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In the Forum: Melquiades Amplifier
In the Thread: Valve Preamplifier for Macondo/DSET
Post Subject: DHT Preamp updatePosted by anthony on: 8/3/2020
So, it has been a while. I have DSET/Macondo in stereo now although there is still some work to do to finish it and tune it to the room. As discussed earlier in this thread I need a preamp with gain and the Placette is just not cutting it for me (no gain). There are three sources for which gain is needed: 2 x phono stages; and dac.
Over the weekend I prototyped a 10Y/801a/VT25/VT62 preamplifier just on a lump of MDF. It uses one of Ale Bartolas Hybrid Mu-Follower boards, a regulated B+ power supply and a locally designed CCS for the DHT filaments and Slagle Autoformers at the output for volume control. The build was relatively simple and trouble free, and when finished it had something like 0.003mVDC on the outputs but a little (3mVAC) AC pickup up through the autoformers (they will require better separation or shielding). Plugged into the DSETs the preamp is silent...no noise.
Output impedance is about 30R before the autoformer, gain is x8, but the autoformer reduces the output impedance logarithmically with attenuation so in normal or even loud use case is going to be 1R or below. 20mA plate current.
Listening to it tonight for the first time I am really hopeful that this is a good solution. Still the honeymoon period but it seems to have hit quite close to the design brief in terms of loudness and sound quality when driving the DSETs. No signs of lag or loss of detail or softening of the sound or overt warmth. I have three SS gainstages here that also get the volume, and this DHT preamp seems to be everything my favourite is and more, at least on the phonostage I listened to tonight.
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