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Vintage threads from the first ten years

Re: Hours of Mindless Fun! :-)

5/26/1999 7:49 AM
Paul Perry	Re: Hours of Mindless Fun! :-) This 'original' vs 'new' makes me laugh.. quite often, the 'stars' that people are trying to emulate had heavily modded units anyway. Even today, I have heard of pedal 'endorsees' with custom modded gear inside the stock looking case! On the subject of dual vactrols, the Allied catalog has a couple of these in the 'analog opto isolater' section. Around $3 or $4 from memory.

5/26/1999 7:49 AM

Paul Perry

Re: Hours of Mindless Fun! :-)

This 'original' vs 'new' makes me laugh.. quite often, the 'stars' that people are trying to emulate had heavily modded units anyway. Even today, I have heard of pedal 'endorsees' with custom modded gear inside the stock looking case!
On the subject of dual vactrols, the Allied catalog has a couple of these in the 'analog opto isolater' section. Around $3 or $4 from memory.

5/26/1999 8:16 AM

R.G.

quote:
"This 'original' vs 'new' makes me laugh.. "

... and cry... things like non-true-bypass on wahs and the MXR line are real, true, tone eating problems. But they are
**original** problems.

quote:
"On the subject of dual vactrols,"

Unless they've updated their line, Vactec doesn't have a dual isolated element vactrol, only a centertapped one. The Mutron style circuit needs isolated elements.

However, the dual element vactrol makes a great replacement for the dual reverse log pot in the univibe, as that has one common terminal...

5/30/1999 5:20 AM
Paul Perry	Those vactrols are VTL5C4/2 and VTL5C3/2, I can't tell from the Allied cat if they are joined or not. But, it occurs to me as I type this that there is usualy plenty of voltage available for these things (having a v drop of 2v or less) so perhaps you could use 2 single ones with the diodes in series!! I know they wont be matched..

5/30/1999 9:42 AM
R.G.	Like I said, they are centertapped, not separate. I have a number of each kind. The 4/2 and the 3/2 are definitely joined. They're like the three-wire LDR's you've seen - one LDR with a centertap. This is much better for the manufacturer, as the two "sections" are inherently matched to each other, if not to anything else in the world. Yes, there is plenty of drive voltage available; in my notes that come with the Neutron, I address exactly this. The Neutron board is laid out for either one LED/dual LDR as in the original, or two single LED/LDR's like the VTL5C3, CLM6000, or NSL32, or the discrete versions of each of these, as well as the LED/photo fet H11F1/2/3 linear optoisolators. I do take some pride in my layouts, and I have to brag a bit here. The layout of the one pattern to fit all of the LED/LDR options in one 14 pin dip space is something I worked several hours on to get right. The board layout will take any of the above solutions. In any case, you could hand match two of any of the above single solutions if you bought extras. It's not that hard. In practice, the matching seems not to make a whole lot of difference to the sound, as I've tried it with deliberately mismatched ones, and as long as they're not grossly mismatched (like more than 2:1) it seems to work fine, as Joe found above with his hatch wired one.

5/30/1999 9:42 AM

R.G.

Like I said, they are centertapped, not separate.

I have a number of each kind. The 4/2 and the 3/2 are definitely joined. They're like the three-wire LDR's you've seen - one LDR with a centertap. This is much better for the manufacturer, as the two "sections" are inherently matched to each other, if not to anything else in the world.

Yes, there is plenty of drive voltage available; in my notes that come with the Neutron, I address exactly this. The Neutron board is laid out for either one LED/dual LDR as in the original, or two single LED/LDR's like the VTL5C3, CLM6000, or NSL32, or the discrete versions of each of these, as well as the LED/photo fet H11F1/2/3 linear optoisolators.

I do take some pride in my layouts, and I have to brag a bit here. The layout of the one pattern to fit all of the LED/LDR options in one 14 pin dip space is something I worked several hours on to get right. The board layout will take any of the above solutions.

In any case, you could hand match two of any of the above single solutions if you bought extras. It's not that hard. In practice, the matching seems not to make a whole lot of difference to the sound, as I've tried it with deliberately mismatched ones, and as long as they're not grossly mismatched (like more than 2:1) it seems to work fine, as Joe found above with his hatch wired one.

5/19/1999 5:55 AM

gfr

quote:
"Yeah, that GIF didn't open on my computer so I couldn't see his diagram. Could the sample-and-hold he talked about be as simple as a cap in parallel with the resistor beneath the LED?"

That GIF (and another one from his site) has some problem. If you have an HEX editor (like Ultra Edit, PSEdit or the one in XTree Gold) you can fix it - just delete everything until you find "GIF89a" or "GIF87a" and then save it. If you can't do the "hacking" I can post you the fixed file.

5/20/1999 2:09 PM
Joe Fuzz	Re: Latest Mods If you can't do the "hacking" I can post you the fixed file. If you could, that would be great. I haven't used a hex editor since my DOS days. I wonder if anyone's told this guy that he's got a corrupt file on his site? Anyway, the latest mod goes like this: As I said in a previous post, I've put a pot underneath the LED which allows me to determine how far the filter swings open. How about a way to determine how far the filter closes? I went to my old text book and, sure enough, there was the filter circuit: a two integrator loop/second order filter. I stated in a previous post that the Q swung with the LED's brightness. Not true: Q is set by the input resistor and the feedback resistor/pot combo i.e. referring to CJ's schematic: Q = (R₉+150k pot)/R₅ So Q (and therefore the Bandwidth) is controlled by the 150k pot. The frequency, w, is determined by R₁₀=R₁₂=R and C₅=C₇=C as follows: w=1/RC As R decreases, the frequency rises. Now the LDRs are in parallel with the 2 Rs in this circuit. The LDRs have a low resistance when on, like 20k or less. So when on, the LDRs are the major determining factor in the parallel resistance. (Makes sense: as the LED lights, the LDRs' resistance goes down, the wah opens=the frequency rises.) When off, the LDRs have a large resistance, like 2Megs, so that now, the 2 fixed Rs determine the parallel resistance (mostly). So, what I did was to insert a 100k dual-pot in series with the 220k resistors R₁₀ and R₁₂. Voila! Now I have a way to determine how far the filter swings closed as well as how far open. For even more control, you could lower the 220k resistors to 180k or so. It's a modest adjustment: changing C makes a more drastic change. However, it may allow you to tweak in just the right sound. BTW: I'm using 1000pF for the 2 Cs and switching in 2000pF. I don't have to light my LED as brightly this way (which means my batteries should last longer).

5/20/1999 2:09 PM

Joe Fuzz

Re: Latest Mods

If you can't do the "hacking" I can post you the fixed file.

If you could, that would be great. I haven't used a hex editor since my DOS days.

I wonder if anyone's told this guy that he's got a corrupt file on his site?

Anyway, the latest mod goes like this: As I said in a previous post, I've put a pot underneath the LED which allows me to determine how far the filter swings open. How about a way to determine how far the filter closes?

I went to my old text book and, sure enough, there was the filter circuit: a two integrator loop/second order filter. I stated in a previous post that the Q swung with the LED's brightness. Not true: Q is set by the input resistor and the feedback resistor/pot combo i.e. referring to CJ's schematic:

Q = (R₉+150k pot)/R₅

So Q (and therefore the Bandwidth) is controlled by the 150k pot.

The frequency, w, is determined by R₁₀=R₁₂=R and C₅=C₇=C as follows:

w=1/RC

As R decreases, the frequency rises.

Now the LDRs are in parallel with the 2 Rs in this circuit. The LDRs have a low resistance when on, like 20k or less. So when on, the LDRs are the major determining factor in the parallel resistance. (Makes sense: as the LED lights, the LDRs' resistance goes down, the wah opens=the frequency rises.)

When off, the LDRs have a large resistance, like 2Megs, so that now, the 2 fixed Rs determine the parallel resistance (mostly).

So, what I did was to insert a 100k dual-pot in series with the 220k resistors R₁₀ and R₁₂. Voila! Now I have a way to determine how far the filter swings closed as well as how far open. For even more control, you could lower the 220k resistors to 180k or so.

It's a modest adjustment: changing C makes a more drastic change. However, it may allow you to tweak in just the right sound.

BTW: I'm using 1000pF for the 2 Cs and switching in 2000pF. I don't have to light my LED as brightly this way (which means my batteries should last longer).

5/25/1999 7:25 AM
GFR	I've sent you the GIF today.

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