Isosceles Boost - No worky

drew.spriggs

drew.spriggs

Well-known member
All switches/knobs do something, but it just sounds incredibly misbiased - no sustain, super farty, etc. It does appear the tone controls are working, but it's really hard to hear with how little noise I get out of it.

Confirmed all components are correct (couple of minor changes; pulldown is 2M2 instead of 10M, 1054 instead of 1044, multiplier diodes are 1N5819s, etc but nothing that should impact it), all joints are good and no visible bridges anywhere.

I don't really get what the BC550 is doing hanging off the front of the TL071 if I'm being honest - if vref is meant to sit about there then everything else makes sense though.

Voltages:
Supply
9.05

LT1054
1 8.8
2 4.7
3 0
4 0
5 .16
6 2.5
7 1.4
8 8.8

TL071
1 .14
2 23.5
3 23.3
4 0
5 .13
6 1.4
7 33.1
8 0

BC550C
1 23.4
2 21.3
3 22.7

Suggestions?
 
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owlexifry said:
the only thing stands out to me is how or why the emitter (3) is idling at a higher voltage than the base (2).

good question though, wtf is that BC550 doing? seems to be part of some sort of negative feedback mechanism in conjunction with the opamp...
Click to expand...
Weirdly enough I have the exact same issues as this guy, just with wildly different voltages around the transistor - which leads me to believe there's definitely some fuckery around there.

devito

SOLVED Thread 'Isosceles Boost Issues: tiny/no signal when engaged?'

Hey all! I am having some trouble with an Isosceles Boost build. This isn't my first pedal or even my first Isosceles. Pedal "works", but output is very quiet unless you play really hard, in which case the little bit of sound that comes out sounds a lot like a gated fuzz / spitty / etc.

Things I've checked so far:

1. Solder joints.
2. Replaced both chips with confirmed working versions (TL071 and TC1044SCPA). No change.
3. Replaced BC550C. Perhaps I had two bad ones in a row but... no change.
4. Compared all the orientations of things etc to my working Isosceles and everything is...

He also notes in his "good" build that the emitter sits higher than the base
 
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owlexifry said:
hmmm... :unsure:

well, time for some pictures...
Click to expand...
Sooo... I was poking around with my multimeter to check other voltage points while it was on and suddenly it started working. I've wiggles and moved every single component I was near and can't make it stop working. Maybe some sort of tiny short I couldn't see? No idea.

With that being said, it really doesn't have the gain I was expecting it to have given everything I've heard about it - haven't scoped it, but barely clips the input stage on my amp. Might be different with much hotter pickups, but again I've got no idea how it's meant to sound so I'm really just guessing at this stage.

I guess we can mark this as solved?
 
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drew.spriggs said:
Sooo... I was poking around with my multimeter to check other voltage points while it was on and suddenly it started working.
Click to expand...
wicked 🤙

drew.spriggs said:
With that being said, it really doesn't have the gain I was expecting it to have given everything I've heard about it
Click to expand...
a long long time ago, i had similar results on my isosceles build that worked fine, but i felt it was lacking (TC pre mode was fine, but the fortin 33/grind modes seemed a bit weak/quiet)

so i changed R4 from 16K to ~20K. this seemed to improve the levels a bit (although this does nothing to TC pre mode).
 
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