New ChipAmp Project Thread

[slipperybidness]

I recently built and measured a GOBO Chip Amp from Boxed Kit Amps. I am wrapping up my report-out for that project in the near future. And, that has been documented (will get updates when needed) on AH and on the BKA forums:
http://forums.audioholics.com/forums/threads/slick-little-chip-amp-kit-and-other-project-ideas.92024/#post-1056965

https://www.boxedkitamps.com/node/121

So, this project got me interested in ChipAmp designs and builds. I think my next amplifier project will be another ChipAmp, but this time I will plan to build it from scratch-- no kit, no instructions, no parts list -- just a datasheet and other reference materials!

After I get a successful ChipAmp under my belt, then I will most likely move along to discrete component amps and higher power.

As part of this build, I have started re-reading High-Power Audio Amplifier Construction Manual by G Randy Slone
http://www.amazon.com/High-Power-Audio-Amplifier-Construction-Manual/dp/0071341196/ref=sr_1_3?ie=UTF8&qid=1415210004&sr=8-3&keywords=g+randy+slone

I have read / skimmed this book previously, but that was before I had the classes in Solid State and Linear Integrated Circuits, so a re-read now that I have a more fundamental understanding seems in order. Also, this book is geared specifically towards discrete designs.

So, I am now in the very beginning stages of this build. I have a notebook to jot down notes and a parts list, and I have reviewed some ICs as possible candidates.

As of right now, I have my eye on 2 different ICs for this build:

1) This is probably my front-runner for now: TI LM3875 http://www.ti.com/product/lm3875

2) More power in bridge mode, but more external components and more complicated circuit: TI lm4870 http://www.ti.com/product/lm4780

So, anybody on AH ever built a design with either chip? Any other chips to recommend?

I realize that AH doesn't have a whole lot of users that are deep into the electronics builds, but maybe we can start getting some interest in this direction. I may set up an account over on DIYAudio and/or PETT too, as this thread would be more at-home over there.

 

[slipperybidness]

Hmmm. After a little more research and reading, here is what I have found about some particular ICs:

*LM3875 is the "big brother" of the LM1875. My recent GOBO uses the LM1875. There is also an LM3876 that seems identical to the LM3875, but has added Mute functionality.

*LM3886 is an updated version of the LM3876. It looks to perform better at 4-ohm loads than LM3876, though on paper it seems to not perform as well in other areas.

*LM4870 is basically 2x dies of LM3886 on 1 IC. It can be used as stereo, bridged, or paralleled into a single load.

At this point, I am starting to lean more towards the LM3886, and the LM3876 as a 2nd choice. I have also found some PCBs for the LM3886 readily available online. For the prices that I'm seeing, I may go that route. It's gonna be about the same $ or more expensive to etch my own boards or do point to point wiring, and both of those require more work (plus handling chemicals for board etching).

 

[lsiberian]

I think the Tripath TK2050 is a better option. My chip amps use those.

 

[slipperybidness]

I think the Tripath TK2050 is a better option. My chip amps use those.

OK. I will read up on them.

Did you build your chip amps yourself?

What is it about the TK2050 that makes it better?

 

[lsiberian]

Nope bought them pre-fabbed. The LM3886 might be better.

 

[ellisr63]

I purchased the Topping TP20 MKII whish has the Tripath 2020 chip in it. I am using it to power my JBL 2360a/EV DH1A bi-amp setup. I was not sure if they would handle my bass bins so I have some pro amps for them. I really should try them full range as they would be nice for my surround channels.

 

[slipperybidness]

OK. I have read up on the TK2050. That chip won't meet my design goals for this project. That chip would most likely be great if 2 of your design goals are to have a small amplifier and to have a very efficient amplifier. It also seems to favor SMPS.

Since small and efficient and SMPS are off my list for this build, I have ruled out the TK2050.

At this point, I think I am just about set for the LM3886 chip. The only thing that looks better and would be more robust would be to parallel the LM4871. However, that will add complexity, heat, size, and cost to the build.

Therefore, unless I find something even better for my needs in the near future, this will be an LM3886 Gainclone build.

At this point, here is what I'm thinking:

*330VA toroidial transformer with +/- 25V rails
*10,000 uF of capacitance per supply rail
*Haven't decided on discrete rectifier diodes or a complete package. 1 of the supply kits I've been looking at comes with the discrete diodes. But, I have several IC rectifier packages that I have scavenged.
*Looking at purchasing PCBs. However, I will most likely make some changes to the circuit and P/S boards. I will most likely piggy-back mod circuits onto perf-boards and then connected to the purchased PCBs.
*Amp case with integrated heat sinks. Probably much more than needed for this build.

Total should come out to about $300!!!

That is not bad at all! Just about top-of-the-line chip amp, with over-spec'd transformer and P/S filter caps, and over-spec heat sinking too!

If I were to cut the P/S to 220VA and scavenge, build, or get a cheaper case, then I could probably shave $100 off the price!

Here's a little eye-candy to drool over. This guy did some amazing LM4780 builds! But dang, those cases probably cost at least 3x all the other parts combined!
http://www.tim.cheapo.cc/index.php?/project/lm4780-stereo-amplifiers/

 

[slipperybidness]

Well, after a couple more weeks of reading, studying, and asking questions, here's the plan!

I have decided to go with a LM4780 chip in parallel configuration, 1 chip in parallel for each channel. This should give me somewhere in the neighborhood of 100 Wrms per channel. Certainly nothing to sneeze at, and this should be about the top-dog of a chip amp design. (At least the top dog of a class AB chip amp design )

Many people on the forums have been building these amps with the boards available from Audio Sector. However, after I studied his schematics for a while, I decided to go a different direction. There are many places on his boards that I would have to make mods to get the components on there that I want.

However, I did find this guy on ebay selling LM4780 boards. I bought 2 of his boards for a total of ~$21.
http://www.ebay.com/itm/111278086423?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT
The main reason that I went with these PCBs is that his layout and design is much closer to my planned circuit than the Audio Sector boards. In other words, I will have to do a whole lot less modding/piggybacking on these PCBs to get the circuit that I want.

I will post my thoughts on these PCBs after they arrive.

Next up, I need to lay out the P/S. Again, I have found several PCBs online for this, and I will most likely go that route. However, point to point wiring for a P/S will be much easier than a 27-pin-package! If it comes to that.

I will most likely be doing a "dual mono" P/S. Not a true dual mono because it will probably be only 1 power transformer (and a rectifier/filter board for each channel).

My next big decision is whether to have the P/S in the same chassis as the amps, or have the P/S in it's own enclosure. Then, if separate PS enclosures, maybe do a true dual mono design. The biggest advantage of doing separate supplies is that I can then build 1 power supply with high quality parts and high capacitance, then use that supply for any subsequent amp builds.

 

[Speedskater]

I may be late to this party, but there is a new chip amp kit that is technically better than other kits. While far from being cheap, it doesn't use expensive boutique parts either.

The Modulus-86 is my latest amplifier design. It is a composite amplifier using an LME49710 precision op-amp to control an LM3886 power amp. The performance of the resulting composite amp, both in terms of measured performance and in terms of sound quality, is dominated by the performance of the LME49710. Hence, the performance of the Modulus-86 is absolutely stellar.

http://www.diyaudio.com/forums/vendors-bazaar/262273-modulus-86-composite-amplifier-achieving-0-0004-thd-n.html

 

[slipperybidness]

I may be late to this party, but there is a new chip amp kit that is technically better than other kits. While far from being cheap, it doesn't use expensive boutique parts either.

The Modulus-86 is my latest amplifier design. It is a composite amplifier using an LME49710 precision op-amp to control an LM3886 power amp. The performance of the resulting composite amp, both in terms of measured performance and in terms of sound quality, is dominated by the performance of the LME49710. Hence, the performance of the Modulus-86 is absolutely stellar.

http://www.diyaudio.com/forums/vendors-bazaar/262273-modulus-86-composite-amplifier-achieving-0-0004-thd-n.html

Yeah, you are kind of late to this party, I have already purchased some 4780 PCBs and many of the supporting components to start that project.

But, you know how this hobby goes!

I purchased some extra components to get the volume discount and minimize the shipping costs. I was also considering a 3886 from scavenged parts and extra parts.

So, you just gave me some more reading and a new resource!

By the way....I like your "donate" button, "buy me a cup of coffee" if you find my info useful. It may not be the most profitable business model, but I like it!

 

[slipperybidness]

Mostly just some documentation here. But, here was my PE order in support of the build.

The running total
PE $161 (with some extra parts too)
PCBs $21
Amazon 500 pc variety of 1% resistors $13

So the running total is $195

Still need: ICs, case, heat sinks, filter caps, and a few odds and ends, may be up to another $200 for these items.


Item Qty Price Total

Parts Express M3 Standoff and Hex Head Screw Kit 100 Pcs.

Part # 320-3287

1 $8.87 $8.87

Perforated PC Board 1-3/4" x 1-1/2" For #320-400

Part # 320-440

2 $0.74 $1.48

Perforated PC Board 2-5/16" x 1-7/8" For #320-410

Part # 320-450

2 $0.87 $1.74

Parts Express Mini Gold Plated Insulated 5-Way Binding Post Set 2 Red 2 Black

Part # 320-3375

1 $9.26 $9.26

10uF 50V High Temp Radial Capacitor

Part # 020-1656

10 $0.08 $0.80

10uF 100V Radial Mini Electrolytic Capacitor

Part # 020-1296

10 $0.22 $2.20

1000uF 50V Radial Mini Electrolytic Capacitor

Part # 020-1256

10 $1.11 $11.10

Dayton Audio PMPC-1.0 1.0uF 250V Precision Audio Capacitor

Part # 027-210

4 $2.03 $8.12

47uF 100V Electrolytic Non-Polarized Crossover Capacitor

Part # 027-352

10 $1.19 $11.90

Dayton Audio DFFC-0.10 0.10uF 400V By-Pass Capacitor

Part # 027-452

10 $0.97 $9.70

Screw Cap AGC Fuseholder Black

Part # 070-610

1 $0.97 $0.97

Avel Y236850 625VA 25V+25V Toroidal Transformer

Part # 122-675

1 $98.00 $98.00

2.2 Ohm 1W Flameproof Resistor 10 Pcs.

Part # 003-2.2

2 $0.85 $1.70

5.6 Ohm 1W Flameproof Resistor 10 Pcs.

Part # 003-5.6

2 $0.85 $1.70

0.47 Ohm 1W Flameproof Resistor 10 Pcs.

Part # 003-.47

2 $0.85 $1.70

15pF 500V Ceramic Disc Capacitor

Part # 020-2006

10 $0.15 $1.50

 

[TLS Guy]

Mostly just some documentation here. But, here was my PE order in support of the build.

The running total
PE $161 (with some extra parts too)
PCBs $21
Amazon 500 pc variety of 1% resistors $13

So the running total is $195

Still need: ICs, case, heat sinks, filter caps, and a few odds and ends, may be up to another $200 for these items.


Item Qty Price Total

Parts Express M3 Standoff and Hex Head Screw Kit 100 Pcs.

Part # 320-3287

1 $8.87 $8.87

Perforated PC Board 1-3/4" x 1-1/2" For #320-400

Part # 320-440

2 $0.74 $1.48

Perforated PC Board 2-5/16" x 1-7/8" For #320-410

Part # 320-450

2 $0.87 $1.74

Parts Express Mini Gold Plated Insulated 5-Way Binding Post Set 2 Red 2 Black

Part # 320-3375

1 $9.26 $9.26

10uF 50V High Temp Radial Capacitor

Part # 020-1656

10 $0.08 $0.80

10uF 100V Radial Mini Electrolytic Capacitor

Part # 020-1296

10 $0.22 $2.20

1000uF 50V Radial Mini Electrolytic Capacitor

Part # 020-1256

10 $1.11 $11.10

Dayton Audio PMPC-1.0 1.0uF 250V Precision Audio Capacitor

Part # 027-210

4 $2.03 $8.12

47uF 100V Electrolytic Non-Polarized Crossover Capacitor

Part # 027-352

10 $1.19 $11.90

Dayton Audio DFFC-0.10 0.10uF 400V By-Pass Capacitor

Part # 027-452

10 $0.97 $9.70

Screw Cap AGC Fuseholder Black

Part # 070-610

1 $0.97 $0.97

Avel Y236850 625VA 25V+25V Toroidal Transformer

Part # 122-675

1 $98.00 $98.00

2.2 Ohm 1W Flameproof Resistor 10 Pcs.

Part # 003-2.2

2 $0.85 $1.70

5.6 Ohm 1W Flameproof Resistor 10 Pcs.

Part # 003-5.6

2 $0.85 $1.70

0.47 Ohm 1W Flameproof Resistor 10 Pcs.

Part # 003-.47

2 $0.85 $1.70

15pF 500V Ceramic Disc Capacitor

Part # 020-2006

10 $0.15 $1.50

It looks as if you are all set! Keep us posted on progress.

 

[TLS Guy]

I may be late to this party, but there is a new chip amp kit that is technically better than other kits. While far from being cheap, it doesn't use expensive boutique parts either.

The Modulus-86 is my latest amplifier design. It is a composite amplifier using an LME49710 precision op-amp to control an LM3886 power amp. The performance of the resulting composite amp, both in terms of measured performance and in terms of sound quality, is dominated by the performance of the LME49710. Hence, the performance of the Modulus-86 is absolutely stellar.

http://www.diyaudio.com/forums/vendors-bazaar/262273-modulus-86-composite-amplifier-achieving-0-0004-thd-n.html

Thank you for that useful post and drawing that kit to our attention.

I congratulate you on measuring distortion at low power. This is something I'm always on about. This is so rarely specified and people do not realize so many class A/B amps have high distortion at low power and that is why they sound lousy. The manufacturers don't want you to know that piece of information and boast their high power specs, which actually mean little except tell you the clip point.

 

[Speedskater]

I didn't write the text in italics, the kit designer 'tomchr' (aka Tom Christiansen) did. He is a skilled circuit engineer. It would be good for anyone that's into building chip-amps to read his blog (he also does vacuum tubes) and some of his many thread responses.

his blog:
http://www.neurochrome.com/audio/

the chip-amp forum:
http://www.diyaudio.com/forums/chip-amps/

 

[slipperybidness]

I took a look at his blog and website. Interesting stuff.

Looks like he actually works (maybe worked) for TI. That is cool, but it looks like he had nothing to do with the Overture series of chips.

 

[slipperybidness]

B.O.M. from ChipAmp

Alps Potentiometer + PCB for Volume Control (#ALPS-POT-PCB)
1 $15.00
BC / Vishay 0.1uF Capacitor (#D1-BC-CAP)
30 $30.00
LM4780 IC (#LM4780-IC)
2 $20.00
Amplifier Power Supply PCB (#AMP-PS-PCB)
2 $18.00

A couple other gooodies for future projects, that whole economies of scale thing
I'm highly considering the composite LM3886 amp build too. Mostly use scavenged parts for that to cut down the cost.
LM3886TF IC (#NI-3886-CHIP)
2 $11.00
Snubberized Power Supply PCB (#PS-PCB)
2 $18.00


Running total for the LM4780 build:
$285.

Still need the Mouser order. I will probably wait until I get all these parts and get started. There is almost certainly a couple odds and ends that I have forgotten, so I would like to make 1 last order to Mouser to cover all those.

 

[slipperybidness]

The layout on this one came out cleaner than I expected. This will most likely be the P/S for LM3886 (ie, not for the main subject project of this thread). But, I at least now have this available for the LM4780 build until I get a bigger badder one built.

About $14 and scavenged parts. Board was close enough to do what i wanted. Good for 100wpc of clean power. You can see the TI LM3886 Audio Power Amp IC in the background on the perf-board.

Sorry about the pdfs. I'll get time to figure out this photobucket you kids are using one day.

 

[slipperybidness]

Under-carriage

 

[slipperybidness]

Mouser order placed. Again bought more than needed for the LM4780 alone, my total Mouser order was right at $100.

Filter Caps
http://www.mouser.com/ProductDetail/Panasonic/ECO-S1HA123EA/?qs=sGAEpiMZZMvwFf0viD3Y3ffldXPLozayIcOjssrTwWA=

Rectifier diodes
http://www.mouser.com/ProductDetail/ON-Semiconductor/MUR860G/?qs=/ha2pyFadugK1NT31NOUG5oP7hwd8BLMgv4WQaDTFRcVJlOgUB4iHA==

A few values of high quality resistors. Since this amp is running in parallel, I need tight tolerances on the feedback loops to set the gain precisely. Probly way better resistors than called for.
http://www.mouser.com/ProductDetail/Vishay/CMF5524K300BER670/?qs=/ha2pyFaduj3GWSt3YxHjiTJM3Jg2iqVL/yCMw46rU%2btiSmPhWB71onQlMKoSVOG

Also, ordered heatsinks for diodes off ebay
http://www.ebay.com/itm/201200715829?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Running total for the LM4780 = $360

 

[slipperybidness]

Nothing new on the LM4780 parallel amp project. I'm trying to work on it some this weekend.

I did order 2x PCBs for the LM3886 project thought.

Why haven't I worked on the LM4780? I finished up my external speaker protection circuit project!!! It's done, and I shoved it into a box that came with a nice bottle of whiskey!!!

It came out amazing. I am quite pleased! The front side has amplifier inputs on one end, and protected speaker outputs on the other end. The backside has unprotected bypass in/outs to allow for easy speaker/amp swapping.

When you kick it on, there is a 5 second delay before your speakers are connected, thus avoiding turn-on transient thumps. If DC is detected on the amp output, it disconnects your speakers immediately. When DC is removed, it has 5 sec delay and then reconnects the speakers. To avoid turn-off transient thumps, simply kill the speaker protector first, then proceed to shut down the rest of the equipment.

Again, sorry, but here are some pics in PDF.