i got one apart on my bench right now, fixing it for local legend jimmy dubonet.
it was a BEAR to get apart. someone had "fixed" the footswitch by tightening the outside nut to the point it stripped and fused on, and they twisted it hard enough to actually destroy the switch inside. joy.
to get it out, only one way to fly. you gotta use a solder sucker and some wick, heat up each node of the totally cheap ass dano style input jacks and then separate the board from them.
they mount the jacks first, then solder the board to the jacks. kinda like an experience pedal, but thank god this doesn't have dual traces on it like the prescription electronics did.
i found the part for the switch at small bear, but ended up buying them from my boy lawrence at bitches love my switches as i could buy a couple of them shipped for what it would cost at small bear, and so thru a bunch of other loot in my sack.
it's an alpha 107-SF12011-L is the closest you can get. from what i understand researching here you have to bend the lugs to get it to fit, i was like... oh, joy. lawrence has the knock offs that are a little closer than the alpha's which i also went for, anyways...
the switch is a short one, a standard stomp won't fit in there at all, and it is designed to solder right into the pcb. my FAVorite.
but i figure while i got it apart, if anybody needs pics or values or any of that crap, let me know and i will do my best to supply the info.
i've only seen one schem for it which is "purported" to be it, figure you don't see many of 'em so it's hard to come by a proper reference.
i will say this, at cursory glance last nite... it's gotta pair of lm308's and a jrc4558 in it... a double rat into a toob screamer? lol
beats me.
but if anyone wants pics, i will try and get them for you. once this thing's parts come in, i won't be able to access them anymore, so....
Nice write about it here, plus mods;
http://www.codtone.com/downloads/2246413/Codtone+Expandra+Build+Doc,+Notes+and+Mods.Rev+2.0.pdf (http://www.codtone.com/downloads/2246413/Codtone+Expandra+Build+Doc,+Notes+and+Mods.Rev+2.0.pdf)
R.G. did a write up on it over at Geofex.
4 knob vero;
(http://www.sabrotone.com/wp-content/uploads/2011/08/Expandora.gif)
that looks wayyyyyyy easier to do than the one i got on the bench.
i was just curious, cuz the schem on the net is "purported" to be correct which makes me wonder if it's legit or a work alike.
i will check geo for it, it's been a while. thanks dino!
Thanks Jimi and Dino.
Saved to file.
WOOOT!! I have some H11F1's at home. Might just give this a shot!! Have to dig up some LM308's though.
Jimi, take a break from the expandora and go eat some pineapple dude. It'll soothe your soul. ;D
lm308's ya can get at tayda. the bixonic one doesn't use the "mojo" can ones.
lm301's work almost identically in a rat circuit.
i'm a gonna go crank me up some pineapple express...
and get a couple photon faces done
Good man!!
Got a line on some LM108's. Waiting on a shipping price. :icon_cool:
you mean lm308, or lm301?
not familiar with a 108 ;)
http://www.linear.com/docs/1704 (http://www.linear.com/docs/1704)
hah, there is a 108!
here's the 301's i use
http://www.utm.edu/staff/leeb/LM301.pdf (http://www.utm.edu/staff/leeb/LM301.pdf)
The 108 is the "heavy duty" version of the 308. It has a wider temperature operating range than the 308, and I think a higher voltage operating limit too.
nice. will the cork sniffers approve? ;)
i like the old metal can chips. they just look cool. i dunno if they sound any better. ;) i always test 'em out in different things, but hardly ever use 'em other than in rats.
Quote from: pinkjimiphoton on March 06, 2017, 04:56:52 PM
nice. will the cork sniffers approve? ;)
Hah! Dunno. That one's going to keep me up tonight.
Not. :P
:icon_mrgreen:
> not familiar with a 108
Most of the "3xx" parts came in 1xx and 2xx grades.
108 is Military, should handle insane temperatures, may have tighter specs.
208 is Industrial, wide but not insane temp range.
308 is Commercial, a temperature range still wider than any you would play at.
Original prices could have been $50 for the 108, $5 for the 308. Obviously pedal-floggers have no need to pay big bucks more for temps they never want to see. So the world is (was) full of 308s.
Now that Military and Industrial demand for 108 is about zero, those old-stocks of 108 and 208 are being dumped for what they can fetch.
HA HA!!! Look what I found!
(http://i.ebayimg.com/00/s/OTAwWDE2MDA=/z/ADQAAOSwImRYkJbq/$_57.JPG)
Yes Comrade! Russian counterpart to LM108. Stick THAT in your toupee Mr. Trump! ;D
Need to go decipher the datasheet now..... never mind, picture is worth 1000 word;
http://xn----ctbgeuhdtdb2b.xn--p1ai/cfiles/market/4092/1480988363.pdf (http://xn----ctbgeuhdtdb2b.xn--p1ai/cfiles/market/4092/1480988363.pdf)
Just need to figure out which are the inverting/non-inverting inputs. They use a little circle, I'm not familiar with that symbol.
EDIT: Praise Google translate! The little circle indicates the non-inverting (+) input.
The pinout is as follows;
1, 8 Коррекция (Correction)
2 Вход инвертирующий (- input)
3 Вход неинвертирующий (+ input)
4 Напряжение питания минус Ucc (- power)
5 Свободный (No connection)
6 Выход (Output)
7 Напряжение питания Ucc (+ power)
Same as the LM308. :icon_biggrin:
lol... i'm just glad canadians still have our first amendment, we won't be using it for a couple years here at least :icon_rolleyes: :icon_mrgreen:
The little circle is the same meaning as when used for "inverted" on logic gates. You usually see them on the output side, but they can equally be on the input as...
(http://users.cecs.anu.edu.au/~Matthew.James/engn2211-2002/notes/diglogimg58.gif)
Quote from: pinkjimiphoton on March 07, 2017, 01:18:01 PM
lol... i'm just glad canadians still have our first amendment, we won't be using it for a couple years here at least :icon_rolleyes: :icon_mrgreen:
The inherent vice of capitalism is the unequal sharing of blessings; the inherent virtue of socialism is the equal sharing of miseries.
~ Winston Churchill ~
Putting together a JMK board right now. I've added the Bass/treble boost switches from the Codtone site. I also decided to use a pot for the drive, instead of the switches. I decided to use a footswitch to jump it into the "Forbidden" zone.
The drive pot that replaces the switches is a 1K linear. Now, the switches, notwithstanding the forbidden setting, give you three resistances; 560R, 1.1K, and about 371R with the two in parallel. Using a 1K pot, I used a 330R resistor between lugs 2 and 3, and a 110R resistor on lug 1. The other end of the 110R resistor goes to the board, as does lug 3 of the pot. Sweeping the pot gives you all the resistances of the switches, with all the in between settings too. As for the forbidden mode, the switch will break the connection between lug 3 and the board of the new pot. In a pinch, you could use a switched 1K pot as well, using the switch to go into forbidden mode. I would however use a resistor instead of going wide open in forbidden mode, which is totally unruly. Maybe I'll try a 1M trimmer to try and find a resistance that will be "out there", but useful.
As for the diodes, I've tried a bunch of different types, including germaniums, but the best sounding ones are some NOS 1S1588 Japanese diodes that I bought a while back. Looking at some Expandora gutshots, the seem to look identical, right down to the blue bands.
The LM108's are great. I haven't got the Russian ones yet, but I really like the LM's so I soldered them in. An old 4558DV is sitting in a socket. I might swap in something else to try, but the DV is working quite nicely. A 5087 is the transistor of choice here.
The H11F1 is what I'm using, and seems to work fine. I must say though, I had to check the units I bought from Ebay, 3 out of the batch of 10 that I bought were defective (no resistance swing with varying voltages applied, just dead).
My initial testing has my ears drooling. From what I've read, there's a bit of a love/hate relationship with this circuit, but I absolutely LOVE it. With the Drive knob set just so, and a setting the Gain pot to the amount of distortion desired, this is one absolutely interactive beast with the guitar volume. Backing off the volume, it cleans right up, and I mean "right up". Very clean. I can maybe push it a tad into grind if I really dig in, but not a peep of dirt if so desired. Dial up the volume, and grind galore comes to life. Quite frankly, I'm so impressed, I just bought a 2000R version on Ebay, and I'm looking forward to looking at the guts of that one. Wish I could find the 2001 version schematic. The links over at the other place are broken, but from the small picture, it looks really different from the other versions.
Found this in my travels. I believe it is the 2001 version.
(http://i64.tinypic.com/25tgle0.jpg)
2206 datasheet note the resistors. That is why the codtone has two added ones by the 5087
http://pdf1.alldatasheet.com/datasheet-pdf/view/92220/TOSHIBA/RN2206.html (http://pdf1.alldatasheet.com/datasheet-pdf/view/92220/TOSHIBA/RN2206.html)
(http://www.diystompboxes.com/pedals/exp2.gif)
You can find this in the "Schematics" link at the top of the page. Wow I drew that back in 99 when I fixed one.
Gus, thanks for that. Your info, along with all the rest was what fueled me during this road trip. I still wonder though if the 2206 has some particular properties that make it best for this circuit, but other than the integrated resistor, the voltages say no.
Chugs, THANK YOU!!!! Greatly appreciated. One for the breadboard... as soon as I figure out the components. IC4 looks like quad opamp EQ section? IC5, some kind of CMOS thing going on?
Quote from: digi2t on April 10, 2017, 06:49:03 AM
IC4 looks like quad opamp EQ section? IC5, some kind of CMOS thing going on?
IC looks like a level indicator to me - a ladder of 4 comparators with LED output. I'm not sure about the base of Q2 - it would clamp the output of IC3-7 when the switch is closed? A resistor could be missing?
IC5 might be a 4049 inverter. Have seen something similar using them as voltage controlled R with one power pin floating at signal level (pin 7 in this case).
Quote from: anotherjim on April 10, 2017, 07:04:45 AM
Quote from: digi2t on April 10, 2017, 06:49:03 AM
IC4 looks like quad opamp EQ section? IC5, some kind of CMOS thing going on?
IC looks like a level indicator to me - a ladder of 4 comparators with LED output. I'm not sure about the base of Q2 - it would clamp the output of IC3-7 when the switch is closed? A resistor could be missing?
IC5 might be a 4049 inverter. Have seen something similar using them as voltage controlled R with one power pin floating at signal level (pin 7 in this case).
Dang... You're right on the comparator. It's for the flashing LED in the pedal. I forgot about that. Thanks Jim!
Early Christmas gift...
Just so were clear;
Version 1, the "Script" model. No gain switches, just a straight forward overdrive. -
(https://i.ebayimg.com/00/s/OTAwWDEwODY=/z/PgMAAOSw4CFYp4tQ/$_58.JPG)
Version 2, the 2000 model, two internal switches for gain only -
(http://farm6.static.flickr.com/5189/5610841284_0eb514c3b0.jpg)
The Godlyke reissue version (2000R, version 3, external switches, two for gain, one for guitar/bass voicing);
(http://files.effectsdatabase.com/gear/pics/bixonic_expandora-exp-2000r_001.jpg)
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/DSCF5307_zpsvgp6crni.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/DSCF5307_zpsvgp6crni.jpg.html)
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/DSCF5308_zpswermssnf.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/DSCF5308_zpswermssnf.jpg.html)
The last version (2001, version 4, all switches replaced by "Drive" pot);
(http://www.guitarfx.it/wp-content/uploads/2009/10/bix_front.jpg)
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/DSCF5311_zpsnlrux9wf.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/DSCF5311_zpsnlrux9wf.jpg.html)
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/DSCF5309_zpsp6fodrsr.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/DSCF5309_zpsp6fodrsr.jpg.html)
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/DSCF5310_zps4w4asz1v.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/DSCF5310_zps4w4asz1v.jpg.html)
My impressions;
I'm not going to cover the version 1, since I haven't tried it. I haven't tried an original v. 2 either, but right now I have a JMK board on the bench. It's representative of version 2 of the Expandora, with a single 4558, twin LM308's (I'm using LM108's), and the PC419 (I'm using an H11F1). Comparing it to the v.3, there are very obvious tonal differences. Quite honestly, given the choice between twin LM308's, or a dual op amp such as the TL072, I'll roll with the 308's any day of the week. Though they're similar gain-wise, the 308's have a bit of a rounder tone to them. Another thing, the version 2 is quieter too, especially when you kick an amps overdrive channel with it. Version 3 is much hissier, though remember, I'm comparing it to a clone of the v.2. Regardless, listening to videos of original v.2's, my clone is pretty close to it. Overall, v.2 is quieter than the v.3. The "Forbidden" modes sound different too. For that, v.3 wins the contest. While v.2 can be quite the beast in forbidden mode, with all kinds of roar, feedback, and cacophony of noises, v.2 offers a more usable effect at the lower drive settings. With run-of-the-mill humbuckers (7K to 8K range), I could get my Jack White on no problem. I could really modulate between gating notes, and screaming feedback at will, just by adjusting the guitar volume. It's quite addictive, and loads of fun. As many have reported, the forbidden mode isn't really usable on the v.2 units, though v.3 makes it quite interesting. Not sure if it's differences between the 072 versus the 308's, or the H11F1 versus the PC419. As for the schematic, I'm pretty sure it's going to be "replace dual 308's by single 072", along with some other component value changes here and there, but I'll confirm this over the nect couple of days/weeks.
Version 4 is a completely different animal. No gain switches, and alas, no "Forbidden" mode. A straight up mild overdrive, to crunch, to all out fuzz machine. OK... the flashing VU LED's are cool. I'm like a moth to a match, what can I say. It's the quietest of the bunch, especially if you're going to be goosing an overdrive channel. While some of the same tonal quialities of v.2 and v.3 can be dialed in, it's got it's own voice(s) as well. The "expandora" effect is still there though, giving you great clean-to-grind-to-clean control, simply by twisting the guitar's volume. The opto, or OPTOS in this case, are a pair of Sharp PC817's, encased in a single package. The actual Sharp number for the dual package is PC827. Interestingly enough, the PC817 is a family of optos, encompassing 1, 2, 3, and four channel models. Hey... ya learn something new everyday. A quick Google tells me that they're still widely available, and still really cheap. Maybe they can be used in the v.2 or v.3 models as well? We'll see. Anywho, v.4 is a nice overdrive in it's own right. Covers a boatload of sonic territory, so no regrets on the purchase. Besides, was worth the price of admission, just to gander at the guts. I'll compare it to the published schematic over the next couple of day/weeks, just to confirm the schematic.
Thanks for the info!
Here is the verified schematic for the 2001 model. Many thanks to Chugs for the original. I did a little cleaning up, and there were a couple of errors that I corrected.
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/2001%20version_verified_zpsheprhsm8.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/2001%20version_verified_zpsheprhsm8.jpg.html)
I suppose if one really wanted the "Forbidden" setting of the v2 and v3 versions, it could be incorporated into the clone. I would try opening the circuit between C5 and the IC5 - pins 6-7 connection. I'll try it when I get to that stage, or if someone beats me to it, let me know how it works.
Off to work on the v3 schematic now. Damn! I hate double sided boards! :icon_rolleyes:
Running on inspiration from the Montreal pedal show, I've completed the trace of the version 3 unit.
Here you go folks...
(http://i214.photobucket.com/albums/cc196/digi2t/Expandora/2001R%20schematic_zpsiy4za3za.jpg) (http://s214.photobucket.com/user/digi2t/media/Expandora/2001R%20schematic_zpsiy4za3za.jpg.html)
That's it. Stickin' a fork in this one. :icon_biggrin:
Thanks!
Are C3 and R2 necessary? All versions have these parts but seems they may be superfluous?
Quote from: Chugs on May 08, 2017, 03:25:25 AM
Thanks!
Are C3 and R2 necessary? All versions have these parts but seems they may be superfluous?
Couldn't tell ya buddy. As my bro Jimi would say, that's above my paygrade. :icon_mrgreen:
Maybe one of our house gurus can chirp in here?
whaaa-aaat, no vero????? :icon_mrgreen:
Quote from: pinkjimiphoton on May 08, 2017, 06:57:04 PM
whaaa-aaat, no vero????? :icon_mrgreen:
I've found that the guys over at Tagboard are a lot faster on the trigger than me when it comes to whipping up veros. I still draw them up, but I've slowed down of late, tending to wait to see if Alex and the gang spit something out first.
hahah, i was just teasing bro... after looking at the epic ludwig vero this is nothing! ;)
i hear ya on tagboard... i use their layouts on MY builds of my circuits cuz they are usually cleaner than my widdle bwain can figger out.
nice to see a proper and verified schematic too! ;) well done bro! i crack this cyber beer to thee ;)
Reposting digi2t's v3 reissue schematic, as it's been missing.
(https://i.imgur.com/fg09KLH.jpg)
It answers the mystery of what the 3rd "guitar/bass" voicing does. A larger cap is switched in at the very end. I built mine on Sabro's v1 layout and changed the high pass values before the output to match v3's, along with switch.
Since his trace, Tagboard has put up layouts for Expandoras v1, v2 and a hybrid version Dino came up with. This v3 schematic should complete the set. He added a lot of helpful hints at the comments over there.
I wonder if it would make any difference to use a diode instead of Q1 @ IC3_B :icon_question:
mac
Quote from: digi2t on April 30, 2017, 02:59:06 PM
Early Christmas gift...
My impressions;
I'm not going to cover the version 1, since I haven't tried it. I haven't tried an original v. 2 either, but right now I have a JMK board on the bench. It's representative of version 2 of the Expandora, with a single 4558, twin LM308's (I'm using LM108's), and the PC419 (I'm using an H11F1). Comparing it to the v.3, there are very obvious tonal differences. Quite honestly, given the choice between twin LM308's, or a dual op amp such as the TL072, I'll roll with the 308's any day of the week.
Is it OK to use H11F1, I suppose you had an opportunity to compare it to PC419. I have few of the H11F1s on hand, but PC419 are not available for me :(
I'd sure try. You may have to mess with the CLR a little to get the appropriate response. I could be wrong ;)
Codtone build documents from the now dead link in the 2nd post:
https://www.scribd.com/document/235013206/Codtone-Expandra-Build-Doc-Notes-and-Mods-Rev-2-0#download
thanks mate, but any way ya can just up it as a pdf or something somewhere? i mean zero offense, but man, i am sick of signing up for accounts just to look at shit ;)
There's much better service called docdroid.net, it's free for PDF sharing.
Quote from: pinkjimiphoton on December 04, 2018, 10:29:37 PM
thanks mate, but any way ya can just up it as a pdf or something somewhere? i mean zero offense, but man, i am sick of signing up for accounts just to look at shit ;)
I feel ya. I actually found it googling. Anyway here's pdf version for downloading
https://drive.google.com/open?id=1GXcNKwDzdOBkgw4rW4wJi-zNVlS-rXUF
I hope I'm not too late jumping on this thread. I'm fairly new to this forum. I have questions regarding the Expandora's opto operation. I'm an EE, so please forgive me if I'm overthinking things here. My questions pertain to the opto's FET resistance and how it affects circuit operation. In a nutshell, I think the FET resistance is too high to do much of anything except in Forbidden mode. Here's why I think that...
The opto's maximum LED current is determined by the resistor between the opto and the PNP transistor. In all of the schematics I've seen, that resistor is 4.7K. Without getting into a detailed circuit analysis, the 4.7K resistor sets the max LED current somewhere between 0.6mA and 0.7mA. The PC419 and H11F1 datasheets contain curves for FET resistance vs. LED current. At 0.6mA, the FET resistance is in the neighborhood of 3.5K (I had to extrapolate since the curves only go down to 1mA). This is the *minimum* opto FET resistance in the Expandora. Depending on the switch settings, the second stage feedback resistors present either 371, 560 or 1.1K in parallel with the opto's 3.5K resistance (not including the "forbidden" setting). My question comes down to this: how can the opto make and difference in the sound when the resistors in parallel with it are so much lower in value? Wouldn't it make sense to reduce the 4.7K series resistor down to 1K or lower? Has anyone on this forum looked inside a production Expandora and can they confirm that the series resistor is in fact 4.7K?
I built an Expandora with a 10K pot in place of the 560 Ohm and 1.1K feedback resistors and a switch to disable the opto drive so I can compare sound with / without the opto in the feedback loop. I'm still experimenting with the opto drive current and will report my findings.
This one's on my "ToDo" list, so I will prepare some popcorn, since the list is very long :) Please share your experiences with this with us.
If memory serves me correctly, I've compared this schematic to my original 2000R unit, and it matches. Note; the nomenclature on the schematic does not match the board. The 4K7 resistor in the schematic (R6) is R14 on the board, and so on.
(https://i.postimg.cc/p9gL00mG/2001-R-schematic.jpg) (https://postimg.cc/p9gL00mG)
(https://i.postimg.cc/tYXCmngj/DSCF5307.jpg) (https://postimg.cc/tYXCmngj)
(https://i.postimg.cc/NL8j4kBD/DSCF5308.jpg) (https://postimg.cc/NL8j4kBD)
There was also a change of transistors between the 2000 and 2000R versions. The 2000 version used the RN2206, which was internally biased, while the 2000R used a 2SA684R, which was a more "garden variety" transistor.
Insofar as the gain switches are concerned, I did away with these, favoring a pot instead. I called it "Edge" control. I kept the "Forbidden mode" as a switch, which I wired to a second footswitch. The pot covers the same range as the switches, but with all the in between settings that the switches can't give you.
(https://i.postimg.cc/hhXkr9xw/EDGE-MOD.jpg) (https://postimg.cc/hhXkr9xw)
And if that isn't enough to keep your brain cells busy, here the 2001 version schematic. Different layout and structure, including different opto;
(https://i.postimg.cc/0bdcdQtF/2001-version-verified.jpg) (https://postimg.cc/0bdcdQtF)
Enjoy!
Thanks for the board pix! I looked up the datasheet for the PC827 used in the 2001 model. Very different beast from the PC419 or the H11F1. The PC419 and the H11F1 are single optos and have FETs as the switch / variable resistor element; the PC827 is a dual opto and has BJTs as the switch / variable resistor. In the 2001, the two optos in the PC827 have the LEDs connected in series and the BJTs connected back-to-back in parallel, for bidirectional operation. The LEDs are operated at a much lower current in the 2001. According to the datasheet, the transfer gain is higher in the PC827 and the operation in the ohmic region is not specified. I would expect the 2001 version to sound different from the other revisions based on the different opto.
Quote from: Chuck D. Bones on February 02, 2019, 10:16:00 AM
I would expect the 2001 version to sound different from the other revisions based on the different opto.
The 2001 is a different sound to be sure, but the different opto angle, I think, only plays a small role. The overall structure is the same, but the IC's are different. The LM308 has been replaced by a TL072, which lends for a slightly more sterile tone. That's not to say that one is better/worse than the other. Just different. Both are good, but within their own respect. As such, I own both. They're that good, at least, to my ears. :icon_wink:
Quote from: digi2t on February 01, 2019, 07:25:29 PM
If memory serves me correctly, I've compared this schematic to my original 2000R unit, and it matches. Note; the nomenclature on the schematic does not match the board. The 4K7 resistor in the schematic (R6) is R14 on the board, and so on.
And if that isn't enough to keep your brain cells busy, here the 2001 version schematic. Different layout and structure, including different opto;
Enjoy!
What's the purpose of LM324 part of a circuit, it is missing in later designs?
UPDATE:
I have learned a few things so far from my Expandora / RAT build. First & foremost, there is an undocumented feature in the H11F1: Pin 5 is internally connected to something, probably the FET substrate. My circuit is built on a Vero board. I did not put a cut between pins 2 & 5 because (according to the datasheet) pin 5 is not connected to anything. That turned out to not be the case. The problem was particularly vexing because the H11F1 tested fine on a prototype board, but the FET would not turn on when installed on the Vero board. I bent pin 5 up, I put the H11F1 back into the socket on the Vero, and voila! Suddenly the opto started working.
As I mentioned in my previous post, I suspected that the on-resistance of the opto's FET, as well as its saturation current, were not a good match with the Expandora's circuit impedances. I tried increasing the impedance of all of the components in the 2nd stage's feedback network by 5x. Using the reference designators from the Expandora 2000R v3 schematic (posted above), R9 was changed to 2.7K, R10 was changed to 240 Ohms, C8 was changed to 1uF and C9 was changed to 470nF. The DRIVE control (replaces SW1, SW2, R19 & R20) is A10K in series with 1.2K. I had also reduced R6 from 4.7K to 240 Ohms in an effort to increase the opto's LED current. Once the opto started working, the effect was extreme gating and a very sputtery sound at lower GAIN settings and/or softer playing. Clearly, the opto was now doing too much. I raised R6 to 1K, but the gating and crossover distortion were still too severe. R6 is now back to 4.7K and this is definitely in the ballpark. The note attack and decay are more natural sounding. There is smooth noise gating at the tail end of the note's decay. When the strings are muted, the output is quiet. I'll probably try 2.2K to see how that sounds.
Next, I started probing the signals at various points with my trusty USB oscilloscope. The output of the 1st-stage opamp was close to 4V instead of the expected 4.5V. I now doubt that the NE5534 is the best opamp for the 1st stage because its bias current is quite high, typically 500nA. In the Expandora, and in my circuit, the input's DC path is 1Meg (GAIN pot all the way up). This causes the offset voltage to be -0.5V in my circuit. This offset consumes headroom and leads to asymmetric clipping when the 1st stage is overdriven. This by itself may not be a big deal, but the other effect of the -0.5V offset is it interferes with the operation of the peak detector because the peak detector is referenced to 4.5V. I replaced the NE5534 with a (vintage) LT1001. Any opamp that has low current noise and very low bias current will work. The LT1001 also has a fairly slow slew-rate, just like the LM308. There are many other choices, but the LT1001 was at hand and works well. Note that the 2000R v3 uses a TL072 for the 1st & 2nd stages.
I'm still experimenting with the 2nd-stage opamp. For the moment, I have an LT1001 installed there. I started out with NE5534s because they are low-noise and externally compensated. That and JHS uses them in The Kilt. Externally-compensated opamps like the LM308 and NE5534 are desirable if you want to dial in the slew rate. I'll try an LM308 at some point to see if I can hear the difference.
Cheers!
Quote from: rankot on February 02, 2019, 04:39:36 PM
Quote from: digi2t on February 01, 2019, 07:25:29 PM
If memory serves me correctly, I've compared this schematic to my original 2000R unit, and it matches. Note; the nomenclature on the schematic does not match the board. The 4K7 resistor in the schematic (R6) is R14 on the board, and so on.
And if that isn't enough to keep your brain cells busy, here the 2001 version schematic. Different layout and structure, including different opto;
Enjoy!
What's the purpose of LM324 part of a circuit, it is missing in later designs?
There is a set of 4 small LED's in this version that act as a VU indication. The harder you strum, the more LED's light up. The 324 is acting as a comparator for the LED's.
At this point I'm ready to retract a fair amount of what I said in my previous post. After more playing & listening, I found that the note decay still had some sputtering / gating noise at the tail end. My circuit is now more-or-less back to the original Expandora component values. The things that depart from the Expandora v3 are:
1. First stage is non-inverting. Input impedance is 500K.
2. First stage gain range is 0db to 21dB.
3. First & second stages are direct coupled via R4 (C3, C4, R2 & R3 are not there).
4. R19 & R20 are replace by a 10KA Drive control.
5. C6 is 1nF.
6. C10 returns to GND instead of Vb.
7. I put a 100 Ohm resistor in series with D1. Loading opamps with capacitors (C10) is generally bad practice.
8. Last stage is a unity gain buffer with a 10KA Level control in place of R14. Output is taken from the Level control's terminal 2.
9. I added a "Contour" control consisting of a 10KC pot, 22 Ohm resistor & 47uF cap in series, all that in parallel with C9. With the Contour control at 0, the freq response is the same as RAT & Expandora. Rotating the Contour control clockwise increases the low mids & bass. At 10, the freq response is flat down to 55Hz.
10. There is a 3 position Diode switch that selects combinations of silicon, schottky & LED clipping diodes, similar to the Proco Solo RAT.
11. There is a 4.7K resistor between IC3b and Q1 base and a 22K resistor from Q1 base to +9V. This ensures that IC3b can turn Q1 completely off.
12. SW3 was deleted because the Contour control takes care of tailoring the low-freq response. C14 is 1uF.
13. SW4 is 3PDT, the 3rd pole takes the place of Q2.
14. I implemented the power filtering and Vb supply slightly differently. C15 goes from Va to GND. C16 is 10uF. R16 & R17 are 47K. R15 is 100 Ohms. D4 is a series schottky instead of a shunt zener. D5 is not there.
15. The opamps in stages 1 & 2 are LT1001. The output buffer & peak detector are TL072.
The Expander effect is subtle, but noticeable. With the Drive at 5 (equivalent to about 2K resistance) there is 5dB of muting at low signal levels. With the Drive at 10, there is about 13dB of muting. Because the FET in the opto acts like a resistor when the voltage across it is <100mV and transitions to constant-current mode at higher voltage drops, it introduces crossover distortion. A tiny bit of crossover distortion adds dimension to the sound. Too much crossover distortion results in gating and sputtering at low signal levels. If you like that kind of thing, putting a 5K trimpot with a 1K series resistor in place of R6 will get you there.
Now about the peak detector. D1 and R11 set the threshold at about 0.3V. For signal levels below 0.3V at the output of the first stage, the peak detector applies max current, about 650uA to the opto's LED. Above that level, the peak detector reduces the opto LED current and when the first stage output reaches 1V the LED is fully off. Because the Gain control is ahead of the peak detector, it also acts as a threshold control. At lower Gain settings, it takes a bigger guitar signal to turn the opto off.
The last thing I fiddled with was R12. I've found the hot end of the Tone control (clockwise in the case of v3) to be of little use, so I changed R12 to 6.8K. With the Tone at 10, the cutoff freq is now 7KHz instead of 32KHz. There is still plenty of top end and more useful Tone control range.
I'm done messing with the innards, on with the playing!
And here's my schematic, in case anyone is interested.
(https://i.postimg.cc/yJfkmKPy/Pandora-s-Other-Box-v1-3b-sch.jpg) (https://postimg.cc/yJfkmKPy)
Great! Why using LT1001?
LT1001 has low noise and low bias current. There are other good choices, but I had some of those on hand. Did not like NE5534 there and have not tried LM308 yet. TL071 should work well also.
Well... it finally came to pass. I managed to get my hands on the rarity. The very first version of the Expandora.
(https://scontent.fyhu2-1.fna.fbcdn.net/v/t1.15752-9/p1080x2048/92655558_2491158957652280_189724476584230912_n.jpg?_nc_cat=105&_nc_sid=b96e70&_nc_ohc=GapZq6dEWyMAX-Ij5Qz&_nc_ht=scontent.fyhu2-1.fna&_nc_tp=6&oh=b5f0f6795705327be52b134b22d27312&oe=5EB666D1)
Time to clear a corner of the bench and dig into the circuit. Plugged it into an amp and gave it a whirl. It's munchy crunchy. :icon_cool:
Hi everyone,
I need to change the footswitch on my Expandora v3 (with 3 external dipswitches). Loud static noise when I stomp on it, like it might or might not turn the pedal on everytime.
the footswitch looks smaller than most pedals. Would anyone have a link to the exact same footswitch?
Thanks a million!
Bump!
Anyone could indicate the appropriate footswitch that would fit in that small expandora?
Thanks!!!
Hi guys!
First of all I wish you a merry xmas and a 2021 full of health and wealth (we all hope so).
I was watching some JHS Kilt demos and I was wondering about the "Cut/Flat" switch... what do you guys reckon it is doing? I uderstand it's maybe swapping some caps, but where exactly?
Cheers!
Quote from: ultrasun on May 31, 2020, 01:46:55 PM
Bump!
Anyone could indicate the appropriate footswitch that would fit in that small expandora?
Thanks!!!
i got one from small bear years ago. wasn't perfect, but it worked with a bit of adaptation