A poor man’s Marantz: adjusting a Superscope R-1270

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In 1964, American electronics company Superscope bought Marantz from its founder, Saul Marantz. Superscope owned Marantz through the 70s, and it had two product lines: quality line under Marantz brand and budget line under Superscope brand. Both included the whole range of hi-fi products (amplifiers, tuners, receivers, turntables, tape decks and speakers), and both were designed by Marantz engineers. While they shared design ideas, Superscope brand products were built to a less strict specs and with cheaper (but still good) components, some of them also in cheaper location – Taiwan, while most Marantz products were made in Japan. In short, Superscope was a poor man’s Marantz. The differences faded towards the end of Marantz’s ownership by Superscope and in the late 70s the products from both lines had mostly cosmetic differences, for example Superscope A-530 was Marantz Model 1050 with a plastic front and microphone input instead of two pairs of speaker binding posts, but otherwise exactly the same down to the cheap cardboard bottom plate.

While originally Superscope products were not as good as their Marantz counterparts, ageing components leveled the playing field and right now unrestored Superscope and Marantz amps and receivers offer similar quality. Unfortunately, flippers caught wind of the pedigree and Superscopes are not dirt cheap anymore. They are still usually a bit cheaper than vintage Marantz though.

Another difference is availability of materials. Specs, user and service manuals for any Marantz product from the 70s are very easy to find. With Superscope it’s difficult to impossible. So, if you have a Superscope that needs servicing or adjustments, you have to get creative.

I bought a Superscope R-1270 5 years ago and liked it so much that I decided to keep it in my collection. With black face, normal tuning knob instead of a gyro wheel and thick veneered board top and sides it does not exactly scream “Marantz”, but the style of tuning dial, signal meter, indicators, push buttons, balance slider in the middle and the entire rear panel are dead giveaways. More under the hood: it has Marantz boards, Marantz output transistors, the same fuse-type lamps and so on. It is a Marantz, no doubt. Superscope R-1270 is a 35 WPC Superscope receiver, top of the line that also included models R-1240 and R-1220. It was also sold as Expert TA-960. According to some sources the amp section is based on Marantz Model 1070 amp, but I think it’s actually based on Marantz Model 2235 receiver: both are quite similar, but R-1270 has the same outputs as 2235, and 1070 has different outputs. The preamp, phono stage and tuner section are more modest, they appear to be “borrowed” from Marantz 2215B. My unit needed a new volume pot, other than that it worked fine. I used it for a while and then moved on to the next toy, and the Superscope ended up on a shelf.

I do take it out every few months to clean it and run it for a few days, make sure it stays healthy. Last time I did that I remembered that I’ve never tried adjusting the amp, so I figured I’d try adjusting DC offset and idling current. Of course service manual for R-1270 is not available (for free anyway), so I tried to figure things out based on manuals for 2235 and 1070. I was working on an assumption that Marantz engineers would not make any major changes to the circuits between two very similar amplifier boards with the same output transistors, so that the adjustment procedures should be similar or the same for Superscope R-1270 and Marantz 2235.

Here’s the amp board and outputs of Superscope R-1270:

ZAMP BOARD IMG_0040

ZSUPERSCOPE R-1270 OUTPUTS IMG_0045

 

 

Here’s the adjustment procedure and amp board layout for Marantz 2235:

 

Z2235 procedure

Figuring out DC offset was very easy. There are 4 trimming pots on top of the amp board, the inner pots adjust DC offset (like in Marantz 1070 and 2235). DC offset was quite healthy (fluctuating within 5mV for each channel), but I still adjusted it to 0.1 mV, because why not.

Idling current was a bit more tricky.

The outer trimming pots on top of the amp board adjust idling current, again like in Marantz 1070 and 2235. According to service manuals for those two, the procedure for adjusting idling current is to connect a DVM to two pins at the bottom of the amp board. These pins (measurement points) can’t be accessed without dismantling the amp board.
But I figured out that I didn’t have to bother with the not-so-accessible pins at the bottom of the amp board, because it’s the same as measuring across the emitter resistors, and those are a bit easier to access (no need to dismantle anything when measuring across single resistor). Using the board from 2235 as an example, adjusting across pins J713 and J717 would be the same as adjusting across resistors R756 and R758 to 8 mV, or across one of them to 4 mV.

That’s what I did and nothing exploded.

But then I noticed that the value of these resistors is different in my R-1270 than in Marantz 2235/1070. In Marantz 2235 (and Marantz 1070) resistors R756 and R758 are 0.22 ohm, their counterparts in R-1270 are 0.5 ohm. So the question was, how should I change the value of the idling current measured across these resistors? The answer is simple: double the value of resistors, double the voltage across them. So, if idling current in Marantz 2235 is 8 mV across two 0.22 ohm resistors (4 mV across one), it would be the same as around 16 mV across two 0.5 ohm resistors, or 8 mV across one resistor.
At first I adjusted with a small safety margin, to 6 mV across one emitter resistor. After consulting and confirming that my reasoning was correct I readjusted to 9 mV across one emitter resistor. As a general rule, the idling current for a class AB amplifier should be 10-30mA. As expected, the value for Marantz 2235 is within this range at ~18mA; similarly for Superscope R-1270, the reading across both emitter resistors can be ~18mV (for an idling current of ~18mA).

Idling current should definitely be checked in these receivers (and Marantz amps and receivers with similar amp board design). In my Superscope R-1270 before adjustment it was 30-40 mV measured across one emitter resistor, which is 3-4 times higher then the recommended value. This may cause undue strain and excessive heating of output transistors, ultimately leading to their premature demise.

About the sound: Superscope R-1270 sounds a bit darker than Marantz amps receivers from the same period, so it’s a better match with brighter, sharp sounding speakers. It was right at home with Quadrals with titanium dome tweeters and with older Celestions. I would not match it with the likes of Tannoy M2 or Wharfedales from the recent Diamond line. It is very generous, maybe a bit too generous with bass, but seems to lose some detail in LF. In general, it is a very pleasant sounding receiver, if not very detailed. Functionally, it is similar to lower Marantz models: 3 line inputs including 1 tape loop, a decent phono stage, unfortunately no main in/pre out jacks, so you can’t use it as a preamp. One function that Marantz stereo receivers from the 70s usually do not have (but some amps do, like the 1070) is Quadraphase, which is a simulated quadraphonic effect obtained by changing phase of the rear speakers. While not a match for a proper quad, It does sound good with some recordings. Like most receivers from the 70s, Superscope handles 4 Ohm speakers without any issues.

Superscope R-1270 is very capable receiver, and definitely recommended. It does not sound or look exactly like a Marantz, its dark face matches the sound, but it shares many qualities with its Marantz family: pleasant, smooth, warm and powerful sound and good built quality. If black is your color, it is also one of the few receivers from the 70s that are black and make black look really good.

 

Technical information:

SUPERSCOPE R-1270
Designed by Marantz USA
Made in Taiwan, China
Years: from 1976

Amplifier:

Output power (RMS, 8 Ohms): 2×35 W
Total harmonic distortion (THD): <1%
Intermodulation distortion (IM): <1%
Channel separation: 56 dB at 1 kHz
Frequency response: 15-70000 Hz, -3 dB
Power bandwidth: 40-20000 Hz
Damping factor: >44
Dynamic range: 100 dB
Input sensitivity: 2.8 mV/47 kOhm (PHONO), 180 mV/100 kOhm (TAPE, AUX)
Output (Speakers): 4 Ohms or higher

Tuner:

FM: 88 – 108 MHz
AM: 525 – 1605 kHz
Sensitivity (FM): 1.9 uV
S/N (FM): 60 dB (stereo), 78 dB (mono)
THD (FM): 0.4 % (stereo), 0.2% (mono)
Frequency response (FM): 30-15000 Hz
Stereo separation (FM): 46 dB

General:

Power consumption: 26 W (idling)/160 W (rated power output)/220 W (max. power)
Dimensions (WHD): 43 x 12 x 29 cm
Weight: 9.6 kg

6 comments

  1. Chris

    You’re right about the relationship between Superscope and Marantz. Those were Marantz output sections. You should try to use 0.22 ohm resistors in your 1270 and set the bias to compensate. That will probably then sound exactly like a Marantz 2235.

    The Superscope receivers I have repaired all had silver faceplates, never seen a black one. Could be the difference between Canadian and US models I guess. They were good sets though, no doubt. It’s too bad that most receivers are being damaged by the hoard of flippers who “recap” receivers. That and the prices are just stupid these days. What people need to do is find a good audio technician who used to work on Marantz receivers and have it properly restored. It would be nice to see them saved from the hackers iron!

  2. rafal lisinski Post author

    Well, I just set a higher bias (mV) to account for .5 ohm resistors, the end result should be the same as using .22 ohm resistors and setting a lower bias, right?

    The black face is gorgeous on this one. I used to have a Marantz 2226 in black as well, that one looked good too (but the Superscope loos better IMO). Now I’m trying to score an older “princess pink” Superscope receiver, but unfortunately flippers have caught on and the prices have gone up on those. I do have a Supersope A-260 amp, it has some pink lights too.

    Luckily most people around here have the “if it ain’t broke, don’t fix it” approach, so most classic Marantzes I see have original parts. But I agree that finding a decent technician for anything is not easy these days, let alone Marantz. I should know, both my quad Marantz receivers (4240 and 4400) needed some repairs.

  3. Wade

    Was wondering if you could tell me the value of the cap that’s on the back of the tuning meter. My friend’s R1220 isn’t working. Think the cap may be bad. Thanks.

    1. rafal lisinski Post author

      Unfortunately I can’t look at my Superscope R-1270 at the moment. But this cap should be the same as in corresponding Marantz designs, and that is: 100uF 10V electrolytic cap.

  4. Gary

    New to researching, purchasing Audio. I just took early retirement and have enjoyed searching, finding and buying such treasures.

    I bought a SuperScope today at a sale for $20. A light is out, maybe 2, on the left side when looking at tge faceplate.

    I hooked it up to the closest speakers sitting idle and it sounds surprisingly good. Listening to Steely Dan at the moment through old Pioneers.

    The seller was awrsome, gave me an old Sherwood Tuner, l believe made in Chicago.

    If anyone knows the Specs on the R-340 Receiver l sure would appreciate any help..

    Also purchased a Marantz 2226e, and havent fpund any info on the “e” model.

    Tuner works good

    1. rafal lisinski Post author

      Gary, congratulations on your purchase! Superscope R-340 is a cute receiver, on my “to get” list (pink lights!). And $20 is a great price for a decent vintage receiver that works, even a low power one like the R-340.

      Superscope R340 is from 1973, it is rated 10W per channel at 8 ohms (RMS), its peak (music) power is 15W per channel. You’ll find other specs in the file I emailed you. BTW, 10 WPC is more than enough for listening at home, unless you have a really big room or like to listen very loud. But better avoid boosting bass or using loudness at higher volume levels.

      For dial and meter lights you will need 8V 250mA fuse lamps (the same ones as in Marantz receivers). My advice is to use regular lamps (not LEDs – my personal preference, regular lamps look better to me) and to replace all lamps, not just the ones that are out. You can keep the old ones that work as spares. Stereo light is probably a 8V (less likely 6.3V) 40mA bi pin lamp. DO NOT USE a stronger lamp (for example 60mA) – it could damage the tuner. If that lamp works, best leave it alone.

      Marantz 2226e is simply a European version of 2226. The same specs apply and the service manual is the same. The only differences are that the “e” has mains voltage selector on the rear panel and a low filter switch on the front panel, the non-“e” (US model) does not have a voltage selector and instead of low filter it has a 25μS setting is for altering the FM de-emphasis. Low filter is more useful, especially if you have a turntable.

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