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Old 27th April 2008, 08:15 PM   #21
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Hi,

I am also new on this and have also been reading a lot trying to decide which configuration to build.

I agree that the LM3886 chip seems to be preferred as it handles speakers with lower impedance and less sensitive. I have single driver jordans JX92S (maybe with BSC): 6 Ohms and down to 85db and that's why I want to use the LM3886.

My idea is to start from the "begining" by using the very basic schematics of the original 47 Lab Gaincard (but using the LM3886 instead of the LM3857) as "translated" by Mick F (which includes the basic PSU without capacitors):

http://dogbreath.de/Chipamps/GainCar...nCardCopy.html

I do not intend to make the design as compact as Mick F but to start by doing what was recommended above by seventenths (thanks 7/10 for this simple good idea) using a proto-board following almost physically the schematic. This will 1) allow me to learn more than using a PCB 2) it will be much cheaper and 3) and will allow more room for future improvements to the configuration and layout. It might end up super compact and buffered, with a snubberized PSU, etc, etc who knows!

Mick F includes the part list (only 9 components like the original), so it seems seems like an easy project to start

I hope this thread keeps focused on the basics of chipamp building for newbees or as said before: '50 watt per channel Dual Dummies"

Thanks in advance to those willing to help or keep helping

Regards

Antonio
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Old 27th April 2008, 08:33 PM   #22
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Antonio,
I just posted a 3886, dirt simple implementation in the chip amp photo gallery. When my camera battery is charged, I'll post a shot of my first breadboard effort and if I can find it, a VERY simple "dead bug" that was my first test effort.
I predict success


7/10
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Old 27th April 2008, 08:40 PM   #23
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Quote:
Originally posted by seventenths
Antonio,
I just posted a 3886, dirt simple implementation in the chip amp photo gallery. When my camera battery is charged, I'll post a shot of my first breadboard effort and if I can find it, a VERY simple "dead bug" that was my first test effort.
I predict success


7/10
7/10

Thanks. Yes, I saw it. It looks very simple. Could you post a photo of the other side of the board?. Which schematics did you use?

Antonio
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Old 27th April 2008, 08:44 PM   #24
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Antonio,
Sure thing ... just waiting on that camera battery.
The 3886 is based on a Carlos FM schematic pulled from "Decibel Dungeon".


7/10
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Old 27th April 2008, 09:17 PM   #25
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Quote:
Originally posted by seventenths
Antonio,
Sure thing ... just waiting on that camera battery.
The 3886 is based on a Carlos FM schematic pulled from "Decibel Dungeon".

7/10
Thanks 7/10

Cool! that's also in my shortlist because I could keep going and implement step by step Carlos FM's snubberized PSU and also build his buffer or jfet preamp, which apparently are very good.

Look forward to see the photo later.

Antonio
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Old 28th April 2008, 12:59 AM   #26
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See photo. Here is LM3875TF (insulated) shown reduced to 5 pins for easy hookup.

EDIT: It now relates to Figure 1 on the first page of LM3875.pdf

(click photo to enlarge)
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File Type: jpg lm3875tf-w-5pins.jpg (30.2 KB, 1178 views)
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Old 28th April 2008, 02:25 AM   #27
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Here's a quick sketch to give you a head start.

Supplies shown:
LM3875TF
Experimenter's board (phenolic with individual round pads)
hook-up wire
pack of 1/4w resistors
A 1w 4 ohm (3.9r) resistor for speaker zobel
200nF or 100nF polyester cap for speaker zobel
22uF Mallory SEK 200v ecap for position CI *note1
3x 4.7uF Mallory SEK 250v ecap *note2
4x 4700uF low-esr 50v or 63v ecap *note3
2x 470uf low-esr 50v ecap *note4
2x 100nF ceramic caps
A block bridge rectifier unit *note5
4x 10nF ceramic caps

Not shown:
transformer
heatsinks
cables

Notes:
1) Nichicon KZ 22uF 50v is another good option; A 47nF polyester cap can be added (paralleled) to give more "air" effect if desired.

2) Elna Cerefine 4.7uF 50v is another good option; although any capacitor can block DC, this component selection is more art than science. A 47nF polyester cap can be added (paralleled) to give more "air" effect if desired.

3) You can parallel additional 100nF or 47nF polyester to a pair of the 4700uF power caps, preferably closer to the bridge rectifier.

4) EDIT: You can use the 470uF shown although 220uF or 330uF are other options, and these options will sound different. Personally, I'd just choose the option that is most pleasant.

5) Although a popular "known good" bridge block is shown, it is perhaps safer to choose a similar option with an all-plastic body. To support a center tap transformer, the bridge block is "ringed" in 10nF ceramic (or polyester) caps, looking much like a propeller.

Additional note: Parts Express carries Tracon polyester, although most economy mylar / polyester will do.

This sketch is to help give an idea on how to layout for an E-board project. Dry fit components first. The power ground wire should be twice as thick as any other wire.
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Old 28th April 2008, 03:05 AM   #28
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A handy chart:
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Old 28th April 2008, 05:26 AM   #29
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Quote:
Originally posted by Peter Daniel
You can build a complete amp as pictured, or use only selected parts and be able to connect amp to the speakers.
Hi Peter!! (hey folks, his audiosector.com products are high quality and durable too).

Questions (2) in regards to Audiosector LM3875 Dual Mono Kit:

What do you think about a pair of these: http://www.alliedelec.com/Search/Pro...p?SKU=967-7475 dual-secondaries 48v transformers, as a nice compact option? I've been pleased with their center tap version, but haven't tried the dualie version (link).

Do you offer, or plan to offer, a preamplifier kit to match the LM3875 power amplifier kits? If so, that would be really helpful (edit) addition to most chipamp projects.

Thanks!
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Old 28th April 2008, 07:13 AM   #30
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DWB,

Many thanks for all this info! This is exactly the kind of information needed for a start and to have it in one thread saves a lot of time.

Regards

Antonio
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