Well , it started several months ago , few boyz at Baby Diyaudio asked for advice which second hand amp to buy . Some members started ( even if that’s really DIY forum) talking about synergy , lalala , blahblah …… while I remember seeing few interesting amps on local adds site , of which one is venerable and indefinitely cute little amp form Yore – Hitachi HMA6500.
Well – it’s hard to buy anything better for that sort of Eu greenies nowadays ….. around 100E .
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 :
Well , here and there these questions are popping on Diyaudio.com – how to check/adjust bias (Iq) ,offset(s) and gain on my X(A)xxx.? PL amplifier; this tutorial will address that.
Take in account that older PL amps are having (small) mosfet based output stage biasing generator , while later ones are having TL431 generator iteration – with some specimens finished without NTC compensation – exactly as amp shown in pictures.
However, I’m sure that you’ll find same logic (shown here) applicable also to earlier models.If not ,and you need some info regarding earlier models, contact me either through blog e-mail thingie , or on diyaudio.com.
Amplifier shown here is X150.5 , late issue (circa 2007 , according to pcb text) , being in possession of DiyA fella known under witty Old’n’Cranky moniker.
As any named Babelfish – my iteration of Papa’s gadget .
This one is iteration of Aleph J , v2 means made as adaptive base for making almost entire power range of Aleph amplifiers .
Naturally – JFet input , cascoded to prevent poof from excessive rail voltage , additional Daughter boards for additional output mosfets.
More info here .
