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Okay, i am placing an order for my custom transformers at the moment. I have decided to go with the 400VA 2 X 20V secondaries, potted and shielded etc. Just a couple of questions.
How would i connect up a dual secondary transformer, as there is only one bridge rectifier and the schematic suggests the transformer should have a centre tap?
Also, what size crimp terminals do i need to use on the secondary leads? They will put them on for me at avel for no charge but i just need to know the correct size.
Thankyou
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Rhys, would you mind saying where you are getting your transformers from and for what price? I haven't started looking for suppliers in the UK yet.
Ta.
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I have bought 440VA 22V transformers from avel lindberg for £40 each.
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Rhys, those will work quite nicely.
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Yes, i have decided to go the monoblock option.
By using a single ended input am i not loosing half the output power? (There will also be balanced inputs available.)
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Russ/Brian,
reiterating Rhys' question from the top of this page, what size are the Faston connectors on the board? The parts list only seems to state "2,54/1,1". I assumed these were the dimensions in mm but I couldn't find anything that matched using Google. Can you clarify please.
Thanks.
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rhys h wrote:Yes, i have decided to go the monoblock option.
By using a single ended input am i not loosing half the output power? (There will also be balanced inputs available.) There is a resistor spot which allows you to adjust the gain of the amp. So you won't have to lose any power if you use SE inputs. :)
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sjalloq wrote:Russ/Brian,
reiterating Rhys' question from the top of this page, what size are the Faston connectors on the board? The parts list only seems to state "2,54/1,1". I assumed these were the dimensions in mm but I couldn't find anything that matched using Google. Can you clarify please.
Thanks. I am not really sure what size they are. Maybe Brian can clarify. As far as I know that are just standard size. I have not looked at them in a while. Cheers! Russ
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Will Sympatico work with 18V trannies?
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It probably would work, but I have not tried it.
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Russ, I am using two 400VA 22V secondaries transformers with my Sympatico. Do I need a soft start before the transformers? Or would a slow blow fuse be sufficient to protect the amp and minimise nuisance blowing?
Also, is it necessary to have a capacitor and resistor in parallel to the speakers "to stabilize the output stage by creating a pole that reduces high frequency instabilities" (from LM4780 datasheet)?
Thanks
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No Zobel is required on the outputs. You can add one if you like between the two outputs, but I have never found it necessary at all. If you like you can use a soft start, but I doubt you will need it. I am using two 500VA 24V transformers and have never had a problem popping breakers or anything. Edited by user Thursday, July 1, 2010 7:25:03 PM(UTC)
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The Faston connectors are .25". There is space enough between the power connectors for any gauge, or you can direct wore to the board.
For signal input, I include both faston and a 3-position terminal block (your choice who h to use). Direct wire is available for all positions.
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I do use a slow blow fuse personally. I believe a 4 amp is currently in place. You could actually probably use smaller. I just had those on hand.
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Thanks Russ.
I suppose a speaker protection module is also not needed as start up pop isn't that loud and if there is any DC offset drift, the OPA1632 should correct for it?
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Correct. No such module is needed so long as you don't apply a differential signal at the inputs. :)
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Just curious why 400VA per channel is recommended. It looks like the LM4780 is rated for 120W (2x60W), so it seems like 400VA is quite a bit higher than 120VA. Does the biasing and other losses really require that much extra juice? I was thinking of a 300VA (150VA per channel) amp because it could be fit into a small enclosure. Edit: I guess that spec for the LM4780 is into 8 ohms. Is the larger transformer needed for 4 ohm loads? Edited by user Thursday, September 15, 2011 8:36:54 AM(UTC)
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Ratings are often for constant power. You'll want a reserve for peak power output.
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Would using a single 500VA transformer with dual secondary be ok to power both amp modules (keep the phase at same position on both amps)? Thanks Do Russ, Brian, Can anyone answer that easy question? And why is my status saying newbie after almost 170 posts? Edited by user Wednesday, October 17, 2012 11:14:00 PM(UTC)
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