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MIDIbox of the Week (Chavotronic's one of the probably most cheap Midibox SID ever)


Chavotronic
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Before building a MidiBOX Sid with whole Control Surface a wanted to build a simple version.

Somebody putted this housing (External ZIP housing)in a trash and i thought its usefull to put the SID inside since it provides 5V and 12V like a Computer Power Supply. The buttons are desoldered from an old keyboard, the encoder sampled from albs, the PIC sampled also. I got the 6581 as donation from a C64 club near, and most of parts were desoldered from old mainboards, connectors also. The cable used inside were also made of old computer cables. I got the LCD for 3 € unfortunately it has no background lightning. Well all in all the costs were around 10€

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Keys are from an old Machine Controlling Keyboard. So nice i still have like 50 of them, 10 "blanco"without any label. I am thinking to use them for a Clockbox!

As for the noise, i didnt noticed any difference to a normal power supply.

i guess a little bit noise is unavoidable, maybe you could hear and tell me?

http://www.file-upload.net/download-258123/sid1.mp3.html

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IS there a simple way of denoising a switching supply?

Some high end test gear uses switchmode, the answer here is a far more complex switchmode, on one hand, or pre-regulate with a switcher, then drop the last few volts across a LDO linear regulator.

On the audio side, the noise is not the only factor. The output impedence of the supply has an effect too, which is why some of those Hi-Fi amps have huge toroids and massive banks of capacitors. Power supplies have response time issues too, which is why some of the analogue boys still use LM723 regulators - they stay stable under all sorts of conditions, and don't let nasties like soft synching of oscillators by power supply coupling happen, (there is a well known mod against this for the PAIA 'Fatman' synth).

I might hazard that a perfectly good sequencer could use a switchmode, because there is no audio in or out: I have a small good quality switchmode from a backup tape drive that I intend to try in mine. In a multi-SID system, it might be possible to run the PIC's and control surface off a 5V switchmode, and have seperately regulated supplies for the SID's.

Another thought about power is to use a seperate supply for the LEDs and backlight, say using an LM317, so that a front panel dimmer pot could be fitted, (and not use the one on the Core board).

One thought as well. One failure mode for a switchmode involves it going'off the clock' before blowing the fuse. Fitting a couple of hefty 5.6V zeners across the 5V rail might save your IC's given such a fault, or build a SCR 'crowbar' circuit to protect the valuable chips by blowing the power fuse in the event of an overload.

Mike

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