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Old 4th December 2012, 11:58 AM   #1021
carcass is offline carcass  Portugal
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Quote:
Originally Posted by AndrewT View Post
(...)

>100dB speakers will require a very low noise value at the amplifier output.
Chipamps do not have that required very low noise value. Peter Daniel developed his implementation that he uses (or used) with 95/96dB/W@1m speaker, I cannot recall if he had reservations on noise.
Agree completely!!, 2myrefC builds v1.2 and v1.3 boards, the hiss is always there, PGDN floating helps. but not that much, better to use less sensitive speakers, myref diserves it IMO
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Old 4th December 2012, 12:58 PM   #1022
AndrewT is offline AndrewT  Scotland
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Originally Posted by bcmbob View Post
Andrew, is this a situation where a discrete soft start module would help?
No. Soft start is for current limiting when the mains transformer is asked to start up. We already need/use that for the close rated mains fuse that we should all be using.

Here (noises in the speaker) we need fast OFF for the relay driver circuit. We already have slow ON.
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Old 4th December 2012, 01:06 PM   #1023
bcmbob is offline bcmbob  United States
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Understood - the soft start would work if the amp was up side down or I was standing on my head.
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Old 8th December 2012, 06:28 PM   #1024
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Ok, I still can't get one of my amps to work, and I have no idea why.

I've replaced the capacitors in the LM318 section, I've replaced the LM318 (I tried two different LM318's), and I've replaced R14 with a 100R resistor, and I still can't get the relay to click on, the power LED to light, or music to play.

I've been through every component and everything is connected properly, orientated properly, and soldered properly.

I'm running a soft start circuit sold by Per-Anders Sjostrom, however that fires up one of the channels, and I've used it on another chip amp project with no problem.

Can someone please help me before I take a sledge hammer to it.

Thanks
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Old 8th December 2012, 06:41 PM   #1025
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Originally Posted by westers151 View Post
Ok, I still can't get one of my amps to work, and I have no idea why.
If rails are good, you checked all parts and they seem the right ones in the right place with the right value, lm318 and LM3386 are good then a faulty board is possible but, IMHO, unlikely...

Can you post some pics?
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Old 8th December 2012, 07:38 PM   #1026
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I will post some pictures tomorrow, Clave.

I have calmed down a bit and reflected on the issue. I'm not entirely convinced that CPC Farnell sent me the correct PF capacitors - I had two Mica capacitors that had 22 printed on them, yet they were in seperate bags, with the part numbers relating to the correct capacitance (22, and 220).

What also makes me think that they sent the wrong capacitor, is the fact that the issue of the LED shining when the power is switched off, no longer happens.

I don't for one minute think it's the boards.

Thanks for the help.
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Old 9th December 2012, 05:20 PM   #1027
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For the speaker protection circuit, R21 reduced to 100k and R14 to 180R has given very dependable operation with both Omron and Goodsky relays, and a wide variety of transistors for Q1 to Q3.

For Rev C, C10 is 22p and C12 is 220p - measure them if there's any doubt.

Recheck the values of R5, R6, R8 and R9 to make sure they're sane. Compare with the working board.

Check for solder bridges/shorts from pads to the ground plane in the small-signal area.
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Old 9th December 2012, 05:31 PM   #1028
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Thanks Linuxguru, I will do that. R5, 6, 8, 9 *should* be the same as they are the parts that came with the kit, but you never know.

I didn't change R21, just R14, so I think I will keep that one in mind.

Attached are some pictures of the board - there are a few components on the underside, mainly due to the ease of fitting the oversized items. I haven't cleaned up the flux from when I was desoldering components, hence some of the gunge underneath.
Attached Images
File Type: jpg IMG_0178-002.JPG (405.6 KB, 171 views)
File Type: jpg IMG_0179-002.JPG (388.6 KB, 164 views)
File Type: jpg IMG_0180-002.JPG (429.1 KB, 160 views)
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Old 9th December 2012, 09:32 PM   #1029
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I would start from cleaning the flux...maybe it's not the problem... but I wold start from there...
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Old 12th December 2012, 07:33 AM   #1030
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Originally Posted by linuxguru View Post
Check for solder bridges/shorts from pads to the ground plane in the small-signal area.
Hi Linuxguru, what exactly is the small signal area that you mention in your post. Is it the LM318?

Thanks
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