News:

Forum may be experiencing issues.

Main Menu

Woodstork Bias Issues

Started by Caesar3693, April 05, 2017, 02:16:10 AM

Previous topic - Next topic

Caesar3693

Hey Everyone, 'First time long time' here. I have built about 15 pedals but consider myself a complete noob. Most of my issues have been found on previous forums, but I was unable to locate anything for this.

Project: Woodstork - No mods
Problem: Pedal gets a fuzz effect with Cont at 10. The attack and clarity are lost once you start turning back the Cont. Volume and Fuzz appear to work normally. The Bias has a subtle effect, though I am not sure what I am listening for on this pot. While attempting to bias I found that T1 turned all the way down only gets me to -3.6v. I am unable to get any lower (to -4.5v) with the BOM resistors.
Troubleshooting: I have taken the obvious measures of confirming res\cap\etc values. I have reflowed all solder points that are accessible. Here's where things do not seem to add up for me. The schematic for the transistors I bought have the R6 stock value of 8.2K compared to the BOM's 1K. But then these specific transistors were biased to 47K on R6. I feel like that is a big difference from the BOM's 1K. I socketed R6 to test (I'm a noob and trying to learn how schematics work). Surprising to me, I was only able to get -4.5 by going down to 100R on R6. Guitar testing produced subtle tone changes from the 1K, but the Cont issue remained.
Substitutions: I am aware that I probably should have bought the size transistors Brian advised. This was only the second time I've bought them and I purchased the wrong size mistakenly. Again, I am a noob, but I'd like to make these transistors work. I believe they should regardless of the size. No other subs were made to my knowledge. Pics in link for community confirmation:
https://drive.google.com/drive/folders/0B-_WdWusHfPgTFhQdklkUU4zeWc?usp=sharing

Any\All help is greatly appreciated. I can also provide any additional details requested.

Caesar3693

Sorry, I wasn't able to edit the original post with voltages.
All stock BOM parts.
Input -
8.97v
IC1 -
1: 8.73
2: 4.33
3: 0
4: -4.28
5: -8.52
6: 0.12
7: 1.22
8: 8.73
Q1 -
C: -3.39
B: -0.09
E: -0.05
Q2 -
C: -0.09
B: -0.04
E: 0

WormBoy

Not sure if this is helpful or not, but the first thing to note is that, in the Woodstork, the 1k is in series with the 10k trim pot T1. So the resistances add up, and you can tweak the total resistance from 1-11k to get the bias right. That should normally be sufficient for germaniums, though the Mangler uses a 20k trimmer, for example. Where did you buy the transistors, and are you sure they came with the advice to use 47k resistance, in a Fuzz Face circuit?

Caesar3693

Everything is helpful, WormBoy! The link to the pictures on my One Drive has the Fuzz Face schematic from Small Bear captured. Their schematic has a stock R6 as 8.5K, but the specific transistors were biased with 47K it shows on the sheet. That's a huge difference to me, but I have no clue what that means for adjusting resistors on the BOM.

Also, I socketed R6 to swap resistors freely. I was really surprised to see that I was getting farther away from -4.5v with resistors higher than 1K. I was only able to get -4.5v when I went all the way down to 100R. Again, this is a huge difference and I am still having issues when the Cont is rolled down. I hear notes, but all of the attack is gone. You can't hear any pick work. These things are hard to explain, obviously. But I assume something else is wrong with the circuit.

WormBoy

Ah, I missed that picture. Well, assuming Mr. Small Bear is correct (which he probably is), you should get -4.5V on Q2 with 47k (ignoring the small differences in the other resistors for now). Since you socketed R6, you can put in something like 43k and see if you can use the trimmer to get -4.5V. But as you say you can only get that when using 100R ... something else is probably wrong ... and I hope you did not fry those nice Mullards, though, by soldering them in ...