LM3876 and 4-ohm drivers

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I am building a Silicon Chip kit with the LM3876 chips - I'd lke to use a pair of car speakers (I have spares) if possible. An addition in the kit mentions using supply rails at +/- 28V for this.
If I use an 18+18 VAC transformer - should this give me the +/- 28V.

Given these speakers will be in my observatory - quite small, used late at night - so quite low volume - should using this chip with 4-ohm loads be a problem??

TIA

Lee
 
Music!!

My amp (one channel so far) produced some music! Stoked! Small amount of hum also - although so far I've not bothered with trying to minimise this with star grounding etc.
It sounded surprisingly good, considering I had the amp board connected to a bare, cheapo, paper-cone woofer alone, without any crossover/filter....

The hum I had completely disappeared upon shorting the inputs, or connecting an ipod - is this hum then due to ground loops??
 
Might be a daft question......

But.... (and I have searched!).....

I now have two working channels - using an iPod headphone out as source, I can adjust volume easily past where I would generally listen, but a line level source (CD player) is insanely loud.

Where/how do I control the volume?? <ducks>
I know a dual linear pot comes into play - do I just insert in the input lines??
Is this where I need a preamp??
I did pick up a "Universal Stereo Preamplifier Kit" (another Silicon Chip kit based on LM833 opamp) - it says "can be constructed for use with a magnetic cartridge, cassette deck or dynamic microphone..."
Did I get the wrong thing??? I'd just like to be able to boost a lower level input if required - or decrease the volume of a loud source......

Hope this isn't TOO basic...... :D
 
about 10k works for the majority of GCs.

you can also make a fake law pot by useing a 100k linear pot and a resistor.. a little googleing is in order...

I doubt you will get good performance with that preamp... look on the site for the pedja rogic buffer there is a pedja rogic buffer for dummies thread... that shows how to wire one up with some stripboard..
 
I think I can wire up one of those..... thanks for the info.

A question: Doing a search for 2SK170 at fibra brandt brings this up:

Stock Database
Part Number Description Price
Found:5
2SK170-TOS N-FET 40V 20mA 0.4W 0.49EUR
2SK170-BL/TOS 0.70EUR
2SK170-GR/TOS ask
2SK170-BL / TOS 2X MATCHED 2.20EUR
2SK170V-TOS 2.09EU

Does it matter which I were to use - I don't understand the differences between these????

TIA, Lee
 
You need the BL version for the buffer. The two letter suffix referrs to the spec of the Jfet in terms or current handling I think. (My memory is fried with 2sk170 specs, I have been working on this buffer myself for two many hours)

The 2xmatched I suspect means that you are gettng two of them that have been tested and are a matched pair. There is a fairly high tolerance on the specs of this Jfet if you check the datasheet.

Matching the Jfets yourself means buying up a bundle of them, testing them and grouping them. The idea being you want the two channels matched with identical (or nearly anyway) specced components.

That will be why a premium is being charged.

I bought my bundle of 50 from someone in the trading post here a while ago. I paid a lot less for them than those prices and will be matching them up myself (this weekend hopefully if the gf will stop making plans for me, got a Kilt fitting already)

Instructions for matching them are available on t'internet, Its a slow process, but relaxing kinda.
 
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