Lovepedal - Purple Plexi 800 [goop-alarm]  [traced]

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andregarcia57
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Post by andregarcia57 »

I rode the pedal with the IC NJM386D, the pedal sounds great, but the potentiometer gain seems to be bad. I'm using Alpha Single-Gang 1K linear drive changes very little with this potentiometer, is there anything to improve it, or it's own project?

is there any way to have less gain pedal?

thanks
André

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Post by HTH »

the gain pot in the purple plexi is 1k (pot) in parallel with a fixed 470ohm, giving an effective 320ohm pot.

not sure if I'm thinking about this the right way, but on the data sheet, the internal resistor (1.35k) is paralleled with an external 1k2 resistor to give a resistance of 635ohms with a gain of 50.

I wonder if using a pot between pins 1 and 8 would give better control of the gain rather than the capacitive-coupled method used in the Purple Plexi (its on my list of things to try).

I'm still playing around with this pedal and am getting it tuned in as I go. Will post a schematic with what I've found to work and sound best (always good to share).

fwiw, I'm using LM386N-1's and they're working out fine.

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Post by HTH »

update... stock design had WAY too much gain at lowest gain setting and just added hi-mid sizzle as the gain was increased, not really adding much extra overall gain. imo, this is too much for a plexi-esque tone and way more gain than I ever use.

I've now got a pot between pins 1 and 8 with a 0.68uF cap in line with it - gain is much better now and the pedal's tonality sounds/feels more plexi/Marshally, imo.

Did some listening bypassing the diodes from Vs and also the 10R resistor - much preferred the tone with these both removed (or shorted out in my case, I'm too lazy to unsolder them).

This is coming together nicely now, definitely some mileage in this design.

okgb
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Post by okgb »

If i goop my pedals will they sound more Love-ly ?
where do you get the goop

but really as mentioned , i'd love to see your updated schematic
even though i gave up on chasing the marshall sound by getting
a Marshall amp [ the 70's head i bought when i was a teen ]

kev93_10
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Post by kev93_10 »

Does anyone have a definitive vero layout for this? The 2 on the previous pages aren't correct.

K

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Post by marmaliser »

kev93_10 wrote:Does anyone have a definitive vero layout for this? The 2 on the previous pages aren't correct.

K
http://tagboardeffects.blogspot.com/201 ... i-800.html

IvIark
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Post by IvIark »

I forgot to post this one here:

Image

I haven't built this one but I think someone on my blog mentioned that he built it successfully. It's based on the corrected schematic posted by sandmannn69 and Ghandi on here.
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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Post by IvIark »

marmaliser wrote:
kev93_10 wrote:Does anyone have a definitive vero layout for this? The 2 on the previous pages aren't correct.

K
http://tagboardeffects.blogspot.com/201 ... i-800.html
:mrgreen: beat'd me to it!
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

kev93_10
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Post by kev93_10 »

Thanks for the above.

I'm getting quite a bit of hum when the pedals on that goes away when a guitar's plugged in?! Anything obvious to check?

sounds ace though!

K

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Post by Barcode »

kev93_10 wrote:Thanks for the above.

I'm getting quite a bit of hum when the pedals on that goes away when a guitar's plugged in?! Anything obvious to check?

sounds ace though!

K
Then you aren't grounding one of the jacks properly. Once you plug in, the pedal can reference the ground on your guitar. Check all grounds.

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Post by Barcode »

Also, who cares what it sounds like without an instrument plugged in??? :)

Also, what the hell happened to the edit button?

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Post by dergroovemeister »

I built it from Torchy's layout. I hope it's ok to post it here.
Attachments
LovepedalPurplePlexi800 vero - Torchy.jpg

jymaze
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Post by jymaze »

Hello all,

I had the same problem with hiss at max gain (cf Renegadrian).

Here is the solution I found: replace the 10 ohms resistor in series with the gain pot with a 22 ohms resistor (or put another 10 in series). It took care of it. If it is not enough, the value of the resistor can be pushed even higher until the problem disappears, the tone changes a little but nothing too bad, the value of the cap in series can then be adjusted to something else than 47u. In my case I settle for 20 ohms and 22u.

Then I decided to get rid of the gain pot alltogether since everyone has to admit is mostly useless. The amount of distortion is way easier to control with the guitar volume knob.

Now it is a great pedal with a convincing brown sound. And with only 2 pots, I have more room on the pedal for some nice graphics.

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ansil
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my hughes and kettner blue 30r

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10 marshall guvnor mods and builds
100 jungle kat boosts
too many penguin love's to count.
5 blues pearl purplexed
dozen tube screamer fulldrive whatever you call them variants

hell i can't type this long it will piss off people what can i say i have been doing mods on toyz appliances gear sex toyz computers and such for 27 years. i started when i was 6 taking stuff apart.

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Post by ansil »

GuitarLord5000 wrote:
dap9 wrote:I only have some LM386 floating around.
Hey dap9, are you still having that problem with the distortion cutting out when you hold a note for a long time?
I'm very curious about this, because I've had this exact problem with the LM386 chips. I've never gotten a good answer for this either.
Posted is '06:
https://www.diystompboxes.com/smfforum/ ... ic=43962.0

Seemed to be a problem with the chip, and not the circuit. All the chips I tried exhibited this problem when I built ROG Big Daddy, and the problem remained when I built a Smash Drive with them.

mostly have to do with the chip itself try a lm386n-3 or n-4. the higher voltage ones seemed to work better in this type of circuit. seems to have some relationship with the input impedance because if you build the 386 discretely you don't have this problem as long as you raise the input imp. but then again its not 100 percent same sound but way closer than i want to deal with the decaying splatiness also try lm380n-8 similar but different pinout. also there is a milspec replacement for the 386 but good luck on gettting them now i applied a few years back and got five samples much better s/n but no extra data on them.

someone mentioned playing it on a ss amp this is not the same circuit it however does rely mainly on the 386 chip and most people think it sounds quite nice let me know what all of you think if you like.

https://www.youtube.com/watch?v=DrPj8WVVwiE

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Post by Renegadrian »

Some time has passed from my previous efforts...now curiosity and a customer made me take back the schem from the virtual but nonetheless dusty wardrobe of schems...

First, made my own layout, better and smaller than the others!
Image

Second, built it the best I could...Strange enough, no whistles!!! Not that is the best circuit around, but it doesn't whistle...so I guess it works properly!!! :scratch: :lol:

CONS
- Noise, exp. with the GAIN maxed.
- GAIN pot, it is quite gainy even at min, and it changes the gain only at the very last part of its rotation.
- FREQ pot, the changes at min and max are very hard to notice, it's almost useless...

Got to try to change the 100n cap as someone suggested...

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ansil
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my favorite amplifier

my hughes and kettner blue 30r

Completed builds

3 jcm 800 builds
4 vintage plexi builds
2 bogner ecstasy preamps [both for personal use]
10 marshall guvnor mods and builds
100 jungle kat boosts
too many penguin love's to count.
5 blues pearl purplexed
dozen tube screamer fulldrive whatever you call them variants

hell i can't type this long it will piss off people what can i say i have been doing mods on toyz appliances gear sex toyz computers and such for 27 years. i started when i was 6 taking stuff apart.

Location: cleveland tn
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Post by ansil »

Renegadrian wrote:Some time has passed from my previous efforts...now curiosity and a customer made me take back the schem from the virtual but nonetheless dusty wardrobe of schems...

First, made my own layout, better and smaller than the others!
Image

Second, built it the best I could...Strange enough, no whistles!!! Not that is the best circuit around, but it doesn't whistle...so I guess it works properly!!! :scratch: :lol:

CONS
- Noise, exp. with the GAIN maxed.
- GAIN pot, it is quite gainy even at min, and it changes the gain only at the very last part of its rotation.
- FREQ pot, the changes at min and max are very hard to notice, it's almost useless...

Got to try to change the 100n cap as someone suggested...



ok after playing with this yeah its quite easy to see whats going on [feel free to correct me if i messed up] but looking at our basic rc filter calc we get

two lpf filters and only a five k pot to blend between the two of them.

4.7n and 4.7k gives us a lpf of 7.2k aprox. and then .1 and the next 4.7k give us a freq response of 338hz lpf with some attenuation offered by the 1.74k resistor if i read the schematic correctly its kind of late here.

or if you wanted to add that resistance to the total resistance of the circuit the it would give us around 228 hz lpf. so since we know basically the treble pot in a circuit is just a balance pot between the extremes then your looking at utilizing just a 5k pot to balance between 5 octaves or so yeah thats not going to work very efficiently. plus who needs 7k of high end i can see piping some 10k back in for a little sizzle but really much over 3k is just hiss anyway.

dropped this in duncans tsc just the last part of it and its more of a volume control with just a hair of treble mod to it this would really benefit from a real tone stack i think the baxandall would work much better.

also try a dual ganged pot for the gain control its much more effective. loose teh 470 ohm resistor there it is not necessary. with it there your effectively trying to sweep 500 ohms as your gain pot thats not really going to work very well utilize a 5 k pot with no 470 and it will be smoother. with the 1k dual you can get a much smoother transition of gain that was a trick over at the second incarnation of diystompboxes.com that we came up with right before the smashbox was released.

lm386n-3 n-4 much better noise ratio than the jrc and the 386n-1. the 1 was really optimized to run on 6v. if you build a 6v reg or get the right zener diode and run it off 6v it will work so much better for you. i do not know about the voltage for the jrc i just happened to speak with an engineer at national about the 386s some time ago via email and he was a very helpful chap but if you get a chance to look up the old bobtavia pedal done with the 386 it sounds great but when i showed that scheme to a friend he thought it was the coolest thing ever and built a layout so that it looked like a v-8 engine anyway i digress and he had some real issues with the consistency of the circuit till he dropped it to 6v. they also seem to work better at 12v too. so instead of 6-12v operation maybe they really meant 6 or 12v operation.

anyway i have a few jrcs here and they do seem much better than the n1s but alas all noisy as piss. but i still have a slew of the other models thank goodness i bought a few handfuls off ebay a few years ago

btw i apollogize for my spelling i am on my laptop and it seems someone has spilled somethign in the keys
pps i guess i should also clarify that the dual ganged 1kpot is set up so that as you turn the pot to maximum one set of terminals is between pins one and eight and the other is wired like the normal gain pot. so you are turning it down quite noticeably

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Post by Renegadrian »

ansil wrote: ...lm386n-3 n-4 much better noise ratio than the jrc and the 386n-1...
...they also seem to work better at 12v too. so instead of 6-12v operation maybe they really meant 6 or 12v operation...

Tried a n1, didn't notice big differences...got to try n4, I got a couple...anyway, as you see my layout has no diode. I am running it at 12V. Yep there is noise...I also added an optional filter electro on the two bottom rows...

As for the tone, swapped the 100n for a 47n (C7 on my layout) - I'd really suggest anyone to do the same!!! Now the pot is useful, it has some good range of treble cut (not that the pedal is rich of highs, but I like the tone with tone and gain pot at min - decent overdrive...I'd say it would be better as a fixed gain OD than the beast difficult to tame we all know...)

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ansil
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my favorite amplifier

my hughes and kettner blue 30r

Completed builds

3 jcm 800 builds
4 vintage plexi builds
2 bogner ecstasy preamps [both for personal use]
10 marshall guvnor mods and builds
100 jungle kat boosts
too many penguin love's to count.
5 blues pearl purplexed
dozen tube screamer fulldrive whatever you call them variants

hell i can't type this long it will piss off people what can i say i have been doing mods on toyz appliances gear sex toyz computers and such for 27 years. i started when i was 6 taking stuff apart.

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Post by ansil »

Renegadrian wrote:
ansil wrote: ...lm386n-3 n-4 much better noise ratio than the jrc and the 386n-1...
...they also seem to work better at 12v too. so instead of 6-12v operation maybe they really meant 6 or 12v operation...

Tried a n1, didn't notice big differences...got to try n4, I got a couple...anyway, as you see my layout has no diode. I am running it at 12V. Yep there is noise...I also added an optional filter electro on the two bottom rows...

As for the tone, swapped the 100n for a 47n (C7 on my layout) - I'd really suggest anyone to do the same!!! Now the pot is useful, it has some good range of treble cut (not that the pedal is rich of highs, but I like the tone with tone and gain pot at min - decent overdrive...I'd say it would be better as a fixed gain OD than the beast difficult to tame we all know...)
with the .047 you will get a 720hz roll off blended with a 7.2k yeah that would be a little more flexible

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Post by mxrmxr »

Is there a fix for the spluttery abrupt decay you get with the LM386 devices ?

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ansil
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my favorite amplifier

my hughes and kettner blue 30r

Completed builds

3 jcm 800 builds
4 vintage plexi builds
2 bogner ecstasy preamps [both for personal use]
10 marshall guvnor mods and builds
100 jungle kat boosts
too many penguin love's to count.
5 blues pearl purplexed
dozen tube screamer fulldrive whatever you call them variants

hell i can't type this long it will piss off people what can i say i have been doing mods on toyz appliances gear sex toyz computers and such for 27 years. i started when i was 6 taking stuff apart.

Location: cleveland tn
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Post by ansil »

yes 3 ways only one I can tell now as I am at work. hand select therm

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