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Quad 405 transistors using more power
Quad 405 transistors using more power
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Old 8th March 2018, 10:23 PM   #11
TonyTecson is offline TonyTecson  Philippines
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Quad 405 transistors using more power
Quote:
Originally Posted by 405man View Post
Has anyone measured the VA rating of the 405 transformer,. I tried loading one until the voltage dropped by 5% but at 500W the load resistor was smoking and I had to abandon the test before I set off the fire alarm.

Stuart
was that with a rectifier into a dummy load was that an ac only test...

a 250va traffo can be overloaded to 500w but only for a few seconds, i will not even try to do that...did you hear humming in the traffo? if not then perhaps the traffo was rated for more than 250...

overloaded to say 300 for say half an hour may heat it up but not to a point it will burn....
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Old 8th March 2018, 11:32 PM   #12
goodguys is offline goodguys  United Kingdom
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The amp works fine with the new transistors, had them in for a while without oscillation, it is a mod recognised by dada electronics and a few forum posters. Didn't sound any better though.

The quad transformer is 350va

Any thoughts on my last question concerning decoupling each amp board, and paralleing the caps in the power supply.

Thanks
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Old 9th March 2018, 01:51 AM   #13
TonyTecson is offline TonyTecson  Philippines
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Quad 405 transistors using more power
more like 220ufd for local coupling....twist the rails wires from psu reservoir
to the amp board..
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Old 9th March 2018, 02:05 AM   #14
stocktrader200 is offline stocktrader200  Canada
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that 350va transformer is the piece I would keep as it is incredibly quiet sonically.
put in the biggest filter caps possible and a new mosfet amp at .001 % distortion will beat the hell out of any stock 405 amp running 750 or 1000 va transformer.
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Old 9th March 2018, 06:51 AM   #15
goodguys is offline goodguys  United Kingdom
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Thanks! Why 220uf? is not a larger reservoir, more juice available, better.

When you say put in the biggest filter caps, are you referring to the power supply. I have got enough caps to up from 10kuf to 17uf if that is what you mean, and i have already puy in a bigger bridge rectifier, 20 amps, compared to the stock which was 7 amps.
Do you have any mosfet in mind.

Thanks

Last edited by goodguys; 9th March 2018 at 06:53 AM. Reason: typo
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Old 9th March 2018, 07:57 AM   #16
TonyTecson is offline TonyTecson  Philippines
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Quad 405 transistors using more power
220 will be faster, you already have a reservoir caps..100uf or less may even be better
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Old 9th March 2018, 08:06 AM   #17
405man is offline 405man  Scotland
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I loaded the AC side of the transformer and at 500W there was no hum but I was only able to run it for about a 90s. I shall weigh the transformer and compair it to some others of known VA

Stuart
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Old 10th March 2018, 05:42 AM   #18
goodguys is offline goodguys  United Kingdom
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Okay, i replaced the 10kuf with 15kuf, is it a good idea to bypass the 15kuf with a small cap, something like 1kuf or 100uf, i heard the smaller cap charges and discharges faster and is better for short fast transients, would this give an audible effect.
Or will the 100 / 220uf cap for decoupling the amp board already take care of this
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Old 10th March 2018, 06:35 AM   #19
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by goodguys View Post
is it a good idea to bypass the 15kuf with a small cap, something like 1kuf or 100uf, i heard the smaller cap charges and discharges faster
But they are in parallel so will both have exactly the same voltage at any time. So how can that make a difference then?

Jan
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Old 11th March 2018, 07:07 AM   #20
goodguys is offline goodguys  United Kingdom
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It is done by manufactirers in some amps, cascade bypassing.
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