PORTABELLABZ

208p DIY sets FAQ


Buying the parts : which, where, equivalents, rare parts, price, BOM, Mouser cart... ?
Corrections : fixes, improvements, differences with other 208... ?
Building : difficulty, help, calibration... ?
Expanding : cards, expanders... ?
Keyboard : 218 ? tracking, external controllers... ?





Buying the parts

Do you or a third party offer full kits with all the parts needed ?
Yes
SAmodular offers parts, kits and bundles.
 

Should I spend undue money on expensive obsolete rare parts ?
No
Contrary to what some may believe or claim, there's no magic contained in old electronic parts and the expensive obsolete rare ones can be replaced without impact on the sound or behaviour, details below.
What makes a nice sounding and good working synth is neat build, careful selection on test of some components, precise calibration and basic understanding of how things work. No snake oil or esoteric belief will ever make up for the lack of any of these.
This is valid for all 208 revisions and for all synths in general.

Can I replace the µA726 / UA726 ?
Yes
T
his part is insanely and unduly expensive
, therefore t
he PCB set includes a pair of
pA726, a very good working drop-in replacement. This doesn't affect the oscillator's sound or timbre in any way and the tracking and stability are better than
with µA726 / UA726.
T
he cards 6 and 7 have the original layout
, so if you have money to waste and do care more of vintage hype than performance, you can use
µA726 / UA726 instead of the pA726.
Beware of the cheap Chinese ones, these are most likely fakes that
at best won't work but might also damage other parts in the circuit.

Can I replace the 2N4339, 2N4340, 2N4341
?
Yes
The very common and cheap J201 works fine instead of those and doesn't impact the sound or behaviour. Other JFET's selected on test should work as well.
Only in Q1 on card 8 (2N4339) I couldn't get a proper CO sine with a J201, but another JFET selected on test should work here too.
Check datasheets for pinout differences.

Can I replace the 2N3565 ?
Yes
The PN3565 works fine
and doesn't impact the sound or behaviour. It should be mounted this way.

Can I replace the MC846P ?
Yes
Dave Brown explains how to replace it with a 74LS03This doesn't impact the sound or behaviour.

Can I replace the LS352 / 2N3806 / MAT03 ?
Yes
The 2N3807, 2N3810, ECG82...
work fine and don't impact the sound or behaviour. Other matched PNP transistors pairs with similar specs should work as well.

Can I replace the 2N1711 ?
Yes
The 2N3019 is a drop-in replacement and various other NPN transistors should work, the 2N1711's are used as a LED driver.
This doesn't impact the sound or behaviour.

Can I replace the DG200A ?
Yes
The 208p PCB set comes with a
DG200A-dapter PCB for the modern DIP or SOIC Maxim DG200A. This doesn't impact the sound or behaviour.

Can I replace the big 390µF Sprague capacitor ?
Yes
A standard easy to source 330µF electrolytic capacitor works fine.
This doesn't impact the sound or behaviour.

Can I replace the big API Delevan
2.2uH inductors ?
Yes
Other 2.2uH inductors
such as Tayda's work fine and don't impact the sound or behaviour.

Can I replace the C&K switches ?
Yes
Taiway switches available from Small Bear are very nice and cheaper.

Any toggle switch can be used for the SPST on-off and on-off-on ones, but I don't recommend to use cheap ones, replacing a faulty switch ain't no fun.
For the DPDT on-on-on switches use Small Bear's Taiway or the BOM's C&K ones only, other ones might have a different pinout and not work on this PCB.
The PCB fits both
PCB mount (with thin lugs) and panel mount (with larger lugs) switches.


Which vactrols should I use ? Excelitas, Vactec, Xvive, Coolaudio... ?
A
good selection on test of a vactrol is more important than its age or the manufacturer name printed on it. These parts  have a large tolerance even in a same batch of the same manufacturer.
However the dual Xvive VTL5C3/2 upset proper LPG behaviour. The cause is their decay tail is too short and no difference can be heard between the combination and LPF modes. The Excelitas
VTL5C3/2 work better for this purpose, although selection on test is recommended as well.
More details on the Muff Wiggler forums
Dave Brown compared accurately different vactrols that he has in stock.
 

Do 1% / 5% tolerance, carbon / metal film resistors sound and behave different ? Which ones should I use ?
5% means a 100k resistor's value will be between 95k and 105k.
1% means it will be between 99k and 101k.
So in a 5%
resistors lot, some will most probably be actually 1%.
In some cases, it's important to have a precise value resistor, in most ones 5% are enough.
In the 70s, 1% were much more expensive than 5%. Today the price is the same and 1% metal film resistors can be used everywhere. No, this won't impact the sound.
I find the color stripes code on carbon film resistors easier to read than on metal film ones, which limits
the risk of using a wrong value and eases troubleshooting, but that's probably a matter of habit.
"
Some people believe that using parts with a wider tolerance range is required to invoke whatever magic they think is contained in old electronics. I built my 208 with all 1% parts, low drift C0G ceramics, and so on. I am very happy. I use it almost exclusively for pitched material so stability and accuracy are more important to me than witchcraft." (nice tarandfeathers quote on Muffwiggler).
Some people also believe that carbon resistors sound warmer and metal film ones sound colder, or that components with golden leads sound richer or that old parts sound more vintage and more musical, or that THT components sound bigger than SMD, or that the expo converter impacts an oscillator's sound and timbre, or that tropical fish caps sound more colored, or that the dust in an old tube amp is an essential part of its "mojo"...

Such beliefs border more on the esoterics and "idiophilia" than on actual facts... but some sellers take advantage of this ignorance and credulity.

 

How much I'd end up spending on parts to stuff these ?
Say in the €1000 range as a rough estimate, with a quite large margin depending on the parts used, on how and where you buy the parts (100 resistors cost 1.20 but 1 only costs 0.10 or more, online Asian sellers are cheaper than the shop around the corner), on the shipping costs (all parts are not available from a single supplier), on your skills (risk of damage or wrong mounting while soldering) etc.

SAmodular's full kits are good value for money and will save you a lot of time.


Do you have the BOM as a spreadsheet or a link in order to load into Mouser  ?
Wiggler sanemalkavian did one.
Wiggler thombet did a new one.
I didn't check
their content and assume no liability for their accuracy.

Which slider pots the motherboard will take ? 
Silder emplacements match both old and new slider pots.
I recommend Farnell's Alps ones (part # 1191730) however, the plastic old ones are really crappy.

Will the other 208 panels fit these PCBs ?
Yes
The PCBs are 100% compatible with all the 208r panels available from other suppliers.
The PCBs are not compatible with the 208e and 208c panels, some holes placement is different.

  

Corrections
 
How close to the original 70s 208 or 208r
are the PCBs ?
The PCBs are a replica of an original 70s 208 (not the modern reissue, which is very different), same traces design, same parts, with some corrections and improvements.
Compared to the 208r :
- No extra wirings or traces modifications are needed and all components can be mounted as shown on the parts layout drawings
.
Only a small trace is missing on board 2
between pins 5 and 6 of IC1 of the bare tracks revision, a 2.5mm solder bridge is the only fix needed on the 208p and is mentioned in the  build notes.
- The noisy headphones out is fixed by the addition of 4 resistors on the motherboard.
- The reverb output is via a shielded cable only to avoid the MO bleed common issue, it won't work otherwise, the related trace on board 12 was removed.

- The enlarged holes for switches allow the use of both PCB mount (with thin lugs) and panel mount (with larger lugs) switches.
- The rectified pots holes emplacements avoid bending their legs and causing stress to the resistance element.
- The extra holes for the trimpots wiper on daughterboards allow the use of various types.
- The gold plated transfer card (between the panel and PCB edge connectors) fits 15mm standoffs, to make the switches nuts easier to screw than with 17mm ones.
-
A +5V connection to the card slot was added to work with the iProgram card or other card needing +5V.  The new silkscreened revisions also features a noisy ground connection.
The iProgram card also needs pins 2 and 4 of both rows on the edge connector  to be connected to quiet and noisy grounds.  These  connections are not implemented on the PCB but details are in the build notes.
- The new revision has all parts value and reference silkscreened and a soldermask.

Should I do the fixes as mentioned on
Dave Brown's page ?
No
The traces fixes on the motherboard and board 3 are for the 208r PCBs errors that are not present on the 208p.
The only error that needs a fix on the 208p bare unsilkscreened boards is the small missing trace on board 2
between pins 5 and 6 of IC1 as mentioned in the build notes.
No fix is required on the silkscreened boards.
Yes
Some of Dave's modifications such as the board 5 ones may be very helpful.

Should I use 1N5236 or 1N5228 on board 5 ?
1N5236 (or other 7.5V Zener diodes).

Do Dunnington Audio's envelope infinite sustain fix and other mods work ?
Yes

What do you think of the new card 12 sold by boops ?
A properly built standard card 12 works and sounds well and I see no reason to change it.
The only new card 12 I've seen so far was in a seriously bugged 208r rev2
built and sold by boops that I salvaged for a customer.
Some of the problems were caused by this new card 12
: noise, clipping, faint sound, inverted waveforms, weird reverb mix... and the required Q-N grounds connection was missing.
I simply replaced it with a standard card 12 and
had no interest in pursuing the investigation.
Some builders seem happy with this card however, so these issues may be more of build errors than design errors.

To improve the reverb mix pot course, use a log pot.
If a lin pot is already installed, add a resistor of 1/10 of the pot's value (if the pot is 10k, 1k resistor, if 50k, 4k7 resistor etc) between the pot's wiper and CCW terminal to make it log.


Building

Is this build a good project for a beginner ?
No
I wouldn't recommend this project to begin with.
This build is
for experienced DIYers. Having built 2 pedal kits or eurorack module kits doesn't make you an experienced DIYer.
This is a complex module. The build itself could be ok if done thoroughly and slowly but in case of problem troubleshooting might be difficult, very difficult.


Which equipment is needed ?
Soldering station, good desoldering tool, oscilloscope, frequency counter.

I have a problem, can you help me by email ?
Given the complexity of this build, I do not offer individual support, related e-mails or private messages will be ignored but I'll reply if I can help on the build thread on Muffwiggler, thanks for your understanding.

I have a big problem, can I send you my 208 to complete or fix my build ?
Yes,
depending on the quality of your work.
This service is chargeable.

Please contact me.

Is there a detailed calibration procedure ?
Yes
Please find calibration details in the build notes and on
Dave Brown's page.

Should I do the wiring as shown in blue on boards 2, 3 and 6 ?
Yes


A hole is missing for IC3 (DG200A) on board 9.
This is normal, snip the IC's lead 7.


Expanding

Does
the 208p work with the iProgram card and Aux Expander cards ? And with the Model 416 Meta Expander ? And with the cOC ?
Yes
This 208 is compatible with most cards and expanders working with the 208r or BEMI Easel.
A very few
own features of the BEMI Easel such as the programmed MO hi/lo range won't work since are not implemented on these PCBs, but all the other features work.
The digital cards such as the iProgram card and cOC also needs pins 2 and 4 of both rows on the edge connector  to be connected to quiet and noisy grounds.  These  connections are not implemented on the PCB but details are in the build notes.

Although older revisions work, the more recent
iProgram card firmware seems to work with the 208c and most recent  208e only. A flashing "both mode-loc sw" message occurs when used on the 208p. This suggests the fault is related to a modification mentioned in a footnote in the 208c Addendum for the manual : "In “Meta-Programming” for the original program card, all five stages are mentioned as solder-able--programmable in value --with a resistor. But since Rev5 of the 208 (and often modified in Rev4), the Sequencer 5 stage has been replaced by a local enable signal by default in order to signal to the card when the control switch is in “both” mode".
I don't know how to modify a 208 to make it compatible with
this iProgram card firmware.

Does the 208p work with the Portabellabz ToolBox, BOB  and VCS3 Card ?
Yes of course !


Keyboard

Do you sell or will you do a 218 keyboard ?
No
SAmodular offers one.

Does another keyboard work ? And a sequencer ? And a midi to CV/gate converter ?
Yes
Any
CV/gate keyboard or sequencer, any midi to CV/gate converter will work, the 208 can be calibrated to match any scaling.
A Synovatron GTPulse is recommended to get the typical pulse needed for proper sustained/transient envelope performance.

Which is the oscillators tracking ?
The tracking via the keyboard voltage input can be 1V/oct, 1.2V/oct, 2V/oct, or any other scaling, it's a matter of calibration and  CV scaling resistors value selection, so this depends on the final user's own preference.
Properly calibrated, the tracking is good over 5 octaves.