[sdiy] Free stuff - ideas? Also, ringmod schematics?

[Tom Arnold]

On Sun, Aug 14, 2005 at 11:19:55PM -0400, Eric Honour wrote:
> Also, a friend of mine works in a junkyard and said he could get me
> car audio equipment cheap or free.  If he isn't a complete flake
> (which he often is) I may get some speakers, but would it be possible
> to use the car amp as the basis for a line-level amp?  Some car amps
> are really high powered for the price I'd be paying (fifty watts x 4
> channels for less than ten dollars)... so if it works out, I could
> save much money on amps.

I wouldnt spend the time trying this.  For one, car amps tend to be very low
impedence.  This is done cause its far easier to get current rather then
voltage from a low voltage DC system.  I mean, you *could* do it, but you'd
be going 120vac -> 12vdc -> +-30vdc or thereabouts and at any decent power
thats a rather large 120vac-12vdc...

In the 60watt RMS/8ohm range there are several cheap ampboard kits you could
aquire.  I like the one from Dick Smith Electronics.  Its really cheap (
about $35US per channel ) runs off +-30 or thereabouts ( its been a couple
years since I used one ).  Steal the heatsink off one of those carstereo
amps, add a power supply and you're cooking.  Check out the K3431 on
www.dse.com.au.  I'm sure there are other options too, I just happen to like
2n3055 based designs for cheapness and bulletproofness.

> One last question.  I know it's possible to make a passive ringmod out
> of 2 transformers and a few diodes, but I can't for the life of me
> remember how.  Anyone have a link to schematics?  I had one bookmarked
> before my computer crashed, but it's gone now...

http://www.synthfool.com/ringmod.html

Mouser 42TM018 worked for me.  I contacted Stancor and they sent me the
specs for the A-4713 and its 10k/10k.
Never could nail the exact germanium diodes called for in that schematic,
but 1N270s and 1N34's sound good.  Build several, they're cheap and lotsa
lotsa lotsa fun.  I did luck out and got a good deal on germaniums so I was
able to pick several sets that were closely matched.  Occasionally you can
find 1N34's on ebay for cheap.

-- 
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