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Realistic 42-2101/42-2101-a Phono Preamps

Discussion in 'Audio Hardware' started by Robin L, Aug 12, 2015.

  1. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Just a little thing I've been working on...since I probably have all the parts around:
    [​IMG]
    I think it compares favorably with the original, if not a little bigger so you can see the resistors and upgrade the capacitors:
    [​IMG]

    This could be re-built super-tiny with SMT, but at that point, you might as well buy a Electronics Salon board with an LM833N, or a Pyle PP444 using an NJM4558 opamp, both $20. The Chinese can make the whole thing for the cost of a hobby box and RCAs.
     
    Last edited: Mar 11, 2019
  2. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Yep, although I planned out a 2101a above, I also think I'd only build a better design, even for a 2 transistor jobby. Kind of interested in making one anyway, as I can do real analysis vs good receiver or ART DJPreII, which is a two-stage op-amp design with about 4x as many discrete SMT components as would seem to be needed.

    The tolerance on the resistors and caps, 1% is noticeable in the filters; 3% or 5% caps are bound to add more randomness than that. Add an parallel component location on your board if you need to increase capacitance or lower resistance.

    A good recommendation I can pass on was to buy a handful .1% tolerance resistors and 0.3% caps, and verify your DMM calibration.

    A better look (using an inverse RIAA source):
    [​IMG]
    Also with the 4202a, more than is indicated above, a real 47k or lower output load (instead of the very high resistance of a scope) increases the 40Hz hump by another half dB or more, and high end roll off (above the rise) is affected by input inductance more than the others. I couldn't find simple component value mods to improve this.

    Distortion + a bit of smile EQ: sounds good?
     
    Last edited: Mar 13, 2019
  3. MattyW

    MattyW Well-Known Member

    Location:
    Brisbane
    Wow, that's incredible. If you were to ever sell these, I'd love to buy a populated board. :)
     
  4. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    Got a spare board laying around?
     
  5. allied333

    allied333 Audiophile

    Location:
    MI
    TCC model TC-750 is a better phono amp. It is all discrete design for best sound. About $45 on ebay.
     
  6. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    The Realistic phono we are discussing here is also all discreet, fyi.
     
  7. allied333

    allied333 Audiophile

    Location:
    MI
    TCC still better sounding. I stated discrete as some new phono amps use cheap op-amps. I heard both, the TCC has an accurate RIAA response and no drop off at high frequencies above 10K. RS at $20 used is a bargain, but I would pay $25 more for the TCC. Typical price RS is below:
    Vintage Realistic Stereo Pre Amplifier Phono Preamplifier Pre-Amp | eBay
     
    Last edited: Mar 13, 2019
  8. TimB

    TimB Pop, Rock and Blues for me!

    Location:
    Colorado
    I looked up the stylus on the Shure V15-RS, and it is Hypereliptical, not a plain elliptical like I thought. Has anyone tried a Shure V15 with brush down on a unipivot tonearm? Does it work ok and sound ok?
     
    The FRiNgE likes this.
  9. keithv

    keithv Active Member

    Location:
    Richland WA
    I was going to redesign the PCB to include the option for the smaller radial lead caps in parallel. Mostly for physical size/cost. Although, I suppose 10x 1uF radial vs. 1x 10uF axial is moot at that point.
     
  10. keithv

    keithv Active Member

    Location:
    Richland WA
    I'm new here. What are the policies on Buy/Sell/Trade?
     
  11. Anthology123

    Anthology123 Senior Member

    I have one of these pre-amps. I only bought it because it was the 80's and I wanted to see if I could play my turntable on a boombox (it was the 80s). It wasn't until I used this Radio Shack Pre-amp I was able do it.
    Also, my cartridge on this setup was (and still is) a Shure V-15 Type IV with the brush.
    It came in this color box:
    [​IMG]
     
  12. MattyW

    MattyW Well-Known Member

    Location:
    Brisbane
    No idea mate, I'm new too....
     
  13. keithv

    keithv Active Member

    Location:
    Richland WA
    There's a 3rd party sales lounge, so I guess member to member transactions are frowned on. You need 30 days to post in there. I'm out of boards anyways. I only got a couple for myself and a friend to play around with. I'm gonna get more though. There were a couple improvements I'd like to make to the layout as well. I'm adding a place to connect a battery w/strain relief holes if you want to go that route. Making all the cap and resistor spacing bigger. Moving the rectifier/filter/regulator to one side of the board and adding holes to mount a shield to further isolate it from the signal path.
     
    MattyW likes this.
  14. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Fortunately, we can investigate that, also:

    [​IMG]

    [​IMG]

    This is with (probably fake at that price) 2sc1815. They also have substituted STC945 transistors, which I didn't bother to hunt down a spice model for.
     
  15. keithv

    keithv Active Member

    Location:
    Richland WA
    Technically, that's the 42-2109. I can't find a schematic for it, or any gut shots, so the only obvious difference is that it has the ground screw on the front. Maybe the 42-2109 is the standalone version of the SA-102a.
     
  16. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    It's a bit different, at least in layout. I mistakenly started tracing out a picture of one of those circuit boards until realizing something wasn't quite right.
     
  17. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Ready to build-and-verify design, refined from a Realistic SA-102 mini-amp. I've gone with standard 5% value components, and trim components for correct value and where tweaking in the prototype might be needed.

    The passive inverse RIAA generator (pictured) indicates more high-frequency than loading an active ideal RIAA model, and using 2N5089 more low frequency, so this is a compromise design for best expected results. BC549C transistors is also a verified option, but general-purpose BJT transistors not recommended.

    The tube-like HF rolloff gives more RF immunity in a discrete transistor-based design.

    [​IMG]
    (sorry, capacitor polarity not indicated, but the same as can be found in the original schematic on the web).

    30Hz-30kHz +0.1dB -0.5dB, (or call it flat with a -3dB @ 20Hz subsonic filter). 40dB gain and +/- 4V unclipped output with a 12V supply, more than a cartridge could drive it to.

    Making your own audio electronics (vs "best preamp under $5000?" threads) is probably beyond the scope of Steve Hoffman forum, so that's good enough for now.

    TINA schematic: realistic-sa102-mod3.TSC
     
    Last edited: Mar 14, 2019
  18. The FRiNgE

    The FRiNgE Forum Resident

    I don't know if the V15-RS would be ideal with a unipivot arm. I owned one and have a few digital files from it. I loved its extended top end and high trackability at very light VTF, only 1 gram without the brush, 1.25g to 1.5g with the brush engaged. The V15-RS does have a hyper-elliptical stylus indeed, and a beryllium cantilever.
     
  19. keithv

    keithv Active Member

    Location:
    Richland WA
    [​IMG]

    I just picked up a NIB 42-2109 unit. It came with the owner's manual which has the schematic in it. It looks like they literally took the 42-2101a schematic and just penciled in the 100p/C21 input capacitance cap. They are also using 2SC1740 transistors. Aside from that, the two units are identical. The 2109 does have a newer PCB design, but it's very similar to the 2101a...it's almost like they used CAD software to replicate the original layout.

    So if you want to try the 42-2101a and you can find a 42-2109 for less, go with the 2109.
     
    MattyW likes this.
  20. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    The same SA-102 mini-amp design (1.8 watts per channel) was continued from 1980 through at least 2010 or so, with the Realistic/Optimus/RCA SA-150 and SA-155 model numbers, the SA-150 having a quite legible schematic in the owner's manual found on the web. It also can be a preamp using its tape out. Curious what transistors they were using so late.

    I just picked up some surplus transistor sockets (not made any more?!) to facilitate some transistor rolling, if I get around to the 12x12/channel perfboard layout I packed in, with standing components. This is a fussy design, with a small bias voltage window depending on the transistor gain.

    Add some LM380 amp chips for the whole mini-amp package.
     
  21. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Spooky, I described a 2N5088-based version of this preamp above, and look at what you can now buy on eBay for $10 from China:

    Through-hole component version:
    [​IMG]

    Surface-mount version:
    [​IMG]

    All that's missing is a 12-24V power supply (external instead of a 10V AC transformer in the Realistic), and RCA output jacks.

    I haven't traced it out to see what it's a clone of, but available pics of traces and resistor values would allow one to do that. It even uses the voltage supply transistor design, so it is unlikely it strays far from the Realistic. Motronix also has op-amp preamps and some other boards cheap (along with 2n2222 transistors for $0.01 and 4x30W amp chips for $2.)
     
    Last edited: May 1, 2019
    33na3rd and cmarti like this.
  22. MattyW

    MattyW Well-Known Member

    Location:
    Brisbane
    Do you have links to those?
     
  23. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    There are links above my pictures. You can see other items from this seller's store, which is "Israel" but shipped from China. There's too little info on this web store for me to trust it, but if you speak Hebrew, maybe you can call and see if they are legit and what the designs are based on (or there could be nothing in Israel and it is just Chinese foolery).
     
    Last edited: May 2, 2019
    MattyW likes this.
  24. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    The 750 sure has the better looking and likely sounding frequency response.
     
  25. vanmeterannie

    vanmeterannie Forum Resident

    I have a 42-2101a that I’ve thought for years I’d like to alter the rolloff point of to make it slightly brighter, or run flat altogether for certain older records. Which capacitor would I remove or reduce to make this work? Or is it possible with the circuit? Thanks!
     

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