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Old 25th September 2006, 05:22 PM   #1
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Default LM3875 chip amp part decisions

I'm currently sourcing parts for a AudioSector LM3875 dual mono premium kit. The PCB boards are arriving soon and I'm have difficulty deciding where to get the most bang for the buck.

What would you order and how much would you spend (min/max):

Toroidal transformer
RCA inputs
Binding posts
Potentiometer
Switches
Internal wiring

I know there are endless combinations and options, just trying to find a nice middle ground of price & performance. Links to part sources would also be helpful.
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Old 25th September 2006, 06:25 PM   #2
Nordic is offline Nordic  South Africa
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Sadly you'll find cases often is the most expensiv component and make the rest look like small change...

I always try using the ceapest (to a point) components I think is reasonable... and then as and when the opportunity or fancy strikes swap out things to see if there is a sonic diffirence.

Mostly the only difirence is pride...

My first (and still favourite transformer) was a custom wound EI type I had done at an industrial winder - should be a bunch in your yellowpages. It cost less than half what toroid would cost, and is offering rock solid performance... plus I even had them add a third low voltage 1A winding for powering smaller saundry devices... VALUE FOR MONEY but a little large to fit into a small (read cheaper) amp case ...

I guess what I'm saying is, it is still a chipamp (yep they are plenty good)... BUT don't go and blow loads of cash on it.

The proverb says "even if a monkey wears a golden ring, it is stil an ugly thing" Ugly is maybe a bit strong word for a GC, but yeah...if the bug bites you you'll probably be grinning at these kind of questions in 6 months...
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Old 25th September 2006, 07:23 PM   #3
wboyd is offline wboyd  United States
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As Nordic said - "I guess what I'm saying is, it is still a chipamp (yep they are plenty good)... BUT don't go and blow loads of cash on it."

That being said, I will tell you my most secret of secrets in locating "High-quality, low-cost" parts for my chipamps.

I head down to my local electronics surplus...or hit a repair shop and see what they do with unclaimed repairs. I grabbed a couple of old Pioneer receivers and BANG, four really nice (big) Elna caps.

You never know what you might find.

Wayne
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Old 25th September 2006, 08:25 PM   #4
Nordic is offline Nordic  South Africa
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Although you will have to mount them offboard due to size I can realy recommend the Ampohm capacitors from RS components, appart from being a little large, they made my GC sound alot better then the cheap stuff I used before, and it still wasn't excesively pricey.
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Old 25th September 2006, 10:37 PM   #5
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I guess my question is do I get a any sonic gains with:

Toroidal transformer: AVEL 250VA 18V+18V TOROIDAL or Plitron 225va 18v+18v

RCA inputs: DAYTON RCA-CHRB RCA or Cardas GRFA-S Thin

Binding posts: Dayton gold banana jacks or Cardas CCBP-s

Potentiometer: Cheap or Alps

Internal wiring: Regular wire or silver teflon wire

I like pretty, but I also I like to be realistic.
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Old 25th September 2006, 10:54 PM   #6
preiter is offline preiter  United States
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The cheaper version of everything you listed is fine, except maybe the pot.

You don't need a $100 pot, but you do want to choose carefully. I'd leave it out entirely if you have volume control elsewhere in your signal path. You can always add one later.
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Old 26th September 2006, 12:03 AM   #7
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I second what PREITER said. Some guys are happy with a pair of volume controls from Radio Shack made by Alps. There is also a way to use a pot with a log taper combined with a shunt resistor to mimic the audio taper of an Alps or Noble control. And there are log taper pots that track much better than cheap audio taper pots. The guys at Audio Asylum had quite a thing about this last year.

An EI transformer, if you can get it in the VA rating needed, is better than a toroidal transformer -- if the price is OK. The EI transformers create a low pass filter due to their electrical properties and better protect your amp from RFI and other junk that comes in on the AC service to your house. The toroidals require some extra film caps on both primaries and secondaries to filter out the junk the EI transformer does not pass. Also, a large toroidal puts greater strain in the power fuse when the circuit it turned on. It looks like a dead short until its magnetic field is energized.

Dick
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Old 26th September 2006, 04:29 AM   #8
wchick is offline wchick  United States
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I used a 100k linear pot from Radio shack and then switched to PEC, a 100k log pot (recomended by Peter Daniel). The PEC seems a little better but the Radio shack is pretty good already. Now Digi-key carries PEC pot.

I used carbon film resistors (Riken), they produces warmer sound than metal film. I just can't stand the Caddock which is too bright in my system. So you may want to consider which one is more appropriate in your system.

Other things are: Kimber wire, Avel Lingberg transformer, Panasonic power supply caps; I did use MUR860 in the dual bridge which I can easily hear the improvement. RCA is Cardas. Considering the limited parts in GC, I can convince myself easily to use "better" parts.

Regards,
Wallace
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Old 26th September 2006, 10:11 AM   #9
Nordic is offline Nordic  South Africa
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100k? isn't that a bit extreme should it not read 10k?

I also buy alps pots mainly from RS components usualy in the $5 range...
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