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 Forum index » DIY Hardware and Software » YuSynth
Stripboard Synthacon Hum
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hoyager



Joined: Feb 16, 2010
Posts: 24
Location: New Zealand

PostPosted: Mon Apr 23, 2012 6:24 pm    Post subject: Stripboard Synthacon Hum Reply with quote  Mark this post and the followings unread

Would anyone know if this was a normal level of hum?



Its the yusynth version, with the multiple inputs.

Input amp is set to be hot for overdriving.

Its def coming from the filter, because when the inputs are turned down...

I've wired the grounds to the dc jack, and its being powered by 9v through an LT1054 as bipolar output, putting at -15.5 and +16.2 ish.

All ground points are within 1mv from each other.

I Changed the 680n to a polar 0.1uf which seems to make it a little quieter.

I read about someone putting a trimpot at the junction of both the 2.2k's and the 1k coming from the positive supply. Would this help eliminate the hum?

Could it be the layout is too tight and the bits are just too close to each other?

Andy


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Uncle Krunkus
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PostPosted: Mon Apr 23, 2012 6:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

My gut reaction is the PSU. Maybe deriving the +15v/-15v rails from a +9v rail is just too noisy?
Try running it temporarily on 2 * 9V batteries, and see what the hum level does.

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hoyager



Joined: Feb 16, 2010
Posts: 24
Location: New Zealand

PostPosted: Mon Apr 23, 2012 6:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok thanks

I've used the psu with a few MS20 filters though, which when wiring the grounds to the jack seems to eliminate any hum / noise.

There are 100uf's and zeners on the psu rails and 100n's on the board

The circuit feels very live, the diodes don't like being touched and a few of the caps react too. The hum does go away if I touch the res pot, but when its grounded its the same.

R13 and the res pot on yusynths discrete version are 22k, while on the CA3096 version they're both 2.2k. That wouldn't be wrong would it?


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hoyager



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PostPosted: Tue Apr 24, 2012 4:35 am    Post subject: Reply with quote  Mark this post and the followings unread

I though I should add that the transistors aren't matched, am using bc547's.

It definitely works but would matching them ease the hum?

Andy
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Uncle Krunkus
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PostPosted: Tue Apr 24, 2012 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm not sure.
If they're part of an exponential converter for 1V/Oct tracking, then I don't think it would make a difference. But if they are somehow inside the VCF, as resonance gates etc, then they might create a hum problem.

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yusynth



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PostPosted: Thu Apr 26, 2012 12:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Hum can come from missing connections to the circuit ground (0V), long un-shielded input and output wires, a poorly filtered PSU (have you tried with batteries as suggested by Uncle Krunkus), capacitance problem between stripboard tracks.
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