21st Century Common Man, contd.

Rhea orders will open 2021-10-09 (this Saturday) at 12:00 CEST (noon). In case some unforseen disaster strikes again and I miss it, please come back the next Saturday.

UPDATE: Rhea orders closed.

UPDATE 2: All Rheas have been shipped, and I have a batch of Phoebes almost ready. I will open orders 2021-10-30 (Saturday) at 21:00 CEST (that’s 9pm) to make it a bit more USA friendly.

UPDATE 3: Phoebe orders closed.

21st Century Common Man

Phoebe orders will open this Saturday (2021-07-31) at 12:00 (noon) CEST. It’s not a big batch but last time it was enough for everyone who ordered.

Wizards sent to Japan and South Korea took their sweet time getting there but should be delivered any day now. Something related to Covid or olympics maybe? Vertical connectors will be available very soon and I expect to resume shipping all the remaining units sometime next week.

Dust storm

I have a small batch of GDEMUs ready to go so I’ll open orders this Saturday (2021-07-03) at 20:00 CEST to make it USA-friendly. No family visits planned but then again the previous one wasn’t either…

I’ve managed to test some Wizards so the ones that didn’t need vertical connectors should start shipping next week – watch your PayPal account. In case some of you didn’t get my confirmation email, here’s what the horizontal connector looks like (left), the correct vertical one (right) and what can be done with a knife and pliers to “mod” the horizontal to vertical in a couple minutes (center). You’ll get 3 of those horizontal ones, the extra one is so you have a spare in case the modding somehow goes wrong.

Also in the center there’s the new switch that replaces ODE/CD-ROM jumper, it’s easier to operate though keep in mind it can only be switched when the power is off – that hasn’t changed.

UPDATE: It seems the USA-friendly times are not very lucky. My Saturday turned out very busy but this one is my own fault, I should’ve planned things better. Very sorry about this. Let’s try again today, same time.

Project Time! #6

Things are going slow because of the recent summer heat wave. There should be some nicer weather coming later this week so hopefully I can do a bit more Wizard testing then.

In the meantime, here’s some random photos of one of my projects, I’m not going to comment much on it. Some of you will figure out what this is, the rest probably wouldn’t even be interested anyway.

From my calculations I got a pretty nice 9.2 kHz bandwidth – I could maybe tweak it a bit more to something between 8.5 to 9 but then again I plan on having three of these so it might just be perfect as-is. Plus then I’d have to accept somewhat higher insertion loss, which is now at about -3.0 dB with impendance of 89 kohm or so, that too is decent. Obviously I can always tweak it later as well if it turns out selectivity is poor, I should get enough gain in the amp stages to cope with a bit higher losses.

In general the plan in my head is ECH81 oscillator and mixer (that stage is already semi-tested and works), EF183 first amp, EBF89 second amp and detector (second diode will be AGC detector), ECL86 double-stage audio amp. Plan is for LW and MW only but maybe I’ll add some SW bands too, if I can motivate myself to make more coils. Power supply will be using old, internally-shielded transformer but with modern input filtering, fuses on both sides, and silicon bridge rectifier. I do have selenium one, and good two-section electrolytic cap from the old days, but the problem is the transformer was meant for 220V and now we have 230V so the output voltages are a bit on the high side, just on the limit of both. Not sure if that would be safe long-term and I plan to keep this project as long as there is something out there to listen too (and/or I’m out of replacement tubes).

A Million Miles, contd.

I waited a bit longer with the Wizards to make sure the PCBs will be ready. Some people don’t like it but I prefer to not make empty promises, I’m a bit old fashined that way. There’s tons of projects out there that start with ordering and then never deliver anything in the end.

First things first though, for some reason I got tons of emails these last few days asking me about firmware and other stuff. I did not get a single message the whole previous month, and then my inbox is suddenly full. Weird. I think I’ve replied to all of them by now but some of you use free email hosts that notoriously block me. The worst offenders are Hotmail and Live.com – if you are using these, consider alternatives. At least when contacting me and expecting an answer. I’ve never had any issues with Gmail yet (other that getting my confirmation emails marked as spam sometimes) so try that maybe.

Back to Wizards, the first PCBs will go through cleaning this week and then I can start programming and testing them. So I think I’m ready to open preorder for the first batch – this Saturday (2021-06-12) at 20:00 CEST to make it more USA-friendly (since I expect most orders to come from there). This first batch will be small and I have no idea how many orders there will be so for now I’m restricting this ODE to one device per person – this limit should be removed once the initial interest dies down. There will be no requirement to provide serial number, as I’ve explained I expect to sell these to modders rather than individual users – that being said, it you try to game the system and place multiple orders (perhaps from different emails) I will cancel all your orders. Please play nice and let others have a chance to order.

I mentioned we have some issues sourcing parts and Wizard connectors are among those parts. When it looked like we will finally get what we need, the supplier made a mistake and got us wrong type of the 3-pin connectors – horizontal rather than vertical. And as luck would have it, the correct ones just got sold out. So you’ll have an option to wait for the vertical connectors (weeks, though) or I can send you 3 of the horizontal ones and these can be, with some tweaking, made to be vertical. Or you can just use them as-is or even solder the wires directly, whatever suits you. Oh and I don’t think I have to mention this but the replacement batteries are not included due to restrictions on air shipping and lithium in general. You’ll need to source CR2430 and CR2450 cells locally – if you want to replace the original pack, these are optional.

The pricing – 150 EUR, for now, I still haven’t fully figured out how to best ship those. Boxes would be preferable but that is way more expensive than bubble envelopes. Also, still need to streamline the testing, right now it takes a lot of time to check even one device. I do not sell untested PCBs, so don’t even ask. For now I will include housings and contacts for making the connector plugs, you can crimp those, solder, or just solder to the PCB directly. Turns out having these wires made in such small quantities is not very cost-effective, but I’m still looking into it.

Well, that’s all I can remember for now. I will update this post if, for some reason, the Saturday window needs to be called off or moved.

UPDATE: Family visit in progress. I just did not make it in time, lets try this again on Sunday, same hour.

A Million Miles

I will accept orders for Rheas this Saturday (2021-05-08) at 12:00 CET (noon in Europe). This will be the first time I’m forced to do this via this whole Gutenberg/blocks thing so hopefully it works as it should.

We kinda have all the parts for Wizards now but there’s still the final assembly and testing to be done – so in a week or two I will open preorders (and these will be true preorders – there will be a waiting time, testing these is super slow, so if you have no patience please don’t participate).

As for GDEMUs – I have a small batch ready, probably a bit too small to satisfy a typical ordering window, so I’m still thinking on what to do. I really dislike having to refuse orders becuase I’m out of stock. We have some parts on order that are being delayed again and again, and frankly I don’t think I will be getting those at all. There’s another distributor I’m talking to, we’ll see what comes of it.

Well, I will probably offer these on sale anyway in few weeks. Then, depending how soon we get the parts, I will either make more or perhaps revisit the idea of a refreshed model that is not so badly memory limited. But that would come no sooner then Q3, maybe even Q4.

A Dashing Enigma

Did you know this site is now 7 years old? Time sure flies. GDEMU itself is older yet by about 2 years, the first version that I’ve made was based on Altera Cyclone II dev kit and mostly worked but had some timing issues. Initially I had no serious intentions of selling it – though a year later I figured maybe a small self-contained PCB would sell two dozen or so units, and would help me raise some money for other projects. Little did I know how it’s going to snowball. Well, at least I can say the project goal was achieved – even if I don’t like how ODEs became the new modchips and everybody expects to get one for a couple bucks to play “free games” (and I’m the bad guy for not mass-producing ODEs to flood the market, forcing low prices).

Anyway, obviously the last post was an April Fools’ effort. The photo was of a dirty 5.25″ double-density TEAC floppy drive, I deal with those only in personal projects and that particular one is now clean and working. Testing it revealed issues with two of my 386 mobos – the one on which I’ve replaced a broken crystal resonator with a tad bit faster device, and is now overclocked, which is nice but also screws up system timers. I need to undo this, the extra 1.x MHz is not worth these issues. Another mobo, and this one was badly corroded from NiCd battery spill, is now acting up – randomly hangs on DMA transfers (so mostly in games that use SoundBlaster voice playback and while using floppy drives). I suspect there is a corroded via under the 82C206 chip but there is no guarantee the mobo will survive desoldering it – there’s already pad damage and wires around to fix affected traces. This mobo was, until now, my “daily driver” for testing 386/486 code but I think I will replace it with a P200 MMX and maybe attempt the fix later. It served its purpose and I have a few other mobos for quick code testing if I need a true 386 system for that.

And speaking of testing 386/486 code, I have collected some performance data from various FM Towns machines using my own benchmark program. Frankly there’s tons of that data but in order to show some of it in a simple, easy to digest way I’ve made one chart that I think best reflects the actual overall CPU performance.

FM Towns - Performance

First, let me introduce the machines present on the chart:

  • A – gen1 (MODEL 1), 16MHz 386DX
  • B – gen2 (2F?), ~18MHz 486DLC
  • B1 – B with cache enabled
  • C – gen3 (40H), 16MHz 486SXL
  • C1 – C with cache enabled
  • C2 – C with cache enabled, clock x2
  • C3 – C without cache, clock x2
  • D – gen4 (CX), 16MHz 386DX
  • E – gen4 (CX), 16MHz 486SXL
  • E1 – E with cache enabled
  • E2 – E with cache enabled, clock x2
  • F – gen2 (2F?), 16MHz 486DLC (*)
  • F1 – F with cache enabled (*)
  • G – gen2 (2H), 16MHz 486SXL
  • G1 – G with cache enabled
  • G2 – G with cache enabled, clock x2
  • G3 – G without cache, clock x2
  • H – Marty, 16MHz 486SXLC
  • H1 – H with cache enabled
  • X – Fresh-ET, 66MHz 486DX2

(*) The F machine used a slightly different version of the benchmark executable and 386/486 CPUs are really sensitive to code position, so over many loops the result can be a few % off (faster or slower, depending how the code changed).

I’ve also added some colors to try and make this more readable. Black is 100% standard machines, blue is 386 CPU replaced with 486 DLC class. Orange is same as blue but with CPU clock resonator replaced as well (there are some serious limitations to this technique and even small overclock can cause issues in these systems). Violet is SXL/SXLC CPU with clock doubler enabled.

So, what can we see here? First of all, the black bars – the gen1 and gen4 machines have identical performance in default settings. The Fresh-ET is a bit faster in the compatibility mode but not by much – it mostly equals a CPU swap to a 486DLC (which all of the towers can do, except generations 3 and 4 require desoldering the old one first). I guess it’s not really possible to perfectly match a 386 performance with a 486 chip on a twice faster system bus. That being said, based on my tests with DLC chips, this is not enough to make a difference if the game doesn’t support FAST mode.

The “fast” in the chart is either FAST mode (for machines that support it) or reduced RAM wait states (as much as it was possible). This offers a decent speedup, in general reducing WS on 386 tower machines gives comparable results to replacing the CPU with 486 DLC – though obviously if you can replace the CPU and then also reduce WS, it’s even better. But if you want to keep your machine 100% original then WS reduction (with ODE) is probably the way to go if you need some extra performance. Even gen1 tower, which can only reduce the WS by 1, shows some speedup.

A 486 DLC with WS reduction or FAST mode can cut the benchmark time almost in half, and keep in mind this offers pretty much perfect game compatibility. You can get even better results by enabling the CPU cache (also via ODE) but that will break some games – some will work fine, some might have audio or video glitches, or even unresponsive controls. It looks nice on the chart but in reality can be quite a lot of trouble. This also goes for any overclocking, as mentioned above. And then there is clock doubling on SXL chips, this has some effect even with no cache and just WS reduction – which is nice, considering the issues with cache, but without having cache enabled you gain maybe a few extra % and that’s it. So it’s not really worth paying extra for a 486 SXL over DLC, unless the price is similar.

I didn’t test x2 clock on Marty because it breaks a lot of things for some reason (tower models don’t suffer from these issues). For example it can completly screw up mouse emulation on gamepad, something that Marty does by default via its BIOS. Not sure about other 386SX based systems, maybe UG series would benefit more thanks to having a native 20MHz clock in FAST mode. Then there is the proper x2 clock doubler in Fresh-ET, with built-in cache coherency protocols, burst mode and faster system bus. A true DX2 class CPU is more than twice faster than SXL and has none of the issues – so if you really need a fast Towns machine for some reason, get a late Fresh (or at least a true 486 desktop).

To sum this up, with Towns the 486 is faster than 386 but only in FAST mode (and most games don’t use it). Even older machines can be “tuned up”, either by swapping the CPU or forcing FAST/WS reduction via ODE. Or both. This is often enough to make Street Fighter 2 playable without major slowdowns for example.

Good Optical Drive

Are you tired of small, noiseless and reliable drive emulators? Looking to impress friends with the oldest, dirtiest computer on the block? If so I have something just for you!

Good Optical Drive 1

Announcing a new device – the Good Optical Drive, or GOD in short. You can now restore your machine to it’s old electromechanical glory with the slowest, most power hungry motors I could find.

  • Nostalgia factor x100 from the smell of old dust and tobacco smoke alone.
  • You get to feel old just by looking at it and knowing what it is.
  • Live in Texas? This will double as house heater come next winter storm.
  • Watch the street lights dim and go out as you power it on.
  • Finally a proper load for that 6MVA military surplus diesel generator you bought.
  • The sweet, sweet whine of dry, rusted bearings – no moving parts were ever cleaned or lubricated.
  • Old, yellow and brittle plastics that will snap off right after unpacking.
  • Makes a quick and simple tester for your house smoke detectors (*).
  • And best of all, it sometimes even works and does not destroy the disc!

(*) actual fire not guaranteed.

GOD will be available in limited quantity on first come, first served basis. Get your GOD now!

Project Time! #5

WordPress decided to finally block the classic editor for good – which makes me very unhappy. This block editor is a disaster, maybe useful if you are one of those my-phone-is-my-life hippies but I guess I’m too old for that. I use my phone for making calls, and not even of the video variety. So as I’m writing this 70%+ of my PC screen is a white, blank space with a small column of text somewhere in the middle, and I can barely see the font. If it wasn’t for FireFox 140% page size I’d be struggling to write anything at all. It’s “progress” like this that annoys me the most so don’t even get me started on Windows “evolution”.

It’s not my intention to turn this into old people rant, I just wanted to warn you that from now on things might look different, and not in a good way. And I dread the next ordering window, I used to be able to just copy-paste the forms directly into page code, I have no idea how to do that now.

Anyway, originally I wanted to make a whole post about choosing the right kind of J-FET transistors for the input switches in meters like Fluke 8600A – especially since the ones they’ve used are not made anymore (and that’s been true already in late ’90) and difficult to find. Usually your only source is another meter as a part donor, or maybe ebay if you don’t mind that a few of those transistors would cost more than what the whole meter (in working conditon!) is worth. And you’re very likely to get an expensive fake anyway. But a very technical post like that would be boring for most people, and with the latest WP changes I don’t even feel like doing it anymore. So I’m just going to mostly wrap this up with a few more photos.

The inputs – a very important part of the meter, you are going to plug and unplug the jacks pretty often, it’s a good idea to have a fuse for current measurement, and – in general – you might be applying high voltages to these so there better be proper clearances and insulation there. Well, if you are a Fluke fan then I’d suggest you never open one of these 8600A, ignorance is a bliss they say. I’ve opened a cheap phone charger once and promptly dumped it into a nearby recycle bin shortly after, even though it was still working – I would not dare to connect it to AC outlet in my house anymore. Anyway, I had to rewire the Fluke inputs because:

  • Clearances, what are those? Surely a thin layer of old plastic and/or half a milimeter of air gap between bare metal parts will handle 1200V AC just fine.
  • Let’s just use a thin, strained wire to connect ground returns to PCB, that will obviously not just snap off on it’s own after years of use.
  • Insulated fuse holder? Like, an actual fuse holder, not a cheap short metal tube on one end? What are you, a safety loving socialist?
  • This here single spring blade will hold the fuse in place just fine 95% of the time. And the fuse will not move to sides and make a poor contact when you turn the “holder” to lock it in, not at all.
  • If it works, it must be a Fluke!

This is how it looks now. Trust me it’s a major improvement over what I found:

FLUKE 8600A inputs

The range-selecting GAL with the capacitor update I mentioned before, and a peek at my first attempt to rebuild the power supply. The AC converter board is still out but everything DC almost worked by this time (BTW note the input fuse, the fabled Fluke quality and safety, it’s why the meter was so expensive):


Unfortunately my idea of using efficient DC-DC converter to create 5V for the logic didn’t quite work out. Even though 5V is not used in the A/D converter, there was enough noise present on the PCB to upset it. Ignore the extra wires going to the rectifier bridge, I was using that with external DC power supply because I didn’t want to have 230V running throught the board (right up to the ON/OFF switch in the front panel) while I was working on this.

FLUKE 8600A power

I could not get a zero reading in lowest DC ranges with this setup, so sadly it had to go. I ordered a custom 7,5V/1A transformer for this project and went with linear 5V regulator. But I was stubborn and decided to keep the +/- 18V DC-DC converters since those feed 15V regulators so there shouldn’t be much noise. And actually the battery-powered option from Fluke uses a similar setup, but there’s a bit more EM shielding. I can’t replicate that here though, no space for it – the battery option has an extra PCB (and a different transformer BTW) which would prevent me from installing the data output unit that I want to have.

Since I had a curious issue with the ohms converter not being able to calibrate – that is until I swapped one of the factory-selected precision resistors for a different value – I decided to create my own PCBs to replace the burned ones. I wanted to know if the carbonized PCBs are the cause (some leakage currents perhaps) and also I was not entirely sure connecting more than 100V input would be safe anymore, considering all the damage to the input divider. Plus it turned out one of the relays on the divider was on it’s way out anyway (yup, that unwrapped one). My PCBs are not 100% identical to the originals but work just as well, if not better – while reusing only the custom parts and semiconductors, the rest is new.


FLUKE 8600A Ohms

This is how it looks installed, with the updated PSU and new transformer:

FLUKE 8600A new PCBs

This transformer is a split-bobbin type but I decided to add a bit more mains RF rejection by running the input wires through a ferrite bead, as well as adding two 100nF SMD capacitors next to the bridge (on the other side of the PCB) to supress harmonics. Original transformer had electrostatic shield but this should be just as good. This one is 230V only but that isn’t an issue for me.

FLUKE 8600A trafo

I was able to calibrate the DC ranges, there aren’t any noise problems except the AC converter, but that one is another story – kinda works but has issues, so I will attempt another reproduction PCB at some point I guess.

And finally the data output unit, now upgraded with USB port so that it can be used with a PC directly, or remotely via LAN+RPi. The DOU output is fully isolated and thus so is the USB. I made it in such a way that USB module is only powered over the host cable, in order to prevent any backfeed between it and DOU.


A small modification to the case was required to make sure the USB port will come through and stick out just far enough for the plug to fully lock. It was either that or a massive edge connector plug with PCB and a lot of extra chips to process all the 5V signals present on the original printer port. I think this approach is better and more importantly, it works.


Sadly, the meter only reports what range it’s in, not what mode is selected. But still it’s pretty useful, I’ve implemented a few SCPI-like commands and this is what the USB communication looks like:

Fluke,8600A,2106127,1.2 (2021-03-13)
+04,953e+0 V DC
+04,954e+0 A DC
04,953e+0 V AC
04,953e+3 Ohms
+04,954e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,952e+0 V DC
+04,952e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC
+04,953e+0 V DC

To sum this up, I’ve fixed or replaced:

  • 50 ohm pot (blown; R8 on DIV board)
  • F2591 J-FET with selected BF245C (blown; Q14 on main board)
  • F2591 J-FET with J111 (suspicious; Q15 on main board)
  • CD4053 chip (failed; U16 on main board)
  • ROM chip with 16V8 GAL (failed; U9 on main board)
  • 2,7M and 4,7M resistors (drifted way above 5%; R74, R82 on main board; R17, R18 on DOU)
  • wire connections on input jacks (broken; on main board)
  • factory-selected resistor with 1% metal-film of higher value (something drifted; R90 on OHMS board)
  • new power supply section of my design (missing parts; on main board)
  • fuses for input and power supply (missing parts; on main board)
  • new PCBs (charred; DIV and OHMS boards)
  • reed relays along new PCB (suspicious; DIV board)
  • 470nF film capacitors (open/short; C14, C20 on AC board)
  • 150k resistor (drifted above 5%; R43 on AC board)
  • 15k resistors (drifted above 5%; R32, R33 on AC board)
  • 25nF ceramic capacitors (cracked; C6, C7 on AC board)
  • FD700 diode (missing; CR16 on AC board)
  • case screw (missing)

The case screw was actually a serious problem. It’s an imperial thread (and it comes in coarse/fine variants too!), kind of difficult to find in Europe.

The Wretched Automatons, contd.

Just letting you know DocBrowns will be available this Saturday (2021-02-20), and this will be another USA-friendly window opening at 20:00 CET. This particular batch is a small one so I might limit it to Marty owners only – we’ll see how it goes.

There will be a short break from mid-March to early April as the Post Office here will introduce some changes to stamps and payment for international shipping. At the same time we’ll also be testing a different internal workflow – this is related to changes in VAT procedures that will soon apply in EU. In general nothing that you should worry about except there now might be a delay (a few days) between your payment and actual shipping taking place. That’s because, for tax related reasons, we won’t be able to ship first and then do the paperwork later as we did so far.

UPDATE: DocBrown orders are now closed. Give me a day or two to process the orders and send out confirmation emails. Just eyeballing the queue and it looks like I should have enough devices for all orders – I hope I’m not short just a few.

UPDATE 2: I have a small batch of Phoebes that are ready to go so I will open orders this Saturday (2021-03-06) at usual time of 12:00 CET. I hope to have most of these shipped before the April break.