Optocouplers/ dual opamp Q

[The Captain]

Hi, Im having problems soucing a particular optocoupler- a CLM600. Its for an 'Anderson Tremolo' diy pedal. Anyone know if a suitable replacement can be popped in instead? I also cant source either an 'IC 5532 or TL072' (either ok for the dual opamp)- again is there a suitable replacement for this too? many thanks, Captain.

This is the schematic: http://www.generalguitargadgets.com/...ms/catrmsc.gif

[Mark Hammer]

It is the CLM6000 not 600. Just one small typographical error amidst the very fine work JD Sleep has done on the site. Actually, a lot of other optoisolators will do just fine there, although you may have to adjust the values of R3 and/or R4. Look here for some choices: http://www.smallbearelec.com/Categor...+Photocouplers

A wide variety of dual op-amps will work just fine in there. The original used a 14-pin LM4739 which is no longer made. NE5532 and TL072 are good quality, quiet, and generally available dual op-amps. You can use a TL082 or TL062, or LM/MC1458 or JRC4558 without noticeable drop in sonic quality. Generally, just about anything with a 4558 pinout will work, but you can order an NE5532 (preferred) when you order an optoisolator.

If the +/-9v operation presents a bit of a challenge, there are many 9v tremolo circuits that work nicely. The Anderton tremolo IS a nice quiet, clean tremolo that can be persuaded to do some tricks, bu many folks have good things to say about the EA tremolo, which does not require a costly optoisolator.

[The Captain]

Thanks alot there Mark. The Anderson one does seem a bit more fiddly, but I can find all the bits for it in UK (bar the CLM6000 which I hope a 525H68 SFH618A-2 I just bought will be ok here-? it may be on your link with luck). Just found a NE5532- great. The EA one had about 3 or 4 film caps values of which are hard to get and pricey. The dual battery thingy needs some brain action to understand, as will be knowing which way round these little black leggy opto/opamp whatnots go! cheers capt

[The Captain]

Ah, I see a bit of difference in cost- the CLM6000 on your link is $8. The one I guessed at and bought as a replacement was 85p- $2.. perhaps it wont work.. be great if it did!

[Steve Conner]

No, it won't work. The CLM6000 is a LDR (light dependent resistor) type of optocoupler, the sort that people casually call a "Vactrol" or "trem bug". The SFH618 is just an ordinary phototransistor coupler, as used by the bucketload in industry.

I know very little about the various kinds of Vactrols on the market, and which ones will substitute for the CLM6000 in this circuit, but I'm sure someone else will know.

If you can't find a TL072 or NE5532, try harder. Hint: Maplin sell both, even if the average Maplin shop assistant doesn't realise it.

PS: Does the 4049 need to be an unbuffered type? I would think so. Maybe an effects guru like Mark Hammer can comment?

[The Captain]

Ah thought as much.. bugger. Maplins sold the 5532 as you said, so its just this CLM6000- unable to find this in UK at all: Id be grateful if anyone would know if there's a suitable alternative, or knows any source bar the US 'Bear' place, or Im stumped methinks!

cheers Captain

[Mark Hammer]

You really owe it to yourself to go to Smallbear for parts. Steve Daniels started it out as a cottage business after asking fellow stompbox forum buddies if they would be willing to buy such and such a part or such and such a price if he could score a good deal. Happily, it blossomed from there to the point where he does a thriving business supplying both hobbyists and "boo-teek" builders as well as some larger commercial clients. In some cases, he gets parts made especially for him to sevre that client base. One of the things he has remained true to is the hobbyist base, and while filling of orders or responding to e-mail can take a bit of time now and then (which is the nature of the beast when you have 1-3 man operations), he always goes to bat for the hobbyist and is often the go-to source for people in places which lack an easy or cheap means to provide parts. He also comprehends the role of the part within the circuit, which is more than I can say for most component distributors.

Obviously if you need it in an hour, Maplins is handy, but if it can wait a week, Steve can often deliver exactly what you need. Yes, I fully understand your trepidation at ordering overseas...much as I'd be a bit skittish ordering trannies here in Canada from an ad I saw in Practical Electronics for some place in Sussex. In Smallbear's case, however, the experience will be like ordering from the shop down the street. As honest as the day is long, and he makes a point of figuring out the cheapest shipping costs possible for both domestic and international customers.

And Steve Conner is correct. An LED/transistor combination will not work.

A bit of design analysis might help you to find something locally. U1B is an inverting gain stage. In such stages, the gain is given by the feedback resistance (R6 in this case), divided by the input resistance (the combined parallel+series resistance of R3/4/5 and the LDR). If the LDR resistance drops down to near zero (rare, but I suppose within the realm of possibility), then the total input resistance is roughly equal to R5, which gives U1B a gain of 4.7/1 or 4.7 (that's why it needs a volume control on the output). Now, the input resistance will NEVER be any greater than the max value of R3+R4+R5 (25k+4.7k+1k). At that maximum resistance, the gain of U1B is equal to 4.7k/30.7k = .15, which means that the output is well below unity, which is precisely how it produces the alternation of loud and quiet that produces the tremolo effect.

The biggest resistance in the R3/R4/R5 chain is obviously the pot, such that if you reduce its resistance, the parallel LDR has less impact on the resulting gain. Ultimately, what you want and need in there is a photocell resistance that can go into the several hundred K range (such that the gain is almost entirely given by R3+R4+R5), down to a range of perhaps less than 20k.

As an illustration, if the photocell resistance was 20k, then R4+R3 in parallel with the LDR could never be any higher than 11.95k. Reduce R4 down to zero, and the parallel resistance is now 3.8k. Stick THAT in series with R5 (1k) and we have a 4.8k input resistance, which is darn near unity gain. If R5 were 470R, it would be a little above unity gain. If R3 were 2.2k instead, it would be decidedly above unity gain. Alternatively, since R6 (4.7k) is part of the calculation of gain, just make R6 bigger to offset what the input resistance is unable to achieve.

I think what you can see here is that it is possible to set the values of R3-through-6 to achieve various ranges of resistance change when combined with the LDR. What you want to get is an LDR/photocell combination (prepackaged or make your own) that produces a wide enough range of resistance change in response to the LED. Ideally, the resistance change needs to yield the sort of resistances that go from a bit more than whatever R6 is, to something around 1/10 to 1/5 of R6's value. Once you have that, you can do some math and tailor the other resistances to produce the desired response. The CLM6000, of course, already "fits" the existing components, saving you the math. But if you can find something cheap locally, you can still make the circuit work as intended with other part values.

And, for the record, the 4049 is functioning as a VERY slow clock not carrying audio signal, so I imagine buffered-vs-unbuffered makes no difference. But, since there are so many fine overdrive circuits one can build with buffered 4049s, it makes sense to order a couple of buffered chips and use one of them for this circuit.

[Steve Conner]

Hi Mark, thanks for the reply.

When I said buffered vs. unbuffered: If I understand right, the 4049 (or at least section C of it) is being used as a linear amplifier/integrator type thing here to generate a triangle wave LFO. I was always under the impression that only the 4049UBE could pull this trick, and any buffered version would melt down or oscillate when you tried to bias it as an amplifier. But maybe I'm thinking of something else, like the 74HC04 vs. the 74HCU04.

FWIW, I have seen a 4049 used as a dirty channel in a Fender London Reverb, and in a small Laney bass amp too. I can't remember if they were B or UB though

[The Captain]

Great help again Mark, I'll go through this to learn whats actually going on with these circuits later. As just sending one clm6000 was ~$14 total, it does seem daft for one tiny component from Small Bear to UK, which is why I hoped to source the little b'stard closer.. it does indeed seem a fine site for the stompboxer especially in US, one Ill note if I make any future pedals to get a listful from. Surely though these clm6000 have other uses besides guitar pedals/ fx.. ie I should be able to get just one from somewhere else.. maybe not. I don't think I could work out how to do it using a different bit.

[The Captain]

I wonder if anyone knows whether this:

'The CLM6000 is apparently long since discontinued, but I am reliably informed that the nsl-32 provides a suitable substitute'

..is indeed a suitable replacement for the Anderton Tremolo? (info from Bitbox.co.uk; I didn't specify the particular circuit in my Q to them). Nsl-32 specs: http://www.silonex.com/datasheets/specs/103708.htm

Thanks for any help- Captain.

[The Captain]

I've just spotted a nsl-32 in Marks link previously- great I'll see if it'll work instead of a clm6000.

Would anyone know whether a 2N 5458 and 2N 5485 (Fet transistors) have suitable equivelents? this is for a 'Rodent' stompbox. these 2 buggers very hard to find!

Much appreciate any help, Captain.

[Steve Conner]

I would be inclined to try the BF245 as a substitute for those. It's a European JFET model that Albert Kreuzer successfully used for audio.

FET parameters vary so much between batches, and with temperature, that the part number hardly matters in comparison

[Mark Hammer]

The Silonex unit will do just fine. It has an LED. It has an LDR of approximately similar resistance range. If you can find it cheap and local, you're home free.

Anderton used the CLM6000 in some projects both for its resistance range AND its rise/fall times. LEDs are of course, virtually instantaneous in their response, but LDRs vary in how quickly they go from max to min resistance under illumination, and how quickly they restore themselves back to max resistance when ilumination disappears. Generally, the chemical compositionof the LDR is such that the time required is much shorter for "on" in response to light, than for "off" in response to restoration of darkness. Very much like the human eye in that respect.

As it turned out, the response-time parameters of the CLM6000 were excellent for things like compressors, limiters, and noise-gates, where fast-attack/slow-decay is often ideal. In those instances, as well, the slow response of the LDR compensated for the use of quick-and-dirty half-wave rectifiers, and would "smudge out" any residual envelope ripple, yielding a clean-sounding dynamic response despite a low-tech approach.

Where the CLM6000 gets quirky, and perhaps nonideal depending on your perspective, is when it responds to LFOs, as it does in the case of tremolos or phasers. If the response time of the LDR is sluggish, then as the speed increases, the LDR has less capacity to restore max resistance before the next ascending half-wave forces the resistance low again. In effect, with sluggish LDRs, the sweep depth is automatically reduced as speed is increased.

Depending on what you're aiming for, this is good or bad. For phasers, it is probably a good thing, since one generally prefers less sweep as speed is increased. For tremoloes, it may be less than ideal. If you want a squarish "chop" function, you want the full square nature of the LFO to be reflected in the behaviour of the LDR, even at faster speeds. After all, you select a square wave in order for it to go from full on to full off, and if it can't exactly do that, well.....

So, in the tremolo context, what makes for a great optoisolator in a compressor, may not be the best choice. To be fair, however, the LDR is placed in parallel with several other components, so limitations on its resistance swing may not be especially evident. I had one of these boxed up for a while (before cannibalizing the parts for something), and I recall it being able to provide reasonably persuasive "chop". Not as sharp as you'd get with a VCA and LFO, but clearly distinct from triangle.

Ideally, if the NSL-32 has a faster response time, you'll be in great shape. There were far fewer choices available at the time when Anderton published EPFM 1 and 2, and if there are more and better choices available now, why penalize yourself by blindly adhering to "vintage orthodoxy".

The FET used in the Proco Rat and GGG-Rodent clone of it are used for buffering purposes only, just to separate the tone/filter control from the volume pot and prevent interaction. You can use just about anything in there and have pleasing results. BF245, MPF102, 2N5457, J201, 2N3819, etc.

Incidentally, if either of you are "wing-it" perfboard types, the pad-per-hole boards from Smallbear are absolutely unique and unparalleld in their quality. Steve had them made especially for him. Top quality fibreglass, tinned pads, rounded edges, available in single and double-sided formats, and cheap.

[The Captain]

I managed to source a silonex nsl 32 for a few quid from Bitsbox.co.uk (very helpul indeed), I saw it had similar 500ohms in/out too with help rereading Marks info- very pleased indeed me. Id like to use Small Bear and other diy small outfits, but post costs across the pond for the odd bit though..

Last Q re ICs and indeed the optoisolator- how do I know which way to mount them? I noticed on an IC (4049) I have it has a small indent/ nick to one end- is that an ident? and links to the oval ident on the IC (on layout below)? and would an optoisolator have a marking on like the CLM600 here: http://www.generalguitargadgets.com/...ms/catrmpl.gif

thanks Capt

[puretube]

Mark: that bold word on the bottom of reply #7 makes me shiver...


btw: recently I was building some analog-to-Schmitt-triggerish PWM thingy,
and was wondering why it behaved "mis" (parasitic oscillations, that the o-scope detected) :
the answer was on the chip, and in the datasheet:
it was a buffered 4049 by accident,
and in the sheet it said they (the buffered ones)don`t like to be driven from "high" impedances of > 1k.