Mods to a Dunlop JH-2 FF??

[Joe Hart]

Quoted from "Technology of the Fuzz Face" by R.G. Keen:

"There is a set of changes collectively referred to as the "Hendrix" mods or the "Roger Mayer" mods. These are:

Replace the 470 ohm output resistor with 1K
Replace the 8.2K resistor at the collector of the second transistor with 18K
Replace the 1K control in the emitter of the second transistor with 2K.

This mod primarily seems to increase the output level and gain of the second transistor."

The biggest problem that I have with this pedal (aside from not sounding too good), is that it doesn't even get unity gain! If I do the first two changes, will this increase the output?

Thanks!
-Joe Hart

[petemoore]

Quoted from "Technology of the Fuzz Face" by R.G. Keen:

"There is a set of changes collectively referred to as the "Hendrix" mods or the "Roger Mayer" mods. These are:

Replace the 470 ohm output resistor with 1K
Replace the 8.2K resistor at the collector of the second transistor with 18K
Replace the 1K control in the emitter of the second transistor with 2K.
 >>>Use a 1k and add a 1k to it to see what that mod does [two paralleled 1k's should come out under 500k close enough or taper the paralleled one till you get 470R...you may have to pull the transistors to test the R value of that Resistor 'in circuit']
 >>>instead of the 8k2 or 18k ...Use a 6k8 and 10k pot in series [or a 20k trimpot] for Q2 collector.
  >>>Use a 2k gain pot, adjust it to 1k and less to see what a 1k would do in that position...or use a 2k pot with a 1k across it's connections...or use a 1k pot and add resistance to taste there.
This mod primarily seems to increase the output level and gain of the second transistor."  
 >>>I'm assuming your'e referring to your build here, FF's should have plenty of gain past unity.
The biggest problem that I have with this pedal (aside from not sounding too good), is that it doesn't even get unity gain! If I do the first two changes, will this increase the output?
  >>>I suggest facilitating Easy Early FF tuning experiences by building a FF testboard...
 >>>socket the caps and transistors, Use a trimpot for Q2's collector resistor, Use 'large' [1k for the 470] resistors for the ones you want to try increased R value on....leave a little lead length atop the board so you can parallel a resistor to it, thereby reducing/ increasing that positions R value easily, without a cap or socket. You 'could' do this with the 33k [make it 100k] and the 100k [make it about 150k] but these two resistors do well at 33k [Q1's collector resistor and 100k [Feedback resistor between Q2 emitter and Q1 base].
 Runoff Groove Multi=Face...Tim Escebedo's 'Many Faces of Fuzz'...good reads and schematics...basically if you look at the schematics you want to try...you can build a test board on perf using sockets and trimpots that will accomodate all of them.
 
Thanks!
-Joe Hart

[Fret Wire]

Joe, I'd adjust the 18k and 33k as normal for proper bias. Keep the 1k output resistor, and the 2k Fuzz pot. Unless you get lucky with the transistors, the nominal spec 18k and 33k resistors probably won't bias the ckt right. After you bias it, you'll find it has plenty of gain. I bought one way back when they first came out, and it had 16k and 27k to bias it correctly.

After you get it going, if you want to brighten it up a little, replace the 2.2uf with a 1uf and 250k or 100k for the volume control.

[Joe Hart]

Okay. I've never biased a transistor before (I know, shame shame). I've read about how to do it, though. So, I just replace the bias resistor with a trimpot (or regular pot) and dial up the resistance that will give me 4.5V on the transistor, correct? I test it "in circuit"? As in, I don't have to take anything out of the circuit except the bias resistor (replaced with a pot)? Thank you.
-Joe Hart

[Fret Wire]

Correct. You want basically half the power supply (4.5 or half your battery voltage) at Q2's collector. Use a 25k pot/trim for the 18k, and 50k pot/trim for the 33k. Some people adjust only the Q2 collector resistor, some adjust both collector resistors. I like the latter. Start at Q2, get it close, then adjust Q1, then back to Q2, etc. Easier than it sounds. Use this (bottom of page) as  baseline voltages to shoot for.
http://www.generalguitargadgets.com/index.php?option=com_wrapper&wrap=fuzzface_inst

If you want, go a half volt either way of 4.5v and see if it sounds good.

[Fret Wire]

Ok Joe, I just read your post again :oops:. You have an existing Dunlop JH fuzz you want to mod. I've modded a few of the Dunlop Arbiter reissues, and a couple had  bad trannies with high leakage. They weren't going to bias right for anything. Two did have good trannies with low leakage, and after I biased them, they sounded good. It has the standard Dallas resistor values, so with the transistors they use (not matched), they hardly ever bias up correctly as purchased.

If you have trouble getting yours to bias, you'll have to check the transistors. Also, it has a .1uf instead of a .01uf. I'd definately go with original value .01uf.

If your transistors are good, do the Mayer mods. You'll like it.

[petemoore]

OK factory unit...no place for trim pot very easy there
 Ge transistors...as above stated, getting the right gains and low leakage is important...
 You can use a regular pot to set bias...connect it using wires, set Q2 for around 1/2 the supply voltage [4.5v]
  Then without disturbing the pots setting, disconnect it from the circuit and connect to your DMM and read the ohmage it's set at...replace install a fixed resistor at Q2 collector using a 'close' value...
 You can 'build' a resistor using parallel resistors [2 equal value resistors parallel = 1/2 of one of their values] two seriesed ones double the value...use the DMM and build a resistor close to what the biaset pot read...

[Joe Hart]

Thanks everyone!! First I biased it. What a difference! One of the resistors that they had in there was TWICE the value that should have been in there!! No wonder it sounded crappy. Then I changed a couple things (Mayer Mod stuff) and it rocks! Again, thanks!!!
-Joe Hart