How to obtain more highs from a Purple Plexi pedal?

[gigimarga]

Hello,

I am a big fan of 386 based distortions, so i made a Purple Plexi clone using this schematic: http://www.aronnelson.com/DIYFiles/up/Lovepedal_Purple_Plexi_800%5b2%5d.pdf

It sounds almost OK for my taste, but i want to get more highs from it...how can i do that?
And, another little problem is that with the gain pot at maximum it squeals...


Thx a lot all!

[gigimarga]

 

[Darkness, Darkness]

Hello,

First thing to look at, is to tweak the tone stack components values or replace the whole tone stack. You can find lots of idea on the great AMZ website http://www.muzique.com/lab/main.htm

You might also alter the value of the input/output cap : if you decrease the input cap value, you will decrease the bass response and you'll get more trebble at the output . Also check out this article, with lots of R.G. tips,  where you should get lots of idea to tweak your pedal : http://www.diystompboxes.com/wiki/index.php?title=Simplemods#Simple.2C_Easy_Mods.2FTips_.26_Techniques

You can maybe also test a trebble bleed on some of the pots.

I don't know if the unit can be used a full gain, maybe it is too much gain which can explain it squeals. You might be able to correct this by adding/modifying voltage divider at the input or output of the circuit. (or maybe you can check if your guitar pickups are wax potted... this could help to maximize the gain without unwanted feedback)

Good luck !

[Der Groovemeister]

Keep us posted with your findings gigimarga, because i'm building one at the moment.

[gigimarga]

Hello,

First thing to look at, is to tweak the tone stack components values or replace the whole tone stack. You can find lots of idea on the great AMZ website http://www.muzique.com/lab/main.htm

Thx a lot Darkness!
My main problem is that i don't understand veryu well how the tonestack of Purple Plexi is functioning...i think that the 4.7nF from the output of the 386 must to be modified or the 100nF one from the tonestack!

[Mark Hammer]

For starters, you can lift the small cap to ground on the input.  Then, you can try changing the 100n cap to ground onthe tone control for a 47n unit.

[Darkness, Darkness]

Hello,

First thing to look at, is to tweak the tone stack components values or replace the whole tone stack. You can find lots of idea on the great AMZ website http://www.muzique.com/lab/main.htm

Thx a lot Darkness!
My main problem is that i don't understand veryu well how the tonestack of Purple Plexi is functioning...i think that the 4.7nF from the output of the 386 must to be modified or the 100nF one from the tonestack!

Well I am not a guru too 

For me, the tonestack is the resistors/caps network between the volume pot and the 4n7 Cap after the output of the IC. Note that the 4n7 cap / 4K7 resistor is a low pass filter. You should try to first tweak their values  (http://www.muzique.com/schem/filter.htm?X2=2000&X1=0.0047&Out=7208.5)

One think I find usefull it to use an audioprobe (basically a a probe followed by a cap and going to the input of a test amp) : it is usefull for testing each stage of a circuit. This might also help you to hear how your tweaking is affecting the tone at specific point of the circuit

[gigimarga]

Thx both of you, Mark and Darkness!

[gigimarga]

I lifted the 370pF cap from input to ground and the squeals became stronger...i replaced the 100nF from the tonestack with a 47nF and it sounded a little better...i replaced it with a 22nF and it sounded better...anyway, the squeal is too strong, so i give up!

[Renegadrian]

I'm getting crazy over that pedal...I actually built two and got the same problem - squeals and whistles like hell at max gain...
I have no clue on how to get it working properly!!!

[slacker]

Use the inverting input instead of the non inverting one, just switch pins 2 and 3. That often stops 386s squealing.

[caspercody]

I found a schematic called 386 anti hiss. Never tried it, and not sure how to attach to this forum. If interested send me a pm, or an email. My email address is on my info page.

[Renegadrian]

yeah saw it on the other forum...but dun wanna try...