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    SP-8 preamp questions

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    Mike17W
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    SP-8 preamp questions

    Post by Mike17W on Tue Dec 08, 2009 8:17 pm

    I am considering purchasing the SP-8 preamp kit but have a couple of questions. The resistors that come with the kit...are they metal or carbon film. I noticed that the upgrade resistor package says that it contains TAKMAN resistors but does not say if they are metal or carbon film. Also does anyone have any recommendations regarding this preamp? Upgrades or changes?
    Thanks

    Bugs

    Posts : 91
    Join date : 2009-04-17

    Re: SP-8 preamp questions

    Post by Bugs on Tue Dec 08, 2009 8:26 pm

    The TAKMAN upgrade was not available when I built mine. The resistors were metal. Roy is great about answering emails.

    Mike17W
    Guest

    Re: SP-8 preamp questions

    Post by Mike17W on Tue Dec 08, 2009 8:45 pm

    Have you done any updates or changes that have improved the preamp?

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: SP-8 preamp questions

    Post by tubes4hifi on Wed Dec 09, 2009 1:13 am

    the SE version of the SP-8 includes PRP metal film resistors in the signal path, and Takman carbon film resistors on the tube grids. It also includes 8 SoniCap capacitors in the signal path. Also the SE version includes an input relay selector so that rear panel inputs are only about 1" long rather than running back and forth to the front panel selector. Also the SE version uses a 24 step precision shunt attenuator for volume in combination with a pair of 12 step attenuators used for individual channel gain and balance.

    Here's some info on the PRP resistors:
    This ½ watt metal film resistor is specifically designed for audio applications. The special construction features flat frequency response, low noise (thermal EMF), and non-magnetic leads/end caps. Every resistor is tested for noise during the QC process. The leads are Tin plated OFHC 22 AWG. Tolerance is better than 1%; TC is better than 50ppm/°C; Rated up to 500VDC;

    Here's some info on the Takman resistors:
    This ½ watt carbon film resistor is specifically designed for audio. The Takman carbon film resistor yields a very warm presentation. It will produce most of the warmth of a carbon comp without all the drift. The special construction features very low inductance and microphony. The leads are Tin plated OFHC 21 AWG. Tolerance is better than 2%. TC is better than 450ppm/°C up to 100K; 700ppm/°C for values above 100K.

    And, here's some info on the SoniCap capacitors:
    The Sonicap redefines the price-to-performance ratio for "audio capacitors". The Sonicap will yield or exceed the performance found in the most prestigious of boutique caps, yet with a price conducive to that of "entry level".
    This is a slightly more lush "colored" capacitor to avoid sounding slightly thin and bright like some "neutral" capacitors. The SoniCap (Gen2) has a nice Midrange bloom, and is very comparable to the well known "AuriCap" brand. Dissipation Factor is typically better than 0.02% @ 1kHz. The Sonicap leads are tinned solid copper (high purity). The shorter lead is shield. Tolerance is better than 5%.

    Mike17W
    Guest

    Thanks Bob

    Post by Mike17W on Wed Dec 09, 2009 11:30 am

    Bob,
    Thanks for the information. I was going to buy the kit and I noticed that you have a resistor upgrade package. Does this package include the relay for the back panel?
    Thanks again.

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: SP-8 preamp questions

    Post by Bob Latino on Wed Dec 09, 2009 11:46 am

    Mike17W wrote:Bob,
    Thanks for the information. I was going to buy the kit and I noticed that you have a resistor upgrade package. Does this package include the relay for the back panel?
    Thanks again.

    Hi Mike,

    Actually the information above came directly from Roy Mottram at the tubes4hifi web site and not from me. Why don't you Email Roy directly at > roymottram@yahoo.com about the resistor upgrade and the question about the relay?

    Bob

    Mike16W

    Posts : 39
    Join date : 2009-11-03

    Re: SP-8 preamp questions

    Post by Mike16W on Wed Dec 09, 2009 12:04 pm

    Sorry Bob. Maybe someone else may know.

    Bugs

    Posts : 91
    Join date : 2009-04-17

    Re: SP-8 preamp questions

    Post by Bugs on Fri Dec 11, 2009 8:57 pm

    Hi Mike,

    I think Roy answered your question.

    My SP8 initially had some pretty cheap pots for the volume and dual balance controls (~$1.50 ea. at Rat Shack), I upgraded to Canadian milspec pots (still cheap ~$7.50 ea.) and that made a marked improvement. I eventually settled on the SE version 24 step volume atenuator and dual mono gain/blalnce 12 step attenuators. The volume and gain/balance attenuator mods are definately the way to go. The preamp was also built with the SoniCap upgrade.

    I used a PAT 4 chassis for the build using the Hammond transformer. The PAT 4 is a pretty small package. If I did it over I would take a good look at the chassis available from Roy. If you go the PAT 4 route (Iwas trying to save a little money on the cost of a chassis) Roy also has a very nice upgrade to replace the old Dynaco input/output plugs.

    Doug

    Mike17W
    Guest

    Re: SP-8 preamp questions

    Post by Mike17W on Sat Dec 12, 2009 1:01 am

    Thanks Doug for all the great information. I already have a chassis about the same size as Roys and may use that instead of looking for a PAS preamp.

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