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Old 16th October 2006, 11:43 PM   #1
zenon is offline zenon  Canada
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Default Use two Transformers per chip amp?

Is it possible to wire two seperate transformers to run one chip amp? For example, I would like to use two Hammond 167V22 transformers.
http://www.hammondmfg.com/167.htm

so I would wire one transofrmer to the +'ve rail and the 2nd to the -'ve rail.

Would the VA rating be 880?
22*20*2=880VA

What negative effects would I experience using non-torodial transformers? I beleive that they emit more EMF. I would be mounting these on a decorative panel to show off the transformers and wire 22VAC into the amp so the actual amp would be far away from the transformers.

I lied up there, I won't be connecting one amp, I will actually be connecting four LM4780's... but for illustration sake pretend there's just one amp and a gigantic VA reserve! :-o

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Old 17th October 2006, 01:47 AM   #2
Leolabs is offline Leolabs  Malaysia
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Want to run in parallel or series???
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Old 17th October 2006, 02:00 AM   #3
zenon is offline zenon  Canada
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I would like to wire them in parallel.
So if you look @ the bottom of the Hammond site.. I would connect the Green and green of one transformer to the two AC1 leads and both the Green leads of the 2nd transformer to the pair of AC2 leads.

http://audiosector.com/lm4780%20psu.pdf
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Old 17th October 2006, 08:39 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
22Vac centre tapped usually means 11-0-11 not 22-0-22.

Check with Hammond what they are selling.

There is nothing wrong with connecting two or more transformers in parallel. I would put a correctly rated fuse in the primary feed to each one.

If the transformers are identical then you can also parallel the secondaries. But this is not as well matched as paralleling bifilar wound secondaries on a dual secondary transformer.

If that v22 is a 11-0-11 then you can parallel the primaries and series connect the secondaries to give 22-11-0-11-22 from your 115Vac and you will still get the benefit of 800VA. You can use the 11-0-11 to generate low voltage for controls, relays etc.

Why have you arrived at 800VA for four chip amps?

BTW. the regulation of an EI is usually worse than a toroid. In addition the regulation of two lower VA transformers will be worse than one higher VA transformer.
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Old 17th October 2006, 08:48 AM   #5
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I would choose 11-0-11 transformers and wire secondaries in series rather than buy a pair of 22-0-22 and wire parallel. When paralleling, any slight voltage mismatch will create large currents to flow which will impact the quality of your supply.
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Old 17th October 2006, 09:13 AM   #6
Nordic is offline Nordic  South Africa
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Isn't this true for just about any transformer... I have yet two see a transformer with 2 exactly matched windings...
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Old 17th October 2006, 09:34 AM   #7
AndrewT is offline AndrewT  Scotland
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Have we found out yet if they are
11-0-11
or
22-0-22 ?
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Old 17th October 2006, 11:29 AM   #8
paulb is offline paulb  Canada
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Hammond 167 series are centre-tapped secondary. So a V22 is 11-0-11.
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Old 18th October 2006, 03:05 AM   #9
zenon is offline zenon  Canada
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Okay, so I should be able to connect them as depicted on my diagram for the secondaries in series? Is the location of Active and Neutral Lines critical on the second transformer?

Does "regulation" just mean how accurate the power is? like 22VAC rated may give you 23 to 21 whereas a toroid would be more like 21.9 to 22.1 ??

I've read here to use 1.5 time the power output in watts to calculate VA. Which makes sense because when I use the National design spreadsheet and add the thermal watts wasted plus the watts power outputted it equals pretty much the exact same value of total watts as if I multiplied the power output by 1.5 soooo........

95.15 Watts * 1.5 = 142 VA per bridged channel, three bridged channels = 428 VA
two stereo channels are 47.58 Watts * 1.5 = 71.37 VA * 2 = 142.74 VA

total = 570 VA for three bridged and two non bridged channels

totals five channels of power, and one sweet amount of overhead when running in stereo. I was hoping to find something in the 600 VA range but this is as close as I could get.. and I think I can display these vintage looking Hammond transformers nicely.
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Old 18th October 2006, 07:37 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi Z,
I see you are bridging these chip amps.

Do you realise that each half of a bridged amp thinks it is driving a load =half the actual load and the current from each half is double due seeing half impedance?

How are you ensuring the bridged chipamps are going to cope with the load you will apply and how do you intend ensuring the chipamps do not shut down?

Now back to your transformer.

the two unconnected primaries are connected to live and neutral so that the primaries are in parallel.
If you connect the primaries out of phase then you risk blowing up your transformers.

USE a mains bulb limiter for all your testing until you are sure the FINAL version is safe to connect across the mains without protection.

Ignore, but insulate the centre taps.
Connect the 0V and the 11V from opposite transformers. Connect a volymeter to the other 0V and 11V and check you have >=44Vac at the secondary ends.

If you have nearly 0V then you have connected the transformers out of phase.
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