Heath's AJ-1510 was one of the very first all digital synthesis PLL FM tuner ever produced, introduced in 1972. (A true historic piece) My problem is that it was mainly designed for the U.S market and can only receive ODD ending channels (like 92.3 or 106.9 MHz) and has 200 KHz frequency increment steps. Even numbered channels (like 92.4 or 106.8) can not be entered or you get a "RE-PROGRAM" error. In Europe both odd and even ending FM channels are used and of course I can't access the latter. I know AJ-1510's were sold in Europe and some circuit modification should have been designed to access even numbered channels (or 100 KHz freq.increment). I have good basic digital circuit knowledge but admit being lost in the quite complex circuits used in this tuner (preload decoder,programmable frequency divider,code converter,etc...) using over 30 digital logic I.C's ... and failed in finding some easy way to convert the tuner for European use. Hopefully there is some "AJ-1510 Expert" reading this who remember how this modification was implemented ? I know the conversion was then published in some British electronic magazine but I have no more details about it. The right person would be Mr DAVID M. THOMAS , Senior Design Engineer on the AJ-1510 Project and later Chief Engineer at HEATH Ltd. Gloucester, England but I was unable to get in touch with him so far. (I'm not even sure he is still with us). Any help to solve the above problem would be greatly appreciated.
NOTE: I have the original AJ-1510 manual/schematics and 3 tuners available for experimentation.
NOTE: I have the original AJ-1510 manual/schematics and 3 tuners available for experimentation.
Check with the FM tuner group at Yahoo Groups:
FMtuners : High End FM Tuners
I own a semi-functional AJ-1510 and am relying on help from knowledgeable owners in that group to perform a set of modifications to improve stability and fix design flaws, as well as a general parts upgrade.
FMtuners : High End FM Tuners
I own a semi-functional AJ-1510 and am relying on help from knowledgeable owners in that group to perform a set of modifications to improve stability and fix design flaws, as well as a general parts upgrade.
I have written up a blurb on the AJ1510A tuner, but it is in word format. I am not sure if I can copy it into here as it is rather long. And you are right, there are several design flaws, very unusual for a Heathkit product.
It does not cover the original poster's problem of changing the tuning, but it does cover a number of flaws. If you have enough information to contact me, I can send it via e-mail.
I would like to understand more about how the FM demodulator works, and possible upgrades. The demodulator includes a 709 type opamp, which is ancient history, and it's suggested that as an integrator the circuit is actually incomplete. I tried once to replace the opamp with something more modern, but lacking a signal source I gave up when the change didn't work. Open to ideas there as well but mostly I'm looking for a clear explanation how it actually works.
This is a pulse (or counting) type demodulator. A basic explanation of his working can be found in the May 1973 issue of RADIO ELECTRONICS which features a 5-page article about the AJ-1510 written by the designer himself. (David M.Thomas). See attached picture. He didn't actually invented the circuit which was already know in the tube-era and sometimes called a frequency-counting detector or frequency differential counter. Just a modern implementation of an old circuit.
I tried various modern (pin compatible) opamps in this position and sometimes it worked,sometimes not (or with degraded performances). Looks many parts of the AJ-1510 circuits are critical and works "on the edge" of the (then) available technology. Replacing the 709 had very small effect on the average sound quality which is mainly limited by the MC1310 MPX decoder chip and the many switching diodes in the audio signal path. I would consider the AJ-1510 as a significant historic piece in tuner technology and a strange-looking device (conversation piece) , but performance(and sonic)wise only a average tuner. Reliability is another issue but can be improved. (see amptramp's post above for more details)
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Thanks for the reprint of the RE article; I'm still a bit lost by the explanation, but it's substantially more information than I had before. I had the impression that the demodulator could handle very wide modulation with less distortion than typical L-C type detectors, and the composite output had less phase distortion insuring better multiplex decoding. I replaced all Rs and Cs with .1% metal films and caps with polystyrenes or silver mica instead of the ceramic disks, on general principle, but I'm still shooting in the dark without at least a Sound Technology 1000A or the equivalent.
Again, thanks for the information; a copy went straight into my AJ-1510A manual!
Again, thanks for the information; a copy went straight into my AJ-1510A manual!
If you notice, the counting detector is linear with period, not frequency. But the error is quite small. The centre frequency, 10.7 MHz is 93.4579 nanoseconds. Full positive frequency shift is 10.775 MHz with a period of 92.8074 nsec and the negative shift is 10.625 MHz with a period of 94.1176 nsec. Positive difference is 0.6505 nsec and negative difference is 0.6597 nsec. Thus, there is some harmonic distortion with a counting detector, but it is small and well-characterized. Maybe the higher frequency compensates for the smaller period when it goes high and vice versa.
At this point, I've little idea on how this part of the AJ-1510s circuits could be 'improved', but I bought the thing expecting to get an interesting and perhaps significant piece of equipment that'd sound good once restored. Had I known the Sony XDR-F1HD and HD radio was around the corner, I wouldn't have bought it as the Sony is giving me excellent service and satisfaction.
But I'm still holding onto the Heathkit because it sounded pretty good itself, when the digital tuning decided to work and I think it's worth restoration and upgrades.
But I'm still holding onto the Heathkit because it sounded pretty good itself, when the digital tuning decided to work and I think it's worth restoration and upgrades.
In the zip on post #6, you can get a lot of ideas about how to do this. The biggest change was putting 0.01 µF ceramic capacitors across each chip in the divider chain from pin 16 Vcc to pin 14 that is conveniently at ground. The designers were counting on a 10 µF electrolytic to bypass a high edge-rate divider chain. I still haven't got the keyboard entry to be 100% debounced, but part of my file shows you the plan for making it better.
Actually, the counting detector will probably have less distorsion than most common (Foster-Seeley, ratio) detectors without requiring any alignment. Proper alignment of the conventional FM demodulator for minimum distorsion was allways a tricky job and required specialized test equipment (sweep generator,ocilloscope...) which most home kit builders didn't have access to. Maybe this was the main reason why HEATH decided to use this kind of demodulator. It is quite remarquable that a receiver of such complexity could be aligned without any test equipment but the small built-in signal meter. Another HEATHKIT achievement...
Wow, nice write up. I have an unbuilt AJ1510A which I am planning to start building next year. I will change out all resistors from the beginning as well as caps. Any ideas of what you might do if you started from a bare bones kit?
Thanks
Just now noticing this.
Really?! Wow... That might go a very large box of pennies on eBay.
Apart from the list of modifications, I'd replace all carbon film resistors with 1% metal film, tantalum coupling caps with film (they'll be much larger), and consider buying new electrolytic caps for the power supply as the units in the kit are likely unformed by age and may quickly fail. If you have a variable DC supply, bring them up slowly over a period of hours.
Also replace the (likely) corroded RCA audio output jacks with gold-plated
parts.
Hope you'll still got the extender board; that's a useful part to have while troubleshooting and modifying.
Hi, guys; I'm a new member here. I just picked up an early non-A version of the 1510 , and I just get a hiss out of it, but no stations; it appears as though the synthesizer is not working. I can push a 10.7 mhz signal through the IF strip, so I know that much is OK. At this point, I'll have to rig up an extender card to do more tests, as none came with the unit. I'm a long-experienced bench tech, so this is going to be fun. I did download amptramp's article on the updates and fixes.
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