Oct 7, 2020

C3g Phono preamp Part 2

Supply and more 

Classic C input supply with two LC cells for excellent ripple attenuation.  

Two other RC cells will floor the rectifier residual to negligible value. Especially important for the first stage where signal is in the mV range.

Great care has been taken in time constants calculation to ensure good transient restitution. For basic calculation refer to LCR phono preamp part 3.

Construction with high quality parts.

I used both electrolytics and paper capacitors. I found the combination well balanced and use it with satisfaction for years now. Paper and aluminum foil are very reliable with a super fast discharge time. These old caps are a must in power supplies along with paper in oil. Unfortunately these are usually too big to fit the chassis I use

I built the preamp on a soldering board, old-fashioned, but very practical and compact. Therefore, it is possible to change a component very easily if necessary.

RIAA capacitors are Philips KS 1% polystyrene and Stéafix silvered mica. These are in parallel to give C5 a correct value and soldered on the opposite side. Value chosen taking in account the E182CC Miller capacitance. About 100pF.

Resistors 1% MRS 25. I use these for a long time and are perfectly suited for this task.

Pay attention to solder load resistors away from the board, they become hot in operation. I chose Kiwame 5W ones.

Grounding needs special care. To avoid hum and ground loops I used a single wire for each stage connected to a central point on the ground bus. Heaters are well filtered and polarized to prevent cathode leaks from V3.

C3g are Siemens, the only ones I stock. Other makers are TFK, Valvo, Lorenz, ITT.

The E182CC is a Philips design and sold under many brand names. Most come from Heerlen plant. Mine are RTC . These professional tubes were sorted at the factory to ensure a long time use and excellent reliability.

The making of

Listening report

Untill today I thought RC network was inferior in all respects to LCR one. Nothing is more untrue.

I am playing this preamp daily for more than a month now and it is just amazing. The most obvious quality is its dynamic capability, but it is not the only one.

Music is vivid, colourful and alive with excellent imaging. Soundstage is wide, not as deep as the LCR. Low end is very tight, ample, well controlled, but slightly rearward. The most remarquable is the medium / high that deserve an A+ note. Clear, precise, well focused and detailed to the extreme. No harsh or aggressivity even on loud music playing trumpet, guitar or drums.

On the very demanding Isao Suzuki trio record, snare & cymbals are rendered with incredible realism and I can feel cello's attacks like never before.

If I had to give on overall appreciation I would say the LCR is sensual and lush while the RC is more Rock n Roll and appealing. These are great qualities considering the music I listen to and it is very addictive. Today my LCR preamp is mainly used for human voice and orchestral music.

Of course this is very subjective and depends greatly upon room and overall setup. For this listening tets I used my old Garrard fitted with a FR24 arm, a Entré EC 30 cart (a rarity by Matsudaira-san also renowned for some of the best carts ever: Kiseki, Acuphase, ZYX and now MySonicLab) and its dedicated ET 100 transformer. The C3g phono is coupled to the 6J5 line preamp driving my MC1/60 SE amplifier.

Speakers are heavily modified Klipsch La Scala with upgraded Alk Engineering network (all original plastic capacitors changed by waxed paper & foil, teflon and some excellent sounding Aerovox V161), Martinelli's sanded wood horn + JBL 2470 and Beyma CP25 tweeter.

Great jazz vinyls for this report











4 comments:

  1. Hello Fred,

    thank you for share your DIY building, always interesting and useful.

    I wanted to nitice one observation. Power supply sounded better if
    before anode capacitor was an inductance, not just a resistor.
    You could make an experiment to learn if it was correct with you too.

    Best regards and thanks again,
    Alexei

    ReplyDelete
    Replies
    1. Hi Alexei,
      Thanks for your interest and comment.
      You can go with inductors all the way if you respect the series resistance values. I just used two chokes because I had them on hand and wanted to build this preamp with parts I stoked (except 1% resistors). Ripple is very low as calculated and I just hear thermionic noise at full level. Anyway thanks for comment I will keep this in mind for a future project and will need a much bigger chassis....
      Fred

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  2. Thank you for posting this phono amp build , I am busy collecting parts !!

    ReplyDelete
    Replies
    1. Hi Martin, hope you will enjoy as I do. It is an easy phono to build with no exotic parts. Please give me a feedback when completed.
      Fred

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