Is this Maestro Fuzz (not FZ-1/1A/1B/1S!!!) schematic wrong?

[gigimarga]

Hello,

After I've finished a Maestro FZ-1 (3V version...thx gez for your help!) which i like it a lot, i've tried to build this Maestro Fuzz:
http://fuzzcentral.ssguitar.com/schematics/maestrofuzz.gif (alternative schematic: http://www.freeinfosociety.com/electronics/schematics/audio/maestrofuzz.pdf).

As i found here http://archive.ampage.org/threads/6/fxgd/265361/Maestro_Fuzz_FZ_1B_Help-2.html and in another post here, it seems that transitors are 2N3391A, not germanium ones, so i've built it with some BC546B, all with hFE around 300 (in the datasheets i found that 2N3391A has hFE between 250 and 500).

When I 'd tested it i could hear only a clean signal with the balance pot at minimum (a dual 50k pot...so, this means the signal from first two stages), while with the balance pot maximized i'd hear no sound.

My voltages are almost the same as here http://archive.ampage.org/threads/6/fxgd/265361/Maestro_Fuzz_FZ_1B_Help-2.html#266046, but with a big problem on Q3: C=8.53, B=8.27, E=8.09!!!

Here http://archive.ampage.org/threads/6/fxgd/265361/Re_Update-4.html are mentioned some errors in the schematic around Q3, but i didn't understand them very well.

Sop, please, anyone can help me with a corrected schematic (the links from the post are dead...)?

Thx a lot all!

[brett]

Hi
this fuzz should work fine with Si transistors.  It looks like it was designed with them in mind.  Your problem lies with Q4.  It is a variable resistor on the emitter of Q3, and your problem is that it isn't turned on.  Have a look at the orientation of the diode to Q4's base.   The voltage on the base of Q4 should be about 0.67 V DC +/- 0.03 V.  If it is less than this (and I suspect it is for yours), then Q4 presents a very high resistance, and Q3 is mis-biased and also not turned on.

When you get this going (or before), I suggest that you change the transistors for "vintage" type devices with lower hFE.  Most devices in the 60s and early 70s were below hFE = 250.  Around 150 is usually good.  Try a BD139 or an MJE340.  These medium-power devices are similar in many ways to vintage transistors.  Also, high-speed switches aften have low hFE.
good luck

[gigimarga]

Thx a lot brett!

I will try to change tha transistors, but i think that there are some errors in the schematic...

[gigimarga]

I've put the Q3's emitter directly to ground and it sounds very interesting...a raw fuzz which can be mixed with the clean signal.
So, as brett said, Q4 is the problem...

[Toney]

Hi,
I had a look around Disco's site... can't find reference to a Maestro fuzz that's just named "Maestro Fuzz" they all have some kind of model number FZ-1 etc as you noted.
What is this unit called?Is it just a general work alike?

[Gus]

If you look close the circuit is a lot like the foxy lady, Shin EI, fuzrite  and other cascaded gain stages two transistor fuzzes.

  This one has an input emitter follower buffer and and the added squelcher section.  The mixing with this one is a dual pot the others have the outer legs of the mix pot to the collectors and the wiper to the volume pot

The circuit change I read in the ampage posts are

anode of diode stock connection

cathode of diode to 3.3meg to ground and .1uf to ground(3.3meg with a .1uf across it)

The cathode and 3.3meg and .1uf node to a 680K the other side of the 680K to the Q4 base

It looks like a balancing act.  It looks like you want enough current to barely turn on Q4 when not playing.
  When playing and the signal going more positive the increased current though the diode raises the voltage across the 3.3meg and the hold cap the .1uf(one of the RCs).  The node voltage increases and causes more current to Q4 base via the 680K turning it on.  The 3.3meg and .1uf and 680k control the turn off time and the turn on is faster via the diode.

Does that make sense how I worded it?

[gigimarga]

Hi,
I had a look around Disco's site... can't find reference to a Maestro fuzz that's just named "Maestro Fuzz" they all have some kind of model number FZ-1 etc as you noted.
What is this unit called?Is it just a general work alike?

Unbelievable!!!!

Look what i found here today: http://cgi.ebay.com/VINTAGE-GIBSON-MAESTRO-FUZZ-TONE-PEDAL_W0QQitemZ320391303624QQcmdZViewItemQQssPageNameZRSS:B:SRCH:US:101

[gigimarga]

The circuit change I read in the ampage posts are

anode of diode stock connection

cathode of diode to 3.3meg to ground and .1uf to ground(3.3meg with a .1uf across it)

The cathode and 3.3meg and .1uf node to a 680K the other side of the 680K to the Q4 base

Thx a lot Gus!!!

As i can see from the picture it seems a little different from what you said, but i' still waiting a better photo.

What i've seen on the photo (after a little processing):

1. anode of diode remains where is now
2. cathode of diode to 0.1uf to ground
3. the 3.3M from base of Q4 to ground
4. a 680K from Q4's base to junction of the cathode of diode with the 0.1uF cap

[Gus]

 I posted what I understood from the ampage posts

It looks like you are correct.  A real schematic from a unit very cool.

The .1uf charges via the diode
the 680K and 3.3meg are a voltage divider bias that "moves" with the cap voltage turning on Q4 more when more + signal charges the cap to a higher voltage.

The diode path charges the .1uf much faster than the discharge path both resistors in series  across the cap.

It looks like adjusting one or both resistors the 680K and 3.3meg bias will adjust the place the transistor sits at idle the 3.3meg might be the one to adjust first.  It looks like the collector voltage of Q3 affects the operation.

[gigimarga]

I've beg the seller to send me a better photo with the schematic...i hope he will do.
Anyway, the 100K and 470K from the collectors aren't too big?

[gigimarga]

I've modified it as i said above and it works great!!!
With 100K/470K for the collectors sounds more like Shin-Ei and with 10K/47K sounds more full.

Thx all!

[brett]

Hi
thanks for that.  I'll have to build one.

I've noticed how the squelch control would be all wrong without the 680k resistor (or a resistor between 330k and 1M). The release time is controlled by the base resistor and the input impedance of Q4 (which is determined by its hFE). THis is a lot less than the 3M3 which it parallels.  Assuming that the impedance of Q4 is about 60k, adding the 680k resistor makes the release time (RC) about 1/10th of a second.  Just right.  I would try replacing the 680k resistor in this circuit with a 470k resistor and a 500kB pot.  That will adjust the amount of squelch and release time.  (less resistance = more squelch and faster release)

Note that there are some interesting articles around concerning early fuzzes.  If you get a chance, get a copy of some of the early patents.  There's one from 1964 for a circuit almost identical to the FZ-1 fuzzes.  I can't find an electronic copy at the moment, but I'm fairly sure that a link was posted here about 3 or 4 years ago.
cheers