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RE: DHT OTL Linestage - Tram 2

Posted by driguy (A) on December 23, 2009 at 17:27:18

In Reply to: RE: DHT OTL Linestage - Tram 2 posted by bcherry on December 23, 2009 at 16:46:17:

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

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