# Triangulum boost - gated/fart like sound ( Solved )



## letthemetalflow (Sep 21, 2019)

Hello everyone, I made triangulum boost , works good, I get around 31v @9.18 v regulated power supply, Vc, Vref voltages looks good, and it's awesome pedal. But when I hit my lower strings really hard, ( on dropD ) I get somehow gated sound, it kinda limits the string, not open sound ( I get a little clipping on clean channel when I do this, then after signal strength decays, it backs to normal, do you have this sorta thing too? Also I'm using bc550B, tl071(ST) , 7660scpaz. Maybe my opamp is clipping? It's like it can't handle the signal coming into it. I triple checked my soldering, parts. Any suggestions? Any specific area i have to look at? I'll try to swap op-amps to see if it helps.

Edit: Voltages

Tl071
Pin2: 29.63
Pin3: 29.32
Pin4: 0
Pin6:20.15
Pin7: 33.6

Q1(550B): C: 29.62 B: 26.56 E:28.94

7660scpa:
Pin 1&8: 8.93
Pin2: 4.27
Pin3: 0
Pin4 :0.15
Pin5: 0.3
Pin6: 4.5
Pin7: 6.81


Thank you


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## Chuck D. Bones (Sep 21, 2019)

Your Q1-B measurement reads low because your meter is loading the circuit.  Q1-E is 28.9V so Q1-B should be about 29.5V.  The only pins on IC100 that you can measure with a DMM are 1, 3 & 8.  Other than that, all of the voltages look correct.  I seriously doubt that swapping opamps will make things better, but it doesn't hurt to try it if the opamp is in a socket.

You could remove Q2, because it is does nothing.

Are you sure all of the Rs & Cs in the tone shaping network (everything to the right of IC1 on the schematic except the LEVEL pot) are correct?  If you back off on your guitar volume, does the fartiness go away?  Where do you set the LEVEL control to achieve unity gain?

Can we get a pic?


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## letthemetalflow (Sep 22, 2019)

Chuck D. Bones said:


> Your Q1-B measurement reads low because your meter is loading the circuit.  Q1-E is 28.9V so Q1-B should be about 29.5V.  The only pins on IC100 that you can measure with a DMM are 1, 3 & 8.  Other than that, all of the voltages look correct.  I seriously doubt that swapping opamps will make things better, but it doesn't hurt to try it if the opamp is in a socket.
> 
> You could remove Q2, because it is does nothing.
> 
> ...



Hello, first of all thank you for your help. Secondly I no longer have farting/ gated sound when I got my strings hard , it was obvious on clean channel. I just reflowed everything, maybe it was because I soldered them somehow windy place,bad solder joints probably.

I checked all my components, they are %100 correct, also I get unity gain when the resistance between 1-2 lugs is 3.5k 2-3 1.3k which seems a bit odd, when I fully turn the knob anti clockwise o get no sound,I think it's normal. But I reach unity gain at pretty high settings, is it the nature of the pedal? 

Also Hfe value of Q1 is around 440, I'm not sure that's a problem, I should try higher hfe transistors with proper voltage rating for that to see if that makes any change.

After all, it sounds good, just I need to crank it up quite a bit to get unity gain, which I saw all the demos of the original pedal,they seem to get unity above noon too,most of them crank it fully tho.

Thank you


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## Chuck D. Bones (Sep 22, 2019)

BC550B is fine.  HFE = 440 is more than enough in this circuit.  

The Triangulum is basically an Integral Preamp with the Bass turned all the way down and the Treble turned most of the way up.  In other words, it's a Treble Booster.  The gain at 110Hz (open A string) is only 4dB, rising to 13dB at 330Hz (open high E).  The gain peaks out at 23dB around 1KHz.  Not a lot of gain in the bass & lower midrange.  The Level setting for unity sounds about right.


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## letthemetalflow (Sep 22, 2019)

Chuck D. Bones said:


> BC550B is fine.  HFE = 440 is more than enough in this circuit.
> 
> The Triangulum is basically an Integral Preamp with the Bass turned all the way down and the Treble turned most of the way up.  In other words, it's a Treble Booster.  The gain at 110Hz (open A string) is only 4dB, rising to 13dB at 330Hz (open high E).  The gain peaks out at 23dB around 1KHz.  Not a lot of gain in the bass & lower midrange.  The Level setting for unity sounds about right.



Well, it's a relief, thank you for explaination and help, I better read more about circuits,maybe put a different circuit on breadboard, this schematic seems it has tons of unnecessary elements, component wise.Nice pedal.


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## Chuck D. Bones (Sep 22, 2019)

letthemetalflow said:


> this schematic seems it has tons of unnecessary elements



Indeed.

https://forum.pedalpcb.com/threads/...mp-omit-unnecessary-parts-save-some-time.645/


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## letthemetalflow (Oct 8, 2019)

Chuck D. Bones said:


> BC550B is fine.  HFE = 440 is more than enough in this circuit.
> 
> The Triangulum is basically an Integral Preamp with the Bass turned all the way down and the Treble turned most of the way up.  In other words, it's a Treble Booster.  The gain at 110Hz (open A string) is only 4dB, rising to 13dB at 330Hz (open high E).  The gain peaks out at 23dB around 1KHz.  Not a lot of gain in the bass & lower midrange.  The Level setting for unity sounds about right.



Can I have more boost ( let's say a couple dB) on this? I assume increasing 220k resistor would increase the overall boost? I'm having troubles to calculate overall gain of this circuit.


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## Chuck D. Bones (Oct 8, 2019)

A two dB increase will be barely noticeable.  The circuit is not that simple; the 220K resistor is part of the DC feedback loop.  The AC feedback loop is the one you're interested in altering.  That is made up of everything located to the right of IC1 on the schematic.  You will have to change pretty much every part in the feedback network if you want to increase the gain, but keep the same freq response.  

There are clean boost circuits here on PedalPCB that have more gain.  There is nothing special about the Fortin 33 except the hype.


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## letthemetalflow (Oct 8, 2019)

Chuck D. Bones said:


> A two dB increase will be barely noticeable.  The circuit is not that simple; the 220K resistor is part of the DC feedback loop.  The AC feedback loop is the one you're interested in altering.  That is made up of everything located to the right of IC1 on the schematic.  You will have to change pretty much every part in the feedback network if you want to increase the gain, but keep the same freq response.
> 
> There are clean boost circuits here on PedalPCB that have more gain.  There is nothing special about the Fortin 33 except the hype.



Thank you for super fast reply, also one more question, what does the BC550 on the left side of the opamp? Is it some type of amplifier?

Thank you


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## Chuck D. Bones (Oct 8, 2019)

Yes, Q1 is an amplifier.  Fortin copied the TC Electronics Integrated Preamp and stripped out the tone controls.  The original Integrated Preamp used a 741 opamp, which are noisy little turds.  I'm guessing that TC Electronics added Q1 in front of the 741 in an effort to reduce the noise.  It is completely unnecessary when using a TL071, or any other low-noise opamp.  One could depopulated 1/2 of the parts on this board, including both transistors, add a few jumpers, and it would sound the same.


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## letthemetalflow (Oct 8, 2019)

Chuck D. Bones said:


> Fortin copied the TC Electronics Integrated Preamp and stripped out the tone controls.  The original Integrated Preamp used a 741 opamp, which are noisy little turds.  I'm guessing that TC Electronics added Q1 in front of the 741 in an effort to reduce the noise.  It is completely unnecessary when using a TL071, or any other low-noise opamp.  One could depopulated 1/2 of the parts on this board, including both transistors, add a few jumpers, and it would sound the same.


Thank you, I should do some reading about transistor uses on noise reducing, appreciated


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