October 2009 - Follow up on Joe's Dream Audio System
Further Improvements since May 2007






Here are Joe's summary and photos of his changes to his impressive audio system within the last two years:

Time passes and so it is necessary to review the changes the setup went through to give you some inspiration and share my experience.

First, I swapped the line stage tube from 5687 to a 6H30. The differences are not substantial, but since I am lazy I decided not to change it back for the moment.





I have changed the subbass amp from differential to push pull and the last stage of the power supply from 10H + 500F to 100H and 1F. This moves the -3dB from 35Hz to 8Hz and tightens the bass considerably. This is pant leg flapping since the speaker goes down to 17Hz! Try this with Kraftwerk's Album "Minimum Maximum" (e.g. Kardiogramm or Mensch-Maschine).


Subbass PP-amp

The midbass driver stage was changed from 211 sakuma style to a differential 7N7. It is easier to handle, saved one of my precious 3 phase transformers and added some clarity. A very fine driver stage with lots of headroom! I take a Lundahl LL7903 (1:4) as Phase splitter and a LL 1660AM/PP (4,5:1). This is enough gain, a fine bandwidth and low output impedance.

For my midrange I started with a LL7905 (1:11,2) and a 801. I tried what happens when adding a driver stage to this single stage design. After my very positive experience with high transconductance tubes (EC8020, EC8010, 5842 etc.) I chose the 6C45 which is cheap and common. The topology is pretty standard (Lundahl 7903 1:1, Lundahl 1660AM/35ma, 801 and Tamura F 7004). Without the driver stage the HF cut off started gently at 17kHz, but now it goes up to more than 35kHz, this is an octave! Not bad!

Before using the 6C45 I had WE437, which is in this set up simply not necessary. The 6C45 costs a fraction of the WE437 and sounds the same. It has only two drawbacks, you have to find two similar tubes (parameters are not as uniform, especially the so you have to buy some more) and it is not sexy. So if you have to impress go for WE437.


 

Midbass amp with differential 7N7 driver stage and 211 SE triode output tubes

 


Midrange SE amplifier with one 6C45 driving one 801 DHT output tube per channel.


After damaging my TAD ribbon I bought the smallest (and cheapest) Goto tweeter SG 06. Compared to the Pioneer PT-9 this is a big step forward, lower distortion and a higher sensitivity! Having such great success with the 6C45 I made a differential amp. This is the only amp with a single phase PSU, because I didn't want to use two 650VA transformers for 2x 3W of power output. The LF-cut off of the X-over is 10kHz, so I can use a simple first order crossover.

6C45 differential amp for the tweeter section

"Besides this" David Haigner altered the frequency response of the Altec 515Bs (resonances between 1100 and 1700Hz ) and straightened the Goto's impedance. A handful of parts but with breathtaking results. Sometimes you ask yourself why use all this stuff when a simple change of a single resistor or a little bit different value of a cap can change the sound so much.
 

Equalization network for Altec 515Bs

So to all the DIY guys: it is the crossover not the driver. David shows this impressively with his Rho-speaker, but you need experience, time and good equipment ...

Overall these mods have been a nice step forward.

What's in the pipeline for the next year: something completely different. Phono amps using 37, a linestage that really lights up (201) and two power amps (RV218 and VT-127).

"Tschau"
Joe


 

Joe's current system consists of:

Differential phono stage (EC8020, EC8010)

Differential cd amp (PC88)

Differential line stage (6H30)


Subbass: push pull 6HS5 amp - Altec 416A

Midbass: Differential 7N7 - Ultrapath 211  Altec 515B

Midrange-tweeter: 6C45, Ultrapath 801 - TAD 4002z

Super tweeter: differential 6C45, Goto SG 06

All in common are three phase power supplies (except the super tweeter amp), transformers everywhere and lots of iron.

Here are some more pics...

Phono (side view)

 

Phono (top view)

CD Amp

 


CD battery power supply 
(impressive and quite heavy)




Crossover

 


 


 

 
 


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