Archive for Amplifying

Iron Pumpkin ; line preamplifier , SE and Balanced iterations

Iron Pumpkin(s) and other smaller vegetable animals

Well , it started long ago …. when I was really young(st)er, full with naivete and BS , came to pretty novel idea to make xformer loaded tube line stage …
Result of first tests , hardly optimal ( using two halves of 6SN7 in parallel and loaded with ancient xformer from vertical section amplifier of ancient B-W tube TV set) , I was blown with ‘till then unknown dimension of sound – everything was so alive ….
Later I made several iterations of line stage with same approach , being so proud for reinventing boiled water , until I got some xerox copies of Sound Practices , where I found that even in boiled water reinventing I wasn’t first ….. boyz from Italia already made Euridice preamp ; anyway , intermediate iteration was with two halves of 6DJ8 in parallel , latest one being with ubiquitous EC8010 and custom made xformer . That being even published on my old site – WOT preamp and battery charger

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Hitachi HMA6500 ,little mosfet amp from Yore ….. resurrection , by ZM

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 .

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Iron Pre

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 .

Schematic sketch and first proto , conveniently put in dreky casset deck case :

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Pass Labs X150.5 , checking/adjusting offsets ,Iq and gain

Well , here and there these questions are popping on – 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

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.

X150.5 front

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Babelfish J , v2

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 .


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