Conference hips::uk_audioo

    One of the cleverest ways I've seen is used on the Naim Nait (You
    thoughjt I was going to say Linn :-).
    
    One channel has no balance and is hence fixed volume (X)
    
    The other has a pot so you can get it's some where between X�Delta
    and hence center the image.
    
    CCT: Note - I know nothing about amp design at all.
    
    	L in -------+----------- out
                    |
                    R
                    |
    	Ground -----+----------- Ground
                    |
                   Pot
                    |
    	R in -------+----------- out
    

    re .0....
    
    Well, Mike, being an audio minimalist I would say go for a high quality
    ganged pot (such as Penny and Giles or ALPS), and not have a balance
    control at all.
    
    Any imbalance you then hear between channels (other than deliberately
    lop-sided recordings, e.g. some live) would be down to component
    differences in L & R stages. You could probably fix this, and get a
    better sound into the bargain, by systematically replacing resistors,
    capacitors, and even internal wiring with the high grade types
    available from Russ Andrews or Audio Synthesis, until you're happy. If
    the amp's design is basically sound (no pun intended!) you should get
    some very good results. You could also tweek the balance and improve
    sound by changing the topolgy, e.g. by changing earthing arrangements.
    
    If you then *still* need a balance control, try the following circuit:-
    
    L in >----------------------------------> L out
                        |
                      4.7K(?) fixed
                        |
                      100K(?) linear pot,
                      wiper to ground
                        |
                      4.7K(?) fixed
                        |
    R in >---------------------------------> R out
    
    This way you never completely shut down one channel. The (?) against
    the resistor values means you should choose the values to suit the
    output impedance of the amp's line stage and the input impedance of
    amp's power stage - the ideal place for the control. I would start as
    high as you can and still keep some control, at least 10x power amp's
    input impedance is as good a place to begin as any.
    
    Have fun!
    
    Dave

	I've been meaning to ask this, and home-brew amps would appear 
	to be a good place.

	I've built a simple passive preamp.  It has two inputs, a volume
	pot to the main output and a switched tape output that bypasses 
	the volume pot.

	Question is, could I put a headphone socket between the volume 
	pot and the output sockets.  Would the 2v signal be enough to
	drive a pair of headphones (seinhiser 480), or will I have to 
	buy (or make) a headphone amplifier that slots into the tape
	loop in the preamp ?

	Iain.

    Buy/build a headphone amp. It will be worth every penny. Unless you
    plan to remove/bypass the socket when not in use, the contacts in the
    main signal route that break when you plug the phones in will almost
    certainly degrade the sound, and lose you some of the benefits of your
    passive hook-up.
    
    If you want a recommendation, the HiFi News/Record Review Headcase, at
    around �80, is a gem. It is basically a 50mW class A amplifier, and is
    designed to go into the tape loop via paralleled, gold-plated, in/out
    sockets. I use Sennheiser 450's with no problem, so your newer 480's
    should work OK.
    
    The Headcase is good enough to reveal changes in the source
    you won't hear without megabux speakers and amplification. It is
    available on mail order through the HFN/RR Accesories Club; it is
    perhaps cheaper to build your own, but you *could* spend that time
    listening to music! It has a sort of sweet, valve-like class A sound,
    which is ideal for the kind of inciveness that headphone listening
    gives. However it will show up a poor source or programme material for
    exactly what it is.
    
    I have seen some small ads for the odd made up model and kit by
    companies whose names now escape me. They weren't familiar and there
    were no prices. The HFN/RR model, a Stan Curtis design, has been around
    about 5 or 6 years - a long time in hifi!
    
    QED also make one, about �50 I think. I don't know what it's like, but
    the Sound Org in York no longer stock it as they weren't happy with
    some aspect of it. Make of that what you will.
    
    Dave               

	Dave,

	Thanks for the information onthe Headcase.  I was in the shop
	on Saturday dropping of my turntable and I asked about headphone
	amps.  They got the Moth products price list out and the Headcase
	is sold by them.  The RRP was 96.75, but the magazine wanted 81.00
	so the shop has ordered one for me at 81.00.

	Should be here by next Saturday and I can't wat to plug it in.
	Another question.  I have QED P1 Incon gold cables between the 
	CD-preamp and preamp-power amp.  Should I use similar quality 
	cables to hook up the headcase ?

	By the time I've got this set up completed, a large part of the 
	investment is going to be in the cables themselves.

	Iain.	

    re .5....
    "Another question.  I have QED P1 Incon gold cables between the 
     CD-preamp and preamp-power amp.  Should I use similar quality 
     cables to hook up the headcase ?"
    
    I'm not sure what you mean by "CD-preamp" and "preamp-power amp", but
    I'm going to asume you mean the output and input connectors
    respectively.
    
    Since the Headcase should be installed as follows.....
    
    CD player-------------->|    |--------------->power amp
                            |    |
                           Headcase
    
    you should invest in similar quality cable for the second run if you
    found it beneficial to use it with a single run. There will be no
    degradation due to the Headcase, as the two pairs of phonos are simply
    paralleled.
    
    I don't know what this will add to the cost. Personally I'm not into
    specialist cables, as they are often so system dependent that upgrading
    a component could mean yet another hunt for a cable that works.
    
    Enjoy the Headcase.
    
    Dave 
        

	Thanks for the recommendation Dave.  

	I got the headcase last night after a two month wait for some
	strange problem at Moth products.

	Plugged it into the tape loop on my home made preamp and sat 
	down to enjoy some music.  Its great !  

	Next problem is finding the right speakers to get a similar sound
	in the main system.

	Iain.