Fancy Fuzzbox (1972) - did anybody get it to fire up?

[LucifersTrip]

it was from a 1972 electronics book. here's the original posted on this forum:


I enlarged and cleaned it up:


so simple, but a quick breadboarding gave me zilch.

Someone's actually selling the HEP 632, but I haven't found a datasheet yet.
http://www.talonix.com/shop/item.aspx?itemid=751


thanx

[petemoore]

  1.5v doesn't leave much ''bias headroom'', looks like it should work otherwise.
  Did you do any device testing or debugging ?

[mac]

I tried something like this in my quest for that "spirit in the sky" tone. I did not used r3 and r4. Not what I was looking for but very fuzzy and creamy, nice tones. This one must be similar. I'll give it a try.

mac

[LucifersTrip]

 1.5v doesn't leave much ''bias headroom'', looks like it should work otherwise.
 Did you do any device testing or debugging ?

Yes, went thru the testing/debugging & even checked for continuity between most joints. I guess I was just hoping someone built it and got something out of it before I spent more time....I do not believe it was ever verified.

I tried a bunch of transistors w/ different gain ranges  & measured voltages. The collectors on both were ~ -1.5 and the bases were 0 or close to 0...not good.  I also subbed a pot for every resistor with a range of 0 - 100K. Also, in a similar circuit a pull up resistor from Q2 helped. In this circuit, it did raise the base voltage, but still no sound.

I'll re-check everything today & try again.

thanx

[LucifersTrip]

I tried something like this in my quest for that "spirit in the sky" tone. I did not used r3 and r4. Not what I was looking for but very fuzzy and creamy, nice tones. This one must be similar. I'll give it a try.

mac

Sounds cool...Let me know if you get anything. Do you actually have the schematic for the one you tried?

thanx

[petemoore]

  Looks like it would work if it works so to s[peak
  Q1 has low R for base bias resistor string and the pot should be able to dial the base bias of most 'usable' transistors, perhaps SI PNP's just for gain/leakage certainties for prelim-tests anyway. Emitter grounded = full on AC gain there, the 10k is also a usual - lowish collector bias resistor for gain stage.
  That should drive Q2 [test here with audio probe] input to 'open' even if it's somewhat 'misbiased' [I think that's the intention here, forces past the gating condition means a good bit of clipping...that and the low power supply means it should be very dirty.
  Seems like it'd work obviously doesn't mean it will/

[mac]

Seems like it'd work obviously doesn't mean it will

Yes, bias will depend on leakage, both collector resistors shoud be trimmers. My bet is that the 1M pot is more a drive control than a bias control. Q2 is leakage-biased.

The one I tested had just a big input cap, both emiters grounded, collector resistors were trimmers, leakage bias (no resistors feeding the bases), and matched germs (gain and leakage) to have almost the same resistors at both collectors. Q2B was coupled to Q1C with a big cap. Output pot 100kA, out cap also big.
3 big caps, 2 trimmers, 2 germs, 1 pot.

mac

[Solidhex]

Cool

  It looks like a Maestro Fz-1a with the buffer removed. I would use something pretty leaky for Q2 and bias it with the 22K off the base.

--Brad

[LucifersTrip]

Cool

  It looks like a Maestro Fz-1a with the buffer removed. I would use something pretty leaky for Q2 and bias it with the 22K off the base.

--Brad

I actually did try a pull-up off the base, but I don't know if I used something leaky for Q2. I just tried various vintage 60's transistors
from hfe 25 - 150.  What I can believe is that I got nothing...not even a lousy gated crackle. Does the bias have to be so accurate that
if you don't hit the bullseye you won't get anything...

thanx for the recommendation

[mac]

If you want lekage-bias, note for example that a leakage of 100uA across a 22k resistor is 2.2v, larger than the battery, roughly; so be careful about leakage and the collector resistors.
If you connect the base then extra current will flow sending the collector more to gnd side.

If you want leakage-bias, you can test your germs leakage by simply connecting a 1K resistor at the collector, emiter grounded, base not connected; read the voltage across the 1k, that's the leakage in milli amperes; then calculate 0.75v/leakage=resistor in kilo ohms needed to have half vcc at the collector.
For example, you read 0.3v across the 1k then leakage is 0.3v/1k=0.3ma=300 micro ampere, quite leaky.
Then do 0.75v/0.3ma=2.5k
This also works for a 9v batt, just replace 0.75v for 4.5v.

But is easier to use a trimmer and tweak the collector resistor to taste

mac

[LucifersTrip]

If you want lekage-bias, note for example that a leakage of 100uA across a 22k resistor is 2.2v, larger than the battery, roughly; so be careful about leakage and the collector resistors.
If you connect the base then extra current will flow sending the collector more to gnd side.

If you want leakage-bias, you can test your germs leakage by simply connecting a 1K resistor at the collector, emiter grounded, base not connected; read the voltage across the 1k, that's the leakage in milli amperes; then calculate 0.75v/leakage=resistor in kilo ohms needed to have half vcc at the collector.
For example, you read 0.3v across the 1k then leakage is 0.3v/1k=0.3ma=300 micro ampere, quite leaky.
Then do 0.75v/0.3ma=2.5k
This also works for a 9v batt, just replace 0.75v for 4.5v.

thanx for the leakage info. I'm sure I used a bunch of leaky transistors for this & others, but have tweaked everything by ear instead of
knowing I was using a "good" transistor with high or low leakage as need...

But is easier to use a trimmer and tweak the collector resistor to taste

yes, that was one of the first things I tried & still got no sound. I couldn't believe it. I built 20-25 pedals in a row with zero errors. This was so simple and I couldn't find any errors so I thought maybe even the breadboard was defective. I couldn't even find any continuity errors between components, so I pulled the pieces.  Afterwards, on a hunch I checked my clip leads. One of the 10 leads I used was open! ...a new one I just bought. That could very well  be the prob, so I'll breadboard again & re-try.

thanx again

mac

[MartyMart]

I'm not being "funny" but you did clock that this is a positive ground circuit .... right ?

MM.

[LucifersTrip]

I'm not being "funny" but you did clock that this is a positive ground circuit .... right ?

MM.

Yes...used PNP...but I actually reversed everything and tried as neg ground also. I thought I checked everything
up until I realized one of my new clip leads was dead

[LucifersTrip]

Just a quick note...it actually was the one bad clip lead. I hooked it up again & it worked....so I guess that schematic is verified.
It's not a great fuzz yet. I'll start experimenting now.

[MartyMart]

I made something similar in about 2005, it may even be the same circuit running off a single AA battery.
I got a half decent "buzzy fuzz" out of it but nothing earth shattering.

Well done spotting the "dodgy" clip lead though - that can be a PITA !!

MM.

[LucifersTrip]

I just spent a few hours swapping transistors after figuring out that the prob was the bad clip lead.

So far, it's an ok fuzz, but nothing great. As Mac got with his similar one, it's more creamy that dirty or trashy.
For me it works best with with something either silicon or germanium in the 150-250 range as Q1.

But the person who designed this really loved germanium, because it simply fails with any silicon as Q2. I tried over 20 different silicons
and 20  different germaniums as Q2 and every single silicon either produced no sound or a barely audible gated fizzle. EVERY Germanium
gave me some type of distortion or fuzz from an hfe as low as 8 (yes, eight) up to the largest one I have (about 200).

It's not good enough to box yet...not enough sustain & no unique fuzz...but a fun, easy build.  I'll experiment with npn before de-breadboarding since I can try higher hfe's in Q1.

[jrod]

Hi,
I have this schematic from about 3 different publications and they all have both transistors listed as 2N2613, which are PNP germanium.

[joegagan]

i used to like 2n2614s a lot. still do , in fact. i would guess a 2n2613 is similar.

thanks for the ongoing reports on tis build, it is interesting.this thread gets an a+ from me.

[mac]

You need to add an extra resistor from vcc to base if you want to try a silicon at Q2. If not it wont work.

mac

[Earthscum]

You need to add an extra resistor from vcc to base if you want to try a silicon at Q2. If not it wont work.

mac

That's what I was thinking this morning, too... I shoulda posted on this thread instead of another, lol...

What I was seeing is that it will take too much to pull it up from ground. I've tried this kind of half wave rectifier approach with some NPN Si's. It didn't work for me, but I later figured out why, and it's the same reason. I had to bias my base so that it was turned almost completely off. Tried same idea, different front end, again later and it did work... now I wanna try this one... "Hey, we gotta stop and get some 9V's and a AA". I wonder how long the battery would last.