, the order of C3/R4 make no difference at all, so for our purposes, you can just say that this is another typo on the schematic.

The connection for the flanger mod is still made in the same place in light of this - the junction of C2/R4/R5. It is C2 that is being used as the decoupling cap, not C3, so the fact that C3 comes after R4 is not important.

--(b) R3 and R4 reside on diametrically opposite sides of C2 on the PCB. The values of R3 and R4 given in the schematic are, respectively, 10k and 7.5k. The values printed on the PCB are swapped from this. I don't know which way was actually intended. The two values are similar enough that perhaps it doesn't really matter.

You are correct. R3 and R4 should be swapped on the PCB, but R3 is being used in a emitter follower buffer, so the value difference there has no impact. The difference at R4 probably makes little or no difference as well. In the original VB-2, they used two 15k resistors in parallel (don't ask me why). Much like the mystery 200pF cap, they have been consolidated into a single 7.5k. The signal path of the VB-2 is identical to the CE-2, DM-2, and DM-3. 10k is used in this "R4" position in all the aforementioned circuits, so I don't think it really makes any difference.

(5) The schematic shows C5 connecting on one end to the R8/R9 junction, and on its other end to the junction of R10 and pin 3 of the 3207 and the emitter of Q2. But the other end of C5 actually attaches to +V. Pin 3 of the 3207 connects the Q2 emitter, and to ground through R10, but nothing else joins that path as far as I can tell.

C5 should go to the emitter of Q2. That's an error on the PCB. We'll correct that in the next revision. Fortunately it's in the first low pass filter and doesn't seem to make any difference whether it goes to the emitter or V+.

Wow! Thank you again for your time on this! I'm pretty sure I'm not the only one that will be using it.