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Forum Index : Microcontroller and PC projects : Balanced line driver/receiver...
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
Hi folks. 
Does anyone know of a circuit for a balanced line driver? This is the thing that converts an unbalanced audio signal, to a balanced one, so you can squirt the audio over a reasonable length of cable without hum problems. The receiver at the other end is just the same thing as the driver, but used in reverse -it combines the balanced line back to unbalanced. Audio transformers have been used like this for years, but I think you can get better performance out of an op-amp based design, from what I remember reading... Anyone got any links? I will hunt the net now anyway, and see what I can find. Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
ADDITIONAL: I have found various options on Element-14, such as DRV134/INA134(or INA137) driver/receiver pair. I think I will give these a try, as they are reasonably priced, and designed specifically for what I want to do, meaning I only need a minimal PCB to use the likes of this pair out of the box, so to speak... DRV134 is NZ$9.35 INA134 or INA137 is NZ$5.05 The DRV134 has 6dB gain. Using it with the INA134 will give 6dB gain, or using with INA137 will give 0dB gain. I will probably use the 137, as I don't really need any gain, as the line is driven from a 19" rack-mount compressor/limiter unit, so don't really need any inherent gain in the link. If anyone else has anything else for me to consider, please post, otherwise I will orger some of these next week, and design two small PCB's for both ends. Smoke makes things work. When the smoke gets out, it stops! |
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palcal Guru  Joined: 12/10/2011 Location: AustraliaPosts: 1873 |
Silicon Chip Mag. had a project in the June 2008 issue that would suit your purpose. I have the issue and can email the article to you if you want. Send me a PM with your email address. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| cwilt Senior Member  Joined: 20/03/2012 Location: United StatesPosts: 147 |
Look here. |
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| VK2MCT Senior Member Joined: 30/03/2012 Location: AustraliaPosts: 120 |
Grogster, From memory one needs both + and - power supplies for chips to send to 'balanced lines'. For resonable headroom at least +- 15 is needed I think. But this does depend on whether you need to send 'broadcast' type levels. What is the model/brand of the compressor/limiter & what level does it send - type of connector used. How long will the cable be? John B VK2MCT |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
I am already using a home-made balanced line, which just consists of 3k:3k audio coupling transformers available from Jaycar. CT of the secondary becomes the common line between each end of the link, and this is working fine, with no noise at all. :) I am just looking at a more electronic method, as I understand that audio transformers tend to give sub-standard performance these days. It feels like the link lacks bass response over a standard cable link, but a standard cable hums, so that is no good. Compressor/limiter is Alto ACL2 rack-mount unit. This unit has both unbalanced and balanced outputs on the rear panel. I could use the balanced outputs, but I would still need something to convert that back to unbalanced at the other end of the link, as the device I am feeding does not have balanced inputs. The chips I was looking at use +- PSU, 18v max, and I was planning to feed them from 7812 and 7912 regulators. At this stage, not sure if I will even bother, as the transformer link is working fine, albeit with what appears to be a little lacking low-end performance. Still chewing over ideas at this stage. Smoke makes things work. When the smoke gets out, it stops! |
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| VK2MCT Senior Member Joined: 30/03/2012 Location: AustraliaPosts: 120 |
Hum!, Checked jaycar and the current! 3k:3k transformer freq response is 2.5 db down at 300hz & 3Khz, hardly hifi (not even lofi really) but explains the lack of bass. (eek, there are 2 in series). Jaycar have a balanced to unbalanced kit - $32. John B |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
Ahh - great - progress.
I remember asking Jaycar about that kit, which is the SC kit, and was told it was discontinued, and they could not get me any. ...unless I am thinking of a different kit - can you please post the Jaycar code, and I will follow it up again. I kinda am now motivated enough(based on your comments about the transformers), to have a go at building my own electronic link, using those line driver/receiver chips. I would expect that the price of these + a couple of homebake PCB's would probably be the same or less then a couple of the Jaycar kits. I will go one way or the other, and let the thread know the results. If I make my own link using the line driver/receiver IC's, would anyone here be interested in my posting the PCB files? I could put them in a ZIP as gerbers... Smoke makes things work. When the smoke gets out, it stops! |
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| VK2MCT Senior Member Joined: 30/03/2012 Location: AustraliaPosts: 120 |
Bal to unbal kits seem to be: http://www.jaycar.com.au/productView.asp?ID=KC5468 $33 & http://www.altronics.com.au/index.asp?area=item&id=K5522 $23 on special Looks like a kit can be cut in half to make a Tx & Rx. Or source end could use the balanced op of the comp/lim. John B. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
I have decided that "Why reinvent the wheel?" I will get a couple of those kits linked to by VK2MCT. Proven design, will work out of the box.  Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9308 |
ADDITIONAL: Jaycar say that code is discontinued, so will get them from Altronics - cheaper anyway. Odd that Jaycar still list the kit, and it is not marked as being discontinued on their website - I drew their attention to that, but weather it gets followed up on...Smoke makes things work. When the smoke gets out, it stops! |
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