t_xen Posted March 12, 2008 Report Share Posted March 12, 2008 This might have been asked before, but would be good for me, n00bs (no insult intended), addicts and gurus that might not know this. ;)Filter caps (C1-2) on the SID module.Is there a difference in audio characteristics on the filter between using polystyrene, ceramic, or tantalum capacitors?I suspect that the speed in the charging and charge dump is different between them.I am also pretty sure that the value of the cap will affect the filter Hz cutoff range.What I don't know is how will the cap type effect this.any enlightenment?thnx ;) Quote Link to comment Share on other sites More sharing options...
Wilba Posted March 12, 2008 Report Share Posted March 12, 2008 The values of the capacitors affect the filter cutoff frequency range.Therefore, it is better to use as closely matching values as possible in a stereo SID pair, so the difference in cutoff frequency between the SIDs is as small as possible when both SIDs have the same cutoff parameter. I can definitely hear the difference between closely matching values and values differing by 10% (eg. when using low-pass on a PWM bass patch). I call this a "phasing effect" (probably incorrectly using the term) which is something you might want and can achieve by setting the left and right SIDs with different cutoff values, but it's better to have it optional.Any non-polarized capacitor type will work I think... the differences are more to do with temperature stability and lifespan and other things which I don't know much about. I'm personally using mylar (polyester film?) capacitors with 1% tolerance, a lucky find on eBay, otherwise I'd be stuck trying to find 1% tolerance capacitors of any kind. Quote Link to comment Share on other sites More sharing options...
stryd_one Posted March 12, 2008 Report Share Posted March 12, 2008 I call this a "phasing effect" (probably incorrectly using the term) Nope, that's right! Quote Link to comment Share on other sites More sharing options...
DenDer Posted March 13, 2008 Report Share Posted March 13, 2008 So when i'm reading this, the idea pops in my head of a on-off-on switch with 3 different values for the cutt-off range. Or is this not a good idea? And do both C1 and C2 affect the filter? Or is for instance C1 for filter and C2 for resonance? Please inlighten me.... Quote Link to comment Share on other sites More sharing options...
t_xen Posted March 13, 2008 Author Report Share Posted March 13, 2008 To quote the -HMOS 6582 datasheet:"both caps should be the same value. normal operation of the filter over the audio range (apprx 30Hz - 12KHz), is accomplished with a value of 6800pF for C1 and C2. Polystyrene capacitors are preferred. In complex polyphonic systems, where many sid chips must track each other, matched capacitors are recommended. The Frequency range of the Filter can be tailored to specific applications by the choice of capacitor values. example, a low cost game may not require full high-frequency response. In this case larger values for C1 and C2 should be chosen to provide more control over the bass frequencies of the filter. The approx maximum Cutoff Frequency of the filter is given by:FCmax = 8.2 - 5/CWhere C is the capacitor value. the range of the filter extends approx 9 octaves below the maximum cutoff frequency."Seems like both caps are only for the cutoff frequency bandwith range. Quote Link to comment Share on other sites More sharing options...
nebula Posted March 13, 2008 Report Share Posted March 13, 2008 I got a bag of 25 and hand-matched them across 8 SIDs. Quote Link to comment Share on other sites More sharing options...
bugfight Posted March 13, 2008 Report Share Posted March 13, 2008 I got a bag of 25 and hand-matched them across 8 SIDs. i did this with 100, very very precise.at the temperature when i did it.erm, plus hand temp etcok, so i'm crazy... Quote Link to comment Share on other sites More sharing options...
lucem Posted March 13, 2008 Report Share Posted March 13, 2008 The type of capacitor doesn't really matter in theory (and in practice, too, most of the time).When you use metal film capacitors, like WIMA ones, you may (under very rare occasions) catch hum,but this shouldn't be too much of a problem at that stage, as the output signal is relatively strong. Quote Link to comment Share on other sites More sharing options...
dj3nk Posted March 13, 2008 Report Share Posted March 13, 2008 So when i'm reading this, the idea pops in my head of a on-off-on switch with 3 different values for the cutt-off range. Or is this not a good idea? And do both C1 and C2 affect the filter? Or is for instance C1 for filter and C2 for resonance? Please inlighten me....Sound like a good idea. I would be interested in this too :Dgreets Quote Link to comment Share on other sites More sharing options...
Jaicen Posted March 13, 2008 Report Share Posted March 13, 2008 The theory with using high-end plastic caps (well, from what I can gather in the HIFI geek land), is that ceramic caps can be slightly microphonic, or piezoelectric, which can cause distortion. Personally, I'm not sure how much difference it makes in this application, but I use the best caps I can (within reason, no $20 Spragues here ;) ). Quote Link to comment Share on other sites More sharing options...
DenDer Posted March 23, 2008 Report Share Posted March 23, 2008 So what kind of caps do you use then Jaicen? And what is the exact function of C1 and C2? Do they both regulate the filter cuttoff range? I've checked the pin out of the 6581 and pin 1 till 4 are for Cap 1a,1b and Cap 2a,2b so i don't get any wiser on that. Like recently i've build a tube vcf which also has a switch for 3 different values on the cut off frequency range. Are these caps(c1,c2) more for stabilization? Quote Link to comment Share on other sites More sharing options...
t_xen Posted March 25, 2008 Author Report Share Posted March 25, 2008 As far as I can see, C1 & C2 are for the cutoff range. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.