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Chip Amps Amplifiers based on integrated circuits

Novice dreams and novice questions
Novice dreams and novice questions
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Old 19th June 2016, 05:53 PM   #1
tatagatha is offline tatagatha
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Default Novice dreams and novice questions

Hello!

tldr: excited to build! Any suggested pre-amp designs? Any recommended power supply?

Pre(r)amble: I've been thinking about building myself a nice amplifier as a summer project. I'm looking forward both to the electronics build and making a beautiful case. I've been eyeing a gainclone as the right choice for me and I'm set on the Non-Inverting LM3886 Stereo Kit from chipamp (Non-Inverting LM3886 Stereo Kit | Chipamp Electronics). I am not an audiophile and this is my first audio project. In truth I'm software developer that somehow found a soldering iron and whose grasp on electronics is tenuous at best. I'm not designing from the ground up, but rather trying to piece together kits and designs I've found. I've been doing some research and there are a couple things I can't quite piece together and are missing from my design(kits added together) and understanding.

edit: I just read this: http://www.diyaudio.com/forums/chipa...le-around.html
I'll find another kit, and source for a couple parts, but in general, my approach remains the same. Any suggestions on other kits?

Volume Control / Preamp: I know that the kit is just a pure power amp. The build instructions suggest a pot to simply attenuate the signal and there is this fantastic sticky: Help in choosing a potentiometer as a "Passive preamplifier". That seemed like it would be fine enough, but, the more I think about it the more I want to be able to use a record player. After googling around, I think this requires a preamp to handle phono line levels and invert the eq (RIAA?)? I believe that this is referred to as "that audio curve thing for record players" in the sticky. I know that a lot of people like to make modular preamp and power amp systems so you can mix and match. I don't really intend to make more projects in the near future, so for now I've decided to build both pre-amp and power-amp in one enclosure and have a dedicated phono input. Is there a good bare bones pre-amp kit you could recommend for handling a couple inputs, maybe some tone control? A kit? Or wholly assembled?

I imagine my likely sources are:
- Record Player
- Line in from mp3 player or computer
- Radio Tuner
- Maybe a bluetooth setup for pairing to phone or computer which is basically another line in, but I would hide it inside the enclosure so I seemed super fancy.

Alternatively, could I have a mostly passive preamp but a dedicated thing for phono? An input selector (Grayhill Selector Switch + PCB | Chipamp Electronics) paired with the pot and a dedicated premp between the input selection for phono and the volume knob? https://www.tindie.com/products/skro...no-preamp-kit/
I'm ok with the fact that the line levels in will be slightly different so that volume at any one pot position will be different per input. It will be one of the lovable quirks of my system.

If I do any of the above, will there be any major changes I need to do to the kit?

Transformer: I'm still a little lost on how to choose the right transformer to use with the kit. The build instructions leave a lot of room for just "picking one", but I don't feel like I have a good hold on how to pick. Hopefully this sticky will help: Chip amp power supply- a beginners guide
I think that this choice affects the speakers I'll be using. I plan on using some Cambridge Soundwords Model 6 speakers I found at a yard sale for 5 dollars. I replaced the foam on them and that was the impetus for this project. These are 8 ohm speakers.

Powering the preamp : Will I be able to share the transformer for the preamp or other needs like the bluetooth, but might need a voltage regulator to drop it down depending on the preamp? How will this affect the transformer I pick.

Shielded wire: I see recommendations for shielded wire for anything carrying a signal. Does anyone have a specific wire/part number/supplier?

Grounding grounding grounding: When I have a farther along design and everything pieced together and wired up, I might come back and ask for a double check on my star grounding but this sticky is really helpful: understanding star grounding

Thanks for any advice/color commentary/well-wishes/head-shakes/pointing out big glaring holes in my understanding you can give me.

-Marc

Bonus, If anyone wants to see the kind of front face plate I'm thinking of, here is a demo of some CNCd patterns I'm making. https://www.instagram.com/p/xF7lyAKp...n-by=tatagatha
I plan on making a case that fits under a standard record player like a technics 1200 and doing the face with some nice black walnut from my sister's property. There are also these strange dreams about curved plaster and pulsing leds, but the enclosure design comes after having the internals in place.

Last edited by tatagatha; 19th June 2016 at 06:11 PM.
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Old 19th June 2016, 06:10 PM   #2
tatagatha is offline tatagatha
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Ok.... wish I had read this thread first: http://www.diyaudio.com/forums/chipa...le-around.html

So I'll find a substitute kit, but in general, everything remains the same.
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Old 19th June 2016, 06:23 PM   #3
Mooly is offline Mooly  United Kingdom
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Novice dreams and novice questions
You can use the same transformer to power the preamp and ancillaries although how practical that would be depends on the voltage requirements of the preamp/Bluetooth etc and the anticipated current draw.

Put simply, although generating a 5 volt rail from a 50 volt rail is easy, if the current draw is high (say 1 amp) then there is a lot of heat to get rid of. If the current draw is modest (say 100ma @ 5 volts) then its practical to do.

A low current draw would not involve changing the VA rating of the transformer.
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Old 20th June 2016, 12:38 AM   #4
dreadnoughtstrength is offline dreadnoughtstrength  Australia
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Tomchr is putting together a LM3886 'Done Right' kit ad we speak

Buy yourself a transformer with quad secondaries - ~25v for the amp and ~12v for everything else.

I'm trialing some cheap (think <$10) regulated power boards currently for the amp. They passed a consistent load test, outputting up to 6A for 20 minutes but with some crazy heat build up - some of the traces actually melted the plastic spool they were resting on. I don't like the PCB design so I'm putting my own together - should get you as much current as you need for a 3886 for under $100 in total with a switchable output voltage (if you change between 4 and 8 ohm speakers, for example).
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Old 20th June 2016, 02:47 PM   #5
tatagatha is offline tatagatha
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Quote:
Originally Posted by dreadnoughtstrength View Post
Tomchr is putting together a LM3886 'Done Right' kit ad we speak

Buy yourself a transformer with quad secondaries - ~25v for the amp and ~12v for everything else.

I'm trialing some cheap (think <$10) regulated power boards currently for the amp. They passed a consistent load test, outputting up to 6A for 20 minutes but with some crazy heat build up - some of the traces actually melted the plastic spool they were resting on. I don't like the PCB design so I'm putting my own together - should get you as much current as you need for a 3886 for under $100 in total with a switchable output voltage (if you change between 4 and 8 ohm speakers, for example).
Maybe I'll be the first "Done Right" customer! I'll keep an eye out for the ad.
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Old 20th June 2016, 07:25 PM   #6
dreadnoughtstrength is offline dreadnoughtstrength  Australia
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Quote:
Originally Posted by tatagatha View Post
Maybe I'll be the first "Done Right" customer! I'll keep an eye out for the ad.
Nope
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Old 20th June 2016, 08:24 PM   #7
tatagatha is offline tatagatha
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Quote:
Originally Posted by dreadnoughtstrength View Post
Nope
I'm still quite new here and I haven't figured out what is where. Is the ad up already and you have already bought one? Are you talking about the Modulus-86?
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Old 21st June 2016, 11:46 PM   #8
dreadnoughtstrength is offline dreadnoughtstrength  Australia
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Quote:
Originally Posted by tatagatha View Post
I'm still quite new here and I haven't figured out what is where. Is the ad up already and you have already bought one? Are you talking about the Modulus-86?

No ad up yet as the kit isn't available yet. I should have it halfway through July, so I'll start a build thread then
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Old 21st June 2016, 11:58 PM   #9
tomchr is offline tomchr  Canada
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I'll be sending the LM3886 Done Right (LM3886DR) out to the board fab within the next day or two. Maybe tomorrow morning. I'll open up for pre-orders over the weekend and post in the Vendor's Forum when that happens. You can also just keep an eye on my website. I should have the boards around the first week of July. The documentation usually takes a bit to get together. I usually have the document ready by the time the boards start arriving at the first customers.

The Modulus-86 is a high-end composite chip amplifier which uses the LM3886 and an LME49710 opamp to perform error correction on the LM3886. You can find the details here: Modulus-86 Rev. 2.1: Composite amplifier achieving 0.000067 % THD.

Thanks,

Tom

PS: Welcome to DIY Audio.
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MOD686: Up to 240W/8Ω, <0.00025% THD. MOD86: 40W/8Ω, 0.000054% THD. HP-1: 3W/20Ω, -130dBc THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 22nd June 2016 at 12:05 AM.
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Old 22nd June 2016, 03:35 PM   #10
tatagatha is offline tatagatha
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So, how would I evaluate between building the Modulus-86 and the LM3886DR? The Modulus-86 looks great and has several revisions and successes, where as the new LM3886DR is... well... new.

Marc
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