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imaginarytime 6th October 2012 04:26 AM

generic components?
 
Hello everyone. I've decided I'm going to make a gainclone. Maybe some of you can remember that starting from zero is a bit overwhelming. I've come up with a few fundamental questions but they are all over the place. Since forums are messy enough I'll keep them separate.

I'm trying to put a list of what I need together and order it all, (plus some other stuff) as I can't stand paying $15.00 on shipping every time I want to build something new.

My electronics kit is growing but incomplete for sure.

Here's my question:

Somewhere in the forums I read a reference to a specific brand regulator. I'm not trying to save $0.005, or even $10, but it might be inconvenient to try to shop for specific labels for some of this stuff.

I'm assuming that for some things (maybe over-specified resistors?) manufacturer can't matter, maybe I'm wrong.

I'm interested to know where "generic" components might be a problem.

Thanks.

wintermute 6th October 2012 04:32 AM

In my oppinion (and it is only an oppinion) the capacitors are the area you are best not to go too generic on (especially the electrolytics).

Buying a good brand such as panasonic (fc or fm series) or perhaps nichicon audio range will be worth spending a bit more (and it won't be that much) over generic brand caps.

Film caps try and go for polypropylene if you can (size could be a problem). I actually used polyester caps in my gainclone for the bypass caps as polypropylene would have been too big.

Any quality metal film resistors should be fine (though I personally do tend to obsess over all components :rolleyes:).

Also buy the chips themselves off a reputable supplier, as there are fakes out there.

Tony.

imaginarytime 7th October 2012 12:27 AM

What say you on transformers? Seems threads point to Plintron for high end and Avel for lower cost alternative.

I realize that you get what you pay for, but I guess I'm not exactly sure what it is that I'm paying for yet.

I also have a suspicious that neither are going to 'wear out.' Maybe this is misguided, but I have a feeling that either brand of wrapped wire will outlast my own mortal coil. Maybe I'm wrong about that, but I'm leaning toward a Plintron because I (perhaps wrongly) assume that it will outlast the chip (and every replacement that would follow) and will not depreciate.

Since I'm just jumping in, I don't know how deep or how cold the water is---In fact, I'm not even sure there is water down there!

imaginarytime 7th October 2012 03:41 AM

For the record, a few hours later, I'm leaning away from this plan. I think I'm going with the avel.

madisonears 7th October 2012 04:02 AM

Wintermute gave good advice. Over the past several years, I've played with lots of different components in the MyRef chip amps. What I have found is that electrolytic caps do make a difference in quality of sound. You don't need Mundorf's, but you should buy caps that are rated at 110 degrees with a long life. Caps do wear out, even if it is a long time.

The quality of your transformer will not matter much. I've never heard of one wearing out or deteriorating. The size (capacity) of the transformer is more important to sonics. You can buy more transformer of a cheaper brand, but I wouldn't get the cheapest junk. Antek seems decent quality and good value.

In descending order of importance, this is what I've heard make a difference, but it a lot depends on where these parts are in the circuit:

Make sure the chips you use are legit.

Electrolytic caps: Elna, Panny, Nichicon are good, basic brands, but others have their favorites. Do not skimp on these. Pay attention to service temp and service life. There are some other technical specs that aren't too important at first. You can use a higher voltage cap than specified, but you should not use a lower voltage. You can use larger value (more uF) cap in some places in the circuit, but it doesn't necessarily mean it will sound better.

Film caps: polypropylene is good enough, teflon the best, polyester okay. Wima is pretty much the standard for a good reason. Avoid the cheapest brands. Film and foil are better than metalized film if they fit. Long leads can be bad, so don't buy a huge cap and have it inches away from where it connects to the circuit.

Quality of ceramic caps for bypassing chip power supplies are not too important. Some report better results with silver mica or polypropylene, yet others say lossy ceramic caps are better. The important thing is close proximity to the chip.

Binding posts and RCA jacks: copper content is important, but you don't need to go nuts to get good quality. Avoid plastic and nickel. Vampire and Furutech are excellent quality.

Resistors don't contribute much unless they're bad. Some resistors do sound a little smoother (carbon film), some a little brighter (metal film), some a bit more open or accurate (bulk metal foil). In critical parts of the signal path, you might want to spend a few more cents or even a few dollars to get something special, depending on the resolution of your system and hearing. I would avoid the very cheapest brands, as they're made to pretty low standards. Vishay/Dale, KOA Speer, and PRP are reliable at a few cents each. Exotics such as tantalum, Vishay bulk foil, Amtrans, Caddock will set you back a few bucks each. Avoid carbon comp, as they can be unstable and noisy. Avoid wirewound, as thick film is generally better for sonics.

Power supply components such as diodes and rectifiers contribute to the sound in subtle ways. Buy brand name parts.

Controversial, as it makes a substantial difference with some amps and listeners but very little or none with other amps and listeners, is the power cord. Beware costly commercial offerings. You can make the best cord yourself quite easily and safely for not much money. Connectors and geometry are more important than the wire itself. Even the power inlet on the amp can contribute. Again, no need to go overboard, but avoid the cheapest junk.

Intimate heatsink connection is critical to dissipate the heat. Spend some time getting it right. Vibration control is important, but basic measures will be adequate. If the chassis you mount your amps on is thin gauge metal, add some damping material around the places where the PCB's are bolted down. It doesn't need to be fancy. Large, non-magnetic washers, pieces of wood, some commercial elastomeric products can be effective in reducing vibration. Avoid silicone products.

These are all refinements, and my opinions only. I'm no expert. Do some research, but you need to jump in and get building. You can always swap parts and tweak things once you have a frame of reference. Don't be afraid to not get it perfect on your first shot. Few of us do.

Be careful with AC mains power. Be safe and go slowly. Check everything twice, then use a bulb tester at first power up. With just a little care, it'll sound great.

Peace,
Tom E

imaginarytime 7th October 2012 04:18 AM

Thanks again to both of you for taking the time to answer. I'll be sure to read your these carefully as I'm still wading through the shopping list and making notes on what fits where.

I have one specific follow up. I think I understand the broad strokes on a power supply, and right now I have a 330VA 2x25 Avel in my cart at Amazon. I think I've deciphered from the TB of data on this forum that this will do just fine.

Am I missing something obvious?

[I plan on just buying two transformers and build two totally separate dual mono channel 3875s. One from the audiosector kit and another sourced from the wild WWW. ]

wintermute 7th October 2012 04:55 AM

Which chip are you planning on using? if LM3886 or LM4870 (and probably others) you need to take into consideration the impedance of your speakers!! 25-0-25 should be ok with 8 ohm speakers but you will not be able to drive 4 ohm loads with that high a voltage.

I went with 20-0-20 which is pretty close to the max you can get away with with four ohm speakers. I think a lot of people go with 18-0-18 for 4 ohm loads.

Definitely read the data sheet (probably a few times) for the chip that you are planning to use, it has a wealth of information. I'd have done some things differently with my build knowing what I know now. Unfortunately it was a very compact p2p build which makes changing things pretty near impossible. The main thing I would change now is the gain, I would have made it lower. (I think that the Brian GT schematic I used had 30X gain, I\'d probably go with 20X if I were to do it again..... This article --> http://www.diyaudio.com/forums/diyau...structure.html is well worth a read)

Tony.

imaginarytime 7th October 2012 05:04 AM

Yeah, that's what I'm coming to understand. I'm leaning toward the 3875, and making two go-s at them. One by a kit and another version that is a little more...freestyle?.

I want to buy 2 transformers that are as universal as possible, as I might want to try something else some time.

Taking a look at the link now...

imaginarytime 7th October 2012 05:42 AM

I don't know. I'm drawn back to the comment above that I need to get a frame of reference.

I have to start somewhere and the choice seems to me to be between 250VA 2x18V and 330VA 2x25V. Maybe I should just get both instead of two of the same.

wintermute 7th October 2012 09:45 AM

1 Attachment(s)
It looks like the LM3875 has the same limitations as the LM3886 with respect to low impedance loads. See attached graph from the datasheet which is available here --> http://www.ti.com/lit/ds/symlink/lm3875.pdf

18-0-18 would be fine for 4 ohm loads.
25-0-25 would be fine for 8 ohm loads, and probably ok for 6 ohm loads as well.

If you know the impedance of the speakers you are likely to be using is 6 ohms or higher then I think that the 25-0-25 should be fine.

Tony.


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