MIDI Ultimate Support Blog

by Admin Admin

Please use this blog to post support questions for the MIDI Ultimate or just to say hi and how you are getting on with your build.


Hi Bill,

The mains adaptor has an internal fuse on the primary side. So my thought and as a rhetorical question, what would be the protection purpose of a fuse on the secondary side? The +/-12Vdc power supply is current limited far higher than the maximum normal operational load current of the synth. The mains adaptor is rated lower than the capacity of the power supply. For a secondary fuse to blow, the mains adaptor will have to delivery sufficent current for a sufficient period of time but it may well not be able to deliver that level of current as its terminal voltage drops when its rating is exceeded. So is the secondary fuse being used to protect the down stream components or the main adaptor. The mains adaptor is internally protected and the downstream components are rated higher than the maximum fault current the mains adaptor can deliver. For this reasoning, a fuse has not been included, you could add one but check that the voltage drop across it does not adverely affect the performance of the power supply. Any other thoughts most welcome.
Am I missing something or do I not see any fuse protection anywhere? The AC transformer routes to the PSU and the PSU feeds the main PCB. Considering there are fairly large capacitors in the linear PSU, I will probably add a 800 mA slow blow fuse inline with the 12VAC to allow for the PSU inrush current. Anyone else adding a fuse?
Hi Nick,Really pleased to hear you are impressed with the. Amazed that we missed a nut for the jack sockets, we buy them in bulk with exactly the right number of the nuts and washers loose. So we carefully count out the 7 nuts and washers for the kit because they do not supply any extras. Anyway, I will get a nut in the post to you. The next article in PE is all about MIDI so hope you enjoy that read.
Nearly finished building the Ultimate Midi, and now at the final assembly stage.
I've been impressed with the quality of the PCB and component kits.
Only one item is missing, a holding nut for one of the mono rear jacks, not bad considering the number of items in the kit!
Could you sent me a replacement please?
Hi Barry,

Yes, the LEDs blink at the frequency of the respective oscillator. The LEDs could either be constantly lit or the frequency is so high they appear to be constantly on. Interesting that you have the same problem on both so looking for a common problem between the two circuits. If you have a scope, check to see if you have a square wave at the Rpt Gate output and the S&H gate output. If the frequency is high, I would check for a resistor wrong value. If after having a look and still no luck, email us some pics of both areas of the PCB, top and bottom and I will take a look.
Built all midi synth all ok apart from static leds lit constantly on rpt gate and s&h gate i guess they should pulse/flash? not gettin random notes in prove s&h test.
Please can u help?
Hi Mark,

A PDF of the PCB can be found in the 'Downloads' tab on the PCB product page which may help. R622 is the top resistor in a group of 3 immediately below the LFO2 frequency pot VR602. Let us know if you still cannot locate it.
I am putting the resistors in the sectiom lfo's kit and can not find r622 do u have a picture i can soon into on the pcb am i going blind or have i put a resistor on that space .?
Hi Chris,

Firstly, sorry but we did not receive a notification of your post so came across it by accident. Issue with website now fixed.
Really good to see that you have tried to solve the issue in a very logical way.
It is never easy to fault find remotely but let's have a go.
Set your coarse frequency pot to mid position and put your scope on the output of U102.1. This is the core ramp generator, the frequency of which should be adjustable using the coarse and fine pots. From your post, I expect you will not get anything but check with a scope as a simple voltage reading is not so useful.
Another simple test is to put a voltmeter or scope on the output of U101.1, the voltage should vary as you adjust the freq pots.
Could you also email me a photo of the oscillator area front and back in case I can spot anything.
Based on your feedback from the above tests, I can advise further checks to make. We are looking for an assembly error or less likely a component fault.
9/4/19 Follow up, Chris found he had a faulty polystyrene capacitor, now replaced and VCO 1 oscillating as it should. The polystyrene caps have very fine leads that can be pulled out when moving the capacitor body around, equally it can have been a faulty manufacture.
Hello there

I'm fairly new to electronics and DIY synths, however I like a challenge :-)

I'm having a wee problem with Oscillator 1 on my MIDI Ultimate synth. I'm building this up in conjunction with EPE Magazine and following the testing that that has been described in the magazine.

All three oscillators were working but I appeared to have a parasitic oscillation on Oscillator 1 which was most noticeable on the Sawtooth waveform.

I decided to start comparing the oscillator with one of the ones that was working without issue. I have removed the ICs from Oscillator 1 and tried them on Oscillator 2, the ICs appear to be working fine. I installed the ICs removed from Oscillator 2 in to Oscillator 1 but this made no difference.

Shortly after this I did some more probing with the Oscilloscope and noticed that I was no longer getting any waveforms out of Oscillator 1.

After reading the circuit description a number of times and trying to follow the diagram my next step was to carryout some readings across resistors with the multimeter. I took readings from different points of the the circuit and everything was identical. However, when I compared R128 with R228 & R338. R128 showed a steady voltage whereas the other two alternated between negative and positive readings suggesting oscillation. R104, R204 and R304 have identical voltages across them. All of the diodes are installed the correct way round and appear to be working.

I did wonder if the problem was with Q103 so replaced it with a new one but this didn't help.

Can you advise what to check next? I'm wondering if the issue is perhaps with C105. I took a voltage reading from it and compared it with C205 and C305 and found that I was getting a reading from the working oscillators but not Oscillator 1. Any pointers would be very much appreciated.

Sorry if this was a bit long winded.
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