RE: Old amps, was Re: Far out man!

[Hoover Alan <HooverA@tce.com>]

Better let someone look at it who is competent at electronics.  It sounds 
to
me like your record player might have a "hot chassis".  This means that no
isolation transformer was used in order to cut costs.  If the speaker leads
were hooked up to make it difficult to get to them, this is likely the 
case.
"Ground" on such a chassis runs at about 75vdc relative to actual earth
ground.  Hooking up to the speaker on such a chassis is dangerous, and
should not be done.

You should always use a proper isolation transformer when hooking up to the
speaker output of an amplifier.  Not only because of the above safety
reason, but also to prevent hum due to ground currents.  And another 
thing!!
If you come off of the speaker output of a guitar amplifier, you should use
a VOLTAGE DIVIDER to reduce the amplitude of the signal going into the line
input, or you will probably damage the input circuitry of your board due to
the high voltage available at the speaker output.  Plus, a filter capacitor
to ground to reduce the highs a little, or the sound will likely be very
"sterile".  This will take some experimentation to get the sound just 
right,
but well worth the effort.

Better yet, get a "Power Soak", which properly loads down the tube amp
output, letting you crank up the volume to get nice distortion, but use the
filter cap when going into a board at line level to eliminate the sterile
sound.  Let me know if you want more details on the divider, capacitor
values, etc.  You can get great direct sound this way if you are willing to
tweak around a bit. 
-----Original Message-----
From: Dave Stagner [mailto:dstagner@icarus.net]
Sent: Tuesday, September 01, 1998 5:01 PM
To: Loopers-Delight@annihilist.com
Subject: Old amps, was Re: Far out man!

> "Get a little project box.  It needs a 1/4 jack going in and rwo 1/4 
>jacks
> going out.  The input jack should be connected to the regular speaker 
>jack
> on your amp. For the two output jacks, wire them in parallel.
> Put a 1000 ohm 5 watt resistor in series with one of the jacks.  This is
> the line out.
> You should be able to plug it directly into mixers, etc...  Make sure the
> speaker is plugged into the other jack!  It is bad for tube amps to not
> receive a proper load.....It requires almost NO electronics knowledge!"
> 
> I have a turntable which is from the 50's and doesn't have a line out.  
>So
> a friend of mine soldered the wires leading to the built in speaker to an
> output jack.  When I plugged it in to a guitar amp. a capacitor exploded
> inside the record player.  
I assume this old turntable has a tube amplifier?  The problem may just be
its age... old capacitors often fail due to aging.  In fact, any tube
amplifier dating back to the 1960s or earlier should be re-capped by a
professional for safety reasons.  Cap failures can take out other
components - especially expensive vintage output transformers.