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I have only been working with LDR's for a short while and had a question regarding measuring light and dark values.

I have measured some LDR's for an effect I want to clone and came up with 6.5K to room light and at least over 20M dark (my meter stops at 20M so I just get "L" on the digital meter screen for over range). The same LDR gives about 39K when exposed to and LED and 1.5M dark (if the LED is driven by an LFO at a moderate rate).

My question is, what is or would be the correct way to measure an LDR for accurate resistance readings? Should there be a waiting period between light and dark before measuring the "Dark" resistance on the LDR? Without a light meter, how much light should I use for the "ON" resistance measurements?

The reason I ask is because I have ordered different LDR's from several suppliers that cover a wide range of values, but when I measure them at room lighting and very dimly lit room for dark, I get almost the same readings from all of them. For example, I have an LDR that says Light resistance 10K - 20K and Dark resistance 10M. When I measure them at normal room lighting and then no lighting at all they measure 2.1K Light and over 20M Dark. Can you see my confusion!!

Any help would be appreciated.

Jim

Here's my first Madbean build. It's called the Echo +, which is a Sea Urchin. Great little delay pedal. I bought the board back around November but have been busy with other projects and hadn't had time to build it. I like the filtering on it. Brian did a good job with it for sure.

This was a first as far as board mounted pots, and a first using the DecalPro FX dry transfer system. Somewhat of a steep learning curve. Anyway, aside from the obvious mistakes I made (I'll point them out later), I would appreciate some feedback on it.

Here's the dry transfer decal.



This is the finished pedal. The decal is slightly skewed. Need a steadier hand on applying these decals. This was my third attempt as the decal kept peeling somewhere on the carrier mylar every time. It was always a small area somewhere. If you look closely at the input side slightly above the arrow, there is a place I had to touch up on the outside border. Another problem was I got the board and pots too far down from the top. Live and learn!!



I had a super bright blue LED, so I used that on it.



And, finally, a gut shot.



I'm going to add some foam so the battery doesn't rattle around inside.

Jim

I wanted to ask all of you LFO experts about the values that are chosen for the voltage divider.

I have seen several LFO circuits, many of which look very similar, that use various values for the divider network. Some use two 10K resistors, others use two 220K, and still others use two 680K (one to 9v, the other to ground and the Vref is picked off from the two resistors that are joined together). Basically, in a nutshell, I have seen many different values used.

My questions revolves around the Vref. If two equal value resistors are used as a voltage divider to get approximately 4.5 volts for Vref, why are so many different values used for these two resistors? Could you use a set value, say 100K, or is there some current limiting going on here as well (the reason for the use of other values) for the op amp?

Just wondering about this. I guess my question is really, is it critical for the different values depending on the op amp used or is it just what ever the designer had on hand to use for the Vref voltage?

Thanks guys!

Jim

I have a question about the circuit below. It is just a snippet of the whole circuit. My question is in regard to the diode in this circuit. Here's the circuit, questions to follow:





First of all, given the voltage range (0.7v - 15v), I assume the diode is to clamp the voltage at the max of 15v. Does this seem like a logical assumption? If not, what is the purpose of the diode?

Would this be a zener or a fast switching diode (such as a 1N914 or 4148)?

I have breadboarded the circuit without the diode and using a 9v trigger voltage and the circuit works just fine. Just stumped on the purpose of the diode. I do not have the actual pedal and therefore cannot read the value from the original diode. The circuit was drawn from a photo and the diode is a glass type. The owner does not want to remove it to see the actual value (can't blame them really).

Those that are more knowledgeable then me, would you shed some light on this please?

Thanks,

Jim

Anyone receive bad MN3207's from Polida on eBay?

I ordered 16 sets of MN3102/MN3207's from them and after spending a few hours on a project I am working on, decided to test them in a known working delay using the same BBD's. Out of the 16 MN3207's, only 4 had delay (although shorter delay time than the original MN3207 in the delay circuit). The rest just passed a dry signal with no delay. Anyone else have this problem?

Jim

I just got my new oscillocope today (first one I've actually owned. Have had other people help me with signal tracing that had a scope in the past), so now I finally own one! Hope to put it to use here shortly. It is an Atten ADS 1062CAL 60mHz dual trace scope. Is anyone here familiar with it? If so, any tips?

Got it as an open box unit, never used. The company I bought it from thought the screen was broken, but discovered that the silica pack was busted causing the rattling noise inside the box. Paid $260.00 (free shipping) for it and was told it sells for around $350 - $400 normally.

Anyway, what brand o-scopes do you use and is there a preferrence? Just curious.

Jim

I finished off some really good flux remover that I had for several years, actually forgot I still had it. The label is unreadable on it except for saying flux cleaner on it. Can't make out the brand, but I remember it was discontinued a long time ago (who knows why?!?). Anyway, I ordered some MG Chemicals Heavy Duty Flux remover and some more hog's hair brushes. I had used some 60/40 rosin-core solder and some 62/36/2 rosin-core silver solder (Radio Shack). The heavy duty flux remover removes the flux, but leaves a very sticky residue on the boards that I can't seem to remove.

So, what do you guys use to remove flux and have a pretty clean board and where do you purchase it from?

Thanks,

Jim

I am working on the Lovetone Flanger and had a question about the biasing of the BBD. There is a trimmer (22K) used to bias the MN3207 at the input (pin 3). When biasing this, what am I looking/listening for? If you need to see the schematic, just click on the link in my signature and click on Daughter Board Schematic. Also, the Morley Sapphire Flanger Box has a similar Bias adjust. I can't find any info on setting this adjustment.

Also, according to the MN3102 datasheet, using a 100pf cap and a resistance of 5k ~ 1m for the R/C network will produce a cp (clock pulse) of 3.2kHz ~ 260kHz. Now, the daughter board has a 120k resistor with an LDR in parallel. After doing some calculations, an LDR of 5k in "full light" in parallel with the 120k resistor gives 4.8k. Is this close enough or should I not go below the 5k limit from the datasheet? If this is good enough, my next question is:

While waiting for my LDR's to arrive (an assortment) could I use a 500k to 1m pot to simulate the LDR as long as I don't go below the 5k or 4.8k limit to see how the circuit responds?

Slightly confused at the moment with these BBD's and LDR's.

Any help is appreciated.

Jim

What's up with Mouser these days? Twice I've ordered TL062's and LM324"s (pin-through-hole versions of both) and twice they sent me SMD versions. Anyone else having problems?

Jim

Just wanted to wish everyone a Happy New Year and hope that 2013 is a good year for everyone. Party hard and be safe!

Jim

I was wondering which simulation software everyone uses. I have MultiSim myself. But I've seen some talk about LTSpice.

Is one any better than the other? Are there other Si, software out there? Do you have trouble finding SPICE data for your parts to simulate?

Just curious.

Jim

Wanted to ask if anyone here has ever built their own enclosure using either aluminum, steel or both and using a machine such as a brake or something similar. If so, how much trouble was it? Harbor Freight has brakes that are not too expensive. I was considering this for special projects.

I have a question about the Neutrik style jacks, both mono and stereo. If you are looking at the top of the jack, with the jack opening facing you, which side is the T, R, S on?  Or to re-phrase it, is the TN, RN, SN the switched side and the T, R, S to jack contact side ( th part the jack actually contacts)? I don't have one  (I can't tell from the pictures on the web) and have never used one before so I am trying to figure out which side to send the signal to and which side switch. I assume the TN, RN, SN is the switch. Is this correct?

Thanks,

Jim

I asked about the J201 in another post regarding the Chunk Chunk and am satisfied with the answers I received. Now, I need clarification on JFETS in general but I'll use the J201 in this post. I am not that familiar with JFETS as I have not used them before in a project.

I ordered 20 J201's from Smallbear and 10 from Mammoth. The one's from Smallbear are Fairchild devices and the one's from Mammoth are IRC devices (manufactured by Fairchild and IRC). My first question:

Can you mix devices from different manufacturers in peddals? In my usual dealings with electronics, it is OK to mix them except in rare instances or critical circuits. But I'm not sure in audio circuits.

My second question is in regards to matching. How close do they have to be matched? I have used the JFET matcher circuit from JMK and grouped them to what I think are close matches. Here's what I have from each manufacturer (single listings didn't appear to match closely with anything, the othere are grouped to what I believe to be close matches):

The specs say that Vgs(off) should be between -0.3mv to -1.5v. As you can see, they are all on the low side, not close to the minimum spec. at all.

Fairchild (readings are in mV and are negative voltages)

.033

.068, .074

.095, .099, .099

.187, .191, .191, .193, .194

.123, .129

.137

.156

.209, .211, .212

.251, .259 (these may be too far apart to be a match)


IRC (readings are same criteria as Fairchild above)

.110

.127, .132

.146

.160, .163, .165, .165

.176

.196

I need to know if any of these can be more groupings and if I am grouping them correctly. I do know I need to order more than 20 or 30 to get more matched sets. I had not read the articles on matching when I originally ordered.

One last question. Do I want to use the highest value matched sets (or for that matter, highest value single devices if ony one is needed)?

Any clarification would be greatly appreciated.

Jim

Those of you who have built the Chunk Chunk (2012 version), did you match the J201's or just plug them in and set the bias according to the instructions?

If you matched the 201's, what Vgs value did you shoot for (low, high, in the middle, or whatever you could reasonably match)?

I have the improved JFET matcher circuit built and ready if I need to do some matching.

Thanks!

Jim