Rabbit hole tube amp

Discussion in 'DIY' started by m17xr2b, Apr 10, 2020.

  1. m17xr2b

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    A choke is a choke, I really wished this would be the case, It would be easy just for the inductance value to have the final say in sound quality, just like the fanatics are chasing distortion percentages, the fools.

    I've been testing the differences in parafeed applications of an active gyrator loading, custom Japanese finemet(nanocristaline), a lundahl 1668/20mA and an absolutely massive Sowter one.

    The solid state option is the best bang for buck, light, small, it has it's own particular subtle sound and does nothing wrong. I'd rather take it than a low to mid level choke.

    For the actual iron, winding technique and core material have a major impact on the sound quality, each with it's own flavour and specific synergies. It'd be cool if I had the tools to measure the capacitance of each. Price seems to follow performance quite well judging on technicalities first and personal preferences second. The Japanese choke is actually worth twice the asking price of sowter and so is sowter to lundahl.
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  2. m17xr2b

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    The whole journey culminated into this amp, what I think an amp should sound like, overly overbuilt PSU, bog standard parafeed schematic, 14 transformers and 9 capacitors, 25kg. In essence it's an output stage but the Wavedream can drive the low input miller PX4 like it's nothing.
    Susvara needs almost max volume but unlike the 801A amp where it got close to grid current below max volume this will sit in class A1 all the way and not break a sweat driving the hungry hifimans.

    Single stage PX4
    100H 60mA Sowter plate choke
    Sowter 8665 output
    2.7u ClarityCap CRM parafeed cap
    35uF ClarityCap CRM cathode bypass
    Running a conservative 35mA, 230V, 12:1 OTP ratio.
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    This time I've built the final PSU version, nothing to upgrade even if I wanted and kept medium-ish parts for output. This way I'll get a good idea of how the PSU sounds like and gauge the changes on individual output components and if they reflect existing impression from other amps. I'm especially interested in how much impact will CMR to Duelund CuSn will be, been using the duelunds almost from the start and don't know exactly what their signature is.
    Another good point to find out, choke quality vs inductance value in the case of parafeed.

    Easily the best HD800 amp I've heard, I'm loading the tube a bit much with 300ohm HPs, this causes a slight 2-3dB of boost at 20Hz because of the inherent tuned circuit of parafeed. Extremely lively low end, will put some planar setups to shame, I always though the HD800 bass performances was limited by the driver, guess not. Reminds me of speaker impressions where some didn't feel they could fill the room while others did. HD800SDR fills the whole stage with rumble, a stage that's complete and perfect.

    The amp was designed with Susvara in mind and it does deliver, there's no substitute for full DHT SET Parafeed flavour.
     
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    Last edited: Jan 9, 2021
  3. m17xr2b

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    I really wish to be more patient with this hobby and life in general, most times I can't really stay with a component if I know I have an upgrade I can use.

    With the power of DIY I quickly converted the 801A amp into a 801A choke loaded driver for the new amp and swapped the CMR parafeed caps to 2.2uF duelunds CuSn, RC coupling with 0.33uF matching CuSn caps. A bonus is the separate PSU for input and output based on the same transformer series and filter caps, no mixing and matching with PSU quality.

    Why are full DHTs amps not popular for headphones? Because they take a huge amount of space, enormous weight, thankfully not much heat with this one but it can be brutal with large triodes.

    This is a single amp just like any DNA or EC, 28 transformers, overkill, overly complicated to build and I love it.
    [​IMG]
     
  4. m17xr2b

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    With just over a year since I started on this unsure journey I'm happy to say it's been concluded just because there's nothing more I can do to upgrade it and I'm over the moon with the sound. And here it is in all it's prototype glory:
    [​IMG]

    It's a single stage 600:600 transformer input with a slagle AVC, 12H choke input with separate 32H PSU chokes per channel , 2.2uF Duelund CuSn parafeed caps, Mundorf Supreme with SGO bypass last PSU caps(15+15+15+4.3+4.3+4.3) and custom output(100H primary) J&K OCC secondary 25:1 output transformers with 120H@30mA plate chokes. The twist is all the transformers except for the filament circuit and AVC are nanocrystalline.

    Above everything this was my initiation into high end amps, constantly gathering knowledge and trying components and topologies to find out what suits my system and preference while trying out and debunking popular ideas.

    At the end of the day I'm left with an impressive stash of components, about 30 different high end transformers, all kinds of caps and a tube stash to make any collector jealous. Most important the experience and know how of single ended tube amps is the main point, learning from mistakes and pushing when things looked bleak and sparky.

    Moving forward while a single stage is impressive it does has limitations and I see two stages is the way to go even with headphones. It's all about compromises and while a high RP tube such as 801A can be driven directly by the wavedream I crave the presentation a PX4 type can deliver.

    This is my end game, reaching this level of audio performance from my own designs and DIY amps with all the components and tubes I could hope for. I assumed once I get the to end of this journey that will be that yet a new one started in its place.
    The thrill of the chase, the big boy amp, the output transformers Donald helped me spec out have arrived and with fresh ideas and components such as silver AVCs, silver and custom capacitors, molybdenum tubes and magnet wire slagle adjustable resistors, I'm my own path and loving it.
     
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    Last edited: May 8, 2021

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