Purple plexi 800

[Blacktongue]

I have built the Lovepedal purple plexi 800 but didn't have and could not find a 370 p cap I used  a 330p cap in its place  the pedal works and sounds good but there is a lot of noise could the cap be the problem
Note this is not boxed yet any help would be appreciated

[Vince]

Hi,

I'm not sure about the cap but a few (including me) experienced noise/squeal with this pedal. Near the bottom of the Purple Plexi thread you'll see Michael explain about killing the noise.

''GAIN 3 wire from board to a 150 ohm IN SERIES and after to lug 3''

If I remember rightly, I used a way smaller value like a 20 ohm resistor and that just took the edge off the gain and killed the noise at max gain.

[Blacktongue]

Thanks Vince
Ill give it a try and let ya know

[Madferret]

+1 for putting the resistor in, this was one of my first builds and it's a great sounding pedal once the noise is dealt with.

[Blacktongue]

Added the resistor no more noise when gain is maxed
Thanks everyone for the help and the quick responses
To my questions

[Smash]

Hello,

I've built this one as well and it has a great tone!
I was wondering if anyone would know how to decrease the amount of distortion at the start of the sweep.
I've already increase the value of the pot C10k, but for my taste is a little too distorted... I was looking for more start to breakup/crunchy sound...

Any tips?

Thanks guys!

[Synsound]

That's great to hear about the inline resistor.

[Smash]

The resistor help indeed with the last part of the gain sweep. But actually I was looking more into less overdrive at the beginning of the sweep.
The datasheet shows a typical capacitor of 10uF in series with pins 1 and 8 for minimum gain (20). Should I low that 47uF capacitor to change the slew-rate?

[Muadzin]

Vince wrote

Hi,

I'm not sure about the cap but a few (including me) experienced noise/squeal with this pedal. Near the bottom of the Purple Plexi thread you'll see Michael explain about killing the noise.

''GAIN 3 wire from board to a 150 ohm IN SERIES and after to lug 3''

If I remember rightly, I used a way smaller value like a 20 ohm resistor and that just took the edge off the gain and killed the noise at max gain.

I'm usually quite good in English but it is not my native language so I have some difficulty understanding this particular sentence:

''GAIN 3 wire from board to a 150 ohm IN SERIES and after to lug 3''

Does this mean that you put a 150R resistor between the gain 3 connection on the board to lug 3 of the gain pot?

[induction]

Yes. It just adds a little resistance to the top of the voltage divider so that you can't turn the gain up all the way.

[Smash]

Maybe if I replace the 10R with a 1k resistor it would make a voltage divider with the internal 1k35 and limit the gain? (throwing ideas...)

[induction]

Increasing the 10R to 1k is functionally equivalent to adding a 990R inline resistor. They are in series, so the resistances simply add together. It is easier to increase the existing resistor than to add another one, so I think it's a good idea.

I keep notes on every circuit I play with. When I breadboarded this (I never got around to actually building it, too much other stuff to do) I made some notes that you might find useful:
----------------------------------
- replace the 10R between IC1 and the gain pot with 100R (to eliminate squealing at max gain).  This will reduce bass, so replace the adjacent 47uF cap with 22uF to compensate.
- replace 4n7 unput cap with 10n because the stock circuit is too trebly.
----------------------------------

The Purple Plexi 800 (much like the Runoffgroove Little Gem amplifier) is really just a variation on the datasheet application notes, so it might be useful to give the datasheet a read, and then compare the app notes to the schematic.

If you want to reduce the gain at all settings of the gain pot, you have a few options.
1. In the stock PP800, the gain pot is paralleled by a 470R resistor. Increase the size of that resistor, or remove it entirely (no jumper), and the gain will decrease, especially at lower settings of the gain knob.
2. You can add a second gain pot between pins 1 and 8 (those pins are connected in the commercial unit so you'll have to cut the vero between those pins. With pins 1 and 8 unconnected the gain is about 20, when they are jumpered, the gain is about 200 (this is from the datasheet, and ignores the effect of the gain pot that is already in the PP800, but the principle is the same). I'd start with a 1k pot and see how it goes.
3.  If you go with option 2, you can also disconnect the stock gain control (just remove the 10R, no jumper), which should reduce the gain even more. This would give the option for high and low gain modes by switching that path open and closed with a SPST toggle.

Whatever you do, I suggest, as usual, that you breadboard it first.

[Smash]

Alright!
Thank you very much Induction!

I did read the datasheet and I thought of cutting the board between pins 1 and 8 but, as my board is already boxed I'll start with the simple mods first.
Now I have some more options to play with!

Thank you!