Bloodshot Drive - Super low volume - Resolved.

[D1chotomy]

Hi Guys,

Been a while since I posted but found an issue after building the Bloodshot overdrive. The pedal works, it has bypass, the LED comes on and you can hear the effect, however it's barely at unity volume cranked. Not to mention barely any gain at all when cranked. The internal trim pots have to be turned completely counter clockwise to hear anything and the internal LEDS do not light up at all when playing. What have I done wrong? Excuse the weird wiring and layout, this enclosure was meant for a different project but got reused.

Thank you,

 

[D1chotomy]

Hi Guys,

Been a while since I posted but found an issue after building the Bloodshot overdrive. The pedal works, it has bypass, the LED comes on and you can hear the effect, however it's barely at unity volume cranked. Not to mention barely any gain at all when cranked. The internal trim pots have to be turned completely counter clockwise to hear anything and the internal LEDS do not light up at all when playing. What have I done wrong? Excuse the weird wiring and layout, this enclosure was meant for a different project but got reused.

Thank you,

So, I may have screwed up and put 100k trimmers in this by accident thinking they were 10k. How to I test a trimpot or know the value of it?

 

[Mcknib]

Should have a code on it

103 = 10K, 10 + 3 zeros 10,000
104 = 100K, 10 + 4 zeros 100,000

You could still tune it in to the correct resistance not as quickly as a 10K but 100K still goes from 0 to 100 so if you turn it a 10th should be around 10K trimmer value isn't critical

I used 100K building a lemon drop didn't have the required 10K still worked no problem so even if you do have a greater value installed just use it save damaging pads trying to remove it

You're probably actually better tuning it by ear to what sounds good to you Q2 is more important you want around 5v on the drain pin but FETs do vary so start at 5v and see how it sounds then adjust it till you like it

 

[D1chotomy]

Should have a code on it

103 = 10K, 10 + 3 zeros 10,000
104 = 100K, 10 + 4 zeros 100,000

You could still tune it in to the correct resistance not as quickly as a 10K but 100K still goes from 0 to 100 so if you turn it a 10th should be around 10K trimmer value isn't critical

I used 100K building a lemon drop didn't have the required 10K still worked no problem so even if you do have a greater value installed just use it save damaging pads trying to remove it

Okay, I am a fool then. These are clearly labeled 102 on the backside, so I am assuming 1k? Is this ultimately my problem?

 

[Mcknib]

Yes you're correct 1K check voltages on Q1 collector and Q2 drain see where they're at you can hardwire additional resistance if necessary but a bit messy

A 1K probably isn't enough to get the required voltages

I'd leave it for now until you suss your low effect problem do you get louder effect if you hit your strings harder if so it's probably a biasing issue

 

[D1chotomy]

Yes you're correct 1K check voltages on Q1 collector and Q2 drain see where they're at you can hardwire additional resistance if necessary but a bit messy

A 1K probably isn't enough to get the required voltages

I'd leave it for now until you suss your low effect problem do you get louder effect if you hit your strings harder if so it's probably a biasing issue

You mean measure the voltage across the two?

I may get a slightly higher audible tone if I strike really hard. All the controls seem to work as they should... the thing is just... quiet. Like just not there fully.

 

[Mcknib]

Measure the voltage on Q1 collector (pin on the right) to ground and Q2 drain ( pin on the left) to ground

 

[D1chotomy]

Measure the voltage on Q1 collector (pin on the right) to ground and Q2 drain ( pin on the left) to ground

Ahh duh. I get about 8.2 and 7.4 respectively.

 

[D1chotomy]

Measure the voltage on Q1 collector (pin on the right) to ground and Q2 drain ( pin on the left) to ground

And thank you for your help on this, btw.

 

[Mcknib]

Those voltages are too high to bias your transistors correctly you'd want around 4.5v on Q1 collector and around 5v on Q2 drain so you'd need to change the trimmers to the correct or greater value

Hopefully your transistors not biasing correctly will be your only fault I don't see any incorrect values or orientation can't see your 2 teep'ed resistors R9 and 5, just for info if you're not using a battery snap you wouldn't need to ground the ring lug on your stereo jack

 

[D1chotomy]

Those voltages are too high to bias your transistors correctly you'd want around 4.5v on Q1 collector and around 5v on Q2 drain so you'd need to change the trimmers to the correct or greater value

Hopefully your transistors not biasing correctly will be your only fault I don't see any incorrect values or orientation can't see your 2 teep'ed resistors R9 and 5, just for info if you're not using a battery snap you wouldn't need to ground the ring lug on your stereo jack

I will order some trimmers and let you know. Thanks for all of your help today!

 

[Mcknib]

As I say hopefully your only problem if you've still got low volume when you change the trimmers and bias the transistors correctly probably the easiest thing to do is audio probe it to find where volume drops off

If you're hitting the strings hard and it changes it, it sounds like a biasing problem you're gonna have to change the trimmers anyway

To remove them I'd advise just snipping the trimmer legs leaving as much as possible to grab with long nosed pliers at the same time heating the solder on the underside for around 4 seconds and gently wiggling them out then just clear the solder from the holes with a solder sucker as normal

 

[D1chotomy]

As I say hopefully your only problem if you've still got low volume when you change the trimmers and bias the transistors correctly probably the easiest thing to do is audio probe it to find where volume drops off

If you're hitting the strings hard and it changes it, it sounds like a biasing problem you're gonna have to change the trimmers anyway

To remove them I'd advise just snipping the trimmer legs leaving as much as possible to grab with long nosed pliers at the same time heating the solder on the underside for around 4 seconds and gently wiggling them out then just clear the solder from the holes with a solder sucker as normal

Great advice. I've got them on order and will report back when I get he new trimmers in. Again, I appreciate your help!

 

[D1chotomy]

I stumbled across some correct trimmers and installed today. Much, much better. Still not sure I am a fan of this pedal... and I am only just reading about biasing trimpots. But, that was my problem all along, I installed the wrong trimmers. Idiot.

 

[Mcknib]

I stumbled across some correct trimmers and installed today. Much, much better. Still not sure I am a fan of this pedal... and I am only just reading about biasing trimpots. But, that was my problem all along, I installed the wrong trimmers. Idiot.

Shoulda said this before but I normally install trimmers of at least twice the value especially if it involves FETs as you know even FETs from the same package can sometimes vary wildly

So having more resistance on tap to me is always a good idea

I usually socket transistors initially and try different ones until I'm happy with the sound

 

[D1chotomy]

Shoulda said this before but I normally install trimmers of at least twice the value especially if it involves FETs as you know even FETs from the same package can sometimes vary wildly

So having more resistance on tap to me is always a good idea

I usually socket transistors initially and try different ones until I'm happy with the sound

That's great information too. I think I'll try that after throwing in some sockets as you suggested. But hey, at least I know now that the pedal is working and it's not some other soldering or wiring mistake I made. .

Thanks!