AM Sunface Board - 2.2k resistor question

[BarnabyHooge]

I'm building the AM sunface (BC108) on the board provided by Mike and using various threads to peice together how this thing is built. I understand this should be simple, but I'm still very much a mental midget when it comes to this stuff yet and am finding comparing the various schematics to the board a good exersize. I think I've got it all worked out except the 2.2k resistor.

From what I've seen, the trace on the AM sunface circuitboard from the bottom pad of the 1uf cap spot to the top of the 8.2K is always broken.There is also what looks to be a jumper from pad C19 to the 1uf cap bottom. (these two pads may have a trace between them on the underside of the board as well, I can't recall for sure)

I'm thinking the resistor must be underneath the board, running from the 390u resistor to C19 with a wire going from C19 to the 5k pot. If this is the case, why wouldn't you leave the trace and mount it on the top of the board? I just want to make sure I'm understanding the logic here. I'm sure it would be easier for me to start from scratch but I want to understand the board layout.

I didn't want to post the picture of the populated board as I'm not certain its appropriate. If anyone has built this or has a board themselves and can explain it to me it would be much appreciated.


Thanks

[Dragonfly]

What I would do is ask Mike. He seems to have been willing to help in the past.

Here's a picture of the topside assembled NKT board, which should be close...it looks like any extra components could certainly be underneath...he may have just "stuck with" the original design since he had already paid the setup csts with the pcb manufacturer.

[jimbob]

I wonder where he gets those trim pots!! Im thinking bout adding another trim pot for r24 and c19- if you look atr a typical tonepad schematic a resistor would be there..Ie..a trim pot for bias.

If you look at his site theres pics where theres a trim pot on top- the only difference is that its underneath. If you follow along with a typical schematic youll see the board is really fantastic!! esp that it is made to incorporate a resistor(8.2) or a trim there using a hole where the .1uf is- moving the .1 capover. Im impressed!!!

[Dragonfly]

I wonder where he gets those trim pots!! Im thinking bout adding another trim pot for r24 and c19- if you look atr a typical tonepad schematic a resistor would be there..Ie..a trim pot for bias.

My local place has some like that, but I dont think they have 5k...

I'll check for 10k ...

[jimbob]

However, now that i think about it..your wanting to change the grounding on this board to incorporate npn bc108's. Im planning the same.

[bean]

I wonder where he gets those trim pots!! Im thinking bout adding another trim pot for r24 and c19- if you look atr a typical tonepad schematic a resistor would be there..Ie..a trim pot for bias.

My local place has some like that, but I dont think they have 5k...

I'll check for 10k ...

I'm pretty sure I have some 5k's of that type. I'll take a look.

[jimbob]

OK. After reading a little more I learned that the trim pot trim( trim103) on the pic is for "It also has an internal CLEAN trim pot which you can see on the top left. This trim pot acts just like turning down the VOLUME knob on your guitar, to clean up the fuzz. It can be used to preset the sound if you prefer the sound with the volume knob rolled back a bit. It can also be used to kill Radio Frequency Interference, which may be a problem on high gain pedals in some areas, by turning it down a hair"

Very cool!!I cant wait to give that a try..

[BarnabyHooge]

I wonder where he gets those trim pots!! Im thinking bout adding another trim pot for r24 and c19- if you look atr a typical tonepad schematic a resistor would be there..Ie..a trim pot for bias.

Isn't that the "sundial" pot on the actual Sunface? Thats what I was thinking anyway.

[jimbob]

In the location for the trim for the sundial-

AM states " It also includes an additional BIAS trim pot inside to set the exact bias on these transistors, for the ultimate sound. The Blue trim pot is for Bias, which should not need adjustment often, while the big White one is the CLEAN (input adjustment) knob. The BIAS pot really helps if you play at different temperatures. You can turn it down a bit at higher temperatures, and up a bit at lower temperatures, to keep the transistors happy and sounding best at their SWEET SPOT which is about 5 volts. The Sunface manual has more information on adjusting this. "

[jimbob]

Look 1/4 of the way down the page

http://www.analogman.com/fuzzface.htm

[Solidhex]

White trimpot is the pre gain, and if I'm not mistaken the "sundial" is the external pot for the 8.2k. His pedals sound very niiiiiice.

--Brad

[jimbob]

I second that-


"White trimpot is the pre gain, and if I'm not mistaken the "sundial" is the external pot for the 8.2k. His pedals sound very niiiiiice"

[BarnabyHooge]

OK, so here's what I've gathered then for the BC108 Sunface board -

Underneath the board:
Lug 2 of the 5k Trim goes to the R24 pad
Lug 1 goes to the bottom pad of the 1uf spot and connects to Lug 2
Lug 3 goes to C19

-2k2 resistor from C19 to top of 8k2
-trace on the bottom of the board between C19 & 1uf pad is broken (or would that trace not effect the trim?)
-trace on top of the board from 1uf to top of 8k2 is broken as seen in the pic.

[Solidhex]

Damn

  Barnaby, I'm all tuckered out from paying attention to this thread! Damn my short attention span. I think you might be stressing a little too hard on the specifics.You mentioned the board was provided by Mike? I'm confused. Anyways you might want to check out some general info on the fuzz face circuit and  all this stuff will make a lot more sense. I'm no expert but thanks to the amazing people on this forum I've come a long way. Thanks everyone!

--Brad

[BarnabyHooge]

I hear ya. I've been reading anything and everything on the fuzz face. Honestly, I've screwed p my last two builds and I'm just trying to be extra careful this time around. I really want to wrap my head around and verify everything before I start in on the populating/soldering. I've put it all on the breadboard and will wire it up today.