2. amps-preamps
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Transformer coupled outputs/inputs in preamplifiers.

I have been a big fan of VAC preamplifiers, both for their musicality and their ability to optimally mate with all solid state and tube amplifiers I’ve owned. I believe this is strongly related to use of transformer coupling at output and input. Are there many any other tube preamplifier companies that use transformer coupled outputs (+/- input transformers). I am aware of the SE preamplifiers recently from BAT with transformer coupled outputs and a recent offering from Prima Luna, I believe. Any thoughts on these preamplifiers or others. Yes, I am aware that transformer coupling has its strengths and weaknesses, but I am convinced (after 15 years using VAC preamplifiers) that output transformers are generally the answer for compatibility issues. Thanks so much for all your kind input.
audiobrian
9 responses Add your response
erik_squires
15,788 posts
 
+1 to the OP, I'm kind of a fan!! :)

I like expensive caps, but there's something quite different about transformer coupled inputs/outputs.

I don't know how many realize that if you listen to a vintage recording, you are probably listening to the end result of quite a few of them.
larryi
3,737 posts
 
My custom-made linestage has input transformers and output transformers.  In my case, the output transformers are kind of necessary because my amp has complementary input transformers and does not play well with all linestages.

bigkidz
3,324 posts
 
Why limit yourself there?  Choke loaded preamps, preamps without capacitors in the signal path. etc. DHT deisgns, etc.

 
three_easy_payments's avatar
three_easy_payments
2,097 posts
 
I didn't even think about this being a factor in why my VAC preamp pairs so well with my Pass amp.  I had attributed much of the synergy to the impedance match primarily but this makes a lot of sense.
audiobrian OP
183 posts
 
Before my 15 year ‘love affair’ with VAC preamplifiers, I did try many well respected preamplifiers including  Halcro, GamuT, BAT, CJ, Audio Research, and Mark Levinson. All of these fine preamplifiers required some matching, sounding excellent with some amplifiers and less than optimal with others. Using amplifiers including GamuT, Clayton Audio, Audio Research, Luxman, Pass Labs and VAC, my VAC preamplifiers were never less than fully compatible. Although it may relate to VAC quality and voicing, IMHO the VAC output transformers seem to contribute much to their supreme compatibility.  This is just my opinion from many years of experience, not circuit or electrical expertise. Thanks to all. 
guidocorona
4,298 posts
 
Well implemented transformer coupling not only increases cross-component compatibility, but also significantly reduces common-mode noise and intermodulative artifacts...

Case in point, for a couple decades, Jeff Rowland has been using Lundahl input transformers on all its amps, and Lundahl input as well output transformers on all its power amps.

Regards, Guido



antigrunge2
1,331 posts
 
Best case in point are Wavac pre- and power amps: all transformer coupled with nary a capacitor in sight. Sheer audiophile bliss, conveying an immediacy and colour saturation that in my estimation hasn‘t been bettered.
atmasphere's avatar
atmasphere
11,615 posts
 
Its possible to direct-couple preamp outputs too.
Transformers need to be loaded correctly; if loaded too lightly (impedance they are driving is too high) they can express more of the inter-winding capacitance and less of the turns ratio. This can result in a peak somewhere in its response curve. If loaded too heavily you can get a bit of a roll-off at higher frequencies. This might not be much of an issue since its pretty easy to get good bandwidth at line levels. But you might want to ask Kevin what impedance he regards as ideal for them to drive.
cey's avatar
cey
204 posts
 

@larryi, do you have ea build thread with pics and schematics somewhere? 

 

 

ceylon

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