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#1 2006-08-29 10:00:25

MikeTorino
Guest

Protect the SID circuits

I've read that you can build some sort of protective circuits for the audio ins and outs on the SID (C64 audio plug) to prevent them from being fried when connecting cables. Has anyone got a clue of what to use? Schematics?
So far I have only managed to ruin one SID when I connected it to my mixer. Don't know what I did wrong, luckily it was an old 6581 revision 1 or 2 and not one of my 8580 babies.. Just don't want it to happen again.

 

#2 2006-08-29 12:04:00

linde
Mad Max
From: Schweden
Registered: 2006-07-30
Posts: 95
Website

Re: Protect the SID circuits

It was probably killed by some tiny power spike. There's a warning in the "getting started" manual about turning the mixer off while the C64 is connected, maybe that's what you did wrong. I'd love a protection circuit, until then I'll just use the TV headphones output.

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#3 2006-08-29 13:12:39

MikeTorino
Guest

Re: Protect the SID circuits

Exactly, and I recall reading something about a protective circuit for those evil spikes.
I kind of hope for some experts on this forum to enlighten us with some nice schematics or so.. wink

 

#4 2006-08-30 14:29:48

AxiMaxi
PROPHET64 GURU
From: The Netherlands
Registered: 2006-07-09
Posts: 548
Website

Re: Protect the SID circuits

Quite often the spikes can be eliminated with some capacitors.
Don't know how to implement them, though.


If everything is under control, you're not going fast enough.

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#5 2006-08-31 20:41:39

ron
PROPHET64 GURU
From: berlin
Registered: 2006-07-08
Posts: 502
Website

Re: Protect the SID circuits

I rely on my good old "Commodore 64 Hardware" book - german "Markt&Technik" publishing.. There's a circuit diagram for connecting the C64 to your home stereo, mixer, etc. Right now i don't have it here but i recall the circuit which looks like this:

http://ronny-james-disco.de/external/prophet64-forum/SID-protect-circuit.png

The capacitor is not from the book, but rather a common way to "improve audio quality", like also mentioned in the P64 peripherials document. I am using this thing for like two years now - at least my SID didn't yet get fried big_smile. For the EXT-In i was using the same circuit the other way around.   

The book says in turn, afair: The diodes are to reduce the evil spikes to 3Vpp which is said to be harmless to the SID.   

The resistor is 470 Ohm and the cap is 1F, but i don't remember the diodes.

Talking to my synth modding friend wintermute (who knows much more bout electronics than me...) last weekend he claimed that 2nd diode leading from ground->signal is quite shady, since it looks like a classic distortion?!? He advised me rather to cut that one out and just leave the one going from signal->gnd (which i didn't do yet).

However he also told me to use multilayer polyester film style (cube-shaped) caps only. That does make sense, since i already exerienced a better conduct using those (see the Background Noise thread).

I'll be on the road for a few days now but if anyone's interested i'll look up the diode type when i'm back...

Last edited by ron (2006-08-31 20:43:05)

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#6 2006-08-31 22:12:05

Jaicen
Centipede
Registered: 2006-07-14
Posts: 461

Re: Protect the SID circuits

That doesn't look particularly good to me!
I'm fairly sure that unless you use some type of Zener diode which turns on at 5v or more, you're going to get distortion. That might be desirable, but I wouldn't use it.
It's possible that one diode could be used as protection from power spikes (cathode to ground i'd imagine), but I'd much rather see an active buffer. Oh, also having only one diode will introduce a dc offset, which is going to mess up your waveforms, so you'll need a fairly large cap following it, which in turn re-introduces the risk of damage! It's  a tricky one wink

Last edited by Jaicen (2006-08-31 22:13:20)

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#7 2006-09-01 13:08:34

MikeTorino
Guest

Re: Protect the SID circuits

That's exactly what I was looking for. Simple schematics!
Thanks Ron!!

 

#8 2006-09-08 09:08:38

ron
PROPHET64 GURU
From: berlin
Registered: 2006-07-08
Posts: 502
Website

Re: Protect the SID circuits

The diodes mentioned in the book are 2 * 1 N 4148

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#9 2006-12-25 13:29:41

Ganjoe_Rood
Bomb Jack
From: Berlin
Registered: 2006-07-10
Posts: 34

Re: Protect the SID circuits

so, does anyone have experiences with this yet? is it advisable or not to build this in?

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#10 2006-12-25 17:27:15

Slorrin
PROPHET64 GURU
Registered: 2006-07-09
Posts: 871

Re: Protect the SID circuits

i will build this over christmas holidays, and let you know how it works for me.

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#11 2006-12-25 21:20:01

Ganjoe_Rood
Bomb Jack
From: Berlin
Registered: 2006-07-10
Posts: 34

Re: Protect the SID circuits

cool, and any idea how it would be implemented to BigMech's audio in circuit?
http://www.bigmech.com/misc/c64mods/sid2audinschem.gif
only the diode to ground?

and happy holidays to everyone! roll

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#12 2006-12-26 16:49:28

ron
PROPHET64 GURU
From: berlin
Registered: 2006-07-08
Posts: 502
Website

Re: Protect the SID circuits

Ganjoe_Rood wrote:

so, does anyone have experiences with this yet? is it advisable or not to build this in?

That diode circuit is somehow advisable to protect the SIDs Audio IN. I didn't get the DC offset mentioned by Jaicen - having it inside my C64s for a few years now, never blew up the SID so at least it didn't do any harm.. I  was using a small general purpose  PCB  and taped it inside my breadbox. Best to use polyester caps..

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#13 2007-01-01 14:50:13

uneksija
GI-Joe
Registered: 2006-09-20
Posts: 12

Re: Protect the SID circuits

The thing is that according to the Commodore 64 Programmer's Reference Guide, the SID's maximum output is two volts peak to peak, and those diodes on the schematic conduct at +/-0,7 volts -> this might mean that a signal higher than 1,4 volts might begin to distort. I don't know how the resistor affects the situation. _Maybe_ that protection circuit is only meant for the SID's audio input, not output.

I too would need to build a protection circuit for the SID but I haven't yet found the perfect solution. If somebody has more info on this, please tell me!

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#14 2007-01-01 17:56:55

uneksija
GI-Joe
Registered: 2006-09-20
Posts: 12

Re: Protect the SID circuits

MikeTorino wrote:

I've read that you can build some sort of protective circuits for the audio ins and outs on the SID (C64 audio plug) to prevent them from being fried when connecting cables. Has anyone got a clue of what to use? Schematics?
So far I have only managed to ruin one SID when I connected it to my mixer. Don't know what I did wrong, luckily it was an old 6581 revision 1 or 2 and not one of my 8580 babies.. Just don't want it to happen again.

I'm quoting an old message, but... I looked at the C64 schematics and noticed that the SID's audio out goes through a little circuit containing a transistor before the actual output - so are you sure your SID was fried? Because maybe it's possible that only the transistor was fried and not the SID itself. Did you try to put a new SID there in place of the possibly-fried SID? If you tried, did it work?

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#15 2007-01-06 20:08:09

Slorrin
PROPHET64 GURU
Registered: 2006-07-09
Posts: 871

Re: Protect the SID circuits

i blew another sid yesterday when i knocked the cord from my sid2 audio out jack.

It was the sid, when i repolaced the sid, i had sound again.

I need a protection circuit.. there MUST be one somewhere!!

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#16 2007-01-06 20:22:13

Slorrin
PROPHET64 GURU
Registered: 2006-07-09
Posts: 871

Re: Protect the SID circuits

When i read things, i see "don't connect the sid to a mixer while it is turned on"

but also "don't turn ON a mixer while the sid is connected"

so this means there is no safe way to connect a sid to a mixer... you can't connect it while the mixer is off, or on..

you can't turn off the mixer with it connected, and you can't disconnect it while it is on....


AARGH

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#17 2007-01-06 22:46:20

Skrenos
Dan Dare
From: South Central Missouri, USA
Registered: 2006-12-22
Posts: 73

Re: Protect the SID circuits

Mixer and C64 off.  Connect them together.  Turn on Mixer, then turn on C64.

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#18 2007-01-06 23:23:43

MikeTorino
Guest

Re: Protect the SID circuits

uneksija:Yes, I'm quite certain. I inserted the broken SID into another (working) C64 and it was still dead..

 

#19 2007-01-07 00:49:16

Slorrin
PROPHET64 GURU
Registered: 2006-07-09
Posts: 871

Re: Protect the SID circuits

Skrenos wrote:

Mixer and C64 off.  Connect them together.  Turn on Mixer, then turn on C64.

I've read many times "don't turn a mixer ON when c64 is connected" though.  There's a brief spike when you turn it on.

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#20 2007-01-07 20:37:04

Skrenos
Dan Dare
From: South Central Missouri, USA
Registered: 2006-12-22
Posts: 73

Re: Protect the SID circuits

Slorrin wrote:

Skrenos wrote:

Mixer and C64 off.  Connect them together.  Turn on Mixer, then turn on C64.

I've read many times "don't turn a mixer ON when c64 is connected" though.  There's a brief spike when you turn it on.

Yes, but the SID is not energized at that point.

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#21 2007-01-08 07:49:50

Slorrin
PROPHET64 GURU
Registered: 2006-07-09
Posts: 871

Re: Protect the SID circuits

how about disconnecting them?

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#22 2007-01-08 16:59:46

Skrenos
Dan Dare
From: South Central Missouri, USA
Registered: 2006-12-22
Posts: 73

Re: Protect the SID circuits

Turn off the C64 first, turn off the mixer, disconnect.

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#23 2008-08-18 11:53:18

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: Protect the SID circuits

The problem with the SID getting burned is the different potential levels of the zero voltage references of the two systems: Commodore64 and amplifier. If these levels are not equal, a current flows from one system to the other causing problems.

So not even the circuit shown in one of the previous posts may protect 100% the SID. The ground of the 2 systems must be electrically isolated.

The solution I took is a ground loop isolator (see my last 2 posts at http://noname.c64.org/csdb/forums/?room … 4145#58651).



Ready.

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#24 2008-09-21 05:22:14

ergcover
Bloody beginner
Registered: 2008-09-21
Posts: 4

Re: Protect the SID circuits

Do you have to worry about spikes from a mixer frying the SID if you are using the audio out from a commodore monitor into mixer?

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#25 2008-09-22 01:03:46

Ready.
Bomb Jack
Registered: 2007-01-04
Posts: 30

Re: Protect the SID circuits

I really don't know. I still would use the device I suggested as a precaution, after all it's not that expensive, look for "ground loop" on ebay

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