Mosky Ch-Vibe - does not sound like a Univibe [Solved]

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howmuch
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Post by howmuch »

Thought I'd pick up one of these to see what it's like.
I was hoping I'd be lucky and it would be a take on the Moen Shaky Jimi/Jimi Nova, which are based on the EasyVibe.
Here's links to the Moen Shaky Jimi and Moen Jimi Nova threads.
And I'd like to thank John Hollis for his lovely EasyVibe circuit. :thumbsup

What's inside then? The highlights:
1 x "ST" 064C
3 x "TI" TL062C
4 x LED/LDR pairs

It does indeed look to be generally based on the Moen/EasyVibe circuit although I haven't checked the entire circuit.
I'd expect the logos on the TI op amps to look better than is seen here, but I'm no expert. They could be real.
It's just that I can't help being suspicious in this area, due to my previous bad experience with the Mosky Plexi-m.
Regardless, they seem to be doing the job of an op amp here, with no audible crossover distortion.

So what's it sound like out-of-the-box?
I'll be kind and just say disappointing. :cry:
It does produce some phasing, but it's nothing like a Univibe.
Basically, I know what to expect for the price - this thing might have some errors. :roll:

Why does it not sound like a Univibe?
In MY pedal (YMMV), the capacitors in the phase shifting stages are not the generally accepted Univibe/EasyVibe values.

Original capacitors
Phase Stage     Univibe/EV      Ch-Vibe
Stage 1         15n             C3 4n7
Stage 2         220n            C4 220n
Stage 3         470p            C5 220p
Stage 4         4n7             C6 1n

C3 (4n7) is the correct value, even though it's in Stage 1 rather than Stage 4. Not a problem.
C4 (220n) is correct.
C5 (220p) should be 470p.
C6 (1n) should be 15n (given that there's a 4n7 in Stage 1).

So I replaced:
C5 (220p) with 470p
C6 (1n) with 15n (as in Univibe/EV Stage 1)

There was no point in moving the 4n7 (C3) from Stage 1 to Stage 4.
I only had to take the bottom plate off (4 screws) to change the caps, and used 0603 size.

So the phase shifts are now all correct, just in a different order.
Ending up with this

Modified/"Fixed" capacitors
Phase Stage     Univibe/EV      Modified Ch-Vibe
Stage 1         15n             C3 4n7
Stage 2         220n            C4 220n
Stage 3         470p            C5 470p
Stage 4         4n7             C6 15n

So what's it sound like now, with the capacitors changed?
Nice, and just like a Univibe should sound. :D
I'm hearing all the expected Hendrix/Gilmour/Trower tones out of it now.
And of course I'm talking about the "CHORUS" mode, not the "VIBE"(Vibrato) mode.
Take time to set the Drive (labelled "COLOR" here) into the sweet spot, otherwise it won't sound at its best.

A couple of other things.
I would have preferred a log pot for the Speed control to get better resolution at the slow end. All pots are linear (B10k, B10k, B5k).
And it's got one of those blindingly bright blue LEDs that I absolutely hate. Just limit the current more FFS Mosky (and others). :evil:
I think they're using a 4k7 CLR. I couldn't be bothered to change it and took the easy route and put masking tape over the LED.
You could probably go to town on this pedal in you wanted to with heatshrink over the LED/LDRs, op amp swaps, etc.
(Oh no, look out for one of these tarted up in a booteek enclosure coming your way soon!)
But I won't be doing any more mods because it sounds good enough for me (for now). I'm not that fussy.

I really don't know what's going on with Mosky. :scratch:
As you can see in the photos below, they took the effort to manually put a big through-hole cap of the correct value onto SMD pads for C4.
Yet they got two other important cap values totally wrong. Is this their intended design (clone) or a mistake in production?
If a mistake, it's unlikely to be a one-off because these are not hand built pedals. They use reels of thousands of SMD caps in their pick & place machines.

Here's some photos.
External.jpg
External.jpg (25.49 KiB) Viewed 3220 times
Internal 1.JPG
Internal 2.JPG
Op amp.JPG
C4 220n.JPG
Capacitor Fixes
Capacitor Fixes
R.I.P. Burke Shelley, from one of my favourite (and much underrated) bands - Budgie
Their songs have been covered by Van Halen, Iron Maiden, Soundgarden, Metallica and more.
If you don't know how HEAVY this band was in the 70s, check Breadfan out.

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Post by CuriousSounds »

Hi,
Nice find on this pedal!
I'm looking in to do this capacitor mod.
How did you find out that the values was wrong? I tried to measure the caps in circuit, but got very high values. All in uF range.
My aim is to try to solder in some trough hole caps, as I'm not in possesion of any smd caps.
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howmuch
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Post by howmuch »

CuriousSounds wrote: 22 Apr 2023, 14:46 Hi,
Nice find on this pedal!
I'm looking in to do this capacitor mod.
How did you find out that the values was wrong? I tried to measure the caps in circuit, but got very high values. All in uF range.
My aim is to try to solder in some trough hole caps, as I'm not in possesion of any smd caps.
Since you measured high values in-circuit, I'm guessing you used a DMM with a Capacitance function. That will give you those high values in uF range.
Unfortunately, DMMs are not good for measuring a cap in-circuit if the cap is in parallel with other devices.
I used my Mastech MS8911 (now discontinued). It gives me a good ballpark idea.
Some people say it's rubbish, but for this type of thing it does the job just fine.

If you want to measure caps in-circuit then you need something that will measure at a lower voltage that does not turn on diodes/transistors.
They can use 0.1V to measure components, so that P-N junctions don't turn on. That low voltage also has its disadvantages though when it comes to measuring caps.
Probably the cheapest tool would be SMD Tweezers. "Shannon Tweezers" look quite promising.

To measure with a DMM, you really need to isolate the cap. Either
1. Remove the cap from the circuit.
2. Remove other (more robust) components to leave the cap isolated on the PCB.
The second method requires that you know the circuit well enough to isolate the cap.
For example, if one side of a cap is only in series with a resistor, it might be better to remove/lift the resistor.
Resistors might withstand the removal better and since they have markings, if you break it taking it off, you know what value to replace it with.
However, in this case, since you're likely to be replacing the capacitors anyway, you might as well just remove them to measure them.
If you're careful, and have "the knack", it is quite possible to remove SMD components, and put them back in successfully.

Your pedal is obviously from a different batch to mine since it does not have the leaded cap on C4 and a different op amp in U4.
So there's no guarantee that the values that I found will be the same in your pedal.
They might all be correct, or wrong values in different places. Who knows?
If yours sounds like a Univibe, you might be the lucky one that got a correctly-build Mosky pedal - no need to change anything.

Bottom line - if you already have replacement caps of the correct values, you could just replace all four and not bother measuring them.
Just follow the Univibe/EasyVibe values I listed in the first post.
Good luck, CuriousSounds. Let us know what you find and how it goes.
R.I.P. Burke Shelley, from one of my favourite (and much underrated) bands - Budgie
Their songs have been covered by Van Halen, Iron Maiden, Soundgarden, Metallica and more.
If you don't know how HEAVY this band was in the 70s, check Breadfan out.

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Post by CuriousSounds »

Finally I managed to get the job done. Had to get hold of a solder iron with smaller tip than my old Weller.
My findings was a bit different than yours howmuch.
I desoldered, measured, and soldered the capacitors back one by one, in order to see that the job was done right.
Used a cheap TC-1 component tester for measuring.

My readings:
Ch-Vibe
C3 14n8
C4 141n
C5 106p
C6 4n8

So I ended up replacing C4 and C5 with the correct values.

Now its sounds much better! And I really recognise the Univibe tone. Thanks! :D

It was a hard time putting C3 back as I ripped one of the pads... :x so had to make a new trace (its coverd in shrink tube).

The conclusion must be that these ch-vibes are a hit or miss regarding accurate components. And I guess "miss" for the most.
Its very nice that it is possible to get it to sound so much better!
Thanks again howmuch, for sharing your little discovery!

Here is what it looks like now:
Image

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howmuch
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Post by howmuch »

Out of curiosity, I bought a second Ch-Vibe.
Always good to have a spare anyway.

Once again, out of the box, it does not sound quite like a Univibe.
And once again, not all the capacitors in the phase shifting stages are the generally accepted Univibe/EasyVibe values.

This one does not have the leaded cap on SMD pads like my first one did. It has an SMD cap there. So this one is from a different batch.
The only cap in this second pedal that matches the first pedal is the one that is totally incorrect and a factor of 2 out!

So what can we deduce from this?
Instead of the usual pick-and-place machines, it looks like Mosky production are using "lucky dip-and-place" machines.
They're stuffing any old value SMD caps in their pedals.

And since these little SODs(sic) are unmarked, most customers wouldn't know what values are in there even if they opened the pedal.

Capacitor values measured in-circuit
Original capacitors
Phase Stage     Univibe/EV      Ch-Vibe no.1        Ch-Vibe no.2
Stage 1         15n             C3 4n7              C3 14n7
Stage 2         220n            C4 220n             C4 190n
Stage 3         470p            C5 220p             C5 245p
Stage 4         4n7             C6 1n               C6 4n6

C4 is 190n instead of 220n - that's 14% off
And C5 is again 220p (in-circuit measurement is 245p) instead of 470p.

I left C4 as it is.
Since I still had the 220p taken out of the first pedal, I just added that on top of (in parallel with) the 220p in this one to give me 440p.
That's probably close enough - 6% off.

Now it sounds better and more like a Univibe.

It looks like the moral of this story is:
If your Ch-Vibe does not sound right, check the caps (C3,C4,C5,C6) and replace them with the correct values.
Their values could be anything.


Here's the findings of the 3 pedals in this thread so far
Phase Stage     Univibe/EV      Ch-Vibe no.1        Ch-Vibe no.2        CuriousSounds
Stage 1         15n             C3 4n7              C3 14n7             C3 14n8
Stage 2         220n            C4 220n             C4 190n             C4 141n
Stage 3         470p            C5 220p             C5 245p             C5 106p
Stage 4         4n7             C6 1n               C6 4n6              C6 4n8
R.I.P. Burke Shelley, from one of my favourite (and much underrated) bands - Budgie
Their songs have been covered by Van Halen, Iron Maiden, Soundgarden, Metallica and more.
If you don't know how HEAVY this band was in the 70s, check Breadfan out.

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Baz1984
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Post by Baz1984 »

Hey All,

Sorry to resurrect this, just a question about the placement of values.

I have 3 out of the 4 values in around a 10% range. But they are mostly in the wrong places, does this matter or do I need to remove them and replace them all?

Cheers

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Post by howmuch »

Baz1984 wrote: 31 Mar 2024, 08:03 Hey All,

Sorry to resurrect this, just a question about the placement of values.

I have 3 out of the 4 values in around a 10% range. But they are mostly in the wrong places, does this matter or do I need to remove them and replace them all?

Cheers
Since all four of the phase shifting stages are in series and are identical apart from the capacitors, it does not matter about the order. The phase shifts just add up.
So just change the one that's obviously wrong and leave the other three 10%'ers alone. You'll hear a big difference.
R.I.P. Burke Shelley, from one of my favourite (and much underrated) bands - Budgie
Their songs have been covered by Van Halen, Iron Maiden, Soundgarden, Metallica and more.
If you don't know how HEAVY this band was in the 70s, check Breadfan out.

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Post by Baz1984 »

Thanks so much for the reply.

I was dreading having to remove so many smd caps

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Post by nooneknows »

does it 'Ticks' on the oscillation like a moen shaky Jimi ? that clicking noise drives me crazy

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nooneknows wrote: 05 Apr 2024, 14:02 does it 'Ticks' on the oscillation like a moen shaky Jimi ? that clicking noise drives me crazy
I just tried it to specifically listen for ticking and couldn't hear any ticking at all.
Any particular settings on the Moen, or always there?
R.I.P. Burke Shelley, from one of my favourite (and much underrated) bands - Budgie
Their songs have been covered by Van Halen, Iron Maiden, Soundgarden, Metallica and more.
If you don't know how HEAVY this band was in the 70s, check Breadfan out.

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Post by nooneknows »

always , I even tried to decouple the supply for the IC, it's a shame because it really sounds good but the clicking noise is a deal breaker

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