Anyone Familiar with the old AN377 FM Radio IC ?

Would getting hold of any of these schematics, so in circuit use of AN377, be any help in adjusting response KENWOOD KT313 AN377 KENWOOD KT313 AN377 KENWOOD T7 AN377 PANASONIC SA5170 AN377 PANASONIC SA400 AN377 PANASONIC ST9030 AN377 PANASONIC SA100 AN377

I can't tell for sure, but it looks as if the NTE788 may be of the similar design to (or even pin-compatible with) the Sanyo LA1230.

If so, it's a single-coil quadrature-detector.

I had a problem somewhat similar to yours with a family of amateur-radio narrow-FM receivers a few years ago... the IF-detector output started clipping at only about 2 kHz deviation, rather than accepting up to 5 kHz or more cleanly. This sounded bad and completely messed up the DTMF decoder.

The problem did turn out to be the coil... not its alignment, but its in-circuit Q. The detector's output voltage depends on the amount of phase shift introduced by the coil, at any particular amount of frequency deviation, and the phase shift depends on the coil Q.

We talked to the manufacturer, and found that they'd had to change suppliers for their detector coil a couple of years earlier when the original coil was EOL'ed. Apparently the new coil they chose, generated more phase shift per amount of deviation due to a higher Q in the circuit. The Q is controlled by the impedances of the reactances in the coil, and by the value(s) of the resistors(s) that are shunted across one or more of the coil windings. My guess is that the new coil had a lower L and a higher C than the original... same resonant frequency, lower impedances, and thus the existing shunt resistor had less effect.

We experimentally bridged the shunt resistor with a second one, dropping the resistance and thus swamping the coil Q to a lower value. The IF detector output dropped by about 50% at any given amount of deviation, and the clipping was greatly reduced. A bit of further experimentation and we were able to find a resistor value which allowed the detector to handle 5.5 kHz of deviation before it began to flat-top.

So, the problem turned out to be a one-resistor substitution in each receiver... audio quality was greatly improved and DTMF detection became reliable.

So, I'd suggest that you try an experiment of that sort... find the resistor which shunts the coil, and decrease its effective value by

2:1 or 3:1 (just bridge it with another, for now) and see if this un-clips the output.

The LA1230 data sheet comments that the chip's THD "depends on phase linearity of the phase-shift circuit used"... I think this is alluding to the same basic phenomenon.

Interesting. Being that getting parts for these old vintage things is not t hat easy, I might have to try that resistor trick.

Do you concur that the difference is in the IC ? If not that owuld mean two defective parts, which in low power circuitry like this, is kinda rare. If it is something with the coil, that means someone was listening to distort ion and all the suddden it stopped working. The way it sounds right now I o wuld have never had it switched to FM to even "wear it out" or whatever.

The print is available the Hifiengine if you'd like to have a look, or I co uld Dropbox it. There is another coil coming off the tank. The tank has two adjustments, but only two connections. Kinda makes me think adjusting that would affect the gain (output per deviation) but it doesn't seem to be wor king that way. When I first installed the IC, the tuning meter only deflect ed to the right, but by diddling I got it to balance out. Adjusting either coree doesn't seem to affect the output amplitude.

One thing of note, which might mean nothing, is the original IC was red ink ed. I know they don't do that for s**ts and giggles. It may have been a cus tom run for Technics. If they used it in all their recievrs, maybe it is a custom IC with slightly different specs. They love doing that bcause it cap tivates the parts market. However I hold no hope of getting one from Panaso nic at this point. Years ago they didn't even have parts for one of their d amn RPTVs that cost two grand.

Know what ? Just because I wrote that, you probably CAN get it from them. I was fairly surprised that you can still get a four gang volume control for a Kenwood KR9400.

But not from Kenwood.

What really gets me is the quality of the front end in these old tuners. Th e new stuff seems to be junk. This thing is in a basement with absolutely n o antenna connected and it is picking up stations. Newer recievers seem to get noting and that is with a wire on the antenna. I bet alot of them actua lly bat their ratings in sensitivity. Now instead of actually designing the thing they just buy a front end from China for like $3 if that, and addres s it by I2C.

I got a newer Technics stand alone tuner. This thing has it's own powers su pply and even an AC outlet on the back, OF A TUNER. It has a rated sensitiv ity of 0.9 uV which is I think about half of the rating of this 300, and th e 300 gets better reception. Even though distorted, it is getting more stat ions. this has been the case with several vintage recievers and tuners I've worked on recently.

Thanks for the tip. Now to figure out what value of resistor.

AN377, be any help in adjusting response "

Thamks, I'll have to give a couple of those a look. Technics is Panasonic a nd their manuals quite frankly suck usually. I remember fixing their bigscr eens, not only was the service menu very unfriendly, but the manual was not clear, with instructions to get into service mode many pages away. Shit li ke that.

I will definitely have a look at that Kenwood manual provided Hifiengine or someone has it. If so I will take a look before doing the resistor trick.

Thing is, on these things I don't like to diddle alot. Bust that core or so mething and you're screwed. Think the IC might be hard to get ? HAHAHAHA.

Thanks.

I think that's the likeliest thing. The two IC designs probably have different "phase shift, to output voltage" sensitivities. The tank circuit which was used with the original quadrature detector (a two-coil type) is probably not quite what the new detector IC was designed to use... and so a slight change in the tank Q might be all that you need.

You might be able to research this if you care to. Look up the specs for the tank coil with the AN377 used in the receiver. Then, look up the specs for the tank coils suggested for use with the NTE chip, or with the Sanyo or similar single-coil detectors. With lots of luck and effort you might be able to compare the coil specs or sample circuits and see where the differences lie.

Or, just try a swamping resistor and see if it makes the difference... if so you'll know where the problem lies.

Yeah, that was one of the significant changes in quadrature detector designs over the years - getting rid of the need for the second (usually fixed-value) inductor in the tank circuit.

No, I don't think it would... or, at least, not a big one. The two adjustable cores (or trimmers) in the tank would adjust the resonant frequencies of each part of the tank... but I think that any change in the Q would be relatively minor. The Q for each of the two halves of the tank transformer is going to be set by the values of its reactive components, compared to the (external) resistor which is shunted across them. To make a big change in the Q and phase shift (which is what I think you need to do) without changing the resonant frequency (which needs to remain at the IF frequency) you'll have to play with the resistor.

A lot of people agree with you. There's a great deal of enthusiasm out there for the "golden age of analog" FM tuners... expecially those with real air-variable capacitors. A lot of 'em have better sensitivity and selectivity than you'll find in modern products (in which the FM section is almost an afterthought). Modern receivers often tend to emphasize DSP and effects and 587-channel operation, and cut corners on the basics :-(

If you do any core twiddiddling, mark and note the "o'clockness" and depth gauge the depth, beforehand , so you can at least get back to where you started. A slight heating of the core with an iron tip may get over any threadlock

I wound up with a 681 ohm resistor to correct the gain. then the tuning met er didn;t wor alomst at all. I removed a 330 ohm across it and shunted a te n K going to it with another ten K. got it to move wlel enough but it will not go both ways.

then, something is different with the muting, so I had to disable that, but the thing actually works acceptably. The tuningmeter is not centered, and tuning it you can tell it is not how it should be, but it picks up stations in a basement with a piece of wire. It works well enough.

I looked at the prices these things are bringing and well, that is good eno ugh. Just tell the buyer the FM isn't quite right. It doesn't hav muting an ymore because I disabled it to be ablre to switch it to stereo.

That is one of my biggest pet peeves about Technics, ganging the mone stere o switch with the muting. You now, I oiwn it and I will decide when to swit ch to mone on a weak signal. And who knows, I might have an extra Dolby dec oder around, and those thigs are great for FM if you now how to set them.

But I shipped it. the sensitivity is good, once you get it tuned it sounds fairly clear although I am sure it does not meet the FM THD specs. But ther e is nothing I can do. Unless I can get the original private spec IC, this is the end of the road. So we get less money for it.

Sometimes it works that way. I got ore toime into it than I should but so w hat, I ma not under the gun here. Plus it comes out in the wash. We got luc ky on a few other units. Now the idea is to get them sold. Iam kinda surpri sed at how fast some of this vintage sells.

The new shit must be pretty bad. Like all bells and whistles but no REAL so und. And I have worked on some of it. I do not want it. Like a 7.1 channel Sony, I would not take it for free if you brought it to my front door. Same with th new Pioneers, Onkyos, just about all of them. All been bought out.

Yup, 587 channels of junk.

I would really have liked to get the old Technics working really right, but oh well. I simply cannot have 100 hours in it. And I cannot make a custome AN377 with red ink on it.

Now that I think of it, in Panasonic equipment when I saw a chip with red i nk on it people told me you cannot use the regular part, it HAS to come fro m them. And it will not come soon.

I always tried to tell the people that it was them who f***ed them over, no t me. A manufacturer back then counts on XC amount of the time they do not believe me. Playing the odds. But when they take it to another shop.. And a lot of the time I was the next shop.

I did cost some of these companies some bransd loyalty, and they had it com ing.

You can buy an AN377 brand new on EBay for $5.00 from a reputable U.S. seller. (In San Jose Ca.) Chuck