janvanvolt Posted October 20, 2009 Report Posted October 20, 2009 Hi there, after using another C64 power supply, i still have very audible HUM, which makes it quite unusable. It is lower if i am using the single outs, but stillnoticeable.Other question: In the passive Mixer design, the attenuation of the individual signals is too high, is there a possible solution ? Quote
Wilba Posted October 20, 2009 Report Posted October 20, 2009 A very audible hum could be because the PSU is unable to deliver enough current. Is the hum present when there is only two SIDs installed? If the hum is gone, then the problem is too much load on the PSU, and the PSU can't deliver enough voltage to the regulators.Some PSUs cause the hum just from being noisy.... other times it's maybe an issue with the PCB, it's hard to say... you might try a test with a temporary power supply, such as 9V AC (or 12V DC) walwart and regulated 5V DC walwart... i.e. some good, new walwarts, to compare. Or some other good power supply you might have for other projects.The passive mixer is a passive mixer - you can't get less attenuation without reducing the resistors, which causes other problems. AFAIK an active mixer is just a passive mixer with op amp stages afterwards to amplify the signal level loss from the resistors. You could build an op amp stage but good ones require bipolar PSU inside the case. Quote
m00dawg Posted October 20, 2009 Report Posted October 20, 2009 When using a pair of headphones, I do find that the passive output is a bit quiet but seems to work just fine when I run it through an amplifier (such as one for my computer speakers). It's definitely softer than the individual outputs but good enough for most purposes I would say. For me, my plan is to use the passive output for my normal music makins and then to use the main outputs from each SID when I'm at the mastering stage. That is largely because I don't have the capability to give the MB-6582 4 discrete stereo inputs. At least not yet :PI would say if you are at the point of adding op-amps, you might want to just build your own external mixer or even buy one. Seems like that would be a fairly involve job trying to do it inside the MB-6582. Quote
janvanvolt Posted October 20, 2009 Author Report Posted October 20, 2009 Wilba: I am using a Original C64 Power supply, so 1500mA shouldn't be an issue.Could it be possible, that the ground connection is somehow broken (e.g. groundloop) ?Just wondering ... Quote
Futureman Posted October 20, 2009 Report Posted October 20, 2009 Have you triple triple triple checked the polarity of the caps in the power supply section of the MB-6582 PCB? Quote
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