All systems go!

[Lo-Fi_Massahkah]

Jausa!

I made it... I posted last weekend (in this thread) moaning about how I couldn't get started on my MBSID although I had all the parts lying beneath my desk. Well, here it is! Thanks for kicking me in the right direction!

It runs pretty cool, sounds very cool, but has a significant ground hum. I'll try and get to terms with that! Well if you have a solution - don't be shy!

Cheers,

Mikael

[jdutcher]

my midibox sid has a problem with ground hum also.  sorry to hijack your thread, mikael...but if we both have ground hum, i wonder if this is a common problem for midibox sid builders.  does anyone know of a solution?  as far as i can tell (i've double-checked), i don't have any ground loops in my circuit.

[smashtv]

Give me the specs on your power supplies/transformers, Voltage, current rating, AC or DC output, etc.

Disconnect the ground wire between SID out and preamp temporarily and note the change in sound.  If the hum goes away completely you can use an isolation transformer to kill the hum and have a great fat sound.....More on this later as I mash various transformers onto my favorite SID  ;)

Don't leave it wired with just the positive audio lead, as this will give bad sound also......

What are you guys plugging the SID into? preamp? mixer channel? make/model?

Be specific so I can re-create this here please.....

Best

Smash

[Lo-Fi_Massahkah]

Smash,

I'm running a 15V/500mA AC wallwart adaptor to power both the CORE and the SID. The SID out is plugged into a Behringer UB1622FX mixer on channel 1 (mic-amp not active).

The problem here is that I'm a complete novice when it comes to electronics. Building this has been like building LEGO. I just follow the schematics, but I have no clue as to what goes on. So when you say:

Disconnect the ground wire between SID out and preamp temporarily and note the change in sound.  If the hum goes away completely you can use an isolation transformer to kill the hum and have a great fat sound..... Don't leave it wired with just the positive audio lead, as this will give bad sound also......

...I really don't understand!  :-[

But I'd be very thankfull if you'd guide me through this.

Regards,

Mikael

[moebius]

Hi,

Remember that 6851s S/N is around 65dB, wasn't it?!

That said, Smash is referring to the practice of "ground lifting". This means cutting or otherwise disabling ground contact from one side of the signal cable (SID audio out in this case). It's an easy check for the ground loops.

Basicly AC wallwart should not create these problems.. but maybe midi cabling? (Some professionally engineered :P commercial gear don't follow the midi specification)

Bye, Moebius

[smashtv]

Heya Mikael!

Sorry about the lack of specifics on that post....

You have two connections that make up the SID audio out, one ground and one positive.

Temporarily disconnect the ground wire, leave the positive wire connected, and see if your hum changes or goes away.

If it goes away completely you have a ground potential mismatch (ground loop!) that can be easily corrected with an isolation transformer.

Ground lifting is an old soundman trick for finding loops/hum in sound reinforcement rigs......

Best

SmashTV

[smashtv]

Whoop Moebius beat me to the reply button!

:P

SID= Sound Is Dirty?  ;D

As noisy as they are, that nasty S/N ratio should not include a few db of hummmm...... ;)

Best

Smash

[Lo-Fi_Massahkah]

Thanks guys!

You have two connections that make up the SID audio out, one ground and one positive.

Temporarily disconnect the ground wire, leave the positive wire connected, and see if your hum changes or goes away.

If it goes away completely you have a ground potential mismatch (ground loop!) that can be easily corrected with an isolation transformer.

OK, bare with me... I have a simple tele female connected to the SID-out.

When connecting the tip to the positive, I get a (seemingly) noisier output, but no hum and a weak (high pass-like) sound from the synth.

When connecting the ring to the positive, I get a almost silent output. No noise. No synth.

When connecting the tip to ground, I get the noise again, but no hum. Only weak clicks from the synth.

When connecting the ring to ground, I get a almost silent output. No noise. No synth.

...by the way... What is an isolation transformer.

Thanks - you've been really helpfull!  :)

Kind regards,

Mikael

[cheater]

Hi,

Remember that 6851s S/N is around 65dB, wasn't it?!

That said, Smash is referring to the practice of "ground lifting". This means cutting or otherwise disabling ground contact from one side of the signal cable (SID audio out in this case). It's an easy check for the ground loops.

Basicly AC wallwart should not create these problems.. but maybe midi cabling? (Some professionally engineered :P commercial gear don't follow the midi specification)

Bye, Moebius

All midi cables at the studio I work in that I haven't made myself have all 5 pins connected! Meaning 5 wires!!

[moebius]

All midi cables at the studio I work in that I haven't made myself have all 5 pins connected! Meaning 5 wires!!

But that's ok. It's only if midi devices use pins that are not supposed to be connected, where the troubles starts..

And I have to take all back that "professionally engineered..." stuff. I re-run tests and everything pro passed - But the worst noise maker (dirties (switcher) powersupply) in my studio: the computer. It has ground connection on the middle pin on both, midi in / out ports. ::)

I could do with some isolation transformers myself :P

Isolation transformer: A device used to create galvanic isolation between two circuits - 1:1 ratio :D

or it's transformer that passes AC signals thru (without metal to metal contact) between the circuits.

I think nobody makes sense of that - but as Smash is more knowledgeable about this stuff, I guess he'll try to explain it in better words ;)

Bye, Moebius

[smashtv]

I guess he'll try to explain it in better words ;)

Try is the key word here, maybe this link can do better:

http://www.epanorama.net/circuits/audio_isolator.html has specific info about isolation as it relates to us.

In the real world I use a few custom made panels with Jensen transformers and connectors mounted for isolation between the FOH/monitor/recording consoles......Each one of these transformers cost several times the price of a complete core+sid, so that's not an option here but at least I know what a SID with iron in the output should sound like done right....... ;)

So far the http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=270-054 Radio Shack ground loop isolator sounds fine, but I have not yet correctly tested response.....

I have a couple of ebtech boxes, sescom, etc. plus some other random transformers in Dallas with the rest of the sound equipment, so I'll grab those up for testing on my next trip.  I'm looking for mutually exclusive things with this, cheap -and- good.  More info as I tinker further.....

Best

Smash

[Lo-Fi_Massahkah]

Thanks everyone!

I'll try to get everything sounding a bit less hummy...

Have a good weekend,

Mikael

[Lo-Fi_Massahkah]

Well, I went down the easy route - I just cut the lo EQ on my mixer. Gets rid of most of the hum. But then I hear a high pitched sound, very vaguely, but it's there. It also seems to follow the pitch of what I played last. Alas it's in tune with the SID. What?!?!  :o ???

Cheers,

Mikael

[moebius]

HI,

As annoying as that sound is.. it's the part of the deal, so called SID bug: http://69.56.171.55/~midibox/forum/index.php?topic=2476.msg16394#msg16394

Bye, Moebius

[Lo-Fi_Massahkah]

Thanks Moebius,

Annoying, but at least I didn't do anything wrong...  :D

/Mikael

[TK.]

Hi,

some experiences I made: the audio ground and the J2:Vs/Vd inputs should be directly connected to J2.

I just have noticed that this change was not part of the http://www.ucapps.de/mbhp/mbhp_sid_c64_psu.pdf diagram yet (corrected)

Best results can be achieved with the optimized circuit for the original C64 PSU - see also http://www.ucapps.de/mbhp/mbhp_4xsid_c64_psu_optimized.pdf

As already mentioned another possible issue is the ground of your MIDI cable. Just unplug the cables and check if the buzz is still there. If this helps, remove the ground connection at J12 of the core module. This ground connection is according to the MIDI spec, but if the MIDI In of your MIDI interface is also connected to ground (which violates the spec), then you will have a ground loop

Best Regards, Thorsten.

[Lo-Fi_Massahkah]

Thanks Torsten,

I'll continue my quest for optimal sound with your clues in mind...

/Mikael