Mutron Phasor II LFO problem

tommycataus · June 18, 2015, 05:42:24 AM

Hey guys, built a Mutron Phasor II a while back based on the vero layout on Tagboard Effects. I haven't gotten around to housing it as I've never been 100% happy with it.

https://m.youtube.com/watch?v=46smOENCed0

http://tagboardeffects.blogspot.com.au/2014/06/mutron-phasor-ii.html

My build sounds great for the most part, but for some reason the flashing LEDs are not flashing evenly i.e. The length of time they are on is longer than the length of time they are off so the phase is uneven when compared to the original. Just wondering if anyone can shed some light (no pun intended!) on which components form the LFO circuit and which might be worth swapping out to even up the phase?

I'd like to understand the LFO circuit, I know that the indicator LED is somehow separate...

Any help would be greatly appreciated! Thanks

tommycataus · June 18, 2015, 08:02:28 AM

So having read up on this I can see that with LFOs in general there are apparently ways to change the rate that the LED turns on independently from the rate that it turns off, which is what I had hoped. My best guess is a capacitor somewhere. There is a link on the tagboard effects page above that takes you to a schematic and it appears that the LFO section is at the bottom. My plan this weekend if I have time is to recreate this and use trial and error to work out what makes this thing tick (again with the terrible jokes)

Luke51411 · June 18, 2015, 08:08:48 AM

Isn't one of the trimmers the balance between light and dark on the sweep? I built on on a pcb and it seems like I had to dial that in to get the right proportion of light/dark

tommycataus · June 18, 2015, 08:23:57 AM

One seems to control the intensity of the LFO and the other changes the brightness, unless I have wired them up incorrectly. The phaser is really lush sounding like the demos but the phase is sort of lopsided if that makes any sense! My OCD sense is tingling. I've kinda been focussing on fuzz lately so getting my head around which part of this circuit is wrong had got me stumped.

Luke51411 · June 18, 2015, 08:31:02 AM

Yeah that makes sense.

tommycataus · June 19, 2015, 01:16:30 AM

So after what you said Luke I did indeed have a look at the trim pots and do some more digging... You were absolutely right! Sorry for doubting you. Turns out the trim pot was doing something funky and should have been behaving the way you described. Replaced and working well

Luke51411 · June 19, 2015, 07:42:15 AM

Awesome, just glad I could help. I wasn't brave enough to build it on vero, it's such a cool sounding phaser!

tommycataus · June 19, 2015, 08:33:43 AM

Honestly you won't regret it! It's a mission but such a beautiful swirly sound. I can't wait to box it up now. Was gonna do it this weekend but the mrs has other plans for me

Luke51411 · June 19, 2015, 09:20:14 AM

Cool! I have to put together some graphics and such. The pcb is designed for a 1590

I used a 125b though and mounted the speed on the top side with a jumbo knob for foot control fun. I also added a univibe switch. I think I changed the caps on the "wrong" stages but it still makes for two unique phase voices.

armdnrdy · June 19, 2015, 10:24:37 AM

If you want to hear this circuit at it's best....try using VTL5C3/2 vactrols instead of the LED/LDR combo.

I built a Mutron Phasor about 4 years ago...and it sounds phenomenal.

The VTLs add a certain (for lack of a better word) "liquid" quality that is more in line with the original Phasor II.

The Tayda photo resistors may work but...I believe that the response time is too fast to be used for optimum phasing in this circuit.

tommycataus · June 20, 2015, 07:45:55 AM

That sounds pretty neat Luke!

Thanks Larry, I've never actually used vactrols so that will be a new experience. I like this build but I'll have to do a bit of shopping by the sound of it. Do a little a/b comparison session. Interesting for people like me who haven't heard originals

zmix · December 29, 2018, 09:02:27 AM

Quote from: tommycataus on June 18, 2015, 05:42:24 AM
Hey guys, built a Mutron Phasor II a while back based on the vero layout on Tagboard Effects. I haven't gotten around to housing it as I've never been 100% happy with it.

https://m.youtube.com/watch?v=46smOENCed0

http://tagboardeffects.blogspot.com.au/2014/06/mutron-phasor-ii.html

My build sounds great for the most part, but for some reason the flashing LEDs are not flashing evenly i.e. The length of time they are on is longer than the length of time they are off so the phase is uneven when compared to the original. Just wondering if anyone can shed some light (no pun intended!) on which components form the LFO circuit and which might be worth swapping out to even up the phase?

I'd like to understand the LFO circuit, I know that the indicator LED is somehow separate...

Any help would be greatly appreciated! Thanks

I just discovered this topic, and have noticed a similar difference between the Mutron clones and the actual Mutron, the issue is that the LFO on the actual mutron is *not* a simple triangle wave LFO, but more like a rectified sine wave, so the frequency change of the phaser is much more gradually at the bottom of the sweep and more quickly at the top.

Here's a thread with some good information on this: https://www.diystompboxes.com/smfforum/index.php?topic=81162.0

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Mutron Phasor II LFO problem