Author Topic: Essential Harmonic Percolator Q1 PnP/ Q2 NpN Transistor gains?  (Read 1083 times)

Rob Strand

Re: Essential Harmonic Percolator Q1 PnP/ Q2 NpN Transistor gains?
« Reply #20 on: February 04, 2021, 09:12:24 PM »
Quote
wow, thats a really cool article! i might just build it since i have all the components in there, the acompanying article is really nice as well, t really makes me have a different view on the Bazz Fuss, maybe ill add some resistors to the first gain stage of my Harmonic Instant Coffee to have some more sustain, and less of a gating effect when the 2nd transistor is set really nasal and harsh.
Yeah, when you stumble on some old articles it makes you wonder what is old and what is new.   

I haven't built a Bazz fuss for a while but seem to remember the Darlington sounding less gated and perhaps Red LEDs more open.  There was also adding the emitter resistor of say 470 ohm to 1k which cleaned it up.  So many things to play with and only one transistor.  Then we move on to the Electra Fuzz ...
The internet:  answers without the need for understanding.

Gus

Re: Essential Harmonic Percolator Q1 PnP/ Q2 NpN Transistor gains?
« Reply #21 on: February 05, 2021, 09:04:53 AM »
This 1978 fuzz article by D.McCabe makes it clear how biasing can affect the part of the transfer curve you are on.    It seems more applicable to Bazz-Fuzz than the Percolator.    The Percolator biases the transistors with low Vce, a few other old pedals do the same trick.

https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-Modern/Archive-Practical-Electronics-IDX/IDX/70s/Practical-Electronics-1978-10-OCR-Page-0052.pdf
https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-Modern/Archive-Practical-Electronics-IDX/IDX/70s/Practical-Electronics-1978-10-OCR-Page-0053.pdf

Thanks for the links

I have not seen that site before. Looking around it I found this
https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-Modern/
https://worldradiohistory.com/hd2/IDX-UK/Technology/

For others using fuzz as a search term you can find a number of scans.
That site looks like a place you can lose a few hours searching for things.

PRR

Re: Essential Harmonic Percolator Q1 PnP/ Q2 NpN Transistor gains?
« Reply #22 on: February 05, 2021, 02:57:14 PM »
> you can find a number of scans.

Don't fool with the 1-page scans. Go to the top of the site. In the left sidebar is a box "A" to "Z" almost every electronics rag ever published. Download whole issues, decades. I have all of WW and most older Pop Electronics on hand. And some obscure stuff too.
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bmsiddall

Re: Essential Harmonic Percolator Q1 PnP/ Q2 NpN Transistor gains?
« Reply #23 on: February 05, 2021, 07:15:12 PM »
i have build a few Harmonic Percolator bastardizations with octave up sounds, but octave down is a new one!
how do you achieve that?

also, what are your emitter voltages like? have you tried changing the emitter voltages through collector resistor of Q1?
i found that having the same collector voltage with different trannies puts you in the same ballpark, sound wise, might have a bit more gain and grit, but the overall profile seems quite consistent with the same voltage

cheers, Iain
I've tuned mine similarly to the Latent Lemon (https://www.youtube.com/watch?v=eKbp9y1ACIo) - you can hear that separate grunty note on the lower E string.  That's what I'm calling an octave down, but i could be mistaken (it happens!).
I used the standard Giblet schematic (20k, 220k, 750k, 91k) but as i said, added the 5M trimpot in series with the 750k.  If memory serves, i chose a Q2 value around 200hfe and swapped a lot of Q1 transistors until i got a satisfactory, grunty HP sound.  I then swapped a few Q2 until i start getting the octave down/ghost notes quite high up on the G or B string around the 12th fret.  Different hfe for Q2 determined if/where these occurred.  Got the best result with hfe at 179.  After this I then started cranking the 5M trimpot which lowered where the ghost note appeared and how strongly.
Voltages (CBE):Q1 1.19, 1.46, 1.52; Q2 3.72, 1.91, 1.52.  I haven't tried tuning the resistors around Q1 but have that planned on the next build (oh yes, there will be a next build  :icon_twisted:).
« Last Edit: February 05, 2021, 07:17:29 PM by bmsiddall »

iainpunk

Re: Essential Harmonic Percolator Q1 PnP/ Q2 NpN Transistor gains?
« Reply #24 on: February 05, 2021, 09:23:34 PM »
if you are going on a next build, can i suggest the Harmoinic Instant Coffee, its not ''final'' yet
i posted an Introduction on the other HP thread going on, i encourage you experiment with the resistor values, the capacitor values, the transistors and the diodes.
at this point i have a BC516 as the PNP, paired with a BYX10 diode, and a reverse Beta 2n2222 and a red LED as the NPN side, both with 39k resistors.
with reverse Beta, i essentially mean that i flipped the C and E of the transistor, it still works, but is less linear and the gain of the trasistor is way lower, heavily misbiassing the 2nd gain stage

some ou you might already have read my recent posts and schematics, but i havent seen this thread before, and it seems a good place to post the schematic and name explain:


the 39k resistors are just place holders, if you decide on building it, i recommend experimenting on breadboard beforehand to find the resistors that match your transistors and diodes best.
the 4n7 was initially selected because its the value i have most of, about 60% of all my caps are 4n7, but in lots of diffetent materials and packages, i tried smaller and larger caps, but i keep coming back to the 4n7, it just sounds the best to my ears.
i have also put my NPN transistor in reverse Beta, that gives a really nasty, nasal, noisy tone

i called it the Harmonic Instant Coffee
Code: [Select]
percolator coffee is nice, high quality, fine tuned by the masters of coffee making and soft in aroma's.
instant coffee is mediocre at best, poor quality, the cheapest beans are used and can be really harsh tasting.
Harmonic Percolator is nice, high quality, fine tuned by the masters of pedal building and is soft in tone.
Harmonic Instant coffee is NOT NICE, simplistic, cheapest parts are great for it, and can be really harsh sounding.

cheers, Iain
cheers
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