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Chip Amps Amplifiers based on integrated circuits

tech-diy LM4780 board questions
tech-diy LM4780 board questions
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Old 13th January 2007, 01:48 PM   #1
Burnedfingers is offline Burnedfingers  United States
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Default tech-diy LM4780 board questions

I just received some LM4780 boards this week. I downloaded a schematic and I am wondering if there is a mistake in the downloaded copy. It shows C6 as a 4.7 uf value and has provisions to install (2) 100uf caps in series. Should this be (2) 10uf caps in series? Actually would the value be critical at all since it is the Ci to ground?

The gain on the non-inverting side of the amplifier looks like it would be 10.7 and the gain on the inverting side looks like 11.7

Am I not seeing things clearly?
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Old 13th January 2007, 02:06 PM   #2
jackinnj is offline jackinnj  United States
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tech-diy LM4780 board questions
the gain on the non-inverting side is 1 + R1/R2 (it's just an opamp on steroids), the inverting side gain is just the ratio of the two resistors.

you have the option of lowering the f3 of the amplifier by using larger coupling caps -- fwiw I used 4.7 uF polypropylene in the AX article.
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Old 21st September 2017, 06:07 PM   #3
Jeekay56 is offline Jeekay56  United Kingdom
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I recently bought a couple of tech-diy LM4780 boards together with the chips and a couple of heatsinks from ebay.

120W Hi-Fi Stereo Amplifier DIY Kit: 2 x LM4780 + 2 x PCBs + 2 x HEAT SINK | eBay

Could anyone tell me the purpose of the solid and dashed jumper lines marked on the pcb please? Any other info on these boards would be appreciated. I understand tech-diy belongs/belonged to Jackinnj, but the web page appears to be no longer active.

Cheers,

Graham
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Old 22nd September 2017, 12:28 PM   #4
AndrewT is offline AndrewT  Scotland
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The white printed lines look like they might be wire connections to take power to a remote part of the PCB.
If so use a twisted pair with minimal loop area at the terminations.
The 4780 chipamp is now obsolete. Do you have some in stock?
Any that are still available via the internet are very likely to be fake.

Jack should hopefully see this and reply.
Try sending him a PM.
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Last edited by AndrewT; 22nd September 2017 at 12:31 PM.
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Old 22nd September 2017, 01:24 PM   #5
Jeekay56 is offline Jeekay56  United Kingdom
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Hi Andrew, thanks for your reply.

I'm still very new to all this, what puzzled me is that the start and end points of the white lines are joined on the back of the board by quite beefy tracks, so maybe the wires are reinforcement for the tracks.

I received two LM4780 chips with the boards and a couple of heatsinks (I intend using some larger ones I have) for the princely sum of 14.

Cheers,

Graham
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Old 22nd September 2017, 02:59 PM   #6
jackinnj is offline jackinnj  United States
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tech-diy LM4780 board questions
The solid and dashed lines just show you where the DC- and DC+ are eventually winding up.
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Old 22nd September 2017, 03:28 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Jeekay56 View Post
Hi Andrew, thanks for your reply.

I'm still very new to all this, what puzzled me is that the start and end points of the white lines are joined on the back of the board by quite beefy tracks, so maybe the wires are reinforcement for the tracks.

I received two LM4780 chips with the boards and a couple of heatsinks (I intend using some larger ones I have) for the princely sum of 14.

Cheers,

Graham
Quote:
Originally Posted by jackinnj View Post
The solid and dashed lines just show you where the DC- and DC+ are eventually winding up.
this appears to confirm that the white lines can be ignored and the power uses traces on the back side to make the required connections.
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Old 22nd September 2017, 04:12 PM   #8
Jeekay56 is offline Jeekay56  United Kingdom
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Jack/Andrew, thanks for clearing that up for me. Have to say the boards look excellent, I hope I can do them justice. :-)

Cheers,

Graham
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