C64 PSU

[Guest tew303]

Hello Midiboxers,

I've a question about the optimized PSU of the C64. Is it  necessary to use this PSU or will a normal adapter do the job as well? I read that the sound quality improves when using the optimized or can a adapter have the same quality in a core,sid,ain, module setup.

kind regards

Tew

[goyousalukis]

It is not necessary to use the C64PSU, but highly recommended. If you don't use it,

Either the output of a 15V transformer, or a wall adapter can be used. 100 mA is recommented

I started with a wall wart, but noticed a big improvement in noise levels when I switched to the C64PSU.

Justin

[pay_c]

The problem with one wallwart is that you introduce ground loops if you´re not very aware of what you´re doing and that the high current stuff will modulate your supply voltage for the SIDs (e.g. the LCD and more important the Midi Lines and LEDs in the Modmatrix). You get much noise this way.

I also tried both ways (wallwart and PSU). With my setup (using 8580s SIDs) the wallwart had a signal to noise ratio about -40 dB at best case, the PSU (with TK´s schematic) about -65 dB!!! Muuuuuuch better!

[arumblack]

Pay_C, (Sorry to go off topic) Could you explain to me how you measure the signal to noise ratio?

Thank you in Advance.

[pay_c]

There are different ways, but I always do it like that (you need a mixer for that).

I play some sound on the SID (any sound at max volume - saw or whatever) and level it out until it´s @ 0 dB appr. Then you stop playing it. Now you go up with the gain (remember how much you go up) let´s say with 50 dB. There should be a signal now. Let´s say it´s -10 dB loud. So now you know, that you SNR is about (ABOUT!) 50+10=60dB loud. Normally you would have to go up with the gain until the noise signal is also @ 0 dB, but most mixers don´t have so high gains.

btw: 0 dB + 0 dB = 3 dB (hehe...)

Greetz

[Guest tew303]

Thanks for the info. The only problem I have now is that there aren't pcb's for this circuit. Do you have to build whole the schematics as mentioned in the pdf. And if so how did you guys did this (veroboard??)

Tnx

[arumblack]

@pay_c: Thanks Alot!

[goyousalukis]

Yeah, it's a pretty simple circuit. I just built it on vector board. Of course you could design your own PCB. If you build it using the original C64 case, you can make it fit perfectly where the power switch, power plug and joystick ports are.

Justin

[Guest tew303]

I just finished my first build vectorboard circuit  :D

[oberg]

I'm currently trying to put together the PSU-circuit on a veroboard. Do you guys have any pictures of yours? It'd be really helpful to see some other designs before soldering my components in place.  ;)

[Guest Zzzz...]

Too late for TEW303....

But I've made a PCB for the PSU,which actually fits perfectly inside of the C64-case....

Sorry ... I had to put it online... huh?

Will do....will do...better: send me PM....

Grtz E.

[Guest tew303]

Hi Oberg,

I don't have a digital cam and no scanner. But as you probably saw, ZZZ.... has a pcb design for it. I would go for that solution since it's more reliable.

Actually I'll probably rebuild it on a pcb when ZZZ... has made layout public.

BTW I'm working on a simplified surface (1 SID only). When it's finished (probably within a month), I'll post the details, panel and code. No leds are in the design which makes assemble the unit far more easy (no DOUT, only a core, sid and din module). But it's not as good looking as the surface which Thorsten made ;)

Greetz

Tew