noise on MN3005 circuit

[fogwolf]

This is a question about a synth delay module (Black Time Machine TM2050), but figured I'd post something here since there are probably a lot of people here more familiar with working with BBDs. Anyway, everything is working great except I'm getting crazy noise on the output that I've traced directly 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 Dry/Wet 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, but there's a trimmer for minimizing clock noise, but it makes no difference at all when I turn it. 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 it seems to be otherwise working fine. This sound at all familiar to anyone? I know it's a shot in the dark with no schematic (I only have a hard copy, and that's because the creator doesn't want it distributed, and I respect that) but figured I'd see if I got any hits.

Any help or suggestions greatly appreciated.

[StephenGiles]

If you could let us have a sample of the noise it might be helpful.

[Valentinych]

I think you have bad filtering after BBD.
Check out my scheme (I don't make a secret!): http://www.diystompboxes.com/smfforum/index.php?PHPSESSID=4c833c01af590941360a3d1dd8df5c70&topic=82708.0 .

[StephenGiles]

It would also be helpful to look at the schematic if you are able to scan it.

See my PM.

[fogwolf]

Thanks for the replies!

Stephen, I PMd you. I'll also post some audio tonight.

Valentinych, I think you're totally right. There are 2 filter chips, one at the audio input to help with aliasing problems, and one after the MN3005 to help with clock noise. Since I'm still hearing terrible noise even when adjusting the trimmer for clock noise, it tells me something might be going on around the filter chip for aliasing. The filter chip has a clock to tell it which frequencies to filter, so maybe something is up there. I'll take a look at your schematic too.

Paul

[Mark Hammer]

Is this a "Black" Time Machine, or a Blacet Time Machine?  The latter has some pretty decent filtering, and is a well-tested design, craved by modular synth players all over.

[fogwolf]

Is this a "Black" Time Machine, or a Blacet Time Machine?  The latter has some pretty decent filtering, and is a well-tested design, craved by modular synth players all over.

Oops - yeah, it's a Blacet. Yeah, it uses 2 LTC1063 chips for filtering as well as a compander section.

[StephenGiles]

Is this a "Black" Time Machine, or a Blacet Time Machine?  The latter has some pretty decent filtering, and is a well-tested design, craved by modular synth players all over.

Oops - yeah, it's a Blacet. Yeah, it uses 2 LTC1063 chips for filtering as well as a compander section.

Ah, I have this circuit - will look at it later. I thought it may be the more recent one which uses LM13600/13700 for filtering.

[StephenGiles]

http://muffwiggler.com/forum/viewtopic.php?p=358907&sid=89014866d11addcfdbc3b3c00652f633

There is an ongoing thread about this delay on this site.

[fogwolf]

Is this a "Black" Time Machine, or a Blacet Time Machine?  The latter has some pretty decent filtering, and is a well-tested design, craved by modular synth players all over.

Oops - yeah, it's a Blacet. Yeah, it uses 2 LTC1063 chips for filtering as well as a compander section.

Ah, I have this circuit - will look at it later. I thought it may be the more recent one which uses LM13600/13700 for filtering.

It is the most recent and it does have LM1600s, but for the VCO, not for filtering. The older version had "discrete" filtering rather than ICs (the LTC1063).

Thanks again!

[fogwolf]

http://muffwiggler.com/forum/viewtopic.php?p=358907&sid=89014866d11addcfdbc3b3c00652f633

There is an ongoing thread about this delay on this site.

Yeah, that's me  Like I said, I was casting a wide net initially, since I know stompbox builders might have more BBD experience in general.