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 Forum index » DIY Hardware and Software » YuSynth
noise and crackle in the minimoog filter!
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cloudberry



Joined: Jun 30, 2009
Posts: 51
Location: uk

PostPosted: Tue Dec 29, 2009 4:17 pm    Post subject: noise and crackle in the minimoog filter! Reply with quote  Mark this post and the followings unread

Hiya.


I've finally got around to testing the minimoog filter. However, while it is behaving as it should, it is very noisy and there's a constant crackling going on as well. In addition it's picking up noise from the computer nearby. I should add that it's not in a case yet. Even with the computer off it's still very noisy and crackly.
When I was building it I had to change the four caps on the ladder, and it's a bit of a mess. Also one of the transistor pairs may have been overheated (I'm using ssm2210s). Would a damaged transistor pair and/or poor connections with the caps cause all this noise and crackle I'm getting?

thanks,

Cloudberry.
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cloudberry



Joined: Jun 30, 2009
Posts: 51
Location: uk

PostPosted: Wed Dec 30, 2009 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Some success!

I swapped the 2 ca3046 arrays around, and the crackling went.(?) I also damaged a couple of pins Sad. I've read Mr. Yusson mentioning that some of these chips are substandard (http://forum.yusynth.net/topic-15.html&highlight=ca3046), though mine are marked Singapore, not Malaya. I'll try and get some Intersil ones.
Still quite hissy, and mains hummy. But perhaps I'll wait until I've got a proper rack for it before I go hunting for earthing problems.
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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Wed Dec 30, 2009 4:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes the quality of the CA3046 is important but not really involved in the crackling you hear. I would first check the quality of the solder joints (they must smooth and shiny). Then I would check the quality of the power supply too. Make yourself sure that you use a linear power supply not a chopped one.
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Yves

Last edited by yusynth on Tue Apr 20, 2010 11:39 am; edited 1 time in total
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cloudberry



Joined: Jun 30, 2009
Posts: 51
Location: uk

PostPosted: Wed Dec 30, 2009 6:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the reply.

I think I'll remove the 3046 sockets and do them again. And check the rest too. Lead free solder didn't help (drove me mad! - even with a tinned tip it took ages to melt, and is very bad for tinning). I've found the leaded stuff much easier to work with.
The psu should be alright (it is linear).
It's quite frustrating, as in spite of all of this I can hear the character of the filter and it's rather lovely!

I'll get there.....
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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Thu Dec 31, 2009 3:14 am    Post subject: Reply with quote  Mark this post and the followings unread

cloudberry wrote:
Lead free solder didn't help (drove me mad! - even with a tinned tip it took ages to melt, and is very bad for tinning). I've found the leaded stuff much easier to work with.

Yes I use leaded solder too, easier to work with and easier to troubleshoot too.

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Aottens



Joined: Mar 14, 2010
Posts: 33
Location: The Netherlands

PostPosted: Tue Apr 20, 2010 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I just got my Minimoog VCF finished (half an hour ago), and I love it. I used 2 CA3046 from Harris, guess that's intersil as well. I've also got some problems with crackle sounds. If I use a Sine wave than the sounds starts to crackle if I open up my emphasis pot and the cutoff frequency potentiometer. Maybe I did the last step off the trimming wrong. I don't really know what the filter is meant to do when its self oscillating. How do I find out? If someone awnsers this please tell me the connections which I need to make when I'm going to calibrate this filter again. Thanks.
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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Tue Apr 20, 2010 11:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Aottens wrote:
I just got my Minimoog VCF finished (half an hour ago), and I love it. I used 2 CA3046 from Harris, guess that's intersil as well. I've also got some problems with crackle sounds. If I use a Sine wave than the sounds starts to crackle if I open up my emphasis pot and the cutoff frequency potentiometer. Maybe I did the last step off the trimming wrong. I don't really know what the filter is meant to do when its self oscillating. How do I find out? If someone awnsers this please tell me the connections which I need to make when I'm going to calibrate this filter again. Thanks.


What do you mean by crackle sounds ?
What is the level of the signal (by the way are you using a sinewave with a flter ?) you input in the filter ? What is the level at the output ?
What type of power supply are you using to power the module ?

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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Tue Apr 20, 2010 11:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Have you connected the ground between the sinewave source and the ground of the filter ?
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Aottens



Joined: Mar 14, 2010
Posts: 33
Location: The Netherlands

PostPosted: Tue Apr 20, 2010 11:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
What do you mean by crackle sounds ?

Crackle sounds as in noise, it is sounding a little noisy when I have the potentiometers for cutoff and emphasis all the way turned clockwise. And at one point somewhere in between for the cutoff pot.

Quote:
What is the level of the signal (by the way are you using a sinewave with a flter ?) you input in the filter ? What is the level at the output ?

I don't know exactly, the sinewave is coming from your oscillator. The one with the matched BC547's. And is going in the input #1 of the filter. Level at output? don't know exactly but at some points it's louder than the input.

Quote:
What type of power supply are you using to power the module ?

I'm using a linear type of power supply. A real simple one. But it's working quite good I think.

Quote:
Have you connected the ground between the sinewave source and the ground of the filter ?


I guess so. If you mean the ground from the power source? Then yes. I've got a power supply, and attached to it is a power distribution board. These are all parallel onto each other. So there is one ground as far as I know.
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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Tue Apr 20, 2010 11:43 am    Post subject: Reply with quote  Mark this post and the followings unread

I did not note the fact that the emphasis was set to maximum. That is the filter is probably auto-oscillating in the ultra-sound domain and this may be causing the crackling you ear by saturation of the output stage. Have you an oscilloscope (a true one, not a sound card + software) to check that out ?

Still I don't understand why you are feeding a sinewave to the filter ?

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Aottens



Joined: Mar 14, 2010
Posts: 33
Location: The Netherlands

PostPosted: Tue Apr 20, 2010 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ooh right. Didn't know that your not supposed to feed a sinewave through a filter. Well, I actually did know it because it's substracrive ofcourse. I fed a square and saw through and the noise was a lot less. I think I have trimmed it wrong also. The v/oct is good. Checked the mV and those are right. Then you have to do the mute thing. (that's why I fed a sine through it I guess). And then you have to do the thing with the emphasis. I think this is the part that I'm doing wrong. The position off the emphasis pot needs to be 95% cw like in the trimming instructions. But I don't know the posistion of the freq pot. Maybe that's it.
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cloudberry



Joined: Jun 30, 2009
Posts: 51
Location: uk

PostPosted: Tue Jun 01, 2010 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Groan. This is proving a pain.
I've replaced the CA3046s, and replaced the sockets. Crackle gone!
However, still much noise and hum. So I've resoldered all the caps. Probably because of prodding things with my finger, it's now sounding very distorted, when it works....
It seems that (when it does work) there's no hum (but still noise) with the filter open with no resonance, but turning the resonance up makes the hum audible. With the filter closed and no resonance there is some hum (?).
It seems to me that the resonance circuit is just magnifying whatever hum is already there.

The power supply is this one: http://gb.mouser.com/ProductDetail/International-Power/IHAD15-04/?qs=0xCm9DOQnC6xCpeYcfqucA%3d%3d

I'm gonna try and setup my oscilloscope to see if I can see any ripple on the psu.

I'm thinking this wasn't perhaps the best 'starter' project. Ambition is good sometimes....
..but perhaps it might be best to start over with this one.
...But while all of this has been going on I've built the Oakley EFG deluxe (envelope follower) and Little LFO, which seem to work fine. I can't get any hum out of the LFO, but there's a small amount on the preamp output of the EFG when the gain is at maximum.

Any thoughts?
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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Tue Jun 01, 2010 11:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi cloudberry
Your PSU looks alright.
I suppose that you checked that all 0V are connected together (PSU, module, source and output amplifier).
From the reading of the firsts posts I gather that you built the bridechamber kit (using SSM2210 is the signature).
Have you checked that these dual trannies were not damaged ? You can make a simple test if you have spare BC547 or BC550 at hand. Remove one of SSM2210 and replace it with a pair of BC547 or BC550 and install them in the socket as shown on the component layout diagram at my site.
Check how the module works if there is a sounding improvement then the SSM2210 may have been destroyed. Test the three SSM2210 the same way.

Cheers

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cloudberry



Joined: Jun 30, 2009
Posts: 51
Location: uk

PostPosted: Sun Jun 06, 2010 8:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Mr. Yusynth

Thanks for the reply. Yes it's a pcb from Bridechamber. I'll check the ladder.
If the chassis is anodized, it's possible it's not properly grounded, so that needs checking too. As for the rest of the grounding, I've got the chassis ground and 0V on the output of the transformer grounded at mains input. The speaker and amp I've been using is just a small battery powered job.
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