First Lm3886 - Page 3

Ted205 · 24th June 2009, 09:26 AM

heres the regulated psu from nuuks site - http://myweb.tiscali.co.uk/nuukspot/...ub.reg.psu.png

one thing you should included is fuses. Ideally one before the transformer and one on the power rail after the PSU to protect the amp.
Personally i use a fuse on the power rail (both +ve and -ve) and the Power Gnd rails (+PGND, -PGND) coming from the PSU to protect against reverse polarity (which is easy to do when modifiying the circuit).

AndrewT · 24th June 2009, 09:39 AM

Hi,
fuse the mains side - definitely.
Keep the mains fuse as low as possible - preferable. This requires some form of soft start.

Use a bulb tester on the mains input.

The PTC of the bulb filament gives automatic protection to the downstream circuit, even wiring faults on the mains side of the transformer and reversing the PSU to amplifier connections.

Atilla · 24th June 2009, 10:03 AM

Quote:

Originally posted by PJPro

Do you think that my two 160VA transformers will be under powered?

I've fantastic results with 2x120VA and chipamp.com power supply modules. If you're doing dual-mono, 160VA per channel should be very solid.

AndrewT · 24th June 2009, 10:33 AM

Quote:

Originally posted by Atilla
I've fantastic results with 2x120VA and chipamp.com power supply modules. If you're doing dual-mono, 160VA per channel should be very solid.

agreed.
If you want 60W + 60W from a two channel amplifier, then generally one will find that a transformer rated from 120VA to 240VA will work well, i.e. VA ~ one to two times the total maximum output power.

PJPro · 24th June 2009, 06:42 PM

Quote:

Originally posted by Atilla

I've fantastic results with 2x120VA and chipamp.com power supply modules. If you're doing dual-mono, 160VA per channel should be very solid.

Result! That's good to know.

I've really been sweating over transformer selection and ended up just getting them. They arrived the other day and look pretty impressive. And they're soooo heavy so must be high quality!

I went for the fully potted/encapsulated ones from RS. Cost almost as much as the dual mono kit from chipamp.com. Still....

PJPro · 24th June 2009, 07:29 PM

Quote:

Originally posted by PJPro

Gotcha. It's my schematic that's wrong. I was comparing the schematic quadtech posted with the chipamp.cpm schematic.

I'll revise mine and repost.

Thanks

Ya know, I made the changes to my schematic and spent some time looking at....feeling that something was not quite right. I finally realised that it was the schematic from chipamp.com that was incorrect. Perhaps I'm learning something?

I have swopped around C6 and R4 on my schematic and will resubmit shortly.

PJPro · 24th June 2009, 07:35 PM

Here's my revised schematic.

Redshift187 · 24th June 2009, 09:14 PM

I don't think the order of C6 and R4 matters.

Ted205 · 25th June 2009, 08:05 AM

c6 & r4 is the snubber network and is commonly put at the output of the power supply i.e after c10

AndrewT · 25th June 2009, 10:40 AM

Hi,
what does the 338 datasheet have to say about fitting capacitors close to the input and output pins of the regulator?

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24th June 2009, 09:26 AM	#21
Ted205 diyAudio Member Join Date: Jun 2008	heres the regulated psu from nuuks site - http://myweb.tiscali.co.uk/nuukspot/...ub.reg.psu.png one thing you should included is fuses. Ideally one before the transformer and one on the power rail after the PSU to protect the amp. Personally i use a fuse on the power rail (both +ve and -ve) and the Power Gnd rails (+PGND, -PGND) coming from the PSU to protect against reverse polarity (which is easy to do when modifiying the circuit).

24th June 2009, 09:39 AM	#22
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, fuse the mains side - definitely. Keep the mains fuse as low as possible - preferable. This requires some form of soft start. Use a bulb tester on the mains input. The PTC of the bulb filament gives automatic protection to the downstream circuit, even wiring faults on the mains side of the transformer and reversing the PSU to amplifier connections.

24th June 2009, 07:35 PM	#27
PJPro diyAudio Member Join Date: May 2009	Here's my revised schematic.

24th June 2009, 09:14 PM	#28
Redshift187 diyAudio Member Join Date: Aug 2008	I don't think the order of C6 and R4 matters.

25th June 2009, 08:05 AM	#29
Ted205 diyAudio Member Join Date: Jun 2008	c6 & r4 is the snubber network and is commonly put at the output of the power supply i.e after c10

25th June 2009, 10:40 AM	#30
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, what does the 338 datasheet have to say about fitting capacitors close to the input and output pins of the regulator?