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Old 27th April 2008, 03:33 PM   #11
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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?
Yes, although I don't adverise it, the chassis pictured here: http://audiosector.com/chassis_integrated.shtml is available as a kit as well all other needed parts:

Premium GC kit, Noble pot, Knobs, Wooden sides, Shaft extenders, RCAs, Cardas patented binding posts, Source selector, AC module, Brass cones, Plitron 300VA toroid

You can build a complete amp as pictured, or use only selected parts and be able to connect amp to the speakers.
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Old 27th April 2008, 04:04 PM   #12
Bluto is offline Bluto  United States
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Gychang -

I looked into gainclones a bit over a year ago. Got discouraged as so many were so far ahead and I couldn't find simple instructions for an easy one. Guys already had them modded to the max.

I'm looking again as I'm interested in the concept of separates.

If you're up to a 'scratch' build and want another (well, me anyhow) Dummy to work with on this I'd be happy to work with you. Apex JR. has 3886 chips for less than $4.

Don't want to steal your thread.

Bluto
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Old 27th April 2008, 04:08 PM   #13
gychang is offline gychang  United States
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Quote:
Originally posted by danielwritesbac
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. . .

I really appreciate all these valuable tips, very helpful, learning quickly but I am old enough things don't click well...

I hope u don't mind more newbie questions to follow, again thanks for all the details to get me started.

gychang
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Old 27th April 2008, 04:17 PM   #14
gychang is offline gychang  United States
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Quote:
Originally posted by Bluto
Gychang -

I'm looking again as I'm interested in the concept of separates.

If you're up to a 'scratch' build and want another (well, me anyhow) Dummy to work with on this I'd be happy to work with you. Apex JR. has 3886 chips for less than $4.

Don't want to steal your thread.

Bluto
Bluto, let's do this thing together, I am sure I am dummer than you. As this thread is useful for a newbie, perhaps our conversation will be helpful to others.

Let me look at the chip at Apex JR. Any other parts that can be ordered from the same vendor? transformer?, heat sink? etc. I am particularly interested in about 50W output model.

gychang
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Old 27th April 2008, 04:24 PM   #15
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About 50 watts.
That's LM3875 with a 48vct (or 24+24 vac) transformer. EDIT: about 2 ampers per chip.

Of the eleven pins of LM3875, 6 are N.C. (no connection), thus leaving only 5 connections to deal with.
EDIT2: See the first page of http://www.national.com/ds.cgi/LM/LM3875.pdf
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Old 27th April 2008, 04:43 PM   #16
gychang is offline gychang  United States
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Quote:
Originally posted by danielwritesbac
About 50 watts.
That's LM3875 with a 48vct (or 24+24 vac) transformer. EDIT: about 2 ampers per chip.

Of the eleven pins of LM3875, 6 are N.C. (no connection), thus leaving only 5 connections to deal with.
EDIT2: See the first page of http://www.national.com/ds.cgi/LM/LM3875.pdf

thanks, is there a proper t/former on this page?, Bluto suggested we order parts from ApexJr.

http://www.apexjr.com/miscellaneous.html

will have to order 2 since your previous suggestion of each t/former per channel may be better.

gychang
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Old 27th April 2008, 04:50 PM   #17
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Quote:
Originally posted by gychang

thanks, is there a proper t/former on this page?, Bluto suggested we order parts from ApexJr.

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

will have to order 2 since your previous suggestion of each t/former per channel may be better.

gychang
There is debate on whether monobloc format is better or not. I'd encourage you to research that one.

Here's an inexpensive transformer that works quite well: http://www.alliedelec.com/Search/Pro...p?SKU=967-7473 each does one lm3875

You'll also need 4 of 10nf ceramic cap, per each bridge rectifier IF using a center tap transformer.

Here's an easy bridge rectifier:
http://www.alliedelec.com/Search/Pro...p?SKU=266-0047

Power supply caps:
http://www.alliedelec.com/Search/Pro...p?SKU=862-0135
About four of those per transformer will give you 9400uF rails.

EDIT: At this time, it would be good to make a shopping list rather than purchasing immediately, because, with a little patience and research, you can reduce shipping expense.
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Old 27th April 2008, 06:08 PM   #18
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Digikey.com is a great source for parts.

Here's the safer "TF" insulated lm3875
http://search.digikey.com/scripts/Dk...me=LM3875TF-ND
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Old 27th April 2008, 06:17 PM   #19
Bluto is offline Bluto  United States
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Hi Gychang -

Sent you a PM.

See more info has arrived. Good point regards helping other newbees who got left behind when the wave came in.

What should we call the thread? How bout '50 watt per channel Dual Dummies' ?

Be forewarned, I'm the guy who started the thread entitled 'electrocution not an option'.

We could turn out to be an inspiration to lurkers, on the other hand , obvious Fools.

Hmmm ...

Bluto
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Old 27th April 2008, 06:52 PM   #20
Bluto is offline Bluto  United States
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DWB & 7/10ths -

Thanks for all the input on this. That's mucho work and appreciated.

I just got the new Digikey Catalog 2 days ago, can't believe those people send me that 40# monster yearly, gotta cost a fortune to print that thing.

I sourced a bunch of needed stuff long ago, a real deal ( me thinks) on heat sinks through an Ebay store I saved as well . We'll do price comparisons with what you provided.

I was familiar with the Dogbreath design and part of the reason I hadn't given up hope, Elliots stuff is good to read and understand 'why' with but too hard for this newbee and his schematics and a soldering iron to risk actual MONEY over.

I'm a year away from serious reading on the subject and just got started again about 2 weeks ago. Already things have moved light years again. Power needed is obvious concern but what I'm picking up is most guys like the 3886 above the 3875. We need a design 1st so everyones input appreciated.

No more to say, it's Gychangs thread and until we talk I'm speechless.

Bluto
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