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PostPosted: 14 Aug 2016, 05:20 
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Joined: 14 Aug 2016, 05:10
Posts: 2
Location: Australia
HI

I'm looking into a DIY project but I can't seem to find any schematic with the input options I'm chasing so I decided to ask if anyone has heard of one. I'm hoping to find quite a simple circuit.

Requirements:

-Balanced (XLR) line level inputs ( L + R)
-Unbalanced (1/4") line level inputs (L + R)
-RCA inputs (L + R)

I thought it would be a bit simpler to find something but I can only find RCA based amps. The purpose is for a mixer and it doesn't have to be really high powered. With my knowledge of amps, I can only refer to guitar amplifiers, and would need max about 30w. Open to suggestions


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PostPosted: 15 Aug 2016, 05:12 
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Joined: 14 Aug 2016, 05:10
Posts: 2
Location: Australia
Also a relevant question maybe adding inputs on a schematic is the same as adding the extra parts and connectors, essentially just recreating the same thing side by side in series? rendering my question mute?

I just figured there must be something different for each one, not just the same electronics, anyway as you can see I'm new and definitely need the schematics and guides


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PostPosted: 15 Aug 2016, 06:35 
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Joined: 08 Aug 2009, 03:11
Posts: 2225
Location: Chilliwack, BC
Is this for professional or HiFi?

Balanced-to-unbalanced is easy, great CMRR (common mode rejection ratio) is not.

Unless you're doing a 50 foot+ run of cable or have a rediculously electrically-noisy environment (like most places DJ's have to work at each night), a balanced input using an op-amp in differential mode will work. Otherwise you might want to grab a pair of matcher transformers. Those can range from $20/ea. Edcor to $700/pr. vintage Altec Lansing.

For simplicity, look at the input and power amplifer stages as two things. There's thousands of power amp schematics on Google.... from the "Muntzy" one I.C. solution to true "Goldburg" designs using dozens of discrete parts.

The input section can be a simple I.C. or transformer, as mentioned. As for having 1/4", RCA and XLR in one go, that's the easiest part ;)

Cheers!

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-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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PostPosted: 15 Aug 2016, 17:07 
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Joined: 04 Jun 2008, 20:59
Posts: 3749
Location: Arizona, USA
I second the use of matching trannies. Easy to do and if you need phantom power at some point a lot easier than with an IC input.

Good listening
Bruce

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Some of my DIY Tube Amplifier Projects:


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