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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 19th September 2011, 10:06 PM   #1
n0nspaz is offline n0nspaz  United States
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Default 8-channel stereo line level switch

Greetings all

I am tweaking this design for a simple passive switchbox that offers selection between 8 balanced stereo line-level studio signals (mostly synthesizer outputs) going into a ADC/audio interface.

My experience is mostly in building a modular synthesizer and various project studio line preamps etc.

Can i expect signal quality to remain pristine? Crosstalk?
Is there a better way, without going active/relay ?
Any suggestions?

Thanks and happy DIYing
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Old 21st September 2011, 03:43 PM   #2
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Your design is good. Crosstalk will be determined by the interconnect wiring. I would add high ohmic (>100k) resistors an all I/O terminals to discharge any static. E
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Old 22nd September 2011, 07:10 PM   #3
n0nspaz is offline n0nspaz  United States
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thanks. where would you put 100k resistors, i am thinking from every tip & ring input to ground? (or output perhaps?)
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Old 22nd September 2011, 10:42 PM   #4
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T+R to G, inputs only. The outs are not switched. E
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Old 25th September 2011, 12:48 AM   #5
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If these are all balanced circuits, then the signals are only between the tips and rings. The sleeves are not part or the audio signal circuit and should only be connected to the chassis. Putting resistors from the Tips & Rings to the chassis is not a good idea.
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Old 25th September 2011, 01:54 AM   #6
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Quote:
Originally Posted by Speedskater View Post
If these are all balanced circuits, then the signals are only between the tips and rings. The sleeves are not part or the audio signal circuit and should only be connected to the chassis. Putting resistors from the Tips & Rings to the chassis is not a good idea.
Don't confuse balanced with floating
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Old 29th September 2011, 09:42 PM   #7
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the advice from Jensen Transformers was that joining grounds at the inputs would allow any noise in one ground to infect the others. However, one of their app notes shows a single-input ground being tied to chassis. Joining different inputs' ground signals, however seems to be a different story. Makes sense to me. Thanks to everyone here and to the great guys at Jensen!
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Old 30th September 2011, 11:32 PM   #8
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With balanced interconnects, the shield is not part of the audio circuit! The shield should not be connected to the audio ground. The shield should be only connected to the chassis at the cable's connector.

The circuit audio ground may be connected to the chassis at one designated point. But this is a point not all the audio connectors.
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Old 4th October 2011, 09:50 PM   #9
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No, you're referring specifically to a floating differential circuit. A balanced line may or may not be floated. I could send a signal on the 'hot' line and tie the 'cold' line to ground via a resistance equal to the hot's source, or indeed I could feed both hot and cold out as currents and tie them both independently to ground via equal resistors to develop a voltage to feed in to a differential voltage amp. Both of these are truly balanced. I'm not suggesting they would necessarily perform as well as each other with respect to common mode noise rejection, just trying to clarify what is balanced.

Last edited by pindrop; 4th October 2011 at 09:55 PM.
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