Novice dreams and novice questions

tatagatha

Member
2016-06-17 3:21 pm
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/chipamp/286405-chipamp-com-people-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: http://www.diyaudio.com/forums/anal...osing-potentiometer-passive-preamplifier.html. 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/skrodahl/muffsy-phono-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: http://www.diyaudio.com/forums/chip-amps/128561-chip-amp-power-supply-beginners-guide.html
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: http://www.diyaudio.com/forums/power-supplies/115698-understanding-star-grounding.html

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/xF7lyAKpsd/?taken-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.
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
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.
 
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).
 

tatagatha

Member
2016-06-17 3:21 pm
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.
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
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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tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
The LM3886DR is an LM3886 with all the components needed to make it deliver the data sheet performance.

The Modulus-86 takes it a giant leap further by providing error correction on the LM3886, thereby driving the THD and a whole bunch of other parameters well below the noise floor. Most importantly, the power supply rejection is orders of magnitude better for the Modulus-86. This is why the MOD86 performs as well on an unregulated supply as it does on a regulated supply or a switching supply.

If you want performance, the Modulus-86 is where it's at. If you're on a tighter budget or would like a straight up LM3886 amplifier, the LM3886DR is where it's at.

Tom
 
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gabe75

Banned
2014-05-20 1:40 am
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).

Can u please tell me what regulated boards are u talking about?
6 amps , what voltage , what voltage drop?
Thanks a lot
 
Can u please tell me what regulated boards are u talking about?
6 amps , what voltage , what voltage drop?
Thanks a lot

They are the LT1083 boards that Tom mentioned. I dropped 5v over them at 6A current output and they worked fine, aside from the heat (I hooked a probe up to the -pitiful- heatsink and it reached 100 degrees in about 5 minutes). With a bigger heatsink and a more reasonable output I think they would be fine.


I'd say they're genuine LT1083's, but pulled from old equipment.
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
I dropped 5v over them at 6A current output and they worked fine, aside from the heat (I hooked a probe up to the -pitiful- heatsink and it reached 100 degrees in about 5 minutes). With a bigger heatsink and a more reasonable output I think they would be fine.

5 V @ 6 A -> 30 W dissipated. Yep. That'll heat things up. The laws of physics are rather inconvenient that way.

Any thoughts about another 25-30v 6amps regulated power supply?

My HP6643A works very well... :)

I plan to measure the LM3886DR with a Connex SMPS300RE. I suspect some switching noise may filter through, but we'll see. I'm planning to show a plot of the THD+N of the LM3886DR powered by two HP6643A lab supplies, a regular linear unregulated supply, and the Connex SMPS300RE. I need the boards to arrive first, though. They went into production yesterday.

Tom
 
Ok , thanks , and I say they are real if u pulled them from an older device.
Any thoughts about another 25-30v 6amps regulated power supply?

I didn't pull them; that's how they came when purchased. I've found 1084's for $14 each which I plan on using for the PSU I'm building now. Providing they keep cool they should be fine for a 3886.

5 V @ 6 A -> 30 W dissipated. Yep. That'll heat things up. The laws of physics are rather inconvenient that way.



My HP6643A works very well... :)

I plan to measure the LM3886DR with a Connex SMPS300RE. I suspect some switching noise may filter through, but we'll see. I'm planning to show a plot of the THD+N of the LM3886DR powered by two HP6643A lab supplies, a regular linear unregulated supply, and the Connex SMPS300RE. I need the boards to arrive first, though. They went into production yesterday.

Tom

I can just imagine some poor sucker trying to draw the rated current from them with the provided heat sink (barely 1x1").
 

gabe75

Banned
2014-05-20 1:40 am
LM3886DR ?
Nice! i still did not try your main amplifier , the Modulus-86, i guess i was waiting to finish some of the project i started and never finished.....
I am actually very curious to hear your thoughts about My_Ref Fremen Edition, i know that you will put together one very soon.
At one point I was very close to buy the parallel version of the modulus(lm4780), but u just discontinued those!
 

tomchr

Member
Paid Member
2009-02-11 12:58 am
Calgary
www.neurochrome.com
Texas Instruments discontinued the LM4780 used in the Parallel-86. Sorry. I can't support a circuit when I can't get the parts. I supported it as long as I could.

LM3886DR is just a straight LM3886 implemented according to the principles I've been advocating here and on my Taming the LM3886 pages. Unlike many of the boards out there, mine will deliver the data sheet performance. It is not a composite amplifier like the Modulus-86, so you won't get the stellar supply rejection and the THD will be a bit worse for the LM3886DR than for the Modulus-86. Basically I'm filling in the void left behind by Chipamp as they don't seem to be able to fill orders these days: http://www.diyaudio.com/forums/chip-amps/292961-chipamp-com.html

Many like to use the LM3886 as a tinkering platform. I'm basically setting them up for success in that regard. The Modulus-86 is better suited if you just want to build a world class amplifier, complete the project, and enjoy the music. It's not as well suited to tinkering as many of the components are critical to performance, primarily stability.

Tom