Subtle distortion on my DX7II

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Subtle distortion on my DX7II

Unread post by blopho » Sun Jul 21, 2019 10:16 pm

Hi guys, I'm new here thanks for reading if you've made it this far. When I have some spare time I'll write a proper introduction somewhere on here.

Anyway, I just bought a DX7II a month or so ago and so far I am enjoying it, however today I noticed some subtle distortion on the LFO.

It's only really noticeable when I have one operator in use, with amplitude (ams) modulation from the LFO. If I have some harmonics in the mix it covers it up pretty well but if it's a pure sine wave it's there. It's showing up in my recordings too :(

I don't know quite what to do about this one. I know sometimes some synths just have noisier outputs but one of the biggest reasons I chose the mk II over the mk1 was because of it's supposedly cleaner output.

The noise isn't isolated to the headphone jack either, but I sprayed it out with compressed air just to see if it would help and it didn't :|

The only other thing I'm considering doing is getting the circuitboard of out there and cleaning it thoroughly with Deoxit but beyond that I don't know what I'd do. I also have never disassembled a synth before and would be a little hesitant to do it.

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Re: Subtle distortion on my DX7II

Unread post by valveandsound » Fri Oct 11, 2019 10:54 pm


Distortion is likely from the analog output stage in the synth. The majority of this is housed on the YA3 board, attached to the main board.

That being said, it could also be dried out filter capacitors on the power supply. If you don't have an oscilloscope, you could pull the board and replace all the electrolytics on the PSU.

Tools would really help you here. A scope, multimeter, possibly logic probe would be the bare minimum setup to really troubleshoot problems on this unit. I suppose it's possible to get distortion artifacts from the digital side, or the Envelope Generator or OPS chip but I'm pretty confident all those signals are just digital logic. Could know for sure by scoping the data lines of the OPS chip while you're playing the distorted signal and see if the logic waveform looks wierd, or at least nothing like a square wave.
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