I ended up with this Realistic 33-1057a, a little later I suspect, but similar stuff inside? I noticed the schematic of the 42-2101 calls for C1327 transistors, mine has C1815 transistors, are these also a FET? Would you suspect this preamp is comparable to the 2101 or 2101a sonically? <blockquote class="imgur-embed-pub" lang="en" data-id="a/uSPIn"><a href="//imgur.com/uSPIn"></a></blockquote><script async src="//s.imgur.com/min/embed.js" charset="utf-8"></script>
Resurrecting once again! I have a 1977 Realistic STA-84 and I've been comparing the phono stage to various others from the time period. It's almost a direct clone of the Onkyo TX-2500, and extremely similar to a couple Marantz and Sansui models too. Unsurprisingly, it's 99% the same as the pre being discussed in this thread with one notable exception: the 42-2101 uses four 2SC NPN transistors whereas the STA-84 uses two 2SA PNP up front followed by two 2SC NPN transistors (just like the Onkyo mentioned above). Other than that they're wired just about identically so I'd imagine the STA-84 performs on par with the 42-2101. That particular model of receiver hasn't jumped up in price like the more popular Realistics, so if you're looking for a solid, all-discrete BJT amp with essentially a 42-2101 built in you can most likely find one for a good price on the bay etc. Oh and hello, I'm new here!
upgrading the 42-2101a realistic phono preamp. well, the basic electrolytic cap replacment is a start and worth while... then you can get into the signal path resistors/caps, swap ceramics with poly film... removal of the power transformer and replacement with a wall wart... total removal of the power supply with 9 volt battery source. upgrading the trasnsisotors mostly just the power transistor, i've started to cut the board into three sections and mounting them seperate. these little preamps are fun!! they far out perform many many other preamps and i would put them against any 'opamp' style unit any day. If you can solder and read a schematic go for it!
I just ordered one of these to try out. Should be fun! Is there anything to know in terms of updating the unit electrically for safe use?
[QUOTE="Mileater, post: 20175683, member: 88148" they far out perform many many other preamps and i would put them against any 'opamp' style unit any day. [/QUOTE] Any other opamp preamp? Even Sutherland Engineering??
Just to be clear, I’m mostly just thinking about whether this thing could ever pass any DC to my integrated amp? Also, can the output impedance really be 50Kohm? That seems so high!
Bump, just curious if anyone out there has more details on this preamp output impedance. For a solid state device, it seems weird to have a 50Kohm output impedance!
@Mileater can you recommend or provide a parts list? Folks do this over at Audiokarma for receivers/amps, etc. It's very helpful. Are there specific caps/transistors that you like or have found to sound better? I'm using the following cartridges: Stanton 881, Pickering XSV 4000 (w/original Stereohedron stylus), and a Shure V15 III with a Jico VN35 [e007443] stylus on a Dual 1229 or 701 TT. I'm curious to see what I can squeeze out of this $20 preamp. . Thanks!
Well, I finally tried this little preamp out the other night. I've been listening to it for about 5 days now, and I'll be damned, this thing is pretty good! It has very tight well defined bass, clear but delicate sound. I love it. It did require some break in at first, but I could tell it had something worthwhile from the beginning. I have heard many phono preamps, from built-in on my former Mcintosh C33 (great phono stage), Lounge LCR, Graham Slee (both Graham Amp 2 SE and Reflex M), Mcintosh C2500 with NOS Mullard tubes, and a Manley Steelhead. While this thing obviously does not have the 'depth' and 'dimensionality' of something like the Steelhead, I have a hard time saying any of these other phono preamps were clearly superior, and in fact, I may prefer this unit to any of them.
Well, a mate of mine has been modding these recently. His most recent creation moved the transformer externally, replaced all elecrolytics with Nichicon Gold though fitted Mundorf Silver Gold in the 4.7uf stage. The case has been made larger with the Mundorf caps at the top to reduce hum. I must say dynamics are greatly improved , as is sound stage depth. The sound is much more detailed and so very smooth. Really, it sounds like a 834P with nice NOS tubes, lower noise floor and greater detail. Not bad at all. It's clearly bandwidth limited compared to my Valab LCR-1 though I think that won't be at all noticeable in my second system. Can't test just now as its away getting Dueland JAM caps for coupling caps. In the meantime I've bought another Realistic 42-2101A and ordered a pair of Jupiter Copper Foil caps for the 4.7uf stage. That should be interesting
Well this thread forced me to buy one as well. Haven't done a thing with it, guess I need to get a larger box to place it in so I've got options. Keep the ideas a coming!
I tried building this on veroboard. It did not work. Voltages were way off, like it wasn't biasing correctly. Ordered an original on eBay and compared the schematic. R03/04 bias resistor is incorrect. It should be 56k. This would explain why it wasn't biasing correctly. Also, R03/04 sets the input impedance. 56k seems a little closer to the typical 47k MM input impedance. I think you could use a 47k for R03/04 just as well. I'll experiment and see. My unit has 2SC1570 NPN BJT transistors in it. Looking at the datasheet, there's nothing particularly exceptional about this transistor. It has a pretty wide MIN~MAX hFE range, so it's hard to say what is "typical", but it could be replaced with just about any common BJT. The 2N5088 would probably be closest. The biggest difference would be the pinout, with the 2SC1570 being ECB and the 2N5088 being EBC.
Using standard input resistance makes sense. Strange it was a specific incorrect value on the original scan. I just happened to have this cheet sheet of audio transistors open, so added the 2SC1327: If you want to not waste a 1327, you could replace the upper right Tr5 circuit with a LM317 voltage regulator at 28 volts (or less), and simply rectify a 5:1 24V transformer instead of using the voltage doubler circuit. I thought of breadboarding and analyzing this, but C11/C13 are weird capacitor values, probably needing a trim cap.
No. I see R03/04, then C01/02, then the base of Tr1/3. The presence of C01/02 ensures that R03/04 is not part of the DC bias for Tr1/3. It's cap coupled, therefore the resistor is just an input load. 8.8K is still a vastly wrong value for that position though. C03/04 looks like it's just some HF compensation.
I revisited the picture from earlier in this thread, apparently the only schematic one might find on the internet. Re-applied the best Photoshopping restoration I can do (through JPEG compression artifacts), while not discarding any analog information (but I did toss out the blue channel), so you can have it without interpretation. R03, like some other values, takes human interpretation as it is on the edge of legibility, but it could be "6 5K" "6 8K" ore even "5 6", it seems a Japanese typesetter added a space and not a decimal point. It definitely isn't 6.8K as that throws the frequency response way off; the discovered 56K seems reasonable. The values for C13 could be .0021uF instead. C22 on the output looks like it is instead a resistor, an error. It would be nice to have verification of any other errors in the diagram, as this was a challenge to implement unambiguously. So I simulated this, trying spice models of a few other NPN transistors. While transistors do affect the response curve, no library choices give the curve the expected RIAA shape, whether simulating a voltage or current source; looks like I'm missing something, this circuit depends on the cartridge load (unlike others) or Tina can't do the filters right. Nodal voltages are within 10% of those indicated. The specs on this preamp, 0.5% distortion and 55dB SNR, not stellar these days, far surpassed by laser-trimmed op-amps with application-specific transistors inside, so only worth pursuing for curiosity. Apparently these bulk transistors used to cost under a penny each in Japan in the 70s.
yes buy one!! these are fun to mess with. they are worth the trouble updating. i've found the thick film metal ox resistors to work sound pretty good. i don't mind which ones ohmite, dale vishay etc. the FR series electrolytic caps sound decent and last LONG time ( sure you can use vishay muse or silmic ii) the 4.7 mf caps are you choice, the carli from madisound fit good, the kemet from digi key fit, and if you want to get a big metal case then you can spend all the money on better caps. but i've found the clarity cap px series to do very good especially for the low cost. just get a good soldering iron and go for it!
