Harmonic Percolator (George Giblet's schem) build report

[Gus]

Selecting biasing resistor circuits.  This is instead of an adjustable power supply to select the resistors for the transistors used.

http://www.diystompboxes.com/smfforum/index.php?topic=85828.0

[Gus]

A 2 NPN HP like circuit idea.

http://www.aronnelson.com/gallery/main.php/v/gus/2npnHPlike.PNG.html

Current is .116ma.

Temp was 78F.

Not tested yet DC readings are from R1,R2,R3,R4,Q1,Q2 part that is built.  hfe readings measured with a cen tech DMM I bought from HF.

[alex frias]

thanks for sharing!

Have you tested it with clipping diodes at the output?

[mac]

just for the record,

si-npn, ge-pnp values:

rc, re: 90k
r1: 680k npn
r2: 220k pnp
npn hfe: 250
pnp hfe: 55; leakage: 70ua
ve: 4.1v, ie: 44ua

mac

[Gus]

Mac to be clear I am aware of the values you posted, they seem to be what people seem to like when trying to clone the circuit.

I posted something a little different to show the HP idea of series powered lower voltage supply gain stage, might be fun to experiment with higher current, different transistors etc.

FWIW I included hfe readings on the 2 NPN schematic from a $1.99 on sale centech brand meter from Harbor Freight.  The same transistors on a transistor tester measured Q2 200 and Q1 190.  The hfe vs Ic is curved and at .05ma I would think the hfe is lower.  I included the cen tech readings because people at this forum might have more DMMs like that than transistor checkers.

[mac]

Gus,

I´m waiting a flight and in the meantime I did some math and solved the DC bias which is valid for all silicon versions, HP & Barge Concept, no matter if they have two npn, or a npn-pnp pair.

Please open your book on page 91 and see Harmida or Barge concept schematics

Let
ra: resistor to Vcc
rb: resistor to Gnd
r1: resistor from Q1 collector to base
r2: resistor from Q2 collector to base
d1,2: Vbe1,2
a1,2: (b1,2+1)

Note that both emiter currents are equal so,
ie1=ie2=i
(b1+1)*ib1=(b2+1)*ib2  [1]

and that
vcc=i*(ra+rb)+ib1*r1+ib2*r2+d1+d2  [2]

[1] --> [2]

ie2=(vcc-d1-d2)/(ra+rb+r1/a1+r2/a2)  [3]

if ra=rb=91k, r1=735k, r2=220k, b1=250, b2=50 then ie2=ie1=0.04ua, which are the values we found in the real world.

You can ask, how do I do to get half vcc at the junction of both transistors?
In this case you want

vcc/2=d1+ib1*r1+a1*ib1*ra
vcc/2=d2+ib2*r2+a2*ib2*rb

using eq[1] and assuming that d1=d2 then

r1/a1 + ra = r2/a2 + rb

If ra=rb then r2=a2*r1/a2

For b1=250, b2=70 and r1=735k then r2=206k.

In the case of the Barge concept where ra=91k and rb=22k then for the same values r2=5M!!!
I do not think that biasing at vcc72 is important in this case.

I did calculations including leakage and estimated values are close to the ones I posted above, but in this case germanium base current is negative in most of the cases.  It looks like the 220k resistor is draining leakage from the base, if not a leakage of 0.1ma across the 91k would be greater than the battery voltage. I remember to have tested germs with leakage well above 0.1ma and they worked fine.
Ideas?

Riiiing. Class dismissed! 

mac

[Frances Rhodes]

hi everyone

i just built a harmonic percolator (first attempt...) based on this schematic http://www.fredric.co.uk/misc/HarmonicPercolator.sch.png with a tru bypass switching, and i get no sound when engaged (the sound gets through when bypassed).
this is point-to-point wiring cause i'm still not able to make my own PCBs.

i used a 2n404 and a 2n3565 from small bear, metal film resistors...
i double-checked for shorts and didn't find any, double-checked for transistors pinout, power supply polarity (i use a regular boss/ibanez like center negative supply, negative pole star grounded to the input jack) and am now clueless about what to do but rip everything out and redo it all over.

here are my eagle cad files :
- schematic https://dl.dropboxusercontent.com/u/1301693/harmonic%20percolator.sch
- and circuit board https://dl.dropboxusercontent.com/u/1301693/harmonic%20percolator.brd (i couldn't add bridges to the board file so i left two tracks open, put 2 bridges on the actual board)

if anyone has some advice, i'd be glad to here it!

regards

frances

[Frances Rhodes]

oh shoot, nevermind!! i found my mistake... 

[Gus]

Has anyone built the two npn 2N2222 HP like I posted? in this thread http://www.diystompboxes.com/smfforum/index.php?topic=68649.160

[garcho]

^ no, but I'm about to     i love anti-mojo circuits!

[Cozybuilder]

Gus- I was just wondering if you might have a book of your circuit designs? I'd buy it.

[mac]

Gus,
What about replacing that 10k with a pot, and connecting the 100u cap to the wiper?
Or using a bigger pot as a variable resistor?
I did that with an all germ npn-pnp HP, I got a kind of 8-up effect.

I'll give it a try.

mac