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MB SID very low output, hanging notes, PSU problems


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Hi there,

so this is it, my first post...

This forum and all the ucapps content have been of great value in understanding and building the mbbox sid project! Thanks to all for that first.

But at the time I'm stuck and haven't found a solution to the problem, so I start this one.

I've build the basic Core-Sid setup for 8580 with pcb core v3 and pcb sid v2. I am using the latest v1.7 engine. with mios v1.9f. all tests passed and as I said I was able to install the sid app. I can change the patches (bankstick installed, lcd responds) via program change. Until here everthing's fine and dandy.

Now here are the issues, which are really seperated from another, I guess.


I can play all patches and they sound ok, BUT all notes are hanging. That means they play in a legato style.

Checked the output of my sequencers and they either issue note-off or note-on with velocity 0. Seems to be ok.

As everything else with MIDI works, I'm a bit confused. Already checked another optocoupler, with same results.

All SID Interconnection Tests pass A OK.


The output volume is very very low. That means I have to crank it up like 70db to hear the sid. Naturally the SNR isn't in the range of usability. But at least I get output

Tried s.th. with a function generator (actually an APC). When I inject the signal of the apc at the point where the sid chip output is it, too, is very very quiet. If I inject the Signal at a later point the signal is loud and clear...

Tried to bridge the output of the sid to tht later point, but to no avail (no sound).

I tested the the transistor and its readings are ok.


An maybe that has something to do with everything else...the PSU. I use the optimized C64 PSU circuit (v2).

I get correct voltage readings, when no IC is inserted and basically my setup works but:

When I power on the PSU nothing happens. I have to detach the SID module from the 14v line and then the core powers on and mios boots. Thereafter I can put in the SID modue supply. So far so good.

As I have many of the c64 psu's I tried several of them and all gave the same result.

Can someone please help with this one? I've been unable to find a matching solution...

Greetings to all midiboxers,


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Note Off issue: MBSID can handle both, Note Off and Note On with velocity 0 - so, it would be interesting if the core really receives all Note Events. I would propose to upload the midimon application, it displays the received events - results?

2 and 3: seem to be related, it sounds like a short on your PCB. The +9V trace is routed around the output amp area - did you already visually check for small soldering clumps, solder bridges, etc.? C3 (1 nF cap) would be one of the candidates which could lower the volume if shortened (or bridged to +9V)

Best Regards, Thorsten.

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Wow, that was fast!

thorsten wrote:

Note Off issue: MBSID can handle both, Note Off and Note On with velocity 0 - so, it would be interesting if the core really receives all Note Events. I would propose to upload the midimon application, it displays the received events - results?

Hello Thorsten,

I've uploaded midimon and used ableton5.2 as sequencer.

When I start the clip, at first it gets 2 times cc123 #0

And the repeatedly note-on #99, and at the end of note-on #0,

So this seems to be fine....

It'll take a bit to check the pcb, back later..


ok, got that ;)

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Hello everyone!

The worst issues ARE SOLVED !!! yipi kay ye!

The sound is loud and clear, and the note-events are doing their thing!


One time I've experimented with a different power supply. That thing ripped

off my pic. It didn't display anything on the lcd anymore (but apart from that worked fine....). I guess that was the point,

when the Voltage Regulator 7809 on the sid v2 pcb was also damaged.

Fortunatly I've made the 7809 pluggable. I tried another one (actually 7808, but hey..)

And that solved both issues: low volume AND the note off problem. (Well if the poor sid doesn't get

enough voltage, it obviously can't pay proper attention)

As Thorsten said, I checked the cap c3 on the sid pcb first, seemed to be ok. Checked the whole area

around the amp circuit, also ok. Changing the 7809 solved it!

But relating to the 3rd problem (see earlier post):

If core and sid pcb are connected to the psu, and I switch the power on, the core won't boot up.

Not even the lcd backlight goes on.... could that be a bad filtering cap? (Measured them, ok).

I've used a graetz bridge from an old c64, will check that also.

btw, I mentioned a funny thing while testing: As I have an isa hardSid, I test my sids there first.

One of them seemed to be totally bend when using the hardsid, but within the mb sid ist worked quite well...

So thanks again,



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