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Path: utzoo!watmath!clyde!cbosgd!ihnp4!qantel!dual!mordor!sjc
From: sjc@mordor.UUCP (Steve Correll)
Newsgroups: net.audio
Subject: Re: Pad line level to phono level
Message-ID: <3827@mordor.UUCP>
Date: Tue, 8-Oct-85 15:19:11 EDT
Article-I.D.: mordor.3827
Posted: Tue Oct  8 15:19:11 1985
Date-Received: Sat, 12-Oct-85 14:58:01 EDT
References: <281@kepler.UUCP>
Organization: S-1 Project, LLNL
Lines: 40

> I'd like to be able to play my CD through my friend's Onkyo receiver/amp.
> Problem is the receiver has no other inputs besides the phono preamp
> inputs.  (Grrrrr.)
> 
> I figure I can either cannibalize the receiver and look for a line level
> input to bring out to the case, or I can pad the output from the CD 
> down to phono preamp input level.  I realize this is a bit of a crock, 
> but it'll be nice for her to be able to record some CDs, and to listen
> to some of my favorites at her house.
> 
> Could one of you with spare time and access to the standards for stereo
> input levels give me values for an H-pad or L-pad that would drop the 
> level and match the impedances?

A magnetic phono input not only expects a much lower level signal (on
the order of a couple of millivolts) than a line-level input (on the
order of a couple hundred millivolts), it also expects a signal whose
bass has been cut and whose treble has been boosted according to the
RIAA equalization curve. Thus, you would need to add not only
resistance (e.g.  an L-pad) but also a network of precision (1% or
better is the norm nowadays) resistors and capacitors to implement the
inverse RIAA curve.

Does the receiver really have no line-level input at all, or have you
merely used up the ones it provides? In the latter case, you might
investigate a cute little passive switching box which Radio Shack sells.
It's meant for adding tape-to-tape dubbing capability to receivers which
have only one tape input, but it also lets you plug 3 or 4 line-level
sources into its inputs, and plug its output into a receiver's tape
input (which is a line-level input).

If your receiver does not even have an input for a signal from a tape
deck, then cannibalizing it to add a line-level input sounds easier to
me than trying to adapt to the phono input. Tapping in just before the
volume or balance control (whichever is earlier in the circuit) usually
works satisfactorily, since the impedance of such controls is usually
30k ohms or more.
-- 
                                                           --Steve Correll
sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc