Vacuum State RTP3D preamp
- Thread starter hvbias
- Start date
First unit started to sing at friends place...first words from him - killer pre...hope to hear more from him later
Huh...I would not say below a month and more realistic forecast is end of Oct/Nov. I want it to be fully tested in several systems back home and they need to make a proper packaging for sending as both units are like 50kg together. But as it arrives I do believe it may go directly to Zurich (Urs) so easy for you to hear it.
I am planning to build one of these but NOS 6922 tubes are getting pretty hard to find. What tubes are you using?
This is quite some project. Congratulations. I was one of the original 10 beta-testers for Allen. It took us about 2 years to build the RTP-3C. I later bought an RTC-3D from Allen, which was built on PCBs. I have been using my prototype RTP-3C as a platform for experimentation. It is now serving as my tape head preamp after I changed the RIAA EQ to tape EQ. My experimentation with different coupling caps led me to use the Wima FKP4. This is a metallized polypropylene film and foil capacitor, designed for pulse applications. It is completely transparent, uncolored and super fast. I don't believe in using caps to "season" the sound. I just want them to get out of the way. I also changed the series type stepped attenuators to a ladder type with constant input impedance. Allen always warned against using other types of attenuators, because a constant 50k input resistance is needed for the RIAA network. I have found a 48-step attenuator using precision resistors that have a pretty much constant input impedance. At least, it does not make enough of a difference that I can detect. The transistor at the phono input stage cascode has been upgraded to MAT2. The RTP-3D uses a different transistor. The power supply capacitors were electrolytic initially, but now, only metallized polypropylene caps are used. I am also using only Lemo Redel sockets and plugs that Allen favored. Even though I don't have a lot of experience with commercial high end preamps, I must say that the RTP-3C/3D is extremely fast, uncolored, detailed and dynamic.
NOS tubes, or new production? From what I understand, Allen recommended Electro Harmonix tubes so that's what I was planning to start with. I'm building a line stage only - no phono preamp.
I am using Mullard/Amperex 7308 (low noise version of 6922) on the phono stage, and Valvo PCC88 (7V version of ECC88) for the line stage. It is simple to change the value of the resistor at each LM317 that regulates the heater supply for the correct voltage/current.
When I was first setting out on the path of becoming a hi-fi addict in the late 1970s I had the great pleasure of becoming acquainted with Allen at his Wentworth Street showroom/lab in Sydney. I was in my late teens and really at that time completely clueless about high end hifi gear. However I was very interested in learning. Allen saw my enthusiasm and desire to learn. He was always very accomodating and went out of his way to allow me to listen to his demonstration system. He had first generation Systemdeck(spelling?) turntable with a SAEC 4xx arm and an Adcom moving coil, his RTP pre and power amps driving stacked Acoustat speakers. I spent many hours listening to his system on many visits. Allen would let me bring along LPs and he would also suggest and play LPs which he owned. To this day I still remember how pure and effortless the sound was. In a way, listening to his system spoiled me. It was very difficult to muster enthusiasm for alternative systems after hearing Allen's system. Most everything else I heard was disappointing by contrast. I'm glad though in retrospect because at that young age I was essentially given a lesson in what to aim for.
Allen closed his showroom after a couple of years and not long after moved to Switzerland. I never saw or kept in contact with him. Like many others I was saddened to hear of his passing. I get a little moist-eyed still recalling his passing. I remember him mostly as a very kind, patient mentor. GOD be with you Allen.
Allen closed his showroom after a couple of years and not long after moved to Switzerland. I never saw or kept in contact with him. Like many others I was saddened to hear of his passing. I get a little moist-eyed still recalling his passing. I remember him mostly as a very kind, patient mentor. GOD be with you Allen.
I knew Allen quite well and frequently visited his business in Schaffhausen. He also made periodic trips to my place. We shared a mutual love for Acoustat speakers (I had 3 pairs) and I reviewed the last version of his preamp…a wonderful machine. I was very sad when I learned of his death…but his legacy lives on!
Oh yes. With the purchase of the ART20 I am much more appreciative of the GT 2000. A superlative and inexpensive second hand purchase. I've had mine since 2008 and the return on investment(I got a GT 2000 and YSA-1 for $1500 US) has been substantial.
Please excuse the off topic conversation, people.
How lucky you were to know Allen to that degree. He was a true gentleman and I am grateful to have been acquainted with him.
An interesting thread at another forum:
forums.stevehoffman.tv
Yet another DIY Preamp - Vacuum State RTP3
I’ll admit that I get as much pleasure and satisfaction from designing and building audio gear as I do from listening to my system (well, almost...
forums.stevehoffman.tv
Allen if I recall correctly had some interesting and unorthodox ideas about cartridge alignment. I only just recalled this so I haven't searched for them, yet.
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