Tube-DI prototype - experiences and questions

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Wolferl

Active member
Joined
Mar 7, 2006
Messages
33
Location
Germany
Hello,

in the last few months I designed a tube-driven active DI-Box with these specs:

-stereo version (not dual mono)
-input is a cathode follower stage for high-resistance sources - gain is 0,9
-followed by a simple passive EQ (highboost, lowcut, lowboost) gained by a srpp stage very similar to gyrafs pultec concept
- output is a transformer 2:1 - I used the OEP A262A7E wired 2k4/600 Ohms

Here are the schematics and some pictures of my prototype:
http://groupdiy.twin-x.com/displayimage.php?pos=-1721

First of all - my tube di works fine - no problems at all! No noise, no undesirable distortion, good frequency response (+/-0,5dB). The EQ is much better than the EQ's of several mixers.

But what I expected was more 'tube sound' (without the EQ). It sounds very clean and I can't here really a difference compared to semiconductor amplified DI.

I tried several tubes in the input stage:
12AX7 JJ
12AX7 SED
12AT7 JAN Philips
E88CC JJ

The sound differences are very very small. And compared with a solid state mixer channel, there's no "tube" effect or something else. It is subjectively the same sound. So I'm a bit dissapointed because tube circuits are much more expensive than semiconductor ones...

What I've built is a good (from technical side) active DI-Box. As good as a semiconductor DI-Box - but that's not what I wanted!

Any suggestions concerning the schematic? Are there possibilities to get a more "tubelike" sound?

Thanks to the experts here and best regards!
 
The cathode follower input will be very transparent. That type of output stage will be much more transparent than an old style single tube single plate driven stage. That would be the first thing I'd try to change. You may want to look for an output transformer that will take DC and run a direct feed stage. You might like that more than a parallel feed stage. If that's not enough you may need to track down some vintage transformers and see if you like the color they add.
 
[quote author="Gus"]what is tube sound?[/quote]
Have a listen. This sound perhaps ?

realtube.jpg


:wink:

But indeed, let's try to define it (less than 100 words).
 
Tube sound for me is:

- a little bit compressed
- full and rich with harmonics
- a little bit closer (maybe because of the compression)
- shining highs (silky)
- defined lows but not too hard

...
 

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