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problem with blacet time machine build
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numbertalk



Joined: May 05, 2008
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PostPosted: Tue Apr 05, 2011 6:08 pm    Post subject: problem with blacet time machine build Reply with quote  Mark this post and the followings unread

I just finished building the larger Rev B PCB. Everything is working great except I'm getting crazy noise on the output that I've traced to the outputs MN3005. It's a cross between a high squealing oscillation sound and noise. It varies a bit with turning the Delay knob. At first I thought that there must be noise coming into the audio signal after the dry signal is tapped out (there is no noise when the mix knob is totally at "Dry") but I just tracked it down and it doesn't show up until the output pins of the MN3005. I thought it might be clock noise, since the docs mention RT3 is for minimizing clock noise, but it makes no difference at all when I turn RT3. What I'm hearing must be way beyond any kind of acceptable clock noise and I'm not even sure what I'm hearing would fit that description anyway. Otherwise I do get delayed signal from the module and was able to calibrate all the other trimmers. One interesting thing I noticed is that if I trim RT5 such that nothing passes through the delay channel, the noise stops. I was surprised by this, since my troubleshooting has been with no input anyway. Once I trim RT5 to pass signal through U10 the noise shows back up, even though the signal is silent on the input pin of the MN3005.

Any help or suggestions greatly appreciated.
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whomper



Joined: Dec 15, 2007
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PostPosted: Fri Oct 14, 2011 1:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, I have the same issue over here.

Where you able to fix the issue? I am experiencing the same issues with a relatively high noise level and RT3 makes no difference.

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diablojoy



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PostPosted: Fri Oct 14, 2011 10:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I got something similar sounding when testing a bunch of mn3005's in a time machine
occasionally i would get one that squealed like a stuck pig
try reseating the chip in the socket as they all seem generally to be a little on the loose side , that seemed to sort mine out they all worked fine in the end.

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whomper



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PostPosted: Sat Oct 15, 2011 12:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Diablojoy,

Have switched between the two mn3005 I have in stock and both exhibit the same issue.

As the noise is composed of hiss and some high pitched tone that changes based on the delay pot, so as I turn the Delay pot, the pitched sound change its tone and the hiss sound gets filtered accordingly, but still present in the out signal (this is without anything on the in jack).

Perhaps the filter or multiplier aren't performing as they should.

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diablojoy



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PostPosted: Sat Oct 15, 2011 6:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

hmm the symptoms sound the same as i was getting
but that is not to say something different is occurring
the filter is only designed to take out the clock noise really
so it only works in narrowish band around the clock freq
I can only guess but i dont think it is clock noise you are hearing
if the filter was not performing at all you would not be hearing
any marked difference in the frequency of the noise
same thing goes for the multiplier so they are both working to a point
although the freq could still be off coming from the multiplier
you would need to compare the ratio of the clock freq and the filter freq
to see if it is correct I hope this is right been a while since i looked at the schematic for this
perhaps check your soldering around the mn3005 socket and
maybe reflow the socket pins themselves
beyond those suggestions perhaps post an audio of the the problem
a scope shot of the mn3005 output pre filter / post filter
and you could also try blacet support themselves
I imagine they will have some suggestions so worth a call

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whomper



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PostPosted: Sun Oct 16, 2011 12:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's a link to an audio file that has me sweep from the biggest delay setting down to the lowest one via the Delay pot and back again.

No input signal is present, Mix pot at its top most setting (internal only), Depth at zero.

Recording level is high to focus on the noise versus to demonstrate S/N.

As I am not owning a scope, can't really post any picture of it. Are there any other checks that I can perform with a DMM perhaps?

MN3005 where sourced from Small Bear, so I guess they should be ok.

Will reflow the area around the MN3005.


Audio 1_01.mp3
 Description:

Download
 Filename:  Audio 1_01.mp3
 Filesize:  690.34 KB
 Downloaded:  204 Time(s)


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StephenGiles



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PostPosted: Sun Oct 16, 2011 7:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like heterodyning, usually caused by poor layout and ground lines where only 1 BBD is in the circuit. Might just as well build on veroboard!!!
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diablojoy



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PostPosted: Sun Oct 16, 2011 2:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

yes it does sound exactly like what i heard from some of my chips
I tested 8 of which about half exhibited that first up but all of mine cleared up with reseating the chips
whilst not the quietest echo unit going around you should not be getting
those sort of noises from it , my build is fine now
I posted a mp3 of mine on the time machine topic a few months ago
so thats what it should sound like to compare
try the reflowing the socket and then reseating the mn3005
also try cycle the power a couple of times after
if none of that works try contacting blacet
it gets a little difficult to go further without a scope
good luck

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StephenGiles



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PostPosted: Thu Oct 20, 2011 10:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Presumably all problems sorted out - I did PM.
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diablojoy



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PostPosted: Thu Oct 20, 2011 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

dont know about numbertalk but whomper still has problems with his.
the freq whine in the background is clock noise and should be
able to be adjusted out mostly, however the crackling hissy stuff after the 13 second point is definitely not and shouldn't be there and sounds like a resistive join in the audio path if it is appearing at the output of the mn3005 and not before that is the most likely place to look
I probably shouldn't suggest this but maybe as a last resort try changing the socket or do away with the socket and solder the mn3005 directly
I used a machined socket and to be honest most of my chips did not fit snugly at all, [ the ones i had real problems with were all very loose
ie i could pull the chips out with my fingers with almost no effort ]
[ wrist strap on of course ]
whomper try feeding in a signal if you can get any echo happening its not
a faulty mn3005

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StephenGiles



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PostPosted: Fri Oct 21, 2011 3:00 am    Post subject: Reply with quote  Mark this post and the followings unread

"I probably shouldn't suggest this but maybe as a last resort try changing the socket or do away with the socket and solder the mn3005 directly"

Good suggestion, I have done this in the past and successfully desoldered them again.
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StephenGiles



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PostPosted: Sat Oct 22, 2011 2:26 am    Post subject: Reply with quote  Mark this post and the followings unread

I find it extremely rude when having sent a PM with an offer of help on this, the recipient cannot be bothered to reply.
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numbertalk



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PostPosted: Sat Oct 22, 2011 8:47 am    Post subject: Reply with quote  Mark this post and the followings unread

StephenGiles wrote:
I find it extremely rude when having sent a PM with an offer of help on this, the recipient cannot be bothered to reply.


Are you talking about me? Good lord. Would you look at the date of my last post here? I'm in the middle of moving my family across country, buying a house, starting a new job and my wife is pregnant with our second child. Keep perspective and save the drama please.

If not talking about me please disregard.
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StephenGiles



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PostPosted: Sat Oct 22, 2011 1:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

numbertalk wrote:
StephenGiles wrote:
I find it extremely rude when having sent a PM with an offer of help on this, the recipient cannot be bothered to reply.


Are you talking about me? Good lord. Would you look at the date of my last post here? I'm in the middle of moving my family across country, buying a house, starting a new job and my wife is pregnant with our second child. Keep perspective and save the drama please.

If not talking about me please disregard.


My apologies, wasn't to know - my goodness you have far more important things to worry about right now. I hope everything works out for your goodself and your wife.
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numbertalk



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PostPosted: Sat Oct 22, 2011 2:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

No worries. Thanks for the offer of help but yeah, been away from my gear for months now, and even longer from my bench and iron.

I think I got my Time Machine to a point where it was acceptable but I still think it could be better. I emailed with Dave Brown about it a lot when I hadn't gotten a response here back in April and he ultimately seemed to think it sounded ok. When I get back up and running I'll give it a listen and jump back in here but now sure when that'll be.
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numbertalk



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PostPosted: Sat Oct 22, 2011 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

And whomper though I haven't listened to your audio file yet what you describe sounds like exactly what I was struggling with. Please report back if you figure it out.
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whomper



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PostPosted: Sat Oct 29, 2011 12:33 am    Post subject: Reply with quote  Mark this post and the followings unread

diablojoy wrote:

whomper try feeding in a signal if you can get any echo happening its not
a faulty mn3005


Feeding a signal in resulting in a delayed sound. The mix pot is at 6 O'clock and the delayed sound is comfortably heard. Along with it is that dreaded noise that my previous audio recording demonstrates, but at a level that is faintly heard.

Could not get a clean sound out of the unit.

Perhaps I should tune the last stage filter. What should I change in order to make the filter cut off earlier?

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diablojoy



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PostPosted: Sat Oct 29, 2011 12:44 am    Post subject: Reply with quote  Mark this post and the followings unread

whomper try running through the full trimming procedure again with a signal in
you should be able to reduce at least some aspects of the noise but if you are still getting that hissy crackly noise then it is down to a resistive connection somewhere in the audio path
either a loose pin or a cold solder joint

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whomper



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PostPosted: Sat Oct 29, 2011 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks diablojoy, I will probably need to check component values as well as resolder the board.

Will get to that this week and see how it will fair.

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StephenGiles



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PostPosted: Sat Oct 29, 2011 2:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Does this unit have a compander?
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diablojoy



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PostPosted: Sat Oct 29, 2011 9:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

yes there is , the compander is made up from 2 sections of an SSM2164
my build notes also suggest that
low level 1 volt input signals should be amplified prior to around 10 volt peak to peak for optimum noise performance
there is also a trimmer RT4 to reduce clipping for higher signal levels
around 15 volts peak to peak
there is also a calibration procedure to go through and you really do need to follow it correctly

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