Rowan Posted October 8, 2003 Report Share Posted October 8, 2003 HiI'm having some problems with the filter in my SID. I'm using MIOS 1.3 and SID 1.5 with step B control surface. I've tried 3 different SID chips:6581_49826581_20846581_07?? (this one is currently in my SID)The filter does not work at all with the first two, and has a VERY limited bandwidth with the third (I'm gussing approx 100Hz too about 1kHz). I've tried filter caps from 47pF too 4.7nF, with 470pf giving best results (ie widest badwidth) on the SID which the filter works. LPF works as expected but the HPF sounds more like notch filter to my ears. I've disabled the filter fix in the main.asm file.I built the SID modual on Veroboard and has tested it for shorts/opens without finding any fults (Every thing works fine apart from the filter).Any IdeasRowan Quote Link to comment Share on other sites More sharing options...
d2k Posted October 8, 2003 Report Share Posted October 8, 2003 On my quad 6581 box each SID sounds different. I came across a few which soundin very farty whilst testing sum of TK's patches - and the filter was the problem :/ Using 470pf caps here too...I have 4x 8580's too - just need to test them and then make up a quad8580 box n all - hopefully with much fuller filters! :)Best, Dan. Quote Link to comment Share on other sites More sharing options...
pay_c Posted October 9, 2003 Report Share Posted October 9, 2003 The same as d2k for me: I use 4x6581 and those filters are very different to each other (especially the different revisions). Also the humming is kinda loud (I do not use TK´s PSU up to now).I´ll change to 8580 and so hopefully get a better filter and better (meaning less) humming. Quote Link to comment Share on other sites More sharing options...
Rowan Posted October 12, 2003 Author Report Share Posted October 12, 2003 HiI got my hands on another 6581, which I tried out yesterday. The filter works correctly on this chip (6581R4AR 4086 S). What I realized is that the first 3 x 6581's didn't have the "R4AR" printed on the chip. I'm guessing that there are differences in the filter operation between the 6581 and the 6581R4AR (Hence the different code on the chip). Has anyone used this varity? I'de like to know if my chips have faulty filter circuitry.My SID is also humming. I got a C64 PSU yesterday too, so i'm going to try it out. I'm currently just using a 12V regulated wallwort to supply the SID. I was reading the data sheet for the 6581 and it's suggested to keep the digital gnd and analog gnd separate to avoid noise leaking into the audio path. I'm unsure if this is causing the hum though. I've just measured the hum, it's at 100Hz (twice the local mains freq). pay_c, can you measure what freq the hum from your SID?Rowan Quote Link to comment Share on other sites More sharing options...
TK. Posted October 12, 2003 Report Share Posted October 12, 2003 The circuit of the 6581 hasn't been changed, but the chip mask has been shrinked over the years by engineers who possibly didn't know what they are doing - the filter hasn't been adapted to the new dimensions and therefore sounds different (-> faulty) with every new revision.Humming sound is mostly caused by ground loops. I spent a lot of effort to eliminate this kind of noise and the final insights can be found in the mbhp_4xsid_c64_psu_optimized.pdf schematic. Seperating the analog from the digital ground doesn't help here, it's more important to wire the power supply lines "star-like"Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
pay_c Posted October 13, 2003 Report Share Posted October 13, 2003 Yeah, alreadz did that. But I think its also just overspeaking from the other PCBs (I have a rather compact design). I'll now try to put grounded material (that alu-paper - dont know what its called) between every PCB layer I have. I think this is gonna kill a lot of that humming (also I'll go for shielded cables now - especially the big power cable). Quote Link to comment Share on other sites More sharing options...
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