RCVR: Harman Kardon 900+ Quadraphonic Receiver

[4morhktech]

Just curious....

....did any of the prototype 700+ units survive...?? Do any images exist..or brochures printed??. It sounds like that unit got pretty close to production, and I've noticed that with some other brands (..Astrocom, CM Labs, Marantz..etc) brochures were printed, or magazine images exist for stuff that ended up ultimately not being produced....

It's very possible one or more prototypes could have ended up in the possession of former employees. They used to have sales to employees of obsolete models. But there weren't too many to begin with and there were functional problems that may not have been corrected, if the project was cancelled. It's very possible that they were just scrapped. I don't recall seeing any brochures but that doesn't mean they weren't printed.

Externally, the 700+ looked very similar to the 800+ and was in approximately the same power output (per channel) class. Internally it was quite different than the 800+ and was to be produced in the USA.

Had the consumer demand for quadraphonic products not sunk to a low in 1975, functional problems would have been corrected and the model would certainly have gone into production as planned. Instead, engineering reworked the whole design into the TA-600 (2 channel stereo) to use up as many of the production parts already in stock. But even the TA-600 was not produced in quantities sufficient to use up all 700+ parts. Many of the remaining unused 700+/TA-600 parts were sold off to surplus brokers when the 55 Ames Ct facility in Plainview was closed in 1980.

 

[Quadrockasaurus]

Cheers....Thanks again for the info....

P.S. An image below for anyone wondering what the (Stereo) HK TA-600 Receiver receiver looks like....

 

[4morhktech]

Cheers....Thanks again for the info....

P.S. An image below for anyone wondering what the (Stereo) HK TA-600 Receiver receiver looks like....

View attachment 4522

Thanks, Quadrockasaurus, for posting that photo. It gives interested parties insight into the reason for the existence of the TA-600. It would never have been produced without the need to mitigate the financial losses of the canceled 700+.

It should seem obvious that the front panel was initially intended to have the joystick in the right hand compartment where the function lights and tape monitor jacks now reside in the TA-600. The appearance of the 700+ prototypes was exactly like the TA-600, except the joystick took up the space on the right side just like on models 75+, 100+, 150+, 800+, and 900+.

Another bit of trivia: There were a few incomplete prototypes built of another model, the A-600. The A-600 was a 2 channel integrated amplifier on the same 700+ chassis and similar front panel with 2 illuminated VU meters for each channel behind the blackout dial where the AM/FM dial scale exists on the 700+/TA-600. The A-600 was basically a TA-600 without the AM/FM tuner. I own one of the incomplete prototypes. The A-600 never went into production. Sorry I don't have a photo of it, and since it is incomplete, it lacks the final appearance most folks are interested in seeing anyway.

You might have already guessed that in assigning model designations, the "TA" prefix for a receiver model stood for "Tuner-Amplifier", just as "A" stood for "Amplifier", and "T" stood for "Tuner". Those prefixes applied from time to time (but not always) throughout H/K's history from the beginning.

By the way, the TA-600 had a very nice FM tuner section. It was far superior in performance to the tuner section in the 75+ & 800+ in terms of sensitivity and adjacent-channel selectivity.

 

[tcdriver]

This is a picture of my Harman Kardon 900+ receiver. This is what it looked like when I took the picture a while back and posted it on another internet forum.

It looks like somebody photoshopped my image and posted it at the beginning of this thread. Whoever edited my original image did a nice job of making it bigger and eliminating the background.

My Harman Kardon 900+ was the first quadraphonic receiver that I ever owned. I bought it used from a second hand Hi-Fi store in 1984 for $100. The store owner told me that it had a bad channel. As it turned out that was one of many problems. I learned a lot working on the 900+ because it had a whole host of problems, some strait-forward and some a bit more subtle. Trying to find lamps for it was not easy. Even back then Harman Kardon no longer stocked replacements.

Thank you 4morhktech for your helpful comments. I sure wish I could have picked your brain back when I was working on my unit. As it so happened the tuner section just went out again. Besides the noisy 2SC458 transistors, were there any other common problems? How well did the CD-4 decoder work? I have never been able to get mine to work well. Was there any common failure mode for the amplifiers?

 

[tcdriver]

I can't tell from the picture if any of the buttons are labeled as such, but did the built-in SQ decoder have any form of Logic, either Full Wave-Matching w/Front-Back (or F/B alone) or Full Logic with F/B Vari-Blend?

It has no logic circuit. The SQ decoder was made using discrete transistors, resistors and capacitors.

From a harman/kardon 800+ - 900+ product brochure:

“The SQ matrix design of these receivers is of distinct professional quality. It employs the highest grade components with super-close tolerances unprecedented in a home music system. Indeed, it follows the close tolerances of the original CBS professional decoder, rather than the less stringent standards often used for receiver manufacture. The result is a superiority immediately discernible even to the untrained ear.

The matrix system incorporates an eight pole filter rather than the less effective four pole type in most competitive systems. The eight pole filter ensures the “localization” of instruments and voices so that they appear precisely where they should through the appropriate speaker.

Your choice of SQ MATRIX 1 or SQ MATRIX 2 enables you to treat a symphony orchestra, a rock group, a string quartet or a solo voice with the difference they each deserve.

In addition, the separation coefficients of SQ MATRIX 2 are virtually those of the “universal matrix decoder”. Thus, these receivers are able to play back recordings made with all matrix systems (SQ, QS and EV) with accuracy, spaciousness and clarity.”


From ad copy published in High Fidelity, January 1974:

“IT’S AS FAR AS YOU CAN GO.

If you’re up with what’s happening in the High-Fidelity industry you’ll know harman/kardon is currently producing the world’s most advanced receiver line.

This 900+ is the cream of that line.

It carries both discrete and matrix four-channel circuitry. So it will reproduce every type of quadraphonic music available. Most four-channel receivers carry only one.

The 900+ puts out an astonishing 32 watts per channel, continuous, with all channels driven simultaneously. That’s a good deal more power per channel than many stereo receivers can muster.

The 900+ does not weasel through the problem of stereo record reproduction by merely shutting off the two rear speakers. Instead, it uses a unique phase shift network to produce an enhanced stereo sound through all four speakers. Your stereo record library will sound better than ever.

Built into this remarkable machine is an analog computer that distinguishes between music and noise on FM signals. No other receiver can pin down a station with such hair-splitting accuracy.

And like other harman/kardon products, the 900+ carries ultra wideband circuitry. This ability to reproduce frequencies you cannot hear, significantly improves the characteristics of those frequencies you can hear. harman/kardon products are world famous for their fidelity. If you are in quest of the perfect sound, this could be what you’re looking for.”



harman/kardon 900+ Specifications from a brochure:

Power Output (stereo mode): 90 watts min. RMS per channel, both channels driven into 8Ω from 20Hz. to 20kHz., with less than 0.5% THD.

Power Output (4 channel mode): 30 watts min. RMS per channel, both channels driven into 8Ω from 20Hz. to 20kHz., with no more than 0.5% THD.

Power Bandwidth: From 10Hz. to 40kHz. at less than 0.5% THD into 8Ω, both channels driven simultaneously at 45 watts per channel.

Frequency Response: From 4Hz. to 70kHz. at less than 0.5% THD into 8Ω, both channels driven simultaneously at 1 watt per channel.

Square Wave Rise Time: Better than 3µS.

Square Wave Tilt: Less than 10% at 20Hz.

Total Harmonic Distortion: Less than 0.5% from 250 milliwatts to 45 watts RMS, both channels driven simultaneously into 8Ω from 20Hz. to 20kHz.

Intermodulation Distortion: Less than 0.15% at rated output.

Hum and Noise: Better than 75dB below rated output.

Damping Factor: 30:1 at 8Ω

Tone Control Action: +/-12dB bass boost and cut at 50Hz. +/-12dB mid-range boost and cut at 1kHz.. +/-12dB treble boost and cut at 10kHz.

Dimensions: 20 1/8 W x 17 D (including knobs) x 6 ¼ H (including feet)

Weight: 45 pounds [20.4kg]

 

[4morhktech]

This is a picture of my Harman Kardon 900+ receiver. This is what it looked like when I took the picture a while back and posted it on another internet forum.

It looks like somebody photoshopped my image and posted it at the beginning of this thread. Whoever edited my original image did a nice job of making it bigger and eliminating the background.

My Harman Kardon 900+ was the first quadraphonic receiver that I ever owned. I bought it used from a second hand Hi-Fi store in 1984 for $100. The store owner told me that it had a bad channel. As it turned out that was one of many problems. I learned a lot working on the 900+ because it had a whole host of problems, some strait-forward and some a bit more subtle. Trying to find lamps for it was not easy. Even back then Harman Kardon no longer stocked replacements.

Thank you 4morhktech for your helpful comments. I sure wish I could have picked your brain back when I was working on my unit. As it so happened the tuner section just went out again. Besides the noisy 2SC458 transistors, were there any other common problems? How well did the CD-4 decoder work? I have never been able to get mine to work well. Was there any common failure mode for the amplifiers?

I would need a bit more symptom details on what you mean by the tuner section going out. If the FM audio is very low and/or badly distorted, it most likely is the MC1307P MPX IC. That's the most common failure in the FM path. If the symptom is something different, please tell me more. Perhaps I can help.

I'm surprised to hear that replacement lamps were not available to you in 1984. I had access to all of them in the parts area up until I left in late 1988. The power button lamp, stereo beacon, in-tune, and matrix lamps were all interchangeable even though they had different part numbers.

The only common type of problems on the amplifier boards were typical driver and output transistor failures. They were impossible to repair without removing the entire assembly and repairing outside the unit. Although each output board had a number imprinted on them, they were all the same. The imprinted number was related to the length of connecting wires to the particular assembly. The output board assemblies were the same as used on sister models 100+ and 150+. I used to swap out the defective boards with rebuilt boards and then spend a day or two rebuilding the duds on a test fixture and reusing them. It made life easier.

 

[tcdriver]

I would need a bit more symptom details on what you mean by the tuner section going out. If the FM audio is very low and/or badly distorted, it most likely is the MC1307P MPX IC. That's the most common failure in the FM path. If the symptom is something different, please tell me more. Perhaps I can help.

Thank you very much for the information and the offer to help. I took my 900+ off line a month ago and need to find time to get it on the repair bench. I will let you know what is happening once I do.

I'm surprised to hear that replacement lamps were not available to you in 1984. I had access to all of them in the parts area up until I left in late 1988. The power button lamp, stereo beacon, in-tune, and matrix lamps were all interchangeable even though they had different part numbers.

Thank you for that information. It is good to know if I need to replace any more lamps in the future.

 

[tcdriver]

harman / kardon 900+ back panel image:

CD-4 phonograph board:

twin power:

 

[Quadrockasaurus]

Thanks for posting the nudies and the rear view of the 900+....we've now got a pretty good all round view of this unit, plus some nice tech info so far. cheers.

 

[Donnabobonna1]

Hello everyone I came accross one of these at an estate sale . it sounds pretty good cosmetically in good shape typical old receiver issue of scratchy pots could use a good cleaning all channels working. Preparing to sell it none on ebay to get an idea of what it worth anyone with an idea?

 

[Donnabobonna1]

here is the link to the ebay listing and there are more photos posted now they were on my partners phone and he was camping

 

[Quadmaybe]

Hello,
I'm a newbie to the forum. I'm in need of a wizard to resurrect my 900+, (working but only in mono and significant noise on one side), that had been closeted for @12 yrs. Any help greatly appreciated. Long Island NY area.

Thanks,
Quadmaybe

 

[Zanne]

Hi!
Im Janne From Finland and i might have a change to buy this 900+ model from Swenden our Neighbor. Its listed 250 and i tried it 200€ with postage. He brobably says no, but what is this worth and is it what i need...
I would need a 2 channel stereo amplifier from the 70s is there a challenger for those Marantz 2230 and others that are less hyped on harman kardon for exampe... is it Foolish to buy this one for parts and so on as someone mentioned, or is it wiser to go for example 930 ?

 

[tcdriver]

Hi!
Im Janne From Finland and i might have a change to buy this 900+ model from Swenden our Neighbor. Its listed 250 and i tried it 200€ with postage. He brobably says no, but what is this worth and is it what i need...
I would need a 2 channel stereo amplifier from the 70s is there a challenger for those Marantz 2230 and others that are less hyped on harman kardon for exampe... is it Foolish to buy this one for parts and so on as someone mentioned, or is it wiser to go for example 930 ?

If you are looking for a two-channel stereo amplifier / receiver, I suggest that you buy a two-channel receiver and not a Harman Kardon 900+ quadraphonic receiver. The circuitry is more complex and the phonograph section is optimized for four-channel and therefore compromised for two-channel stereo use.

 

[Zanne]

ok.

 

[4morhktech]

If you are looking for a two-channel stereo amplifier / receiver, I suggest that you buy a two-channel receiver and not a Harman Kardon 900+ quadraphonic receiver. The circuitry is more complex and the phonograph section is optimized for four-channel and therefore compromised for two-channel stereo use.

When functioning properly, the 900+ makes an awesome stereo receiver. In the stereo mode the front and rear channels are bridged (slide switch on rear apron in stereo) and the result is a receiver with an amplifier able to deliver a minimum rated 90 watts RMS per channel into 8 ohms.

The phono section is not compromised at all for 2-channel stereo. One caveat however is that the (LD3130) ICs used for phono amplification on the CD-4 board do fail from time to time and new replacements are not commonly available from most sources. So if you lose one or both channels in phono, then you may as well forget about using the 900+ in phono mode (stereo or quad mode). The solution is simple and inexpensive for non-CD-4 use only; obtain a widely available external magnetic phono preamplifier and connect it to the aux input on the 900+.

 

[tcdriver]

When functioning properly, …

My problem was that I owned two 900+ units and they both were noisy and never functioned properly. In a properly operating CD-4 phono preamp the high frequency response is cut off at or before 15kHz. Since you are an expert on the Harman Kardon units, is the low pass filter bypassed when playing ordinary two-channel sources?

My solution was to add a two channel stereo phono preamp internal to the unit. Since it has two phono inputs, I used one for the built-in CD-4 and the second for two-channel stereo and matrix quadraphonic records. My add-in was much quieter than the original built-in phono section and it provided full bandwidth for the audio signals. It just sounded much better than the original circuit.

 

[tcdriver]

harman / kardon 900+

back panel image:



twin power:

 

[Quadchuck]

I've had 2 800+ that I got in the 90's. The first one had a bad cap in the cd-4 board, when fixed it had very good decoding.
Since it had a bad transformer, I ran unit from a single trans and gave it away.
The second had everything ok, but didn't use it regularly and when I went to use it again the cd-4 board was bad.
I got another board on Ebay but I havent used it much since I have other demodulators.
It did have a good demod and one very interesting thing about the cd-4. It is hard to follow the circuitry and
layout without a schematic, but it is one circuit that uses no BANDPASS filters, at least in a metal shield blockform.
Some circuits have up to 3 filters and yet this one worked fine without them.
I've always wondered how they managed that feat.

 

[slo_dat]

When I was younger my first Quad receiver was a 900+ . I can honestly say it was a beautiful sounding piece easily as good as the Sansui's I had later.
The stereo separation in particular is very very nice. A really nice wide and warm soundstage. Lots of power and punch a fantastic receiver. Maybe that was a result of their seperate twin power transformers ? As in the post look at the power caps and transformers- there is some grunt !!
Unfortunately when it had problems I couldn't find anyone who could repair it. The electronics for the time were very advanced and few people could approach repairs .Sadly it faded away., a heavy beast I just couldn't keep moving with it
Years later I found an awesome tech who could work wonders on anything with power buzzing its caps, but I had moved on to Sansui's (which are awesome of course) but I really regret ditching my 900+ ! Honestly one of the best quad receivers out there IMO, hopefully I might find one again one day. The joystick is a bit of a negative but if you find a good one- buy it ! If you know someone who can repair one - do it! You won't be dissapointed these things are awesome. Also there quad decoders are very, very good, as good as Sansui !