Well ,it started as solution for two customers; both having my Babelfish amps, both driving Dynaudio Contour 1.3 with them.
Whatever solution they had for preamplifier in that time, they weren’t on par with amp quality ….. so logical development of situation is to mate amps with line stage simple enough but not simpler than necessary …… simply put -preamp made in same manner.
After some chat , consensus was that “plain” buffer (so , no gain ) is adequate,so I decided to make a quick mockup with buffer pcb I had from yore,as part of Poor Serbian Man Lightspeed project.
Frankly – not “plain” buffer anymore , but I simply couldn’t go with less .
Basically-4 separate buffer cells , and simple but witty bipolar (+/-12V) shunt reg on board.Cells are made of scarce and expensive Toshiba JFets (2SJ74BL , 2SK170BL) as source follower. In this case , just two buffer cells are populated, as not needed more for unbalanced operation. For more details, it’s easy to check my signature on diyaudio.com .
Schematic sketch and first proto , conveniently put in dreky casset deck case :
After some tests in situ (in systems), it was evident that, even if no-gain situation is OK for most digital sources, there is a problem with large part of DVD concerts collection – SPL is in low-ish side, so we agreed that’s better to gain some gain on my side, than searching it in dvd player electronics.
After few days with problem circulating in back of my scull, thinking what can be simplest and best sounding solution (without resorting to something more complex I already have , or something which someone else signatured recently) I stumbled on new idea ….. and how’s often the case , I actually just remembered something which I already forgot …. xformer !! …… in fact – autoformer.
I remember my first CD player , and how I put repeater coil (telephone tech. slang, name for telephone trace/line xformers, mostly declared as 600:600 and derivatives of that) on it’s output and how I immensely enjoyed more with them, than without.
So , few days later, sketch is like this and proto is looking like this, after I chose adequate autoformers, stashed on my shelf; they’re mostly from yore Iskra telephone facility modules, and chosen one is giving free 6db of gain:
Same day it was gone to evaluation and I was pretty sure guys will have same impression as me – knowing from before that Iskra Iron , when chosen correctly for task , can compete with most expensive Iron from anywhere in the world.
And that I’m saying , having some experience (and still some having in boxes and drawers) with many brands of iron …. Sowter,Lundahl,Beyerdynamic,Picatron,Telefunken,Plesey …. just to name a few.
Ok, few days later , they flashed with green light in my general direction and we could proceed with rest of things needed of solving. Deal was done – we are going to make two of them, pronto.
Cases -after some time ,who else than Leonardo.
He’s well known on Baby DiyA, with hands (brain and his handy CNC) in many successful DIY and commercial gadgets in this area .
As we agreed, boys negotiated everything about cases, while I sent just few tech. details to Leo, along with graphic for front .
We also agreed about choice for RCA inputs, then we had just to wait for cases to arrive.
Week or so later, Leo sent me this – just look how immaculate packing is :
I’m still greenin’, when I remember how nice I felt ….. pure pleasure of assembly is in front of me … and how that was, you can see from these (mostly random) pictures :
And later, prior to lid closing and packing …… in fact , putting them in a car :
…….. boys in Novi Sad are happy, I’m happy , Babbelfish-es are happy and Dynaudio’s are happy.
So , again , if you’re content with moderate gain (who isn’t,nowadays),certainly most raw and possibly one of finest solutions is to use xformer/autoformer gain.
Especially when autoformer solution is possible,with less intrinsic compromises than xformer , you can hardly achieve that level of signal energy preservation with any other (active) approach angle.
Repeaters are everywhere – on junkyards , surplus stores , you can even find them new – only if they’re calling them today “line level transformers” or even “isolation transformers” .
And , when you compare today’s expensive specimens with some from yore,everything becomes even more funny.
You can even have slightly more gain (winding ratio!) …. say 9-10db, without sacrificing in Rout area; it’s something as 100-110R now .
I’ll not bother you , and especially my self, with measurements and accolades about sound – everything here is old beans, so if you’re looking for tech. mumbo, do your own home work.