Please try to turn all pots to minimum and play with T1 and look if you can reach 20Hz This minimum frequency is set by the trimmer T1 When u turn all pots down - the vco should produce the minimum frequency The value of the trimmer t1 should not be so crucial, but in the schematic the value is 220k -> do u have a 100K? Last edited by hoby on Sat 2:05 am edited 1 time in total I dont have a 22k/or25K so Ill have to get some before i can test, but perhaps that could be explanaiton? Just noticed that i only have a 20k port for the T2 10 turn trimmer. I do use the beatstep on my TTSH (arp 2600 clone) and don't see the issues there. But I did that without the VCO connected, so perhaps I should double check that I also get the corect voltage at input terminals on the vco-board when the beatstep is connected. I have measured the voltage out of the beatstep, and it generates the right voltage when i measure the output with my multimeter.
The out of tune "drift" happens below 200 Hz regardless of the pot setting, as long as the "offset" of the frequency knob is low enough, so that 0 volts CV will genereate a frequncy below 200. Yes, I can easlily make it go down below 200 with the pots. If not you should search for unwanted offsets, i would start at T1 and R8 If so the question is what comes out of the beat step, also do they use the same GND? I would like to know if u can go below 200Hz without the beatstep only using the pots? I have also tried to replace the 394 with a matched pair of BC547, but same result. I have built the 12v version using the LM394s from ERicaSynth, (shifted so the pins match). When I go below 200 Hz the it goes out of tune, and, it also takes log before each note becomes stable - it glides before setteling. I have calibrated the v/oct, and get good tracking for 6 octaves as long as I stick to frequncies above 200 Hz. I have just finished building 3 yusynth VCO's using circuitboards from soundtronics.Įverything seems to work - different waveshapes etc, but i can not get the VCO to track at below 200 Hz - on all 3 modules. Subject description: VCO tracking problem
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