Mu-tron III LDR's

[JaviCAP]

Well, I'm decided to build a Mutron III.

Not a difficult project except for the photocouplers..... Vactrols are extremely expensive. I've been taking a look, ant 2 units would cost about 18 euros shippin' included.

Other option, recommended by Harald is the NSL32. Musikding: 2 units + shippn' 11,20 euro, but I'm afraid that Harald means the NSL 32 AA, tha has very similar specs to the Vactrol VTL5C3 (~40kO light, 10MO dark), and the AA version is not available  in Musikding, Banzai nor even ebay.

Brian from Madbean recomends MI1210CLF, just available on Smallbear, $22 including shippin' (Smallbear s&h is just insane for small components) or the Vactrol.

Let's say that these photocouplers are extremely expensive wherever you look at.

Brian tells too to use instead a super bright led and a LDR rated 20-50k light 10M dark, and once again, refers to Smallbear: $0.95 each one...and again $10 s&h.


I've just bought 20 units of GL5549 LDRs (100-200K light - 10Mdark). My experience with Vactrols, LDR's and so on is very small, but when dealing with Morley wahs I could see that the light resistance is a bit lower when dealing with super bright leds, and a LDR rated 100k light, did reach  600R in front of a white SB led.

So, if anyone has some wider experience, do you think that the 100-200k light 10M dark will do the trick for the Mu-tron III?

BR

[Dave]

I'm interested to hear any answers to this as well, I'm planning on building the lovetone meatball which is a        very similar circuit.
Thanks
Dave

[GoranP]

Same here. I have no experiences with vactrols (either production or roll-your-own) and quite a few projects lined up that use them.

Prices of VTL's are quite insane and I'm looking for an alternative. I have 5 of the Tayda ones coming in the mail. Those are not vactrols but LDR only. Only information I have on them is that they are 650nm which I can only assume means that they respond best to red light? How exactly does the brightness affect it? What's the light resistance range one can get?

[JaviCAP]

Mistery solved:

If you don't want to spend a fortune in vactrols, just use 2 x GL5549  ($2 x 20 pieces on ebay). 2 red water ultra bright leds from Tayda and a 20k timmer.

Mark, now you can publish your layout, my effect is done! :P

BR

[GoranP]

Thanks Javi!

I have some 10k ldrs, guess a few clicks on ebay are in order...

Funny enough, all the vactrols I've rolled so far worked far better with regular diffused leds. It could be my bum ear, though...

[JaviCAP]

You're welcome Goran,

But I think it's time to quarantine this effects as I've seen that is extremely unstable. Everytime I plug it, sounds different! From a great envelope fiter as it should, to a gated fuzz and as a clean booster too.  Don't really know what's the fuck with this effect, as I've double checked everything, reflow all the board, swapped the pots and so on.

The problem is that it sounds great... when it wants, five minutes later can sound totally different. Maybe a defective cap ... who knows. On thing I've noted from the start is that gain pot has to be set really high (being a reverse log!), and that the leds of the ldr, sometimes lit as you play and sometimes they remain lit no matter how hard you play.

I'm not really on the mood to keep on debuggin it, this weekend with the Magnus Modulus and the Mutron  has been too much.

Maybe Mark has his layout ready :P


BR

[mim#1]

Hey you guys, I'm using a pcb madbean nautilus hardwired in low-pass mode and it sounds great. I think its well worth the price of vactrols when you consider the finished result is a Mutron III for cheap!
It took some tweeking to get mine sounding the way I like but its killer now. I imagine that if you dont use vactrols then your in for hours of fun trying to get it to work.

[Ross]

I built Harald Sabro's SVF envelope filter using the GL5549 LDRs. I'm getting some of the same symptoms as you. When you dial everything in perfectly, it sounds great, but tweaking the Sensitivity knob at all forces me to rebias the LEDs. I would like to try the Smallbear LDRs, but his shipping costs are lunacy even in the United States.

[JaviCAP]

Goran, Ross.... finally..... SUCCESS!

I left this board in a drawer, but had ordered some GL5539 (50-100k light / 5M dark) too, just to have several values. They came on past friday  but han no much faith, so I didn't try until today.

Well, don't know if this values make a great difference, but I built the hand made vactrols, replaced the former ones made with 5549,  reflowed  several rows as the desoldering was hard (to many close components), pluged it.... and it works!

The new ldrs? the reflowing? Who can tell it for sure, but it works and sounds wonderful, don't need any more explanation :).

If your GL5549 fail, just try <gL5539.

Have to box this one sooooooon!

[GoranP]

Thanks Javi!

I need to stock up on the LDRs anyways, good to know which one to get to cover this build!

[JaviCAP]

Finally, after about a month of working, desperation an finally hope, I can introduce my MU-tron III.

A real pain to build, a real pain to box and a glorious envelope filer that gets you to forget the wasted hours building it. Hope you like it!

Mark: You have until May 4th, 14h:00 if you want to break therecord!

Pedal:




Guts:




In the guts pic you can see at first sight two of the potential problems sourcing parts. The tantalium input cap and the 15uf bipolar output one.

- The tantalium 4,7uf input cap: I always tell that doesn't matter the cap, just the value except if the circuit calls specifically fot tantalums. The Mutron sounds different if you use a regular electrolithic, instead of the tanatium. Don't ask me why, becuase I don't know and even less, understand, but the tone is different.

-The output cap: Must be BIPOLAR, if you use a normal electrolithic, the effect won't work. The value is very rare too: 15uf. Best way to get one  is to make your own cap with two 33uf ones, soldered by the positive pin.

BR