Tannoy Westminster amp matching question.

An amp with a 600 ohm input is designed to be used with a preamp with a transformer output (like professional gear in the old days).

FWIW our preamps can drive that load but have a direct-coupled output rather than a transformer.

I have a capacitor coupled amp that can drive 600 ohms too reasonably well, but, it also is fairly high in gain (18 db) and has a massive 30 uf coupling cap. My friend said that the huge cap is what makes this linestage suitable.

I spoke to the designer and the 600ohms load input is in fact a transformer not set with a resister. So it would seem that this is a transformer coupled design. I tried a CAT ultimate Mk11 last night (100ohms output) and its very good, transparent, non fatiguing etc but I still don't get the extended bottom octaves. On Patricia Barber modern cool I can follow the Double bass line down to the point where I am missing the lower notes. I Still get the leading edges etc of these notes just not the meat ,depth and scale that I've heard before. The best I've had the bottom end so far is with my 75ohm output pre off my headphone amp. but its too noisy.

Can someone please suggest why their 600ohm matched impedance , tranformer coupled design, might work better than a using a lower impedance pre in a bridged model into the 600ohms as I am trying. I know that matched impedance delivers better power transfer lower reflections but that Bridging delivers better voltage transfer. Maybe I just cant get the differential high enough with the low 600ohm input ??

As you can see I've read enough just to confuse myself. maybe keeping and eye out for an Atmasphere pre is the way to go. It does appeal to me.

Thanks again.

I don't know about "theory," but, I do know that I like the sound of a number of transformer coupled gear. That is what I am currently running. The "problem" is the limited compatibility of the amp with the transformer input. From experience, I know that if a capacigtor coupled tube linestage is used, it must have a BIG output cap and a pretty robust output (my Emotive Audio Epifania fits that bill, certain Audionote linestages also work at a local dealership which sells transformer coupled amps). Most tube linestages have something like a 2 uf coupling cap and sound thin and totally dead with such amps. Atmasphere says that his directly coupled linestage will work, so you have another fine alternative.

I have not tried solid state linestages which have very low output impedances that could easily meet the supposed at least 10 to 1 impedance ratio that is often bandied about.

It is the immense size of the coupling cap at the output of many tube preamps that also limits the abilities of said preamp. When you are driving a 600 ohm load, the cap has to be at least 120uf (FWIW 30uf cuts off at 8 hz) in order to not have phase shift problems in the audio passband.

Look at what the output impedance of the preamp is at 20Hz and compare that to the 1000Hz figure and you will see what I mean! If you want the preamp to play bass without coloration, the two figures should be exactly the same.

By the time the cap gets over about 3-5uf, it is offering significant coloration at all frequencies due to inductive effects and increased dissipation factors due to its size.

In the old days, to drive a 600 ohm load with tubes, you needed an an output transformer in the preamp. Of course such transformers have problems of their own. But we developed a patent (we are an OTL manufacturer after all) that allows direct-coupling. Even if driving a 100Kohm load, getting rid of the output coupling cap in the preamp is an easily-heard increase in transparency.