Possible Power Supply

MIDIbox SID
1

Hi,

I have read round and round the Power Supply topics and am still stuck as I have not had to build or adapt a power supply before. So have a few questions…

I would like to keep my power supply simple for now, but with the option to add more SIDS of different types easily later on and eventually a full control surface.

My current SIDS are 6581s.

Could this be used instead of the original C64 power supply, with the optimized 8xSID PSU circuit starting with 1 Core, a Stereo Pair of 6581 SIDS and the Minimal Control Surface (LCD etc)?

http://www.amazon.co.uk/Lacie-Model-ACU057A-0512-Adapter-equiv/dp/B004VL5JV4/ref=pd_cp_ce_2/275-2315380-3087453

Later if I add another Core and Stereo Pair of 8580s, could I then add a circuit / transformer to derive the 9v from the same power supply?

My two main concerns are:

whether the current is overkill, and whether because of this the chips will overheat.

Would the extra current be available, but not drawn initially (with my original set-up), or would the Chips be forced to drain the spare current?

Thanks,

2

You might want to read this?

http://joemaller.com/1424/worst-component-ever/

3

There is no such thing as “current overkill”. The current rating is always a MAXIMUM rating, telling you how much current the PSU would be capable of delivering. The current sink (in your case the MIDIbox) only draws as much current as it needs.

Before you get much deeper into building a power supply, take some time and look into Ohm’s Law and some basics of electronics. Otherwise chances aren’t too bad you’ll release some magic smoke :slight_smile:

4

Thanks nILS… I know… it was a stupid question. I knew that the current was a max value, but had a moment of late night doubt and better safe than sorry hey? I still always have to check which way round the impedance of speakers can be if they don’t match (greater or smaller than the amp). Every single time!

I’ve built a few electronics projects before: 2 theremins; a CV to MIDI converter (which I used to have the game twister control beat-slicing, time-stretching and glitch effects in Max/MSP); a compressor; hacked my wah pedal to work better with my clavinet; amplifier; ring modulator; timer based oscillators; tape-delay; chip based 8-bit sampler (which I did design myself very slowly); USB footpedal; MIDI controller for Ableton Live and so on. However, except for the simple projects and hardware hacking, I have just built circuits from instructions, with some small adjustments. I’ve never had to fiddle with mains related stuff, which is why I want a pre-built AC->DC power adapter between the mains and my circuits. :slight_smile:

Thanks for the heads up Gilejuk, it seems from the update at the bottom of that article there is a replacement which is reliable:

http://eshop.macsales.com/item/Other%20World%20Computing/ELITE4SAUS/

So, as I’m now slowly getting my head around it by looking through old posts here, googling and books, it looks like I am going to go with the above adapter and:

Include HF filtering capacitors (2x 2200uf electrolytic and 1x 220nf /330nf polyester)

Include 2x crowbar circuits (12v and 5v) to be extra safe

Remove the part of the circuit combining the 9VAC and 5VDC from the mbhp_8xsid_c64_psu_optimized.pdf

Can anyone please answer any of the following:

  1. Am I right in concluding that I don’t need a 7812 in my circuit or the 7805 in the Core circuit as the power supply (ELITE4SAUS above) will be regulated enough already?

And looking at the following circuit:

http://en.wikibooks.org/wiki/Practical_Electronics/Crowbar_circuit

  1. Can anyone suggest values for SD1, Q1 and C2, or point me in the right direction for research?

  2. Should I use resettable or regular fuses? Or both?

  3. Is there a crowbar circuit floating around here that others have used that I can compare to this one?

Thanks again :slight_smile:

5

I really dont see the point to a crowbar circuit in something that can use 78xx vRegs. Those have a huge input range (up to 36V!) and are damn near indestructible. Keep it simple: 12VAC or 15VDC wall wart, 7812 for the 12V Rail, switching 5V reg for the digital side. Done

Those HD power supplies are all switching supplies so depending on their switching frequency, they may need filtering or they can be noisy. I cant comment on them personally, but general consensus seems to give those the thumb down for audio applications. I would also be VERY careful about assuming that they are “regulated” in the linear PSU sense. Switching supplies have specific load requirements to function correctly, i.e. the reason you cannot just put a volt meter to a computer PSU to determine if it is working correctly

6

Isn´t the ground from the 5V switched supply shared with the 9v/12v analog ground from the 78xx in the mb6582? Wouldn´t that affect the sound quality if we had a low-freq 5v switcher?

Sorry for that noobish question, but I´ve been wondering about that for some time nao :slight_smile:

Greets,

Peter

7

Grounds MUST be connected. If there’s a lot of noise on the 5V rail, you’ll get more noise on the 9V/12V rails.

8

Thx for the clarification, so we still need a high-quality switcher for the “digital only” 5v supply -

in that context I´d still see room for a 7805 + big heatsink + crowbar circuit - mda asked for a reference - i use the one from retro donald which works fine for me (there are better ic-based solutions out there, though): http://www.retro-don…wernetzteil.php

Many greets,

Peter

9

Hi,

check this out. This is easy to build, works perferctly and doesn’t produce noise in the audio path:

http://discourse.midibox.org/t/topic/16241

Cheers

orange

10

I really dont see the point to a crowbar circuit in something that can use 78xx vRegs. Those have a huge input range (up to 36V!) and are damn near indestructible. Keep it simple: 12VAC or 15VDC wall wart, 7812 for the 12V Rail, switching 5V reg for the digital side. Done

I miss to see your point here I think. What do you think happens if the vreg fails because of whatever reason, and it fails in a welded style? Wow, u get unregulated jumpy high voltage on your rail. What do you do? U regret u didn’t throw a crowbar in there, coz that would kill the rail in an instant, and blow the fuse, and hopefully save as much as possible can be saved in both the load and psu. No?

Should I use resettable or regular fuses? Or both?

There are positive and negative with both. If a normal fuse blows, you gotta have it available to change it without having to open the psu case right? - or at least that’s practical way to do it. If you use resettable fuses, if I got it right, they need cooling time after blown. And it’s not really a circuit breaker / fuse, but close to it - when it trips, it makes the resistance through it so high that almost nothing can pass, but some. Someone will hit me on the head if I’m wrong, but this are things to be aware of. But resettable fuses are widely used in all kinds of electronics, so why not? :). Your choice :).

Grounds MUST be connected. If there’s a lot of noise on the 5V rail, you’ll get more noise on the 9V/12V rails.

Great clarification!

(there are better ic-based solutions out there, though)

Yeah pete, I remember I found some IC based solution a while back and fiddled a bit with it, but eventually put it on hold. The idea is that a zener diode solution as a referance voltage used to trip the thyristor is a bit unreliable because of heat and tolerances. It’s kinda the same thing as using vreg ICs instead of a zener voltage regulator and a pass transistor. I suspect (as u say yourself) that both of the solution will work pretty good.

I just finished up my 6582 powersupply - it got +/- 12V, 9V and 5 volt. All rails fused, all positive rails have crowbars. And I have been designing it with 2% tolerance zeners, and the zener voltage about .4 - .5 volts above normal rail voltage - that is the minimum zener voltage in the datasheet. So in reality the zener voltage is more like .4 to .8 volts above normal operational voltage. I have no idea if it works the way it’s supposed to, but I’ll try it out with some load and see what happens if I increase the voltage on the rails. Should give me a nice blown fuse pretty fast hopefully.

11

I just finished up my 6582 powersupply - it got +/- 12V, 9V and 5 volt. All rails fused, all positive rails have crowbars. And I have been designing it with 2% tolerance zeners, and the zener voltage about .4 - .5 volts above normal rail voltage - that is the minimum zener voltage in the datasheet. So in reality the zener voltage is more like .4 to .8 volts above normal operational voltage. I have no idea if it works the way it’s supposed to, but I’ll try it out with some load and see what happens if I increase the voltage on the rails. Should give me a nice blown fuse pretty fast hopefully.

Any news on your power supply? Working?

@Orange_Hand - As you’re in the UK at least I know the input voltage would be correct. I would need 12v, 9v and 5v though, as I will eventually have a mixture of both types of SID. Would I just need to duplicate the 9v section with different mini PSU to produce the extra output?

Thanks

12

no news, still lacking one transformer before I can give it life, and then I’ll test it :). It’s nothign fancy, just standard textbook / datasheet circuits, but with a few twists - an idea smashtv gave me, for example the leds on each rails - to safely drain the big caps on powerdown, also usefull for service work. I was hoping to implement some more stuff for controlling the rail current draw and also a IC based crowbar solution, but for now I just need to get my psu up’n go. My next psu will be all switch mode, since it’s for non-musical midibox systems. Not sure wich app to use or if I should write some myself to get what I want. But I’m definetly finished with synth building for the next couple of years :). Exception would be the 4 ssm filters I have on their way in the mail atm.

13

@mda

If you build the PSU like I did, then you are on the safe side. You can support both SID’s. The 9V is sourced from the transformer and the 5V is provided by the switching PSU. On the MB6582 the 12 V are generated by adding the 9V with the 5V. So no need for a separate 12 Switching PSU.

General comment: It is not required to build a crowbar if a proper switching PSU (e.g. 5V) is used. In my example the switching PSU has a protection against shortage and doesn’t produce noise in the audio path. I have recently check this with my scope.

Cheers

orange

14

Thanks for all the input.

As i’m building mine in the old school modular way - I can’t afford to do it all at once - I would need to add the 9v and 5v myself, giving me 12v for the 6581s, 9v for the 8580s and 5v for the cores. I presume this could be done as on the optimised PSU, tapping out the 9v before the addition. Is there a circuit diagram for how the MB6582 achieves this?

Thanks again,