PORTABELLABZ

208 DIY sets FAQ

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 :
- the traces are error free, so no extra wiring is needed unless you want to implement modifications
- 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
- extra hole 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

Are the promotional offer PCBs different from the final ones ?
They just don't have 2 very small improvements mentioned above : dedicated reverb shielded cable pads on board 12 (the cable wiring is detailed in the build notes) and trimpots wiper extra hole. This won't upset the build in any way.

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.


I have a problem, can you help me ?
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.
The PCBs are error free, they were thoroughly tested and all the 208s I built using them are good working. Of course in case the problem is an obvious manufacturing error or damage on your PCB, please send me pics and a description to get a replacement one free of charge.

Do you have the BOM as a spreadsheet or a link in order to load into Mouser  ?
No, I have plenty of parts in my own stock and use these, not necessarily coming from Mouser. 
Maybe a builder will do a Mouser project and share it but I won't, I have more important work pending and anyone is able to do a Mouser cart from a BOM.

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


Are the nice panel or reverb frame available separately ?
No, b
ecause of the high manufacturing cost of the panels, these are available as a bundle with the PCBs only. See this as a service kindly offered to people buying the PCBs.
 

Will the old siddarthianinnovations or electricmusicstore panels fit these PCBs ?
Yes, the PCBs are 100% compatible with all the 208r panels.

Will this 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 all the cards and expanders working with the 208r or BEMI Easel.
Take note that a very few
own features of the BEMI Easel such as the MO hi/lo range or midi connection to the 218 won't work since are not implemented on these PCBs, but all the other features work.

Will this work with the Portabellabz ToolBox ?
Yes of course !

Does Dunnington Audio's envelope infinite sustain fix work ?
Yes

Is there a detailed calibration procedure ?
Not yet but I plan to write one and it will be available on this website, please don't ask me when ;)
Meanwhile please refer to Dave Brown's page.

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 whether you'll buy parts for this project only or in bulk (100 resistors cost 1.20 but 1 only costs 0.10 or more), on the suppliers (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...


Will you do a 218 keyboard or other modules ?
No

Does another keyboard work ?
Yes, any keyboard works, as long as the 208's tracking matches it.
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 on 5 octaves.

Can I or should I use A726 / UA726 ?
This part is insanely and unduly expensive, therefore the 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.
T
he cards 6 and 7 have the original layout designed
for A726 / UA726, so if you have money to waste you can use it instead of the pA726.
Beware of the cheap Chinese ones, these are most likely fakes that
at best won't work and at worst will damage the circuit.
 
Which vactrols should I use ? Excelitas, Vactec, Xvive, Coolaudio... ?
My experience showed that
a good selection on test of a vactrol is more important than its age or the manufacturer name printed on it. These parts may have a large tolerance even in a same batch of the same manufacturer.
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. Also, in the 70s, 1% were much more expensive than 5%. Today the price is the same.
On the motherboard 120k 1% for the sequencer sliders should help reduce the small difference between the sliders CV at same setting, but this won't compensate for the slider's own tolerance. Anyway, I adjust the sliders by ear, not visually.
1% can be used everywhere.
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 film resistors sound warmer and metal film sound colder, or that golden legs components sound richer and NOS parts sound more vintage or more musical, or that the expo converter affects an oscillator's sound and timbre, or that the dust in an old tube amp is an essential part of its so-called mojo. That's their problem.