Updated: 11-Jan-03
Welcome to the DDDAC Column!


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......

  1. New loudspeakers:
    4 way system with:
    SUB Bass: 2x  ETON  12"  with SW6.0  Module (500Watt) giving straight bass from 18Hz-70Hz
    Bass: Thiel C220 driven by the TUMOS amp, 6dB slope from 250Hz
    Midds/High: Thiel C79 and C12 combination  driven by the Golidav SE amplifier, active 6dB roll off  under 250Hz, passive switch at 2kHz 6dB serial filter
  2. Laboratory Power Supply (all you need to test tube and other equipment):
    Regulated outputs: 0-500V 200mA, 0 - NEG100V (negative grid) 0-25V  1A   (2x), 0-100mA  current  source, 100mA  - 1A current source
    AC outputs: many, many, all you need to feed filaments from any possible tube....
    LCD Voltage meter
    LCD  Current  meter
  3. New Line and RIAA amps, modular setup
    Basically the existing DD PRE, but with 3 chassis, Power supply, RIAA amp  and line amp. The Line amp will use the Siemens SIF Ba Tube. The RIAA amp will be reduced to a 2 stage with passive RIAA in between the 2 stages, some new design ideas are cooking and should lead to..... wait and see ! The Power supply will use the latest and greatest Black Gate Power supply capacitors and independent current sources for the filaments.


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