General Building Guide

Posted byreviewsandanalogues

FAQ: Global Shortage of 100k 9mm Pots

In 2021 there was a global shortage of 100k linear-taper 9mm vertical PCB-mount potentiometers: exactly what most fricko boards use. A synth DIY store even posted in public to ask board designers to use different parts or values. This shortage was still (4Q 2022), sporadically, affecting supply in some markets.

Substitute values for 100k Pots:

  • Changing a pot value will change performance: sometimes it will restrict, sometimes.
  • Pots that connect directly to audio inputs or outputs can be substituted by 100k log (audio) pots with the least disruption.
  • Pots that connect to directly to audio or CV inputs or outputs can be substituted by 50k pots with the least disruption. However, it will alter the gain structure, making the module more prone to distortion or softer.
  • At a pinch, any 100k pot can be substituted by a 220k pot with a 220k resistor between the wiper and the low end. (See this document by Elby Design’s Laurie Budduph for info.)
  • I do not recommend substituting pots in filters (Splice, Vox H) or multi-vibrators (Blip!) unless you also calculate new capacitor values. Rasp is particularly sensitive to small changes in values.
  • Prism is perhaps the most readily changed: substitute the 100k pots for 50k pots (or 47k pots: same thing) for the RC filters and double the value of the associated capacitor to maintain the same cutoff. (You may also consider lowering the value of feedback resistor on the buffers for a less hot output.)

Brands: You can use any brand. The standard dimensions for these pots are Mounting diameter: 7mm, Body width : 9mm, Length of shaft (without thread): 9.5mm, Length of thread : 5mm, Shaft diameter: 6.35mm. I tend to use “Taiwan Alpha” pots

Sources: I tend to buy bulk on Ebay. I have found no difficulty getting pots with threaded shafts, which work well with a push-on knob or (with a soft metal shim) with a screw knob. However, many builders prefer to use knobs that need a round shaft.

Harder-to-Find Components: Fricko boards were designed to avoid harder-to-find parts (Vactrols, OTAs, synth-on-a-chip.)

  • All the board parts have been easy to source from a major supplier (Tayda, RS, Mouser, Futurlec, etc.)
  • For panel components like sockets and pots, you may find you need to go to a synth DIY supplier (Thonk, SynthCube, SmallBear, MusikDing, etc). EBay is often a good source: if you are in a hurry, do not buy from a distant supplier.
  • For longer term, I have used AliBaba successfully to buy bulk; you can get the price down to say $1 per pot. (Go in with some friends or resell the ones you don’t need for a profit.)
  • Many previously unavailable chips are being revived: we have no designs with them, yet. We do have some new designs on the drawing board that use some 70s automotive chips still being made by ex-Iron Curtain makers, but we will supply these with boards.
  • The Switcheroo module requires a guitar “Super Switch”, which is a 5-way, 4 channel switch: the original Fender brand switches can be quite expensive: I can get clones in as a special order by arrangement, sourced from China
  • The Bus Voltages module uses typical voltmeter components and 12V marine switches: I have a limited stock, and I can get more in as a special order.

General Building Guide

  1. To build these fricko modules you will need solder, a soldering iron, snippers, and a volt meter; plus a desoldering sucker or wick for repairing booboos. An oscilliscope is always handy, but should not be not necessary.
    There will usually be no need for wires, wire cutters, crimp tools and so on, unless there is some error with the board design that needed to be corrected: read the release notes for the version of the board.
    Depending on the module, test equipment will be a oscillator providing a sawtooth and square waveform will be useful, as will a sequencer or keyboard or other control device that can provide Gate, KCV and Velocity signals. The waveshapers are typically designed for a wave (say, a sawtooth) of +/-5V and will be less effective on lower amplitude waves.
  2. Source your components using the Bill of Materials (BOM). The release notes will mention any unusual components or substitutions. If there is some confict or confusion, please trust in order:
    1. the Release Notes, over
    2. this General Building Guide, over
    3. the BoM, over
    4. the Interactive Components Placement pages.
  3. The Bill of Materials and Interactive Component Placement Guides are generated from the PCB layout program, so they have whatever seemed the most obvious component during design: so sometimes the parts listed are unnecessarily specific or have old brands that may be hard to find. If there is some specific requirement, the module’s build notes will mention them: otherwise you can assume you can use typical generic substitutes from your stash.

    NOTE: We cannot recommend strongly enough that you install a shrouded power socket, and make sure the orientation is correct. The PCBs all show a 16 pin socket, however many projects do not access the extra signal on the bus (+5V, CV, Gate) and so you can install the smaller 10 pin socket, depending on your supply of power cables.

    In general:
    • The NPN transistors are very generic: substitute or mix any of BC547C, BC458C, BC549C, BC550C; other series may be used too such as 2N2222, 2N3904, PN100, 2N4401, BC337 and so on, however you should note if they are CBE transistors and manipulate the pins (use heat shrink on at least one, is a good idea) to match the original trannie.
    • Single op-amps can be just be TL071. Dual op-amps can be just be TL072 (voltages) or 5532 (audio). And quad op=amps can just be TL074.
    • The pots are more commonly available as “Alpha 9mm”
    • Some waveshaper modules’ audio signal paths specify non-polarized (NP) capacitors. These are electrolytic capacitors, but a special kind that does not have specific + or – sides. When you order them, look for capacitors that called non-polarized or bi-polar: these will be marked with “NP” or “BP”.
    • MK2 capacitors are often called WIMA and but you can often use other square caps or ceramics etc.
    • The decoupling capacitors for op-amps tend to be labelled as e.g. 10n, while the same schematic or BoM may give some signal-filtering caps as e.g. 0.01u. These are the same value, and there is no significance to the different notation.
    • In general, you can substitute other, better, JFET op-amps for the TL07* or 5534 op-amps, though I would discourage ancient 741s or LM301As, etc.
    • Where a germanium diode is specified or allowed, just buy the cheapest ones with the lowest diode drop.
    • Where a 1N4*** diodes are specified, there is no need to find particular versions of that diode that exactly matches the any electrical characteristics given in the BOM: of course, if a 1N4001 is specified, use a 1N4001 not a 1N4148.
    • 50k pots: if the schematic says 47k pots, you can certainly use 50k pots.
    • Most modules are not dependent on exact resistor values, however a small number (e.g. Rasp, 5×5, Klatt) may be sensitive: use 1% or selected resistors for these, as guided by their Build Notes.
    • Suggestion: use switching sockets, even where the schematic says switching is not required; these may allow you to install normalized (default) connections later, behind the panels.
  4. Check the release notes for variations and additions.
  5. Install and solder the non-panel components, starting with the lowest profile to the largest. Typically this will be:
    • shorts (little wires) on optional or obsolete resistors or capacitor, from the release notes,
    • diodes
    • resistors
    • chip sockets
    • small capacitors
    • shrouded Eurorack power sockets
    • large capacitors.
      You may find you get a neater result by bending component leads on some long-nosed pliers’ nose, to get a well-formed fit to the PCB.
  6. Test for shorts: set your voltmeter to 20k and check that there are no shorts between the power socket inputs (check each permutation of rows 1,3,5, and 6 if the module uses 5V.) Check that the positive and negative power supplies connect through to the chip sockets. [OPTIONAL] This is a convenient stage to clean the board from marks, rosin, flux, etc. Whether you use water, IPA or decide not to depends on the kind of solder you used: consult the manufacturer’s website. If you have a loupe or magnifying glass, this is also a convenient stage to examine each solder joint you made and check there are no holes representing missed components.
  7. Add any fixes or improvements detailed in the release notes that require shorts between components, resistors or capacitors to be added to the underside of the PCB.
  8. Install the panel components into the PCB but do not solder. (NOTE: The most common kind of potentiometers have a litte metal tab at the front which gets in the way of the panel: use long-nosed pliers or similar to grab, work and snap the little tabs off.) Fit the front panel and screw the components too it. Now that the panel components fit snugly, solder them.
  9. Our current products do not require off-board panel-mounted components, but if that happens, this is the time to wire them.
  10. Smoke test. Connect the board to power cable: check that side with the red band on the power cable ribbon matches the side with the word “Red” on the PCB. If it does not, figure out what the problem is (power socket installed backwards?).
    If OK, switch on: note with interest any smoke or flames. Switch off and unplug immediately on a problem.
    Wait a minute and feel the transistors: if one is running very hot it is a sign of some problem (usually a short from bad soldering or a wrong resistor installation.)
    Power down.
  11. Install any IC chips. Double check that they are pointing the right way. At this stage, you may be fatigued and make a silly error with installing them. Oh, all right, that was me.
  12. Connect a simple input, and check the output (with a voltmeter for CVs and by audio for audio signals.) If you have an oscilliscope use that. The modules provide test points for zero-ing in on problems; the release notes will have details.

There are numerous more detailed instructions on building available from other vendors. If you are starting off, I recommend:

Parts Gotchas

New to DIY? Here are some tips and gotchas to avoid:

Sockets

  • We mainly use the PJ302M sockets. There is no problem using a switched one, even if the BOM says non-switched.
  • This component is not available from Mouser, Tayda, Futurlec, etc. It is usually on Ebay. It is available from synth stores such as Thonk in UK. In USA there is Modular Addict and SynthCube. In Australia, I buy the bulk bags from FoundSound.

Knobs and Pots

  • When you order knobs, check that they can fit the shaft of the potentiometers you have. A t18 knob requires a t18 shaft: these use the metric 6mm not the imperial 1/4 inch (i..e. 6.35mm). A D knob (quite old style) requires a D shaft. A press on knob usually requires a fluted shaft.
  • When you order potentiometers, check that they meet your knobs. All current fricko products use vertical “right-angle” 9mm pots: the Alpha pots come in 6mm or 1/4″ (6.35mm).
  • Some pots have little anti-rotation tabs on them.  These need to be removed (with pliers: once you know how it is a simple twist operation) or the will push the board in odd ways. In order to remove this tab, you would need to unsolder the pot. (The secret to unsoldering is to add extra solder rather than just try to heat the existng solder, as merely heating the existing solder can cause it to flow to the other side of the board, leaving you merely heating the PCB traces.)

Op-Amps

  • Fricko PCBs are “through-hole” (THT) not surface-mount (SMT); so make sure you order the versions of chips that are in DIP (Dual Inline Package).
  • When ordering op-amps, in all cases you can use TL07* op-amps, which is the basic cheap and cheerful opamp. (I.e., for a single op-amp, the TL071; for a dual, the TL072; for a quad, the TL074.) Please do not use archaic op-amps, such as the 741 or 301.
  • For the CV paths (such as the envelope modules), there is no point substituting higher quality/cost op-amps for the TL07*: no current Fricko module has precision CVs. (Lower current consumption op-amps may be worthwhile, if your power system is stretched, however.)
  • For audio path op-amps, I like to think of five levels:
    • Bad: Please dont bother with antique op-amps on the fricko boards, such as 741, 301A, 1458, etc.
      • Please be aware that the claims in a datasheet that an op-amp is “low-noise” were often true when it was written, but that could be 50 years ago!
    • Good Enough: For the audio modules, in many cases, you can substitute any JFET op-amp (with the standard pinouts, and unity gain) for the TL07* op-amps.
    • Better: For better clarity and noise, for op-amps in the waveshapers, I often use 5532 (single) or 5534 (dual), for slightly more cost.
      • I am hearing good things about the price/performance of OPA1678 as modern “jellybean” dual op-amp, beter than the 5534, however it needs an adapter for DIP use.
      • Op-amps in the audio path before the final VCA are, in effect, gated by the VCA. So it is not super-critical that they are low-noise. However, op-amps in the audio path in VCAs and mixers etc, can produce noise you may hear when no note is playing: so these are good candidates for using better op-amps with.
    • Best: For best audio quality, I am a big fan of the dual op-amp LME49720 (a.k.a. LM4562), which has astounding performance; however, it seems to guzzle current, so best used in audio path only (It is available in quad LME49740.)
      • Be careful if buying on Ebay: you want to avoid rip-offs priced over $15 per chip. Some people insist that China is full of fakes and substitutes, but I have never found any problem, so I don’t want to propogate hearsay: nevertheless, if you are squeemish, then avoid chips that are under US$1 each, say: at the cost of a bargain. (The substituted chips are often quite good ones, not necessarily complete rubbish, according to the scuttlebutt.)
      • These are no longer produced, and may not be stocked at Mouser etc now. A hifi replacement might be the OPA1612 op-amps with a DIP adapter, but I have not tried it.
    • Sillly: paying more than $3-50 per op-amp? (ie $14 for a quad) Overkill IMHO.
  • When ordering op-amps, be careful that it is actually an op-amp: comparators uses the same symbol on schematics as op-amps. You should NOT substitute comparators to ones with completely different numbers: the pinouts change. In particular, if you see LM311 that is a comparator, not an op-amp.
  • For Op-amps and transistors, the same design product is often sold with a myriad of different minor numbers. In the datasheet, you can see the major number is the title of the datasheet. In general, the minor numbers can be ignored for fricko products: they can relate to how much a chip (or die) has been successfully tested against some military/aerospace criteria, for example. Of course, some minor numbers relate to packaging, but you will only pick standard DIP op-amps, so those numbers are irrelevant.

Transistors

  • Fricko circuits are designed to work with most common transistors: e.g. BC547B, BC547C, 2N3904 and (the one I used for most development) BC550. (Note that if you do substitute, you need to confirm that the pinouts are the same, or do some sculpturing.)
  • For transistors, there is very often an A,B or C suffixed version of the product: usually fo different gain characteristics. Don’t worry about that.

Resistors and Capacitors

Most resistors and capacitors can be substituted for another that is, say, plus or minus 10%, without problem (and perhaps without perceivable difference.)

The one exception to this is the resistors on the comparators of the Rasp and Shell waveshapers.

Please be aware that at least one BOM lists the same part under two sizes: e.g. .01uF and 10nF. (I will reduce the number of these over time.) Please do not be phased.

Many audio modules use bipolar (NP) capacitors on Input and Output, to block DC. You can substitute the bopolar electrolytics for some other NP type or shape, but do not put in polarized capactors.

For capacitor terminology: bipolar = non-polarized (NP) as distinct from unipolar = unpolarized. The only bipolar capacitors are tantelum or electrolytics (most).

Panel Alignment

Do solder the pots after first putting them into the panel.  (I.e. do not solder them then try fit the panel on.)

So here are the general fixes for DIY (some brands of pots may have slightly different sizes and our current panel pot holes are too snug to provide enough give):

  • Pot too far from panel. Add washers. Is there an anti rotation tab still in place?  Either remove or cut washer to fix.
  • Pot too close to panel. Check for anti-rotation tab
  • Pot skews up or down. Check for anti rotation tab.  Check the hole is really aligned:  file out the hole for better alignment (eg using a circular rasp, or electric drill or dremel.)

Procedure for Boards with Standing Resistors

The 5×5 Distributor uses standing resistors (“Japanese style”, but used by ARP in some synths.) Boards with standing resistors require a different build order, but again on the principle of installing the lowest components first.

  • Install the panel components (pots, sockets) on the back side LAST: it is very difficult to solder other components with these in the way.
  • Install the lowest components first: any diodes, IC sockets and Power header, being careful about orientation.
  • Next, install resistors. Make them stand up neatly like little soldiers: the screenprint on the board shows where the body goes and where the bent lead goes. They should be oriented all the same, to reduce the chances of shorting if the resistors get pushed over (as is easy): you may choose to add heat shrink to the top of the leads for extra protection. Do have a little gap between the resistor body and the hole, to reduce thermal problems when soldering.
  • Next, install capacitors, transistors and other components.
  • Next, install the pots and sockets on the back side. Do so with the pots and sockets semi-secured to the front panel, so that they fit.
  • Then, test with a multi-meter than the +ve, -ve and 0V pins of the power header are not shorted. You may plug the power in, and check that the IC sockets are delivering power as expected.
  • Finally, install any op-amps or other chips, paying attention to orientation.
Design a site like this with WordPress.com
Get started