# Isosceles Boost - who else has built one?



## owlexifry (Jun 12, 2021)

3rd pedal build.








had high hopes for this pedal.
i wasn’t really sure whether to post this on here, or ‘troubleshooting’, because it appears to be working just fine.. 
completed the build. it works well. no noises/hum.
the tc integrated preamp mode sounds great.
the ‘fortin’ (33/grind) mode sounds good too, but for some reason, the output is considerably less compared to the ‘tc pre’ mode. i’m not sure if the fortin modes’ output is supposed to be like this or not. still adds saturation etc., it just seems to be quite a low output for a drive..

would be good to hear if anyone else that has built one has also observed this difference in output between the x2 modes.. ((haven’t really seen this issue pop up at all in any searches)

i reviewed every demo vid of this pedal i could find on youtube and a few appeared to demonstrate this lower output on the fortin modes also, but i dunno it just doesn’t seem right..

is it possible there’s a fault somewhere? 
(is it worth checking/resoldering the caps / resistors in the circuit for the fortin modes?)

perhaps if it’s supposed to be like this, i’m wondering there’s something that can be done (modified) to increase the output on the ‘fortin’ modes.. 🤔

ah well, tc pre mode sounds really good at least


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## mnemonic (Jun 12, 2021)

I haven’t built this specific model, but I did build the Triangulum (just the 33) and the Integral (tc pre clone) as well as I have made tagboard tc pre clones in the past and have an original. They’re all the same circuit but with a fixed eq for the fortin models, rather than adjustable. 

the 33/grind cuts a ton of bass so that will reduce overall output. If you turn the bass to 0 and leave treble at noon, is the tc pre mode the same volume as the Fortin modes?


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## Feral Feline (Jun 12, 2021)

mnemonic said:


> the 33/grind cuts a ton of bass so that will reduce overall output.


That's disappointing — I got the Isosceles to use with bass.

Is it just cutting at the input cap (C10 47n), and I'm guessing it's cutting at C13 as well (10n)?

Wasn't planning to breadboard this ...  😾. Ah well. Another shot in the dark.




@owlexifry You could try playing with R7 (220k) and or R4 (16k).


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## mnemonic (Jun 12, 2021)

Feral Feline said:


> That's disappointing — I got the Isosceles to use with bass.
> 
> Is it just cutting at the input cap (C10 47n), and I'm guessing it's cutting at C13 as well (10n)?
> 
> ...


The 33/grind settings cut bass by design, meant to make a loose high gain amp sound very tight with a guitar. I doubt the fortin 33/grind settings will be useful for bass.

the tc preamp setting won’t cut bass unless you turn the bass lower than noon though. So that should be useful with bass as a general eq and boost.

May be a good idea to increase that input cap if using with bass though. I’m not sure if it will audibly roll off lows.


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## owlexifry (Jun 13, 2021)

mnemonic said:


> I haven’t built this specific model, but I did build the Triangulum (just the 33) and the Integral (tc pre clone) as well as I have made tagboard tc pre clones in the past and have an original. They’re all the same circuit but with a fixed eq for the fortin models, rather than adjustable.
> 
> the 33/grind cuts a ton of bass so that will reduce overall output. If you turn the bass to 0 and leave treble at noon, is the tc pre mode the same volume as the Fortin modes?



thanks for the response!

so i had another go. even with the tc pre with bass set to ‘zero’, and the treble at noon (or less), the output is still much higher than the fortin modes.

i really don’t know if i’ve done something wrong, but compared to the tc pre mode, the fortin modes just kinda suck :/

it doesn’t sound like they even have as much of a bass cut as the tc pre does with the bass turned down (to like 9oclock)

the 33 mode is kinda ok, but the grind mode, damn i can barely tell if it’s even on or doing anything, when switching between on / bypass.

also, in fortin modes, i’m pretty sure the output is actually slightly reduced switched on vs bypass.
is this right? what kind of ‘drive’ pedal reduces output? yeah i get the whole shtick of the fortins is that it’s basically a fixed eq pedal, but it’s a bit of a bummer when you’re struggling to hear a difference. 

i had a bit of a play around and tried to bring up the output volume of the fortin modes by inserting different resistors to ground from the mode switch pin (to reduce the amount of negative feedback - increase output) starting with 1M0, 470K, 100k, 10k, 4k7, 2k2, 1k8, and 820r
only started noticing a difference at 10k. 
i had a temporary spst switch hooked up to see the immediate difference, and yes this certainly brought up the fortin modes output, but unfortunately adding more output only reduced the filtering and flattened the eq response..

i’ve been trying to find out anything and everything i can about this circuit, and i’ve been seeing a few comments here and there, that there may be a few design flaws with this circuit.. (particularly the triangulum) not sure if that’s anything to do with my issue though..

there was a solid review on youtube where someone was comparing the fortin modes to actual fortin pedals, and it was noted that the output is less on the isosceles boost compared to the real thing..

i just don’t get how the tc pre mode absolutely kicks ass, but the fortin modes are comparably redundant


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## owlexifry (Jun 13, 2021)

Feral Feline said:


> That's disappointing — I got the Isosceles to use with bass.
> 
> Is it just cutting at the input cap (C10 47n), and I'm guessing it's cutting at C13 as well (10n)?
> 
> ...


looking at the schematic, it appears R7 (220k) would affect the overall output, including the tc pre mode..

i noticed R4 as an option, but i’m not sure if this would affect the RC filtering for the overall ‘fixed eq’, since R4 (16k) is in series with a 10n cap..
(but these aren’t going to ground...so maybe it won’t affect this)

perhaps if i increase the value of R4 (to reduce negative feedback), could this increase output without affecting / flattening the fixed eq?


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## Feral Feline (Jun 13, 2021)

Yeah, I was thinking juggling between R7 and R4 might bring balance to the Force, erh Fortin and Pre.

Thanks @mnemonic. I'll play around and either have the input cap on a pot with a larger parallel cap or on a switch ; maybe kajigger a couple other values.


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## mnemonic (Jun 13, 2021)

owlexifry said:


> thanks for the response!
> 
> so i had another go. even with the tc pre with bass set to ‘zero’, and the treble at noon (or less), the output is still much higher than the fortin modes.
> 
> ...



sounds like there may be a wiring issue or a wrong part somewhere, my Triangulum is about the same output as my integral with the bass at zero, and my real tc pre with bass at zero.

actually, the integral preamp is slightly louder than my real tc pre.

the 33/grind modes should sound almost identical, the grind version just has slightly less top end, like the difference between treble at 1:00 vs treble at 11:00 on the tc pre mode.

May be worth starting a thread in the troubleshooting forum with some high res pics of both sides of the board, to see if anyone can catch an issue.


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## owlexifry (Jun 14, 2021)

update: all is solved. 

@Feral Feline was right! R4 was the key.

only just realized last night i had substituted a couple values cos i couldn’t get the exact values from the online store i was ordering from (subbed 160R for 150R, and 16k for 15k -> R4). i thought maybe that 1k difference was causing the issue...
so i took out R4 (15k) and replaced it with two 39k in parallel for an overall 19.5k (didn’t have anything else available and stores closed today)
fortin mode output is much better now.
actually seems to be level with the tc mode.

not sure if altering the R4 value (16k) changes the eq much (doesn’t appear to) but it certainly helped increase the lacking output!
very pleased!


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## music6000 (Jun 14, 2021)

owlexifry said:


> update: all is solved.
> 
> @Feral Feline was right! R4 was the key.
> 
> ...


This is where you need to try an temporary external pot, in this scenario a B25K as a variable resistor with 2 tapered probes that sit firmly in the resistor pad holes.
Then you can dial it in where it sounds/works the Best!
Find the sweet spot & remove the probes without moving the pot & measure the resistance & replace with the matching Resistor.


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## Feral Feline (Jun 14, 2021)

Great idea music6000.



I checked the R4/C13 corner freqs here: http://www.muzique.com/schem/filter.htm

The stock corner 16k/10n = 995.2Hz

Your 19k5/10n corner will = 816.6Hz


Of course, I've no idea how the rest of the EQ in the circuit will affect R4/C13.




This thread has been very helpful for my previously unplanned build. It is now very much planned...

TOP ROW WILL BE: Bass Vol1 Treble
BOTTOM ROW IS : Character Vol2 SW-33/Gr-sw
🕛 🕕 🕛 Channel A (TC Pre)
🕛 🕕 📍 Channel B (Fortin)


🔘____🔘
A/B and Bypass


The 2nd stomper replaces the TC/Fortin SPDT toggle for a 4PDT that switches the mode at the same time as swapping out master vol pots.
The "Character" will put a parallel cap in place with C13.
The input cap will be socketed and have a play until I find a happy-median for bass and guitar (or put this on a pot or a switch, too).


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## owlexifry (Jun 14, 2021)

Feral Feline said:


> Great idea music6000.
> 
> 
> 
> ...



damn, that’s such a good idea!

thanks for the info 🤙🏻


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## Cucurbitam0schata (Jun 14, 2021)

@owlexifry - can you tell us about that (instrument?) cable for the jacks you used? why'd you go that route? glad you solved the issues you were running into! it's such a thrill to finally have that ahHA moment.


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## owlexifry (Jun 14, 2021)

Cucurbitam0schata said:


> @owlexifry - can you tell us about that (instrument?) cable for the jacks you used? why'd you go that route? glad you solved the issues you were running into! it's such a thrill to finally have that ahHA moment.



yep it’s just shielded single core cable
(MOGAMI 2333 UNBALANCED MIC CABLE - OD 4MM)
basically a smaller gauge instrument cable.
prior to ever building any pedals, i built a couple high gain tube amps where shielded cable is absolutely necessary in some spots to minimize noise/interference. i prefer to reduce noise wherever possible, so i figured why not use it in pedals too 🤷🏻‍♂️ 
haven’t seen it used that much in many builds though, not sure if it’s really that necessary..

cheers! oh yeah for sure, it was quite a relief to be honest. been losing sleep reading schematics lol


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## Feral Feline (Jun 15, 2021)

😸 Owlexifry, I thought pedal-building was the gateway drug to amp-building, not the other way around!


Yeah, shielded cable is necessary in some high-gain pedals, and I think it helps where clock-noise is a consideration such as flangers and chorus pedals etc.

I didn't use shielded-cable on a recent Uni-vibish pedal (couldn't find it my stash) and am getting a faint ticking. The layout puts the output cap right next to the clock-chip though, so that might be my problem. I've found my shielded, so I'm going to replace the in/out wiring with the shielded, and put some tinfoil or something between the chip and the output cap.


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## owlexifry (Jun 15, 2021)

Feral Feline said:


> 😸 Owlexifry, I thought pedal-building was the gateway drug to amp-building, not the other way around!
> 
> 
> Yeah, shielded cable is necessary in some high-gain pedals, and I think it helps where clock-noise is a consideration such as flangers and chorus pedals etc.
> ...



haha yeah it's funny how that turned out...
i guess it's made the whole pedal building experience a lot more fun, and seemingly fast compared to amp building. overall build process takes up a lot less space on the workbench too.

ahh yeah that sounds logical, shielded cable seems like a no brainer to me..


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## burger-patty-and-bacon (Sep 16, 2021)

owlexifry said:


> update: all is solved.
> 
> @Feral Feline was right! R4 was the key.
> 
> ...


My isosceles is doing exactly what u describe in this thread.   I used all stock values and my R4 is 16k.   Are u saying u put an equiv of a 19.5k at R4 and it fixed the fubar volume issues between the Fortin vs TC mode?


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## owlexifry (Sep 16, 2021)

burger-patty-and-bacon said:


> My isosceles is doing exactly what u describe in this thread.   I used all stock values and my R4 is 16k.   Are u saying u put an equiv of a 19.5k at R4 and it fixed the fubar volume issues between the Fortin vs TC mode?



yep, sure did. 
so i guess if you had something around 20k available, this should do the trick


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## burger-patty-and-bacon (Sep 16, 2021)

owlexifry said:


> yep, sure did.
> so i guess if you had something around 20k available, this should do the trick


Mine was not r4..  I had to reflow switch1 and it's working beautifully now.


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