Mini-Modules : Minimoog DIY clone on its way.

[Dominox]

I take a look! Thanks for the infos I hope it help.

Thanks Dom

[Zensac]

Has anyone else had problems with tuning of their oscillators to the effect of not being able to set any of the three osc's correctly?

Bought my kit in 2017, but first started to build in late 2019 and now I've finally gotten to the step of adjustment and tuning.

- Power supply is OK and trimmed. All voltages correlate with the +10V, -10V, +9.3V, -5V and -4V for the analog board.

Now, for step "2. Tuning Oscillators" I have set all controls as suggested. I am using a bench top lab supply to generate +2.000V (measured with a Brymen BM867 DMM). (Or +0.75V and +2.75V for the A0 / A2 inputs). I then apply either 0 or 2.00V to the KB-CV jack and can measure the CV on the analog board, JP34 pin5 (KB-CV). Range Switch is set to 2" for VCO1 (and VCO2/3). I'm measuring the frequency of VCO1 directly on the 6 pin header for VCO1 (sawtooth).

Then it should be a standard VCO tuning job, using the range and scale trimmers (R66 and R64) to adjust for 1V/Oct operation. I've tried with both A0/A2 (corresponding to 0.75/2.75V) and C0/C2 (0V/2.0V) but I simply cannot dial in a correct range! It seems that I cannot get a full octave span (or two in this case) with my setup.

Here's a more detailed description of how I try to adjust, but fail to adjust:

1. With the Range Switch set to 2" for VCO1 and 2.00 V applied to the KB-CV jack (confirmed on JP34, pin5) I measure an approximate 1000 Hz Sawtooth on the VCO1 header (4-chan oscilloscope). I then use the Range trimmer (R64) to get the frequency to 1046 Hz (corresponding to the C2).

2. I then remove the 2.00 V input to the KB-CV and can confirm 0.00V at JP34, pin 5. The frequency at the VCO1 header is now downto 429 Hz. I would like this to be 261.6 Hz, corresponding to a C0. Using the Scale trimmer I can get this to 367 Hz, but not less! If I use the Range trimmer to lower the frequency more, I then get out of calibration for the C2 (2.0 V) and vice versa.

Here's an attempt at visualizing the effect of the two trimmer on VCO1 frequency (Range Sw. 2"):

- Range trimmer fully Counter Clockwise: Scale Trim (CCW) -> 145.3 Hz, Scale Trim (CW) -> 107.6 Hz
- Range trimmer fully Clockwise: Scale Trim (CCW) -> 442.5 Hz, Scale Trim (CW) -> 367.6 Hz

Changing the Range Switch to 4" doesn't help and gives the same relative trimmer intervals.

The same phenomenon is present for VCO2 and VCO3, leading me to believe it could be related to the Range Ctrl circuitry.

After my first attempt and VCO calibration I have carefully measured and verified all components for VC01. I have even carefully selected the 1% resistors to 0.1% or better.

I might also mention that I could not get any signal from the main out (or low out) jacks, when also applying a 5V Gate CV, so that's why I measure the oscillator frequencies directly at the headers. I wanted to tune the oscillators first and then I can proceed to debugging/fixing the filter and/or VCA.

What can I do next to tune the oscillators? I have the schematics (thanks Julien) but cannot figure out what to try next!

Are there any specific voltage measurements I can do to figure out my issue? I've tuned lots of other eurorack VCO's, but can't figure this one out.

Thanks

[Zensac]

I just saw Fuzzbass' post earlier in this thread (page 75), which I missed before posting my issue.

I think my bench top supply (CV/gate generator) must have been pulled down and exhibiting the same symptoms as Fuzzbass describes.

I have changed R355 and R388 to 10Mohm. I tried using a Mutable Tester to generate a 10s alternating 0V/2V CV signal, which I have fed into each of the individual Oscillator inputs (CV1,CV2 and CV3). The Range and Scale trimpot now works as expected and I could tune to C0/C2.

Thank you very much for reporting and describing this Fuzzbass. Now on to testing of the other sections...

[MerkDak]

Can anybody give me an estimate price for the BOM? I understand it is dependent of ur geography, so anybody in western europe ordered that BOM lately?

[Altitude909]

Can anybody give me an estimate price for the BOM? I understand it is dependent of ur geography, so anybody in western europe ordered that BOM lately?

Mouser stuff was ~ $300, which leaves pots, knobs, jacks, rare stuff. IIRC, it was close to $500 USD in parts when all was said and done

[sduck]

Currently building one of these.

I remember seeing this thread when it started, but it seemed like a pie in the sky plan at first, and I stopped watching it - I became a mod here about then, and had other things to attend to. And now its 77 pages! And completely unrelated, I bought the pcb/panel/rareparts kit from the website a few years ago, after seeing someone mention it on facebook or instagram or something. I never put the two of these together in my head until the other day. Anyway, with the pandemic bruhaha basically making me unemployed, I've been working through some backlog, and this came up, and I started throwing parts into it. So now I'm waiting on the mouser parts order to arrive, having filled about half of the main pcb with parts I had on hand.

BTW I want to really applaud the build guide for this - that online parts finder that keeps track of what you've placed is a godsend.

Back in 1971 my dad took me to see the minimoog unveiling at Cornell - I was 13 at the time. I had been fascinated by the early moog modulars, and thought this would be more of the same, and I was actually disappointed at the time that it was actually a reduction of the modular. I got over that disappointment pretty quickly though once I heard it a few times.

[fuzzbass]

That is such a great story about your dad, sduck.

Tips for builders of this project:
1. Take apart a DIP socket and make a little three pin socket for the noise transistor. You will probably go through a few until you find one that generates the right output level.
2. Don't pull your hair out trying to get the VCOs to track >4 volt span. The old CV / Gate distribution circuit from the Model 3 is still in here, and it was designed to only track across a 3.5 octave keyboard. It's odd too, there is a sample and hold circuit for CV incorporated into it. It has Dr. Bob's V-gate to S-gate converter built in. There is no point in putting a long keyboard controller on here, just use the range (length) controls.
3. The pots I used had round shafts and I used classic synth pointer knobs with set screws. The rotary switches will have knurled shafts. Try to find identical knobs but with brass inserts for the knurled shafts, for the rotary selectors. I think I found these with one of the German pedal suppliers.
4. Since pots are not well anchored to the control board, put lock washers on them before fitting the panel. This will prevent the pot from turning and shorting out when you tighten the panel nut.

[sduck]

Do you remember offhand which one is the noise transistor? I don't have the schematic - don't know if it's posted in this thread anywhere, I haven't read the whole thing yet.

[fuzzbass]

Do you remember offhand which one is the noise transistor? I don't have the schematic - don't know if it's posted in this thread anywhere, I haven't read the whole thing yet.

Q86

[sduck]

Thanks! (I suppose I could have just searched for the transistor that only had two connections, but this was easier)

[KSS]

Transistors 'tested' for noise use should be kept apart from new and either not used, or only placed in non-important locations, since the reverse diode 'high voltage' application destroys them for normal use to a greater or lesser variable degree.

[sduck]

Ok, mine is up and running! Oh - mostly. Osc 3 isn't responding to CV - either from the main input or the secondary input. All the other controls on Osc 3 seem to be working correctly. If I switch the Osc 3 control switch on or off I get a small change in pitch, but no difference otherwise. I've done all the calibrations up to the Osc 3 calib with no problems. Most likely it's just a flubbed connection somewhere - I'll get to trying to trace the routing this evening.

5-minutes-later-memebase-com-39505212-325-240.jpg (24.09 KiB) Viewed 487 times

Ok that was easy. Just a missed solder on the Osc 3 control switch. Missed solders seem to be my thing - I'm really good at them. I've gotten pretty good about searching for them first. Now to finish calibrating...

Edit: And done. Everything works. Yay! Took me a while to figure out how to get correct mod wheel performance, but it works.

[sduck]

Oh - and while full size chicken head knobs will technically fit, don't use them. There's certain settings where they bump into each other, causing some interesting combos that don't work.

(waiting for small bear to reopen so I can get some decent knobs for this application)

[sduck]

(those are just some placeholder knobs on the rotary switches until I can get some decent ones)

[KSS]

Nice work sduck.

I'm still bugged that the filter and EGs are 90 degrees from the original. Asked about it early in the design, and never got a reply. No one else seems to care. With many years of mini under my fingers, i'd always be grabbing for the wrong knob. major FAIL. YMMV.

Other than that, it's a stellar design.

[Kevin Mitchell]

I'm a fan of the original knobs suggested for this build as they're the odd-one-out from the 4 knob series. While 3 are used on the actual full mini (medium, large and pointer) the smaller ones suggested for this build are a perfect representation/nod to the original. Perfect for this compact panel.

-KM

[abelovesfun]

I'm a fan of the original knobs suggested for this build as they're the odd-one-out from the 4 knob series. While 3 are used on the actual full mini (medium, large and pointer) the smaller ones suggested for this build are a perfect representation/nod to the original. Perfect for this compact panel.

-KM

I've been searching this thread to see if there is a link to the full size panel from FPD, but can't find one (might have missed it in the 75+ pages). Do you know if there is a link to that full sized panel?

Thanks!

[devinw1]

Beautiful pics,sduck. Those are some purdy TH boards. Dense!

Bloody lot of trimmer pots on there, innit!?

[Space Cadet]

Hey guys, quick question:

I'm trying to find a trimmer resistor (Bourns RJ24FW103) for an MME project that doesn't seem to be available on mouser or any other source that I know of. It's a Through Hole 3/8" SQ 10K 3/8" 10% MultiTurn Cermet rated for 300v, that's R390 on the PCB. Anyone have any suggestions on equivalent trimmer resistors?

Thanks!!

[sduck]

If you enter the BOM specified part number in mouser, and then check a bunch of the boxes and search for similar, it'll turn up a variety of options. I found one that looked pretty identical to the specified part, but when I got it it was a bit larger than the other ones. It would have worked though. I ended up finding the right sized one in my stash of old leftover parts from some other project.

[Sim0n]

Bugger!!!! Started again!!

[acinonyx]

I'm trying to find a trimmer resistor (Bourns RJ24FW103)......

Bourns RJ24FW103 pricing and available inventory:

https://octopart.com/rj24fw103-bourns-974022

Gerber Electronics in MA is selling it for $1.00..but I don't know the shipping cost.

[tmontata]

Finished my build today... none of the oscillators oscillate...

+10V, -10V, -4V, -5V voltages are all ok. Reflowed bad joints, checked for shorts.

I also did all the tests around the expo converter that Julien suggested to another user and all seems fine except the voltages around pin 2 of Q8, Q21, Q24, which range from -0.008V to -0.015V depending on octave/freq. settings.

I suspect a batch of faulty 2N3954. Can anyone help me confirm that before I go on a hunt for a good batch ?

Cheers,

[Kipling]

I'm trying to find a trimmer resistor (Bourns RJ24FW103)......

Bourns RJ24FW103 pricing and available inventory:

https://octopart.com/rj24fw103-bourns-974022

Gerber Electronics in MA is selling it for $1.00..but I don't know the shipping cost.

You can use the Bourns 3296W trimmer (three pins in a line, not staggered), much cheaper and readily available.

[frozenkore]

Hi, question for anyone willing to help. I saw someone up a few pages with the same issue, but I'm not sure if it was resolved. I'm not getting any output from the output jacks. I have confirmed all of the voltages in the first calibration section. I see all of the waveforms on the molex connectors. CV affects them. OCS3 control works. If I turn it on, the CV affects it too. I have traced the components the gate goes through to a point I just don't know what it means :\. But there definitely nothing on the output. I did continuity testing on the micro connectors, and everything is connected. I haven't touched any of the other calibration steps.

Right now I'm not sure if it's the gate circuit, VCA circuit, or something else. Any thoughts? I'm go over an verify everything looks soldered well. I appreciate any help.

Thanks!
Brian