Harmonic Percolator (George Giblet's schem) build report

[foxfire]

"It's alive, it's alive!!!"

Well I'm happy to see this recent movement about this thread. I'm absolutely obcesed by this little monster. And, yes, I will try those last tips just to say something about it.

Noel, what can you tell us about the glass encapsulated resistors you used?

And if the known band is using a kind of HP in its new record, good for them. So we must hope they use it for the light side of the force!

i know what you mean i have built 4 of them. well one harmonic percolator and 3 harmonic jerkulators. my favorite being the jerkulator i made with old salvaged parts. anyway i don't really have anything to add other than my fascination.

[alex frias]

Nice to see you, Mr Hammond, a honour, really.

Well, it's a so mojoable circuit... I can't bet anything for sure!

I'm really satisfiesd with my results about it, but you all know, it's unstopable. If there is another option, tip, clue, anything, we must try it out.

[sean k]

Heres my one on the verge of being wired up.

Metal can 2N2222A and a 2SB171 with a gain of about 60 and leakage of 40 - 50uA.

Not too much space in there but it'll be enough.

[smallbearelec]

I found NOS 1N695 diodes and have posted for sale. No shortage of these, or of the 2N3565. For the germanium device, note that if you don't insist on a type number, you can have a bag of 5 devices with measured gains in the 50s and 60s for as little as $1.50 a pop. My SKU 0114B and 0114C. I have a fair stash of NOS 2N404 and 404A, and I will offer these audited at some point when I can make time to build a jig.

SD

[alex frias]

So, Sean, how it sounds?

May you publish any kindo of sound samples?

Soon I will do a new video using my gig partner HP (Expresso Tone Machine for the old friends) with a new version with some small changes...
Let's see, and this time all done with real amps and mics.

[sean k]

Alex, I haven't tried on the end of a guitar yet, I've only used it on the end of a signal chain after one of my experimental instruments, clari(not),cmos nyquist then the jerkulator, but I managed to pickup that it had some very nice even harmonic distortion added as an after note... or octave I suppose, that came in a second or so as the note decayed off. I'm going to get a guitar out today and try some stuff but I haven't got my recording stuff together at all.

[Gus]

Finally finished the build, built it in a tomato can.  It is not a real HP for the top I used a 2n2222a, 47K collector resistor and a 470 K base to collector for the bottom 2n2907 part  I used a 10K collector resistor and a 1.2meg base to collector resistor.  I used a .047uf input cap and .1uf between stages and a .1uf output to 1n4148s 47uf cap at the emitters.  Used 100K audio pots at the in and out

Voltages 1.017VDC PNP collector, 3.31VDC emitters, 4.27 NPN collector.

It compresses and the sound will swell up if the input volume is max an the guitar volume is maxed if the volume is reduced it does not do this.  It feeds back in a controlled way.

Q1 a 2n2907 PNP 190   moto metal can
Q2 a 2n2222a NPN 210 moto metal can.

Even not being a real HP with the Ge PNP and having stock voltages it is a fun circuit

[DougH]

Sounds good, Gus. It is a lot of fun to play with.

I finally breadborded JJ's schematic and I must say, this is the best version of this I have heard yet. There is something very right about the way it sounds. IMO the two key elements are the 1u coupling caps (vs. the .1u I was using) and the 1n695 diodes. Yes, these diodes do make a difference. 1n34a's will work and sound okay but the 1n695's sound fatter and fuller. They are the same fwd voltage too so I think the difference is in the diode curves.

This is no longer a quirky funny sounding fuzz box but a real "tone machine" for lack of a better word. No whininess or upper octave- it's very smooth and oozes harmonics in a way that makes the guitar want to play itself. I'm not sure if it really needs the 390p or 1nf caps, if not I'm going to mod my "Brick" with the coupling caps and diode sections.

[Ben N]

Been following this quietly. I like the upper octave.

[DougH]

It's still there, just more subtle.

[Gus]

Thinking about the diodes used with the HP.

From the posted voltages and resistor values.  +9VDC supply and 2.49VDC at the NPN collector and 91K. about 6.5 volts across the 91K for an Ic of about .07ma(70ua).   The available current is not that much for the diodes and the output volume control is a part of the load on the circuit.

So if I was to test diodes for this circuit I would check the voltage drop at a few different currents.  .07ma, .04ma, .10ma etc.  Another thing to check might be the diode capacitance  differences.   Also I would look for the spec for the junction capacitance of the diodes.

[DougH]

FWIW I measured the fwd voltages of both the 1n695's and the 1n34a's at .223 V.

[Gus]

I just looked up the diode test currents of the fluke 77

About .4mA (400uA)
At .6VDC it .3mA
At 1.2VDC it is about .2mA
At 2.0VDC it is about .1mA

So it look like at .225VDC the test current is >.3mA maybe to high to show the difference in the diodes at lower current.  Maybe a 9VDC supply and a 120K or so resistor(100k 150K add some together etc.)  9VDC -.225VDC = 8.775VDC
8.775VDC / .07mA = about 125Kohm.  Measure the diode drop with current like the Ic.  Maybe that will show the difference.

http://assets.fluke.com/manuals/7x2xiii_cieng0200.pdf

[DougH]

Sounds like a plan. I wondered if the more or less exact same voltage readings had something to do with my cheapo DVM. I'll give this a try when I get a chance.

BTW I modded the Brick last night and it sounds great. Subbed the .1u caps with 1u's and subbed out the 1n34a/10k diode network with the 4.7k/1n695's. Essentially it's the same sound as the HP circuit on the breadboard, slight variation but not enough to be significant IMO. I left out the 390p and .001u as they don't affect the sound, that I can tell. They may be there for RF and/or oscillation due to layout or etc.

[edvard]

OK, NOW I'm in a pickle...

First, I get an itch to build a Percolator, so I come here (naturally...).
I find this thread and see GG's schematic and I totally facepalm because I've built two percolators (one for me, one for a friend) using Alfonso Hermida's schematics (the one with "unknown transistor values") which I had to tweak to accommadate silicon transistors (I had no idea Q1 was a germanium).
They sounded... ok, not great. Almost, but not quite, entirely unlike a Percolator.

So I breadboarded one using all the advice I found here but for transistors I had to settle with what I had: a 2SB173 and a BC239.
How'd it sound? Very good.
Nice 'fat' tone to the fuzz, not overly buzzy nor bassy. Lots of sustain without a whole lot of noise to go with it, even though I'm playing an '84 Fender Bullet right in front of my CRT monitor. Whether I play chords or single notes, I can hear a very subtle-yet-audible decay into upper harmonics like it's begging to be fed back in front of a Mesa Boogie twin (which I sorely wish I owned *sigh*), even though I'm wearing headphones right now as I test it (family's asleep, you know).

I have now discovered a whole new world of Awesome. Thanks guys, you've made my day.

I was going to be happy and just box this one up and post a pic, but then the experiments began...  
I swapped around the various resistor values, but everything worked best using GG's original values.
Tried some other transistors for the BC239, but none sounded as good.
Then I very foggily remembered somebody on some forum or blog somewhere wondering if you could simulate Ge transistor leakage on a Si transistor by strapping a Ge diode from collector to base, ala Bazz Fuss (probably wrong, but somebody actually said it...).
So I tried it for Q1; a BC309 and an unmarked army-green glass Ge diode.
Guess what?

Yet another world of Awesome!

It actually sounds pretty good!
When I first tried it, it seemed to have just a tad more gain (which I don't mind at all, but putting a 47-100k on the collector instead of the 20k tames it down a bit) and there's a subtle difference in the overall tone, but closer than you'd expect.
There was no loss of fatness, and was not overly harsh like many silicons tend to be.
I noticed the harmonic bloom was a little more obvious, but that could be because of the increased gain.
It also sounded "quicker"; very responsive to pick attack, which I found very nice.
After playing for a while, I noticed I was using silicon diodes instead of germaniums for the clipping at the tail.
Swapped in the germaniums, didn't like it (too... fizzy), so I swapped the silicons back in.

So there's my pickle. Which one do I put in the box?
It would be exciting to have a reasonable facsimile of the original for bragging rights if nothing else, but I really like the sound of the mods I did.
I'd upload some sound clips if I wasn't stuck with free dial-up... 
Would anybody like to try them and let me know what you think of the sound?




P.S. Using a metal pick adds extra mojo  

[DougH]

So there's my pickle. Which one do I put in the box?

That's easy- both.

Build two different versions and enjoy both of them.

[edvard]

*facepalm*
But I only wanted one. Oh well...

Heeeeyyy... How about if I tie both configurations to a 3pdt toggle switch? 

[George Giblet]

My original schematic was on geocities, if you didn't already know geocities is closing near the end of oct 2009,  I've moved the schematic to photobucket,

http://i476.photobucket.com/albums/rr130/ggeffects/percolator_later_rev1_1.png

[skrunk]

Hope no-one minds me bringing this thread up again.
I've been mucking about with it on the breadboard and am interested in Gus' suggestion to bias the two gain stages separately.
How do you go about this?
Do you treat each section as a  separate, closed circuit or just disconnect them by, say removing the 22uf cap or something?

[Gus]

Been thinking about this circuit again.

Now take a close look at the hfe vs Ic numbers in this PDF

http://www.datasheetcatalog.org/datasheet/philips/2N2222.pdf

Use ohms law and figure out the collector current Or read the thread

Some other notes from a sencore transistor checker hfe 200 cheap DMM($1.99 HF cen tech special like some might have) hfe 166, other transistor sencore hfe 190, HF 159

The hfe you measure with an inexpensive tester might not be the hfe of the transistor in circuit.