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-   -   Commercial complete Gainclone kit for a beginner? (http://www.diyaudio.com/forums/chip-amps/122062-commercial-complete-gainclone-kit-beginner.html)

gychang 27th April 2008 12:26 AM

Commercial complete Gainclone kit for a beginner?
 
I have soldered before, is there a complete kit (including tranformer, power supply etc) to try a Gainclone for strictly plug one end on the wall outlet and connect to my DIY speaker (fullrange).

I can follow a "pictural how to" but not schematic, would prefer to order all in one kit form, is there a vendor for this?

thanks,

gychang

Bluto 27th April 2008 01:08 AM

Hi Gychang -

I can't help you but am on a similar quest.

I'm a Fan of yours from your B20 project and followed many of your other projects.

I had thought you'd done a gainclone and had troubles with the 1st one? If I'm correct can you elaborate? I can't afford $100 mistakes. Your answer will help me know what to avoid.

I've e-mailed 3 manufacturers to date with questions regards their instructions being clear enough for a newbee to handle and I don't even get replies.

Hope you get some feedback on this, seems 10,000 built them but had some 'Universal Knowledge' the rest of us don't possess.

Bluto

WJMIII 27th April 2008 01:37 AM

I just finished the BrianGT chipamp.com 3886 kit - I know very little about electricity, can't read a schematic, and that was my first kit ever. I am surprisingly good with a soldiering iron, so that made it very easy.

The instructions at chipamp.com - ok, but not so great. AudioSector.com has a very similar kit, and the instructions/manual on the site is very easy to follow and has some pictures - I have never put that kit together, but I wish I had gone with the audiosector kit simply due to the ease of instruction included.

Neither kit comes with a transformer/toroid, plugs, cords, connectors, or a chassis. Those can be had fairly cheaply if you dig around, so don't be afraid to try some experimenting and hand craft some components for your amp.

However, now I believe I am a professional and can't wait to build my own custom 300b single-ended tube amp - NOT

seventenths 27th April 2008 01:48 AM

Gychang,
I bet that with a piece of proto-board, a couple 3875's and a handful of components you CAN make an amp that you'll enjoy a great deal. There is certainly nothing wrong with the kit route, but from scratch is VERY attainable.
Print out the schematic in question and physically lay each component over it's symbol. Add a wire for each line and voila... noise, er-ahh MUSIC:D


7/10

danielwritesbac 27th April 2008 03:06 AM

Re: Commercial complete Gainclone kit for a beginner?
 
Quote:

Originally posted by gychang
I have soldered before, is there a complete kit (including tranformer, power supply etc) to try a Gainclone for strictly plug one end on the wall outlet and connect to my DIY speaker (fullrange).

I can follow a "pictural how to" but not schematic, would prefer to order all in one kit form, is there a vendor for this?

thanks, gychang

Complete? That's a rather important concept.
And here's a caveat:
Complete, as in achieving advertised results, also involves a preamplifier. The chip amp is a power amp, technically incomplete without a preamplifier.

Brian, BWRX, has two chipamps that include the preamp /w regulator, and this is the most complete design that I'm aware of. See www.transientharmony.com


Let's look at it from a "module" viewpoint:
Power amp
Power supply
Preamp /w regulator
Transformer
Chassis /w heatsink

Although the module viewpoint looks intense at first glance, actually its easier in practice--because this makes for several small projects instead of one large unit.
(Approach is, several smaller problems instead of a big problem.)

That's enough for one post.
I will follow up with more later, and possibly a few shortcuts.

seventenths 27th April 2008 04:41 AM

This is quite instructive and demonstrates simplicity of design.
A simple pot can be used instead of a "proper" preamp.

http://dogbreath.de/Chipamps/ThreeRe...reeResAmp.html



have fun,
7/10

danielwritesbac 27th April 2008 07:54 AM

For beginner use, chips with only five connections may be easiest. Those are LM3875 and LM1875. Both have five active pins.

Select either LM3875's 55 watts and plan to use a preamp,
or
select LM1875's 25 watts.


The purpose of a preamp is so that you don't have to increase the distortion with a gain of 45 on a power amp. Instead, the preamp does a portion of the gain and the power amp does a portion of the gain--with no stress on either.


Next, its transformer shopping time.
How to select?

Take the "watts output" of your amplifier and multiply by 1.5 to get the VA requirement for transformer.

Here's an example of VA, volt ampers: A 36v center tap (18+18 ac) transformer with 1 amper makes 36va.

Relating back to LM1875 above, 25 watts x 1.5 = 37.5, so you can see that the 36vct (18+18 ac), 36va transformer above can probably run a single LM1875 monobloc per each transformer.

Relating back to LM3875 above, 55 watts x 1.5 = 82.5. And, I didn't mention it yet, but LM3875 likes a 48vct (24+24 ac) transformer. That's 1.72 ampers. You can readily find 2 amper rated 48v (2a x 48v = 96va) center tap transformers, and that can run a single LM3875 monobloc per each transformer.

Stereo sidenote:
Although I'm going to cover monoblocs, here's a note for stereo layout. That implies using just one transformer running two amplifiers. Simply use double the VA, meaning select a transformer that's twice as strong. For the final note on stereo layout, its nice to have any left side connections exactly the same length as any right side connections.

My own personal preference is monobloc layout, inferring that each amp chip has its own transformer (no matter how few or how many are inside a given chassis/enclosure). Advantages and disadvantages are well documented, so you can decide for yourself.


And now where are we?
Hopefully, there's enough information in this post that you have selected a power amplifier and a transformer to match.

That's enough for now.
More to follow. . .

danielwritesbac 27th April 2008 08:01 AM

The directions:
LM3875
http://www.national.com/ds.cgi/LM/LM3875.pdf
LM1875
http://www.national.com/ds.cgi/LM/LM1875.pdf

Also,
LM3875TF has a build-in insulator.

However, these need a mica insulating pad between chip and heatsink:
LM3875T
LM3875TA
LM1875T
LM1875TA

danielwritesbac 27th April 2008 08:37 AM

2 Attachment(s)
This photo illustrates where the five connections go.

Right side is speaker output with a protection zobel (pitched higher than the audio band)

Center is the power circuit.
The two small ceramic are 100nF (0.1uF, Bar 104).
The two large e-caps pictured are 220uF, although you could use 330uF or 470uF.

Top left is the NFB, Negative Feedback Loop, that is responsible for setting the gain. It is normally two resistors, although the presence of a optional 22uF (or greater) cap there indicates potential for using this particular amplifier without a preamp, as a cap there can prevent the amplifier from amplifying DC (makes zero dc offset).

Center left is shown an optional "ground lift" resistor, as you can see it connecting the ground of both NFB and inputer circuit (input star ground) over to the power ground. It can be 0R, 4R or 10R.

Lower left is the input circuit. There are many options shown.
Going in order from left-center to lowest left. . .
Most important at the input circuit is the resistor from input + to input -, as this presents a load for the source to drive.
Next is the small 330pF (Bar 331) ceramic cap, also a load, as this shunts away stray RF signals.
The ecap is a dc blocking filter, aka input filter cap.
Next is a 1 megaohm resistor set as a load.
Lowest left is a 1k resistor (optional) providing isolation, but also affecting tonality (can use any "pleasant" value there or 0).


See photo and compare to the circuit in the PDF's above.
EDIT: As you can see, this doesn't require a kit.

danielwritesbac 27th April 2008 10:42 AM

Kits:
(listed because their documents and photos can be useful)
K50 (QK50)
http://www.electronics123.com/s.nl/it.A/id.425/.f
K50 document
http://www.electronics123.net/amazon/datasheet/k50.pdf
K50 spare Printed Circuit Boards (without components)
http://www.electronics123.com/s.nl/it.A/id.1801/.f
*not exactly hifi as shipped, but can be modded easily by installing better components.

Basic power:
http://www.electronics123.com/s.nl/it.A/id.347/.f
power document
http://electronics123.net/amazon/datasheet/k114.pdf
*you can make better for less, but the document is fantastic.

Preamp:
http://www.electronics123.com/s.nl/it.A/id.311/.f
preamp document
http://electronics123.net/amazon/datasheet/k100.pdf
*an adjustable preamp that doesn't run your signal through a bunch of potentiometers

Flux:
http://www.radioshack.com/product/in...entPage=search
*this is quite necessary for neat, easy, soldering--can use #0000 steel wool to wipe carbonized flux off from the soldering iron tip to maintain a bright, glossy, silver color at each solder joint.

Iron:
http://www.radioshack.com/product/in...entPage=search
*a bit short on power, but it won't hurt components

Desoldering iron:
http://www.radioshack.com/product/in...entPage=search
*this tool removes errors quickly

Another useful tool is a multimeter that's sensitive to DC (and readable at millivolts) so that you can check the dc offset of the amplifier before connecting speakers.


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