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This is the "Before Restoration/Upgrading"
This is the "After Resto"
I have posted more than a few times concerning these Japan sourced stereo tube phono preamps I call the "chrome cutie." These were available from the early 1960s through the seventies from many electronic distributors with various name tags. This one does not have a brand name tag pasted on one side, so all sides are shiny chrome; very pretty and cute. The "Lafayette" brand decal/tag probably fell off. The "before" pic shows some sorry looking, original factory wiring inside. As I have mentioned previously, despite the many brand names these could have, they were more than likely only wired in three or four "factories" in Japan.
Their original circuitry mimics the GE UPX-003 and Fisher PR-6 preamps of the mid to late 1950s; only this is a stereo version. Their original circuit has inadequate Tape and Phono EQ parts installed; plus a wimpy power supply. Besides upgraded, precision phono EQ installed accommodating two turntables, this latest version of mine has a power supply with a UF4007 diode and beefy, dual mono capacitor banks installed; yielding fantastic soundstage imagery. The separation, width, height and depth of the 3D image, plus the "sweet and fast" sounding active feedback EQ phono stage is indeed very impressive. Those green coupling caps are mil-spec Russian polystyrenes; very recommended and always available on the bay. Phono EQ caps are also polystyrene from Euro and USA sources. All caps were matched to 1%. As you can see, room to work underneath is limited; but possible.
Again, while these units are quickly "catching on" with rising prices in Vintage Electronics at the bay, stock factory units will not impress your ears favorably. However, with some sensible upgrading, these chrome cuties sound very endearing...
Follow Ups:
That's pretty much what you've done here. The only substantive part that you've kept is the chassis.
N. Thelman, SSI
Big J
"... only a very few individuals understand as yet that personal salvation is a contradiction in terms."
than in the old days :-)
Smaller, too.
Very nice work. I don't think I have the small-muscle control to do work that neat in a space that tight (even with hemostats and decaf).
all the best,
mrh
Mark, you totally cracked me up! It's true for me as well!
why I believe "modern" tube electronics don't have to sound "tubey" or rolled off at the top.
Current polystyrenes (like used in this project) and various film and teflon caps have measurably better linear response. They are also available in larger sizes in high voltage for stiffer power supplies.
I have one of these "Chrome Cuties", as you call them. I picked mine up at a Ham Fest back in the early 1990s for $1. It had two good 12AX7s in it, and I've kept it on a shelf for decoration all these years. Mine has an AMD sticker on the back, and Japan stamped into the metal, under one of the output leads. 0.1 µF oil caps too, for what that's worth.
Now the million questions. Did you follow a schematic for your restoration? If so, would you be willing to post a copy? The power supply I could probably figure out, but how did you know the values to use for the RIAA equalization?
Speaking of the power supply, you said you used a UF4007. Is the power supply a half-wave? I see the one of the secondary leads on mine ties into a small square device (just to the right of the AC in leads in my photo). Is that a selenium rectifier? If so, did you keep it in the circuit?
I guess that's enough for a start. Thanks for posting, IT. You do nice work!
"You won't come back from Fletcher-Munson curve"-Jan and Dean
The schematic as Eli posted below is the one sometimes included with these, inside their boxes, along with very few specs and info, on one page. However, this schematic is not right for most mm carts. The original RIAA EQ feedback circuit lacks high frequency deemphasis and yields too much mid bass emphasis. The original phono EQ relies on a low input resistor to cut some highs, which was popular in the 1950s for the Variable Reluctance carts. Thus, the original chrome cutie, like original GE UPX-003 and Fisher PR-4,5 and6, are actually feedback and passive EQ equipped. The cartridge that the Japanese designers seemed to have designed these units around was not imported as often as the chrome cuties. There are a few USA and Euro made carts that will "work" with these preamps; but not as favorably as their potential abilities.
The classiest, classic '60s vintage preamps, like the Marantz 7 and McIntosh C-20, C-22 and C-11, as well as many others, favored feedback EQ solely. My preference seems to agree. Standard RIAA EQ requires certain "turnover" bass emphasis and "rolloff" treble deemphasis. If you were to study and/or list and chart the many active feedback EQ schemes of yesyteryears' 12AX7 preamps, you will quickly notice significant resemblances to one another. In fact, in spite of the differing voltages and topologies(ie: whether using cathode followers before the feedback, cascode or cascade, etc.)the EQ parts' values have many more similarities than uniqueness among any vintage 12AX7 feedback equipped phono preamps.
Rather than jump into a technical discussion here, let me answer your other few questions. Having repaired, restored, upgraded, modified and built from scratch for many lunar eclipses, I have been rebuilding the chrome cuties for over a decade. I have tried many EQ arrangements. We can use test equipment, including signal generators, test records and inverse phono EQ circuits along with a quality o'scope to provide absolute precision of our chosen circuitry. We can also use tried and tested, proven circuits. Ultimately, if you DIY and listen to well known discs on a well known playback system, plus really know the sound of instruments, your ears and brain will probably become the final answer.
I can tell you that using a full wave bridge rectifier arrangement might sound better to you; maybe not. I get excellent results with a half wave or full wave rectifier within this small chassis. I bypass the selenium rect, but it might work fine for another few decades. In my unit above, I used the selenium leads, folded and wrapped to support other leads. There really is only small space to work with. The AC power in leads are disconnected from their tie posts, then spliced and insulated cleanly, resting under the power supply caps. That freed up space for the power supply cap connections and positioning.
Please take some time to check the archives in AA, as I have discussed the variances in equalization values and my thoughts on AC filaments more than a few times. If you like, you can email me thru the asylum or the asylum trader. In my systems, hum level is low enough with the AC filaments' center tapped winding grounded. You might get lower hum with DC filaments or biasing them with a low B+ value. Keep in mind the truly limited space in these chassis.
For the DIY crowd that is watching the progress of the chrome cutie projects, let me first recommend dual mono power supplies. Two power transformers for each channel, even with high resistance B+ windings, will sound best. The dual cap banks for each channel sounds great, but, separate trannies providing high voltage and filamnets for each channel will and do sound better. Finally, I guess this is a good time to summarize some EQ choices I have made. Different cap types, mica vs. mylar vs. polystyrene vs. polypropylene vs. ? will all sound different and the defining cap values will differ among the types. I prefer the feedback to be arranged with the high frequency rolloff EQ pole first(thus lowering the noise from the later stage; then the bass boost EQ pole connected to the earlier stage. So, the classic typical RIAA EQ pole value, providing 75 usecond treble deemphasis, is 750 pf across 100K Ohms. 820 pf across 91,500 Ohms might be your preference. 680 pf across 110K might be mine, with certain cap types. More modern 12AX7 preamp phono designs might use 450 pf across 165K or 390 pf across 192,300 Ohms. These values provide the necessary 75 microsecond RIAA EQ for treble rolloff or deemphasis. The bass pole EQ differs even more among classics and modern designs. The classic vintage bass EQ pole (connected in series to the treble EQ pole of 750 pf across 100K) is nominally 2750 pf across 2.2 Megohms. Variations I like have been 2200 pf-2500 across 2.2-3.9 Megohms, depending on the EQ cap types as well as the slight bass boost some prefer. 3300 pf across > 2.2 Megohms seems to have been a choice among two peers with bass heavy speakers. Modern designs show many deviations and listed precision EQ tolerance frequency response.
The chosen EQ and coupling cap values you end up with are your choice; literally. It is your musical playback enjoyment factor at stake here...So...ENJOY !
As Crazy Dave said, thank you for an excellent post. I appreciate you taking the time and effort to share so much information with us.
I will save the information you've posted, and check the archives for your other posts on the subject.
Thanks again for sharing your work.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Thank You for the kind words.
I truly enjoy "sharing the knowledge" so we can all enjoy "sharing the wealth (of enjoyable sound)."
I believe these sensibly modified chrome cutie phono preamps could be the best budget phono stage available; especially if you can DIY. I often watch them disappear quickly on the bay, offered reasonably as a "buy it now" in clean cosmetic condition. With some resto skills and spare parts to upgrade the circuit, these sound competitive and totally enjoyable...ENJOY !
I have never seen one, but I think I'd grab it if I did.
Dave
I've uploaded a schematic for that sort of phono preamp. Yes, the B+ is half wave rectified. It's pretty easy to switch to 4X UF4007s, for full wave bridge B+ rectification.
Those GE style setups rely on the inductance of the cartridge's coils for part of the RIAA EQ. IT will tell you how to fix things up, including the 47 Kohm load modern carts. require.
FWIW, I suggest that, instead of grounding the CT of the filament winding, you bias it off B+ to 60 or so V. Another hum/noise control tweak is using Sovtek 12AX7LPS tubes, which are genuine 7025 equivalent that contain a spiral wound/hum bucking heater.
Eli D.
I only did a quick glance yesterday when I opened it up to take the picture. My first thought was wondering if I could fit four UF4007s in there.
I'm going to have to do some homework on your suggested bias scheme, and how to impliment something like that. As for the Sovteks, I'm currently using them in my Vorhis, a modded PAS, courtesy of Jim McShane, and I'm very happy with them.
This is one of those "someday" projects I'll get to after I retire, but I always like to acquire as much information as I can, when I can, and keep it squirreled away.
Thanks again for the schematic and the feedback.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
The output coupling cap is .1 uf; not the .01 on the scheme.
In some versions of these units, the Center Tap of the filament is sometimes connected to ground internally. An internal connection, inside the tranny, makes it tough to change the filament supply topology. Worse, I have seen this on some chrome power tranny versions as well as non-chrome power tranny versions that were available. So, check your units before purchase or rebuilding.
While the Sovtek 12AX7LPS might have a "genuine, 7025 type spiral wound filament," so do many, many vintage 12AX7s. Unfortunately, to prove this, you would have to break the older tubes apart since the spiral winding technique might not be noticeable looking through the glass. Most tubes "look" like they have a V shaped filament because we usually only see the V shaped white filament leads under the tube plates' structure.
Also, the Sovteks are wider than vintage 12AX7 tubes. Thus, Sovtek 12AX7 glass actually contacts the tube shields on the chrome cuties. This last fact is sad. The manufacturer definitely seems to have had an ulterior motive for the purchaser to require new sockets and shields. Remember planned obsolescence ? This is an example of "required changes to accommodate the replacement." That said, I like the sound of the LPS (Long Plate Spiral) as well.
Thanks an impressive job!
I don't think I've ever seen a tubes lowered like that?
But it looked like a fun little project.
enjoy
charles
Thank You for the nice comments !
What did you mean with "...lowered like that ?" Do you mean the socket mounting ? The socket bases are actually above the chassis, supported by rubber grommets both above and below chassis. The socket frames you see on the underside are indeed unique to these chrome cuties. Socket quality among these original units are usually good; especially compared to anything new from so-called worldwide sources.
Considering these units were available everywhere during the sixties through the seventies, you can find them today rather easily. Finding new in the box and/or mint chrome is not common. I have seen more NIB with corrosion than NIB that were actually kept NewInBox. You can luck out with low prices; but not like the prices during the decades they came from...If you can work inside tight quarters, these chrome cuties are indeed fun resto projects. With sensible upgrades, the listening enjoyment factor is genuinely very large and very real...
Thanks again for the complimentary comments !
I just got one of these today, restored in a similar fashion as to the one described in this old thread. And it is terrific. I've had lots of really nice phono's over the last 20 years, tube and ss, and this one is as good, if not better, then all of them .
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