subminiature tube
preamplifier
6H16 mikro tube
preamp with the sound of a giant !
May 2010
My dear friend
Paolo, who is famous for using capital letters and
overdose exclamation marks sent me this mini preamp , asking me "to
take a look inside".
Or should I say
- TAKE A LOOK !!!!!!!!!!!!!!!!!!!!
He bought
himself a 100 dollar gimmick from China and he expected
miracles. Perhaps, he was tempted by the glow of the tube in
Amsterdam brothel-like window on the front of this preamp.
As if making a
window wasnt vulgar enough, and as if putting a curved
mirror behind it wasn't good enough, the designer decided not only to
glow the tube filiamenrts even if THIS TUBE IS NOT PLAYING, IT S NOT
CONNECTED ! In addition to that - they mounted 8 LEDs behind the tube
to add a fake glow. Oh man, this is so kitch that it goes beyond the
kitch and its is preatty again.
And if all that
was not enough - The window is A MAGNIFYING GLASS
!!!!!!!!!!
Paolo - I
sympathize with your exclamation mark addiction. Apparently -
you like excess !
So, I decided -
dear Paolo - I will KEEP the not connected tube in the
window. Instead of throwing it away immediately - I will preserve the
first reason you chose it and I will modify only the guts.
Sorry - the bad
news is - you gonna have to live with the Amsterdam
preamp forever. ;-)
Xiang Sheng is
proudly silk-screened on the front plate. Who knows,
maybe in 10 years it will be synonymous with high end, and Mark
Levinson and Conrad Johnson will be forgotten. Xiang Sheng will be the
new Gucci, the nu black.
Dont be
surprized by the PHONE - you cant make a call from this box.
But you can probably plug headphones there.
The Glowing tube
looks okay compared to the horrible MHZS jobs, because
this one is backlit with amber on low voltage glow, while MHZS gives
the srtongest blue they can possibly source which can blind you in
seconds. It would be good perhaps to harden the polymere tooth fillings.
The internal
look of the preamp - as documented below on my pictures -
is already AFTER the rework by Lampizator.
The stock sound
is very loud and rough and dirty, although it does have
good aspects like slamm, bass, speed and lively character. It is sort
of a punk concert kind of sound.
I must applaud
good power transformer, good power supply stage with
nice caps and great tube regulation. The chassis is also quite okay.
All That is
what I decided to keep.
What I
immediately changed was the cheap pot - and in went the blue
alps.
Then I removed
the entire three tube PCB with the line stage and
the headphone stage, both based on Chinese tubes: two 6N11
(looking like ecc83 clone) and one SN3 (looking like a ecc82
clone)
It is worth to
mention now, that Paolo allowed me to get rid ofthe
headphone output and concentrate only on line stage.
And thats what I
did.
Mikro Preamplifier
by Lampizator:
I decided to
build a super cool, small SRPP scheme based on 6H16P
subminiature tube from Soviet Union.
It mounts easily
on a prototype PCB without any sockets.
The optimal
scheme is this:
200 V DC supply
6,3 V heaters
SRPP scheme
Rk = 1k, Rg =
300k, no C on the input, cathode resistor bypass Ck = 100
uF / 16 V (a high quality oscon or black gate)
Caps at the
output are minimum size 1 uF my minimum 160 V DC rating.
Everything has
been described in my mikrolampized Behringer article.
Ia is 2,8 mA per
tube, total 5,6 mA current draw from PSU.
The oryginal PSU
board produces quite clean DC of 300 V which I dropped
by installing a 28k resistor / 2W in series to my lampizator. That
reduced the voltage from 300 to 200V. After resistor I added a large
cap 220 uF / 385V (size can differ but the volt rating is minimal)
connected with minus to the ground.
That whole
project if you have the parts can be completed in one
evening and the sound is worth the effort.
The 6H16P tube
is unbelievably good tube. It sounds heavenly pure, it
has the magic, the inner light, it is powerful and dynamic. The sound
"sounds expensive" so to speak. This tube is also completely free of
any microphony effect.
Connected just
for fun to a 100 000 Euro system, in place of a 20 000
Eu Verdier preamp - believe it or not - was almost indistinguishable
from the Goliath. My David was very attractive thanks to its enormous
speed and slamm, in the face sound that seeemd natural like live music.
It's the sound that would sell like crazy.
The base pre,
plus the minature tubes plus some caps and a pot still cost
under 200 USD - what a way to blow that kind of pocket change and
experiment. Recommended.