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RE: DHT OTL Linestage - Tram 2

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In Reply to: RE: DHT OTL Linestage - Tram 2 posted by bcherry on December 16, 2009 at 00:36:09

Very nice concept Brian. I built a similar unit using a 26 tube and a cap coupled output. You may want to leave some room for folks to experiment with different output caps as they make a large difference as one would expect. I use a battery for the filaments but your supplies should work as long as they are really quiet. Any noise will be heard as you already know especially with high efficiency speakers.
I do not have any experience with your FCUPS module but if it sounds like the specs read it should be very nice. The power supply needs to be really good to get the best out of the DHT tubes. I used a tube regulated supply after trying it without it. The soundstage really opened up after putting in the regulating tubes.
The CCS on the tube works very well just as it did on my LadyDay amps. After building a unit like this I think a lot of people will really be blown away by what it will do to their systems overall sound. It is truly revelatory especially for those who have been used to SS, TVC's or even units based on the smaller dual triodes like the 12AX7 and even the 6SL7's. Good luck with the unit. I would encourage anyone who has not heard a DHT driven preamp to give this one a shot.
Happy Holidays to all!
Tony

Follow Ups:

RE: DHT OTL Linestage - Tram 2 - bcherry 16:46:17 12/23/09 (2)
Hi Tony
Yes we will use a largish chassis with suspended subplate. As is our standard now, this will be all film caps.
I'm interested to know what noise levels you were able to achieve at the output of your 26 linestage. Is it all in one chassis?
I agree, the sound of the DHT linestage is mostly undiscovered and only the brave dare go there.
regards
Brian
DIY - Done Right!
- RE: DHT OTL Linestage - Tram 2 - driguy 17:27:18 12/23/09 (1)
  Hi Brian, I was able to reduce the noise to a nearly inaudible range even using a single chassis and a toroidal power transformer. I did use a shield between the AC and DC sections much as you do with your LadyDay amps. I did use a thicker plate (4mm)and I think that helps with low frequency problems better. I can barely hear any AC hum component at all and only if I put my ear within 1 foot of my 100bB sensitive speakers. I actually get more noise from a little tube "rush" than from the power supply. I think I would be able to completely eliminate what little hum I have by using an "R" type transformer as a supply especially since the need for current is so low. I accomplished my low noise by using Mundorf M Tube caps and chokes but as you can imagine this is expensive, bulky and heavy.
  Getting rid of electrolytics in the power supply IME is almost as important as it is in the signal coupling area. Even Blackgates cannot reach the level of musicality that film caps seem to be able to reach with relative ease.
  The largest problem as you may be aware with the DHT's in a preamp, is the filament heater supply. I could not get it quiet enough with a regulator and caps. If you have one of your filament heater modules set up for very low noise like the TentLabs "low noise" units, that in my mind would be the very best way to go especially from a product packaging point of view.
  I do not want to push too hard on any particular point but as with the LadyDay amps, a CCS setup works extremely well with my 26 tubes. Of course it adds some power supply rejection as well but it does require additional volts to drop across it as well.
  I was using a highly modified Audio Note M3 kit before I built the '26 and without any break-in and some (well, lots of) noise from the filament supply I could tell within a minute that I made the right choice by building it. Personally I feel that other than making the choice to go to tubes and especially single ended amps that your customers will look at choosing a unit like this will make the biggest difference in how music is presented in a system. Good luck with it.
  Happy Holidays to you,
  Tony
  - RE: DHT OTL Linestage - Tram 2 - bcherry 23:16:00 12/23/09 (0)
    Thanks Tony
    Appreciate you sharing your experiences.
    Playing now with 45's and we're getting there. Agreed about film caps 100%.
    Brian
    DIY - Done Right!

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