Salas hotrodded blue DCB1 build - Page 53 - diyAudio
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Old 23rd October 2010, 09:22 PM   #521
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Hi Salas,

Off topic (kind of) this, but I know I can find you here:

I just got the R-core transformer for my TDA1541A DAC.

It is 20v and 12v 12v 12v 220VAC to achieve -15v and 5v -5v 5v DC

Because of my countries 240Vac (nominal) system, the results are quite high.

I am getting 23.5v and 14.4v 14.3v 14.2v from the leads, which is high even for the 220/240 discrepancy. I was expecting 21.8v and 13.1v, 13.1v, 13.1v

After rectification using 4x Fairchild Stealth Diodes per channel and 10x Panasonic FC 2200uF caps, and a WIMA 0.1uF decoupling cap per channel, I am getting DC of 31.4v 18.7v 18.5v 18.3v, so to achieve 15v 5v 5v 5v will mean a LOT of voltage lost in the shunt regulation. I haven't hooked them up to the shunt regs yet, as I still need some small bolts for the mosfet to heatsink connection

I am wondering if I will be OK with these small sinks and the planned 10R 5W current resistor, as there is going to be a lot of voltage wasted here. I am thinking 22R might make more sense, or bigger sinks, or both. Any thoughts?
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Old 23rd October 2010, 10:05 PM   #522
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I've got these wakefield heatsinks (287-1abe) from my other dcb1 build that I didn't use.

I'm hoping these would keep the mosfets cool enough - they're rated at 56C @ 4W.

Here's the link to mouser...

567-287-1ABE

I do believe I would need insulators between the heatsink and mosfet, right?

Thanks,
JG
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Old 23rd October 2010, 10:05 PM   #523
AndrewT is offline AndrewT  Scotland
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the Salas Shunts draw constant current.

You can add a series Power resistor to each feed line and it will drop a fairly constant voltage.

10r and 200mA for CCS will drop 2V and dissipate 400mW
20r and 400mA drops 8V for 3.2W

An RC before the regs uses up spare voltage and cleans up the supply making for an easier job for the Shunt.
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Old 23rd October 2010, 10:52 PM   #524
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Thanks Andrew. So what do you think about 31.4v to 15v DC regulation and 18.5v to 5v DC regulation? Is it a problem to reduce the voltage by this amount? Will this generate a lot of heat? Should I set a lower current than 200mA?

Thanks
Lucas
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Old 23rd October 2010, 11:23 PM   #525
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JG/Merlin,

You don't need insulators as long as the sinks are independent (ie not touching one another.)

Insulators would only make them less efficient at conducting heat away. Thermal paste is best.

Those sinks look borderline for a Hot Rod. They'll work, but with mosfets running hot, life expectancy will be reduced I think.
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Old 23rd October 2010, 11:25 PM   #526
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Quote:
Originally Posted by AndrewT View Post
the Salas Shunts draw constant current.

You can add a series Power resistor to each feed line and it will drop a fairly constant voltage.

10r and 200mA for CCS will drop 2V and dissipate 400mW
20r and 400mA drops 8V for 3.2W

An RC before the regs uses up spare voltage and cleans up the supply making for an easier job for the Shunt.
What about a bleeder resistor after the caps? I have some 220K 5W Kiwame Carbon film on order for this purpose, as it was on the schematic I am following, but I am not sure of the effect they will have.
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Old 23rd October 2010, 11:52 PM   #527
Salas is online now Salas  Greece
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Quote:
Originally Posted by merlin2069er View Post
I've got these wakefield heatsinks (287-1abe) from my other dcb1 build that I didn't use.

I'm hoping these would keep the mosfets cool enough - they're rated at 56C @ 4W.

Here's the link to mouser...

567-287-1ABE

I do believe I would need insulators between the heatsink and mosfet, right?

Thanks,
JG
Not for 10R setting resistors. For low current setting with the two small resistors, yes. Insulators you will need only if the sinks are going to be touching the chassis or one another.
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Old 24th October 2010, 12:21 AM   #528
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Thanks!

So, what sort of heat will the heatsinks need to dissipate?
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Old 24th October 2010, 03:22 AM   #529
Salas is online now Salas  Greece
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4W per rail with 10R. Just bolt them on your chassis floor using insulators. Mount the Mosfets underneath like in power amps.
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Old 24th October 2010, 01:00 PM   #530
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Project accomplished!


Click the image to open in full size.

To get the maximum
"switch and turn feeleing"
i installed an Elma Switch for the input selector and the Blue Alps for the Optical Volume Control.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Here my new DCB1 besides my new AMP III and my Audionet multichannel pre-amp.

Click the image to open in full size.

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