Mosky Plexi-m [schematic]
- howmuch
- Breadboard Brother
This is obviously based on the Single Channel Carl Martin Plexitone.
I really like the sound of this pedal. It's got that Bright-Channel Plexi character and a lot of gain.
If you're after a pedal that will help you get an EVH brown sound, you could do a lot worse than trying this one.
At less than £20 new, you can't go wrong.
I can't find a schematic of the Single Channel Plexitone - I wonder how close the Plexi-m is to it.
It would be interesting to see a schematic of the CM Panama to compare as well (do you have one bugg?).
Guessing it's very similar, with an extra variable-HPF "Damping" control.
The circuit is slightly different to the (discontinued?) Caline English Man, going by the schematic that was posted here.
I've sketched a schematic based on the visible traces on the component side and referring to the "PlexiTuna" and "Boneyard" schematics.
So some of it will be correct and some of it is guess-work.
Some of the SMD capacitors can't be measured in-circuit, so I've included values in parentheses from the other schematics.
Since the Single Channel Plexitone was tweaked from the original, those capacitor values could be wrong.
The 7660S is configured to generate -Vcc from the supplied Vcc.
Nearly all of the components are on the bottom side of the full-size PCB.
There's a smaller PCB for the pots, LED, DC Jack and a 1N5819 (could be 1N5817) diode.
The two ICs are LF347 quad op amp and 7660SCBA voltage converter.
The asymmetric clipping is done with 3 red LEDs.
The only thing I don't like is that the In/Out jacks are only hanging on by their nuts.
Here's some photos and that rough schematic.
Let me know if you spot any mistakes.
I really like the sound of this pedal. It's got that Bright-Channel Plexi character and a lot of gain.
If you're after a pedal that will help you get an EVH brown sound, you could do a lot worse than trying this one.
At less than £20 new, you can't go wrong.
I can't find a schematic of the Single Channel Plexitone - I wonder how close the Plexi-m is to it.
It would be interesting to see a schematic of the CM Panama to compare as well (do you have one bugg?).
Guessing it's very similar, with an extra variable-HPF "Damping" control.
The circuit is slightly different to the (discontinued?) Caline English Man, going by the schematic that was posted here.
I've sketched a schematic based on the visible traces on the component side and referring to the "PlexiTuna" and "Boneyard" schematics.
So some of it will be correct and some of it is guess-work.
Some of the SMD capacitors can't be measured in-circuit, so I've included values in parentheses from the other schematics.
Since the Single Channel Plexitone was tweaked from the original, those capacitor values could be wrong.
The 7660S is configured to generate -Vcc from the supplied Vcc.
Nearly all of the components are on the bottom side of the full-size PCB.
There's a smaller PCB for the pots, LED, DC Jack and a 1N5819 (could be 1N5817) diode.
The two ICs are LF347 quad op amp and 7660SCBA voltage converter.
The asymmetric clipping is done with 3 red LEDs.
The only thing I don't like is that the In/Out jacks are only hanging on by their nuts.
Here's some photos and that rough schematic.
Let me know if you spot any mistakes.
- FuzzMonkey
- Breadboard Brother
I've been tempted to pick up one of these as I also heard it was based on the single-channel PlexiTone.
- Manfred
- Tube Twister
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I ordered a Plexi-m today.
When I receive it I can find out the missing capacitance values in the signal path.
With my PEAK LCR45 LCR and impedance meter I can measure the impedance of the RC circuits and determine the capacitor by calculation.
When I receive it I can find out the missing capacitance values in the signal path.
With my PEAK LCR45 LCR and impedance meter I can measure the impedance of the RC circuits and determine the capacitor by calculation.
- Ice-9
- Degoop Doctor
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I think I would be tempted to just remove and measure the caps, far quicker
It looks like\a nice little pedal especially for £20 ish
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !
No silicon heaven ? preposterous ! Where would all the calculators go ?
No silicon heaven ? preposterous ! Where would all the calculators go ?
- Manfred
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Thanks for the hint but measuring and calculating is faster for me, I know how to calculate AC circuits with the help of complex numbers.
I won't touch the SMD components.
- Manfred
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Yesterday the Mosky Plexi-m I ordered arrived.
I found the following capacitance values:
C4 = 150pF, C7 = 100nF, C9 = 47p.
C14 is shorted by BF1, so I could not measure its value, the capacitor makes no sense at this point.
The measurement of the leds showed that they are all of the same type:
Vf=1,89V at 5,00mA
Here is the measured P/N junction curve:
I found the following capacitance values:
C4 = 150pF, C7 = 100nF, C9 = 47p.
C14 is shorted by BF1, so I could not measure its value, the capacitor makes no sense at this point.
The measurement of the leds showed that they are all of the same type:
Vf=1,89V at 5,00mA
Here is the measured P/N junction curve:
Last edited by Manfred on 03 Apr 2021, 00:21, edited 1 time in total.
- howmuch
- Breadboard Brother
Thanks Manfred.
I've added them to the schematic. Here's v02
- Manfred
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i have searched in some applications with ICs 7660S and LT1044. In most of them there is no film capacitor connected in parallel to the electrolytic capacitor on Vout.
Only one circuit had a 100nF connected in parallel, so I think that also here C16 = 100n is correct.
Also you can remove BF1 and C14 from the schematic.
Only one circuit had a 100nF connected in parallel, so I think that also here C16 = 100n is correct.
Also you can remove BF1 and C14 from the schematic.
- howmuch
- Breadboard Brother
Cheers Manfred. I won't bother re-doing the schematic again for that; next time round.
Yes, technically I could remove BF1, BF2, C14 and D6, but I drew the schematic to represent the Mosky Plexi-m, so since those components are there, I'll leave them.
If anyone wanted to build their own from this (although even if you already had all the components, it's far easier to just spend the £20), hopefully they'd have the sense to optimise those parts.
- Manfred
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The PN-junktion V/I curve I measured seemed strange to me, so I repeated the measurement.
It is difficult to contact the SMD components in the circuit.
I edit the curve and the value in the above post.
Here are the curves of D3 and D1&D2 together in one picture.
It is difficult to contact the SMD components in the circuit.
I edit the curve and the value in the above post.
Here are the curves of D3 and D1&D2 together in one picture.
- Manfred
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Finally I recorded the frequency response depending on the position of the tone potentiometer.
- howmuch
- Breadboard Brother
Hey Manfred,
My Plexi-m is giving a fizzy, crackly-ness to the notes, which is especially noticeable on note decay or when you play softly or reduce the guitar's volume.
Best way to reproduce it is Tone=Max, Gain=Min, into a clean amp.
Does yours have this fizz also?
My Plexi-m is giving a fizzy, crackly-ness to the notes, which is especially noticeable on note decay or when you play softly or reduce the guitar's volume.
Best way to reproduce it is Tone=Max, Gain=Min, into a clean amp.
Does yours have this fizz also?
- Manfred
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Yes, I was able to reproduce that with the settings you gave.howmuch wrote: ↑30 Jul 2021, 13:07 Hey Manfred,
My Plexi-m is giving a fizzy, crackly-ness to the notes, which is especially noticeable on note decay or when you play softly or reduce the guitar's volume.
Best way to reproduce it is Tone=Max, Gain=Min, into a clean amp.
Does yours have this fizz also?
I fed the effect output into the input of the Mooer Hornet in clean mode.
I will look at the output signal with the oscilloscope the next few days.
- howmuch
- Breadboard Brother
I looked at a few YT demos of the Plexi-m and the comments were interesting.
A few people say that they have had the fizz problem, one person with three bad units.
They all seem to be from 2021. Perhaps they were OK before this.
Anyway, I finally got around to de-bugging this fizz problem.
BTW, in the process, I removed C4 and measured it - it was 100pF.
I got the sig. gen. and 'scope out.
Looking at the output of the "clipping stage" op amp, I could see crossover distortion.
So now I know what crossover distortion sounds like. I figured the only way that could happen in this circuit is a bad op amp.
So I replaced the LF347 with a new one, and that fixed it.
With a guitar, note decay is now clear and natural with no fizz.
Mosky must either be using bad chips or damaging them in their process.
A few people say that they have had the fizz problem, one person with three bad units.
They all seem to be from 2021. Perhaps they were OK before this.
Anyway, I finally got around to de-bugging this fizz problem.
BTW, in the process, I removed C4 and measured it - it was 100pF.
I got the sig. gen. and 'scope out.
Looking at the output of the "clipping stage" op amp, I could see crossover distortion.
So now I know what crossover distortion sounds like. I figured the only way that could happen in this circuit is a bad op amp.
So I replaced the LF347 with a new one, and that fixed it.
With a guitar, note decay is now clear and natural with no fizz.
Mosky must either be using bad chips or damaging them in their process.
- temol
- Solder Soldier
I have couple dozens of cheap TL072 opamps (from Aliexpress). All with a similar issue.I figured the only way that could happen in this circuit is a bad op amp.
So I replaced the LF347 with a new one, and that fixed it.
- Manfred
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There arises neither the question fakes or bought out rejects what is sold there in certain countries of East Asia.
As mentioned elsewhere, I am cured after some negative experiences and no longer buy in these countries.
Also, you have to be careful, there are, I call them container companies,
that pretend to buy goods from your own country.
- Manfred
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Yes, C4 with 100pF is the correct value. I made the mistake and did not take into account the capacitance of the LEDs connected in parallel.Anyway, I finally got around to de-bugging this fizz problem.
BTW, in the process, I removed C4 and measured it - it was 100pF.
I measured the capacitances of red LEDs of different sizes and different current ratings, unfortunately I don't have SMD LEDs available.
The measured capacitances were between 5pF up to 45pF.
- howmuch
- Breadboard Brother
I can be stupid sometimes. I forgot to make a recording of this fizz problem before I fixed it.
So could someone who has the fizz make a simple recording and add it here for posterity?
I'd suggest this - Gain=Min, Tone=Max, Level=whatever, into a very clean amp/channel. Strum a single chord and let it die out slowly.
Thanks.
BTW - Looking at that manufacturer logo on the LF347 in the photos above, does anyone know what manufacturer that is?
It looks a bit like Texas Instruments' logo if you squint. Is this chip just a bad/fake rip-off?
So could someone who has the fizz make a simple recording and add it here for posterity?
I'd suggest this - Gain=Min, Tone=Max, Level=whatever, into a very clean amp/channel. Strum a single chord and let it die out slowly.
Thanks.
BTW - Looking at that manufacturer logo on the LF347 in the photos above, does anyone know what manufacturer that is?
It looks a bit like Texas Instruments' logo if you squint. Is this chip just a bad/fake rip-off?
- Manfred
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The logo looks familiar, it looks like a fake Texas logo.
I recently had this on transistors I bought from a dealer in Germany with this logo.
The measurement with my semiconductor analyzer gave values far from the specifications.
This dealer pretended to have purchased them from a well known distributor, that's how far it has come in the meantime,
It is funny that Mosky became a victim of fakers from their own country.
I recently had this on transistors I bought from a dealer in Germany with this logo.
The measurement with my semiconductor analyzer gave values far from the specifications.
This dealer pretended to have purchased them from a well known distributor, that's how far it has come in the meantime,
It is funny that Mosky became a victim of fakers from their own country.
- temol
- Solder Soldier
If you still have this IC you can make a simple setup and check with the oscilloscope if there's crossover distortion present.
Build a simple gain stage, insert 1kHz sinewave and that's all
Build a simple gain stage, insert 1kHz sinewave and that's all