Updated:
11-Jan-03
Welcome to the DDDAC Column!
#8
Happy New Year Wishes to all Audio
Friends !!
Happy New Year
New project: TUMOS & how to set up active Loudspeaker systems
Transformers vs OPAMPS (again)
In the pipeline....
Happy New Year
With what else could I start my column in the year 2003 ?? For every reader
of my side the best wishes for 2003! I wish every one a lot of inspiration and fun with
building audio equipment !! For me 2003 will be a great Audio year as well. Still
great projects are in the pipeline with all the same objective: Great Music
reproduction and fun with the design and construction.....
New project: TUMOS & how to set
up active Loudspeaker systems
This started after a lot of discussions
with my audio friends on how to build a 3 way system with supporting Subwoofer, so 3
1/2 ?? After the great experience with the DD Master SUB and some
other set ups with Gydo and Jan, I am absolutely convinced, that every system is improved
by adding a normal closed speaker system with a Subwoofer module where the lowest
Octave Roll Off can be compensated(like the SW2.0 from Thommessen), leading to power full
bass foundation from as low as 20 - 30 Hz. But I am dwelling a bit... The discussion is on
a 3 way system where the first cut off is round 250-300Hz. Normally this leads to
very large Capacitor's and Coils. Not to mention that filter design is complex in
this area any way; the speaker impedance is far from constant due to the impedance peak
round the systems resonance frequency. The pro was that the sound would be homogeneous,
the pro for an active solution is the direct drive of the low speaker plus the fact, that
the SE amp (what else would you use for the mid/highs, hahaha !!) could be filtered at 200
Hz, leading to much higher output as the low frequencies normally use the most power from
the amp, less distortion etc etc.... But what to use to drive the low amp?? An other Tube
amp ?? PFFFF, very expensive and the bass reproduction is not the best in this world. A
Subwoofer module ?? may be.... but these have normally lot's of OPAMPS, and lots of
negative feedback, probably not leading to a nice co-operation between the lows and
midds, which I prefer to do 6dB any way... So I decided to built a hybrid
amplifier, Tubes for Voltage Gain, MOSFET's for Current amplification, no NFB of
course.... Than I realized that the Voltage gain is already done in the SE amp's driver
stage, so why not use this signal and only give it a simple 6dB filter (one RC at the
input) and design a simple 1x current amplifier ??
Well I did and when I listened to it as a full range amp, just for fun, just to hear how solid state was all about, I realized I built some thing with absolute tube sound, just by accident ...... You better read all about in the TUMOS section
Transformers vs OPAMPS (again)
In the DDDAC 2000 I used successfully Sowter Transformers directly uplifting the
current output of the PCM63. When I bought the Sony 777, I was wondering how
OPAMPS could sound so good. Actually they really do in the 777.... Never the less I
designed the tweak which was on my page already for quite a while. I recently finished the
tweak (read about this in the Tweak section) and after a few weeks
(yes, the transformers need quite a while...) I was presented more precise
music, sweeter highs and more spatial information. The transformer section is selectable
by a frontpanel switch (the former headphone volume control is used f or that
purpose....) so I can try it over and over again, just A-B comparison. Compared to
the transformers, the OPAMPS sound harsher. It is a very relative world we live in eh? The
777 with the opamp output is indeed very good, till you hear how good it becomes
with a transformer output...... For a short while I thought OPAMPS could do the job,
but now I know better, they are a limiting factor.... Why is Sony not doing this
than ???? Very simple, The output impedance is far too high for many amplifiers. You
should NOT load my output with less than 100kOhm, which makes it unusable for commercial
use, but for private use, who cares ????
In the pipeline....
Just a quick peek in my design kitchen to keep your appetite in visiting my
Site......
Happy Listening and Building !!!!
Doede Douma
IMPORTANT: The information provided on this page is intended as guide for DIY activities and therefore free to copy and or publish. If any one wishes to use any of the information from my WEB site, please make sure to refer and footnote to my URL Link as source! Doede Douma