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.
They are quite readable in the paper version. It is out intention now the articles have been published is to also add selected info to our website. So, I have just uploaded the drawings to the product page for the case 7250-015, see the 'Downloads' tab.
Hi, I’ve purchased the July 2019 edition of Practical Electronics in Pocketmags. I’m making a mock-up case before I get my expert woodworker brother in law to make a case out of black walnut for me. The dimensions in the magazine are very blurred in Pocketmags. Is there any chance of obtaining higher quality files please? Otherwise I’ll have to track down a print copy and hope they’re better. Thank you.
Richard Jones06/06/2019, 10:00
No problem at all, happy to help. Good news that you have also resolved the white noise source as well.
The last part of the magazine article comes out within the next 10-14 days as it has just gone to print. That will explain the remaining calibrations including the oscillators.
Hi Paul....so, how embarrassed do I feel now? I have quite a lot of experience with analog synths, although not necessarily modular. The bit that caught me out was the VCA Level. I thought that was simply the volume of the VCA output. What I now realise is that it's the volume of the VCA when it is unmodulated. If I turn it down so I hear silence when the sequencer is stopped, then start the sequencer, the ADSR envelope is applied to it because I have the ADSR Mod pot on the VCA turned up. Apologies for wasting your time, I understand it now. In fact I also resolved the noise issue by reflowing a few solder joints in that module and it is working fine now.
Thanks again, looking forward to getting this cased up and in use in my studio now!
Richard Jones23/05/2019, 16:56
I'm not sure that we actually have a fault here. The VCA looks to be working from what you describe. Not sure of what experience you have with analogue synths but there are two fundamental considerations, pitch and signal level. The MIDI interface outputs a voltage that directly relates to the pitch of the note and that seems to be working fine and a gate signal that is on whilst a note is being played. A MIDI interface to an analogue synth always outputs the voltage of the last note played which yours is doing.
Now comes the signal amplitude which uses the MIDI gate signal, there are two ways of doing this, one is to use the VCA and the other is the VCF. Both need a voltage envelope which comes from an ADSR. Switch ADSR1 to MIDI Gate and set the attack to 1, decay to 1, sustain to 7, release to 5, time to Short. Now, each time a key down command is received from the MIDI, it will trigger the ADSR to create a voltage envelope. Let's now route that voltage envelope to the VCA by switching the VCA to 'ADSR1 Mod'. On the VCA, set the initial level to 10, ADSR modulation to 10. Run your sequence and gradually turn down the VCA initial level pot until you start to hear the note played varying in volume. With the sequence stopped, if you can still hear a note playing, turn down the VCA initial level until it just goes silent. You can vary the ADSR mod pot to vary the peak amplitude of the note and the ADSR timing pots to get the profile best suited to the sequence.
You can do something similar with the VCF, set the VCA initial level to 10 but this time we are going to vary the amplitude of the note by using the filter cut-off. Switch the VCF to ADSR1 Mod, set the VCF ADSR Modulation pot to 100% and run your sequence again. Adjusting the VCF Freq cut-off and ADSR modulation pots will give amplitude modulation like the VCA but with a harmonic change as well. As with the VCA, if you can still hear the note at the end of the sequence, turn down the VCF Freq cut-off.
Let us know how you get on. Hopefully I have not made a mistake as I am describing it without a synth in front of me!
Thanks for your reply Paul - so I did this - I powered on, started my sequencer (I'm using a beatstep pro over MIDI) and I heard as before - a drone which changes pitch according to the midi notes. When I turn Initial Level to 0 (all three VCA switches off) I hear nothing. When I turn it back up, I hear the same as before. Stopping the sequencer just leaves the same note playing. I've also tried sending all notes off from a midi app on my ipad, but with no success.
Richard Jones23/05/2019, 13:38
Okay, this is different then. I assume that with all mixer controls at a minimum, you hear nothing in which case you need to look at the VCA. Make sure you have calibrated the VCA, the 'Initial Level' panel pot is fully counterclockwise, all three VCA switches to centre off, there should then be no audible sound coming through. If you still hear something, check what the dc voltage on the output of U502.1 pin 1 is. This is the summating control voltage amp.
OK, thanks - I'm hearing all 3 VCOs either independently or together depending on the mixer. The same result either with the headphones or the line out. It's like the ADSRs envelopes just aren't getting applied to the output.
Richard Jones23/05/2019, 10:35
You say you can hear a sound from the oscillators, is that all three or just VCO1? There is a known issue with cross talk from VCO 1 (and only VCO1) which is discussed in Part 6 but that does not get through the VCF so not too much of a problem. Also, are you using the line or headphones output when you hear the oscillators?
As for the noise generator, after checking your circuit, if you still cannot find a problem, try changing Q1 and make sure the collector leg is snipped off.
I’ve finished my build and it’s all sounding good (except the noise circuit, I’m getting nothing, but I need to debug that) except there is always sound coming from the oscillators. It feels like I should know why this is but I’ve tried every knob, switch etc I can find. So there’ll be a drone, then when I fire a midi signal in, it will switch to that note. The ADSR manual gate switches just re-fire the same note. Midi all notes off doesn’t have an effect. Any help would be gratefully appreciated! Thanks.