ITS8 Problem: Too much volume, harsh distortion

[afrogoose]

Hey All,

I just built an ITS8 from GGG.  As stated above, unity volume on the pedal is only about 1/5 of the way around the dial.  Also, the distortion is slightly weak (I think there should be more) and harsh.  I sourced the components myself, and built on the GGG board, so it's possible I've got a value wrong, although I've quadruple checked everything and I can't find any mistakes.  Has anyone had this problem and or have any insight?

Thanks!

[the-bna]

ITS8, is that a tube screamer knock off? Anyway, my real question is, do you have a solid state amp? Cause on tube amps a boost will cause the amp to overdrive itself, thus creating the illusion that the pedal has more gain. That's why I cant wait to throw away my solidstate amp and get myself an Orange.

[afrogoose]

Yes, the ITS8 is a tube screamer clone and no I have a tube amp.  I'm no stranger to OD pedals though, so I have a pretty good idea of what I think the pedal should sound like.  Also, I've seen some clips of the pedal online and mine sounds very different.

[erick4x4]

I would check your diodes. My guess is they aren't working so you are hearing the opamp clip, which is harsh and allows more volume.

I would definitely check them.

[afrogoose]

Eric, thanks for the suggestion.  I'll try swapping in some new diodes.

[afrogoose]

Also, I'm curious if the size of the LED matters when it comes to clipping diodes?

[MikeH]

Using something other than LEDs (Like 4148s) for clipping will make for less output and smoother distortion.

[afrogoose]

Hmm, well I installed a three way switch to switch between LED's and Si diodes and while the Si diodes are indeed quieter, the pedal still sounds nasty when distorted.  Also, there is not enough gain/distortion even when maxed.  I also measured the two transistors and the opamp and all of the levels were high by a few volts i.e. insead of 4.5v it was around 6.3.  Is this in the acceptable range?

 

[nebucanazza]

Looks like you made a mistake in the voltage divider to derive your Vref from the power. Get it to Vcc/2 and things should improve.

[afrogoose]

nebucanazza, thanks for the input.  Do you think it's possible that the Vcc might be too high because I sourced the wrong transistors?  The instructions came with a long list of transistors that supposedly worked and I selected the only one they had at Radio Shack (I couldn't wait).