Energized by a recent build where I stuffed 6 different "classic" 2-knob distortion/drives into a single enclosure with a rotary switch to pick one, I decided to take on a trio of classic 3-knobbers in a single box. One of them is a Superfuzz, using this schematic:
(http://3.bp.blogspot.com/-cBIzyse_wes/T0EHt4QmTvI/AAAAAAAAA88/Y1fbps_nMsQ/s1600/univox_superfuzz_schematic.gif)
The perfboard I'm using doesn't have a lot of room, so I've had to resort to various space-saving tricks, like vertical installation of 1/8W resistors and such. To save even more room, I thought I would try using a 2SC1538 matched NPN-pair for the "mirror" you see in the middle of the circuit. Worked like a charm! Sounds great, and provides decent octaving. I also used Dino/digi2T's trick of inserting a small value resistor (220R in this instance) in series with the diode pair to soften the clipping, while still retaining the Q&D limiting they provide. Also worked like a charm.
But but but the Superfuzz is NOT a "3-knobber", you say. Correct. I subbed a variable resistance to ground from the 100nf cap in the midscoop filter, like ZVex does with the Octane (Madbean Poindexter). Works as well as the Tone switch, and means you can forego the Tone switch and the 47k/10k divider.
Actually, let me add to what I wrote.
Holy crap, the octaving is fantastic! I can get very robust octave-up below the 5th fret, something that was well out of reach in previous Superfuzz builds. This is at least as robust an octave-up unit as the Foxx, if not better. I'm impressed.
As a sidenote, the remainder of the transistors are plain vanilla 2SC828,
Is HFE important in this case or not?
No. It's not amplifying the signal in any discernible way, merely combining two opposite-phase copies of the signal. The reason why I thought of using the 2SC1583 (and 1538 was a typo...sorry) is that the two transistors in that 5-pin package are very precisely matched. And when it comes to octave-up generation, the two complementary copies of the input need to be very closely matched to optimize that. Normally, I would simply check the values of the emitter/collector resistors on the phase splitter, and resistors on the emitter and collector outputs. But since I already used 1% components there, I decided to try something that would go a step past that level of matching.
Those who have followed posted info and drawings of the Superfuzz will likely be familiar with drawings like this one, that include a trimmer for adjusting the balance between the biasing of the two mirror transistors.
(http://files.effectsdatabase.com/docs/schematics/univox_superfuzz.gif)
I've built that and still got nowhere near the robust and reliable octaving I get with use of a matched pair of transistors. I should emphasize that it does not have to be a 2SC1583. There are a number of available transistor-array packages that could probably work well, like the CA/LM3046 (regularly used in analog synths) or LM3086. Both of those chips have 5 discrete transistors, including a pair with a common emitter. With the addition of another discrete transistor, I'll bet they could make pretty decent octave-up units.
Hmmmm.... this calls for an investigative visit. Perhaps I'll distract you with a Bi Phase while I noodle with your SF. :icon_wink:
Very cool Mark. I've been going through a lot of old era devices lately because I've been separating out the schematics for that era from the later ones.
I wonder if adding a 8.2k to 10k in series with the bottom 470R would further help matching. I suspect it might because as there's a natural imbalance caused the output impedance of the phase-splitter working against the bias dividers of the "diffamp".
QuoteI wonder if adding a 8.2k to 10k in series with the bottom 470R would further help matching.
Not so simple. With some signal levels it seems to make things worse!
Apparently the virtues of using a matched pair for the doubling has come up here before: https://www.diystompboxes.com/smfforum/index.php?topic=110775.0
...although the thread seemed to meander to other, less electronic, connotations of matched pair. :icon_rolleyes:
QuoteApparently the virtues of using a matched pair for the doubling has come up here before
I actually went through exactly what is going with this pedal the other day but I didn't post anything because it was a little long winded and techy to explain.
When we match transistors it can mean different things because they have more than one parameter. "Matched" transistors often matches Vbe for a given current (as well as gain to a degree). As it turns out Vbe only has a small effect for the Super Fuzz. What is very important is to match the hFE.
The reason can be explained as follows:
From the perspective of the phase-splitter we want the signals at the collector and emitter to be equal magnitudes. To simplify the argument we will ignore the effect of the transistor's output impedance at the emitter (re) and the fact the collector current doesn't quite equal the emitter current. Under these assumptions: The gain for signal at the emitter of the phase-splitter is 1 So for matching we need the signal at the collector to have gain 1. And for that we need the load on the collector to equal the load at the emitter.
Now, the load on the emitter is: the 10k emitter resistor, the 22k bias resistor, the 100k bias resistor, and (most importantly) the input impedance of the rectifier transistor all in parallel. The load on the collector is
the 10k emitter resistor, the 22k bias resistor, the 100k bias resistor and the input impedance of the *other* rectifier transistor all in parallel. We could throw in the effect of the 470R's we well.
The key point here is the input impedance of the rectifier transistors need to match. That impedance is actually quite low compared to all the other resistances making up the load impedances. The input impedance of a transistor stage is directly proportional to hFE (actually hfe+1). So if the rectifier transistor gains don't match the input impedances don't match and that stuffs up the balancing of the signals on the collector and emitter.
With this in mind the, mod of adding the resistor in series with the emitter output of the phase splitter obviously doesn't help matching the collector and emitter *voltages*; which is exactly what I saw.
Another issue with unmatched hFE on the rectifier transistors is it makes each rectifier transistor operate at a different current and that makes gain for each arm of the *rectifier* unmatched. This is much less of an influence than the input impedance issue. Typical the side with the high gain transistor will have a higher rectifier gain and higher voltage gain so it make both mismatching mechanisms on that arm worse.
Some solutions were,
To combat the impedance imbalance issue:
- Add buffers to each output of the phase splitter, or
- Add a buffer to the input of the rectifiers, or
- Make the rectifier darlingtons, or
- Add a trim pot to match the input impedance
- (less effective) reduce the resistance of the base bias networks for the rectifiers, and the lower phase splitter resistors.
To combat the bias point imbalance (which affects the rectifier signal gains). These I didn't fully explore.
- Use a current mirror in the emitters but bypass the emitters with caps!
- Possibly use separate emitter networks for each rectifier to stop hogging of the bias current.
- Use lower base-bias resistors.
- Use a trim pot to balance the collector current.
Ideally I wanted to come up with a scheme so that when you adjust the collector currents to match it automatically tweaked the input impedance as well.
Feedback bias might work but it cannot have AC feedback, only DC feedback. The AC feedback linearizes the signal and we lose the octave!!!
I wonder why VC = 6V and VE = 3V, not VC = 7V and VE = 2V
according to https://www.electronics-tutorials.ws/amplifier/phase-splitter.html
is phase-splitter it self intend to be distort, compare to Acetone FM2 with 100K resistor?
It's a bit more complicated 'cause, for AC load line, Emitter/Collector equivalent resistors are 10k // [470R + (22k // 100k)]..
try to draw it, correct me if I'm wrong
(https://i.postimg.cc/KkfNDJN1/sf.png) (https://postimg.cc/KkfNDJN1)
if I m not mistaken, if the 150K replace with 100K then
VB = 100/(220+100)*9 = 2.81
VE = VB-0.6 = 2.2 --> 2V
VC = 9V-VRC = 9V-(VE/RE*RC) = 9V-VE = 6.8 --> 7V
FY6 Uni Super Ibanez Aceton Kay Fuzz
Q3
RA 220 220 220 510 220 47 K
RB 150 150 150 100 K
RC 10 10 10 10 10 10 K
RE 10 10 10 10 10 10 K
Rin 0.47 0.47 0.47 1 1 0 K
Q4/5
RA 100 100 100 150 100 100 K
RB 22 22 27 22 15 10 K
RC 10 10 10 10 10 10 K
RE 2.2 1.8 1.8 1 1.8 1.8 K
Q3 VBE (0.6)
VB 3.65 3.65 3.65 2.81 V
VE 3.05 3.05 3.05 3.97 2.21 -0.6 V
IE=IC 0.3 0.3 0.3 0.22 mA
VRC 3.05 3.05 3.05 2.21 V
VC 5.95 5.95 5.95 5 6.79 9 V
Q3 ref 3 – 6 3 – 6 3 – 6 4 – 5 2 – 7
VB 3.27 1.85
VE 2.72 3.97 1.84
VC 6.23 5 2.54
Q4/5
VB 1.62 1.62 1.91 1.15 1.17 0.82 V
VE 1.02 1.02 1.31 0.55 0.57 0.22 V
IC 0.46 0.57 0.73 0.55 0.32 0.12 mA
VRC 4.65 5.68 7.3 5.51 3.19 1.21 V
VC 4.35 3.32 1.7 3.49 5.81 7.79 V
4.5 3 6 V
assuming for 2 - 7V, we can get good octave at louder signal
There might be a simple way to get matched transistors you can use for a push-pull frequency doubler.
Use an LM318 op amp and connect the bal/comp pins (1 and 5 on the 8-pin device) and use this junction as the collector. It does limit the input voltage between the inverting and non-inverting inputs with diodes but if you keep the level below where the diodes conduct, they have no effect. Of course, if the diodes conduct, they give a fuzz effect, so that may be what you want anyway. You don't use the output of the op amp since it would follow the difference in collector voltages, but we have shorted them together.
Since the transistors in an op amp are formed at the same time from the same process, they tend to match very well for gain and Vbe.
chips too expensive
what if for Q4/5, 100K replace with 56K and 22K with 12K
It will lower Base bias, hence Emitter voltage by about 35mV..
So..?? Are we looking for a stiffer voltage divider configuration..??
In my current understanding impedance imbalance mean zout <> zin
zout Q3 = 10K, so I try to make it same by (12*56)/(12+56)=9.88K
then I realize not include rpi (I learn from electrosmash) which
"(most importantly) the input impedance of the rectifier transistor"
my mistake, so I calculate with good ref VE=1.11 VC=3.1 VCC=8.88
IC=(VCC-VC)/10000=0,000578
IE=VE/1800=0,000616667
to make it simple I use 0.6 mA
rpi = 25/0.6 = 41,66
hfe zin
100 4166
150 6249
200 8332
250 10415 ???
300 12498
then I go to "- Add a trim pot to match the input impedance"
what ever hfe we can adjust to 10K, by triming IE
zin=hfe*rpi
zin/hfe=25/IE
hfe/zin=IE/25
IE=hfe*25/10000=hfe*0,0025
hfe IE (mA) RE(VE=1.11) VC(VCC=8.88)
100 0,25 4440 6,38
150 0,375 2960 5,13
200 0,5 2220 3,88 ***
250 0,625 1776 2,63 *** 3.1
300 0,75 1480 1,38
If 3.1V so good wouldn't be hfe between 200 - 250, good for impedance?
assuming Q4/Q5 also low I guess is ok if zQ3 <> zQ4/5, (10K <> 4K4)
but maybe is even better if match
Replace RE 1K8 with 5K trimpot, so whatever hfe we can adjust impedance
and what ever VC also, learn from master Paul when learn bigmuffpi :)
so I feel ok, beside the range is 1.7 (superfuzz with trimpot 10K) - 7.79V (Kay Fuzz)
for hfe what I learn is, in circuit can be 100 - 700 range,
but at higher hfe I fill it more sensitive, so I tend to choose lower.
for
"The key point here is the input impedance of the rectifier transistors need to match."
been overcome by Sir Digi2t and Sir Mark,
I choose 1% resistor 99% luck
Would a AS394 work, or is the hfe too high?
https://cabintechglobal.com/pdf/ALFA_RPAR_AS194_AS394.pdf (https://cabintechglobal.com/pdf/ALFA_RPAR_AS194_AS394.pdf)
(They look pretty cool in their nifty 8-pin metal can, even if they are a bit pricey.)
(https://cabintechglobal.com/images/prod/AS394H.jpg)
I could not say about match pair transistor
but on solution
"- Make the rectifier darlingtons, or"
" ... or: (J)FETs" :icon_wink:
You could always use a precision fullwave rectifier with the same effect as the push-pull amplifier used in the circuit. It requires a dual op amp but this should not be a hardship since these items are cheap.
(https://i.postimg.cc/qMKTNHGv/fwrect.jpg)
In this schematic, the 4.7K resistor should be 5K which you can create by using two 10K resistors in parallel. There are several similar op amp fullwave rectifier circuits but this will give balance as good as resistor matching allows. In this diagram, ignore the ± supplies and assume the grounds go to Vcc/2. Most op amps should work in this circuit.
Quote from: zbt on November 29, 2022, 05:23:55 AM
In my current understanding impedance imbalance mean zout <> zin
zout Q3 = 10K, so I try to make it same by (12*56)/(12+56)=9.88K
Now I've got you.. :icon_wink:
There is no need to make them equal to Q3 respective output impedances (unless you care about maximum power transfer..).
Just lower their value, togheter with Q2 Collector & Emitter resistor value lowering, for the rest of impedances to be scaled up (as seen from respective drivers view point) so their inequality to be scaled down..
I might confused you, so just think of A // B //C1 and A // B // C2 for A = B = 10k, C1 = 100k, C2 = 101k and then for A = B = 1k with C1 & C2 retained the same..
Quote from: puretube on November 29, 2022, 06:48:02 AM
" ... or: (J)FETs" :icon_wink:
I mean darlington has high hfe
for Ben
Quote from: duck_arse on May 31, 2015, 10:10:42 AM
all my transistors are BC547, 8 or 9 of various makes/grades/ages. the first 3 are 190, 130, 118 hFE, the rectifiers are 472/474, output is 283. I trimmed the bias on the phase-splitter for best headrooms (the 9k1's are what I have). the octave lift shown is what I'm going with. the extra capacitor is meant to AC ground the unfed base without shifting any DC's or poppings. it will work in either leg of Q3. if you don't want that nasty distortion, lift the collector.
(http://i.imgur.com/yfbYEvl.png)
in the rectifier, I found it easier to see what it wants to do if you lift the diodes during the breadboard stage. that's why I've fiddled the base resistors, the collectors are now at 4V33 and provide the largest clean swing, small signal, which sometimes peeps-out from under the diodes. I think I observed higher hFE gaving greater rectifier output, but it seems the octave goodness varies with frequency. changing transistors changed the balance and the freq peak. most of this is obscured when the diodes are 'in'.
lifting the octave may increase the noise as well, in which case you can tweak on the balance trimmer, and it may disappear. I've got 1% bias resistors and can tune with a 500R trimmer, but 2k is on the bb now, still keeps the tune 'close' even when 'way off'.
diode lift is just a 1k resistor. the volume increase makes stock sound puny, so it can stay as is. stock volume is puny, by the way, even after messing the last stage for more gain and using a log balance pot.
I dunno if I've come to the same outcome as digi, but I have found some things. there's mayhems in all directions; saturations, disappearings, louder re-appearings in the tail. lotsa times it screams 'feedback', but doesn't actually. someone who can actually play a note might even get some toans from, but not me. I haven't got a fork, so I'm sticking my toothpick in it, no more changes.
Quote from: amptramp on November 29, 2022, 07:06:27 AM
You could always use a precision fullwave rectifier with the same effect as the push-pull amplifier used in the circuit.
Thanks for offering me another crispy circuit, Sir Ron, I reserve for later.
Quote from: antonis on November 29, 2022, 07:41:45 AM
There is no need to make them equal to Q3 respective output impedances (unless you care about maximum power transfer..).
a! ok now
I would clarify again my mind
"When we match transistors it can mean different things because they have more than one parameter. "Matched" transistors often matches Vbe for a given current (as well as gain to a degree). As it turns out Vbe only has a small effect for the Super Fuzz. What is very important is to match the hFE."
https://dragonflyalley.com/synth/images/TransistorMatching/ianFritz-transmat0011_144.pdf
it's a relief, only hfe :)
"From the perspective of the phase-splitter we want the signals at the collector and emitter to be equal magnitudes."
-1V 0 1V, ? Volt value
"To simplify the argument we will ignore the effect of the transistor's output impedance at the emitter (re) and the fact the collector current doesn't quite equal the emitter current."
IE = IB + IC, IB so small
"Under these assumptions: The gain for signal at the emitter of the phase-splitter is 1 So for matching we need the signal at the collector to have gain 1."
A = 1 = RC / RE
"And for that we need the load on the collector to equal the load at the emitter."
RC = RE
"Now, the load on the emitter is: the 10k emitter resistor, the 22k bias resistor, the 100k bias resistor, and (most importantly) the input impedance of the rectifier transistor all in parallel."
RE = 10k // [470R + (22k // 100k)]
"The load on the collector is the 10k emitter resistor, the 22k bias resistor, the 100k bias resistor and the input impedance of the *other* rectifier transistor all in parallel. We could throw in the effect of the 470R's we well."
RC = 10k // [470R + (22k // 100k)]
"The key point here is the input impedance of the rectifier transistors need to match."
maybe at this point I'm confuse, imbalance between rectifier transistors itself
"That impedance is actually quite low compared to all the other resistances making up the load impedances.
The input impedance of a transistor stage is directly proportional to hFE (actually hfe+1)."
zin = (hFE + 1) * re
"So if the rectifier transistor gains don't match the input impedances don't match and that stuffs up the balancing of the signals on the collector and emitter."
diff
hfe ohm
10 450
20 900
30 1350
different value of 30 already make 1K differences, what makes a bulk differences? 10?
"With this in mind the, mod of adding the resistor in series with the emitter output of the phase splitter obviously doesn't help matching the collector and emitter *voltages*; which is exactly what I saw."
ouch, I thought the 470 was to avoid distortion, and that value for 10 differences, now become accessories, why not just replace it with diode
might be Kay Fuzz dont use it.
"Another issue with unmatched hFE on the rectifier transistors is it makes each rectifier transistor operate at a different current and that makes gain for each arm of the *rectifier* unmatched. This is much less of an influence than the input impedance issue. Typical the side with the high gain transistor will have a higher rectifier gain and higher voltage gain so it make both mismatching mechanisms on that arm worse."
find low match hfe
find my luck at digikey 2SC4207-Y, but not at my local store :-\
not know would be match, may be others can test it.
this also interesting
"- Possibly use separate emitter networks for each rectifier to stop hogging of the bias current."
These were a popular sale for me in the 90's ... you only need to match hFE and use 1% resistors in the rectifier section to get consistent results // matching signal caps doesn't hurt either...
http://www.lynx.net/~jc/pedalsRoyal.html (http://www.lynx.net/~jc/pedalsRoyal.html)
QuoteI mean darlington has high hfe
I mean (J)FET has high input-impedance.
That would be interesting too, since the JFet only requires a 1M resistor bias
does it have to be matched too?
once again I would clarify my reference interpretation
Base on Solidhex
C B E hfe
Q1 6.01 0.66 0.117 C539 100
Q2 8.88 6.01 5.41 C828 200
Q3 6.23 3.27 2.72 C828 200
Q4 3.1 1.7 1.11 C539 100
Q5 3.1 1.67 1.11 C539 100
Q6 5.75 0.98 0.361 C539 100
suppose it use C539 TO18 hfe MIN 250 for low noise version
and C828 TO92 hfe MIN 65 as plain vanilla
I try to search and I could not find with C539, it is easy to spot because,
it would be different package, I found only all with same C828-Q
so by batch it would be all near low or high hfe
Using VCC set to 8.88V I try to check for another transistor with 100, 150, 250, hFE
and all voltage are close to Solidhex ref for hFE all around 100
So I replace Q2 and Q3 to test if it using different transistor with 250 hFE
interesting enough Q2 dont make different voltage, but Q3 go near 3V and 6V
so I am sure enough it all using same transistor.
But for Q4/Q5 I am curious why VC can get so low, cause lower hfe tend to be higher VC
would it be using high hfe, just for this two, my measurement for VE are bit lower and VC are bit higher
then I check I am using 22K transistor, so it probably it because 10K trimpot
I change 22K to 27K, and it come closer,
Test using 250 hFE would be below 3V, so Q4 and Q5 also around 100 hFE
**The good reference using low hFE and using trimpot to set it right**
now it even lower, how about 200 is easy to find
Quote from: Eb7+9 on November 30, 2022, 11:09:25 AM
These were a popular sale for me in the 90's ... you only need to match hFE and use 1% resistors in the rectifier section to get consistent results // matching signal caps doesn't hurt either...
http://www.lynx.net/~jc/pedalsRoyal.html (http://www.lynx.net/~jc/pedalsRoyal.html)
agree
mentioning fuzz face, kind dejavu it took my pride away
meh, is just easy circuit, took BC550 on it, and the result ...
Q1 and Q2 look like that, I try set Q1 lower as already test Q2 can be 200
also Q3 and Q6 200, for Q6 headroom (4.5) I just change RB 15K to 22K and RE 1K to 2K2
**Q4/Q5 should be match**
but still curios for Q4/Q5
Quote from: zbt on November 29, 2022, 06:15:36 AM
I could not say about match pair transistor
but on solution
"- Make the rectifier darlingtons, or"
Why? Does overall hfe matter? The originals were under 200. IIRC.
I was anxiously awaiting delivery of a transistor tester I had ordered, so I could evaluate transistors for a variety of purposes - stompbox and aynth. It arrived yesterday, and I was disappointed to find that it was the plexiglass enclosure for the tester, rather than the tester I *thought* I was ordering. Make sure you look and click carefully before hitting "Buy now".
Why?
I just dont have 2SC1583, LM3086, etc
darlington has higher hfe so it probably work also, but I dont know about AS394H the internal also not so simple
other result
"I think I observed higher hFE gaving greater rectifier output, but it seems the octave goodness varies with frequency. changing transistors changed the balance and the freq peak. most of this is obscured when the diodes are 'in'." duck_arse
"Typical the side with the high gain transistor will have a higher rectifier gain and higher voltage gain so it make both mismatching mechanisms on that arm worse." Rob Strand
Does overall hfe matter? The originals were under 200. IIRC.
depending on who's looking
If design for perfect could be yes
If I ask uncle Matthews, why Sir is just one transistor different?
This transistor is called John Whatever (with a cigar) :)
If I have to put C539 and C828 may be two batch, have to measure each,
would not be so costly? Make simple buy bulk
For under 200 could be ok
Then if I throw all for >200hFE, could be a problem for some topology like Q1 & Q3
is like fuzz face which in my experience Q1 better be low,
for others Q3 dan Q6 probably not
Stay safe Sir Mark,
May we ask you how much hfe 2SC1583 of yours, is it lower than 200?
Thanks in advance
Quote from: Ben N on December 01, 2022, 07:17:30 AM
Why? Does overall hfe matter? The originals were under 200. IIRC.
absolute hFE levels don't matter in the rectifier section ... as long as they're not stupidly low
"(In case of a tie, the professor wins.)" Hayt Neudeck :icon_lol:
Quote from: Ben N on December 01, 2022, 07:17:30 AM
Quote from: zbt on November 29, 2022, 06:15:36 AM
I could not say about match pair transistorbut on solution
"- Make the rectifier darlingtons, or"
Why? Does overall hfe matter?
It surely DOES matter for Q4/Q5 stages impedances inequality settlement.. :icon_wink:
(the higher the impedances values seen from Q3 outputs the lower their practical difference..)
hfe Rpi zin //18K (100K//22K)
100 4500 3600
200 9000 6000 change RE/RC Q3 to 5K6
300 13500 7714
400 18000 9000
500 22500 10000 close to RE/RC Q3
600 27000 10800
700 31500 11455
800 36000 12000
900 40500 12462
1000 45000 12857
(unless you care about maximum power transfer..).
use 500 hFE or change RE/RC Q3 as close zin
the higher hfe zin more depend on RA//RB (100K//22K)
for Q3 phase splitter
IE=IB+IC less IB more hFE, VC === VE should be improve octave, but how much compare to 10K 5% vs 1%
VE>VC around 6mV wouldn't be 470 ohm at collector side better be shorted
for VC=7V and VE=2V only add 0.75V headroom, the amount is controlled by expander,
so guess is ok, mod is simple change 150K to 100K
of course JFET is better, but again is expensive, hard to find today in my case
the problem with vintage, I feel tied to the past.
if I could go back in time, and build it with an hFE 200, the question whether it would be preferable too
looking https://wiki.analog.com/university/courses/alm1k/alm-lab-phase-split
change 100K//22K, make a single reference using 10K as 4.5ref and use diode
dunno this would work...
BOSS FZ-2 also use 100K, and weird 4K7 with 10K and 1K and no value of RE ???
but of course RE=RC so RE=4K7 :icon_mrgreen:
(https://i.postimg.cc/qhsXfkLm/Screenshot-from-2022-12-03-06-50-24.png) (https://postimg.cc/qhsXfkLm)
world full of imbalance, using all 5% for mojo, in the end trimmer is enough, trim at emitter to reduce noise :)
Quote from: zbt on December 02, 2022, 07:12:29 PM
world full of imbalance, using all 5% for mojo, in the end trimmer is enough, trim at emitter to reduce noise :)
trimmer is for "bettering" during (mass) manufacturing using random devices ... likely done somewhat crudely by ear before boxing
bettering is not the same as best ... trimmer is there to compensate somewhat for device mismatch, nothing to do with noise ...
for doing DIY onesies and twosies use a DMM and get quite likely better performance than BOSS did
no need for ultra-matched packages in single-ended rectifier stages
it's about dealing with statistical factors, blown away by the mighty DMM
maybe because I tried it on a breadboard, yes the trimpot might change more.
so i tried this circuit, sing like celine dion and a little raspy like mariah carey ;D
using only one reference, so there are only four resistors that are match.
(https://i.postimg.cc/Sjn6GXcJ/sfoneref.png) (https://postimg.cc/Sjn6GXcJ)
Finally ... low hfe is more pleasing for me :)
here is another board
(https://i.postimg.cc/sGJ0C99k/Companion-Fuzz-68x50.png) (https://postimg.cc/sGJ0C99k)
Enjoy!
When considering balance, the current through the emitter in the phase splitting transistor is higher by the amount of the base current than the current through the collector. The emitter output is also lower impedance, so even with matched resistors, you have an output that is imbalanced by the ratio of 1/hfe. A FET phase splitter would not have this problem since no gate current means the source and drain currents are equal. A Darlington transistor would reduce this imbalance while retaining the predictability of biasing voltage, which can be all over the place with a FET.
The effect of imbalance is to allow some of the fundamental frequency to get through. How much of the fundamental can we tolerate? Do we really need to eliminate the fundamental? There might be a fuller sound with some of the fundamental still in there.