mwhouston

I assembled on Vera-brd this discrete ESP transistors preamp for another. He boxed it and made the PS. He claimed it was really excellent from only off the shelf components. Wouldn’t mind building another. https://sound-au.com/project37.htm http://mongreldogaudio.blogspot.com/2010/10/esp-p37a-distcrete-component-class.html Mongreldog is an old blog of mine.

the foil is not needed and with the pot on the backend the microphonics aren’t an issue. You’ll be shocked at thier transparency if you build a preamp with them.

“MWH” DHT UX-171A preamp schematic.

If you are having problems with a Xtalk from terrestrial beings try this.

I’ll put up a schematic tomorrow but for now those who would like some figures; HT = 100V bias = 3V current = 2mA Rp = 2.7K Rk = 1.5K Ck = 22uf (NP) Rg = 3K Cout = 1uf 400V Rin = 100K Vf = 5V If = 125mA Rout (pot) = 250K Cout = 1uf (PIO)

Single stage with 100K across the input and the stepper AFTER the output cap. The output RCAs are connected to the wiper of the stepper.

Has some additional hum issues with thIs DHT 1920s tubed UX-171A preamp. Tried a number of earthing arrangements with did nothing. Then like the four or so SRPP (not that this one is) tube preamps before it I put the stepper pot on the backend. Bingo! That fixed it. At good volumes laying down in front of my 90db woofers I can just hear a faint hum. And even better, it sound absolutely glorious. Spoilt for choice now with three excellent and different tube preamps and one with a headphone driver in it. Metsl film resistors and a 1uf Russian military PIO cap on the output and ceramic socket make for a nice simple build.. Just parts from de lab. I’ve called it “MWH”, after me. Or “Music With Heart”. Time to enjoy my new creation.

I finished the DHT preamp yesterday about 1am in the morn to discover a loud hum. No matter what earthing arrangement I tried the loud hum remained. Because I was using DC on the heaters I put Rk and Ck off the positive pin which caused an imbalance in the heater cct. Because there is no cathode the heaters are very sensitive to hum or voltage differences. By putting two 100ohm resistors across the heaters and connecting the balanced point between those two to Ck bypassed by Rk I eliminated any imbalance. A multi-turn pot 200ohm trim pot inplace of the resistors would be better but for now 95% of the hum is gone and sounding good. Also I noticed the left channel louder than the right. With a little tube rolling the perfect balance has been struck. I have four pairs of tubes.

Quoting myself again. I may to go to balanced even with DC on the heaters.

Parts for a F5 amp for another.

I believe my current system is an “End Game” system. It started moving to Altec 511B Horns with FaitalPro Pro compression drivers on 12” woofers. The clincher was Holton Precision 300W amp modules in my own DIY power amp. All my gear is DIY. The Holton amp has such excellent bass and transparency it shouted “End Game”. I can listen to my system day in and day out and continue to marvel over it. End Game system? Sure is but would I take it to a desert island where no change of gear or swapping is possible. Strange as it may sounds there is one component I would change. Assuming the island has clean power and WiFi I would take my DIY; Pi4 server DXD DAC ”Icon” Tube preamp Horns and woofer here is the clincher, I would take my (“Silver Supreme”) DIY 6L6 SE UL wine box 2W power amp That makes little sense when my end game system includes the 300W Holton amp. I’ve made this comment before that when I drop in my flea power tuber I feel at home. Sure after a few weeks the Holton back in doing what it does best. I think if stranded on a desert island and couldn’t hear, once more, my 6L6 wonder I would miss it. So take it with you. Who else has an end gamer but would take another setup to the island? Or just tell us about your “End Game” system.

Under test. Plays music and sounds OK so far.

No balance pot required. DC is king!

Where did I say cathode follower? Quote me!

Just made from bits laying around in de lab here is the 99% finished DHT preamp. Just have to limit the filament voltage down from 12 to 5V and the HT down from 250VDC to 90. Two 5W resistors should do the job.