TOTL tuners. Required generator distortion specs for alignment

Jauk

Active Member
Hi. I have an idea that I don't know if it works in practice, and would like to ask if anyone with experience can chime in. It's obvious that you can't align a high end tuner with very low distortion with a generator that doesn't have similar distortion specifications, preferably lower. However, what about if the specs of the generator are just a tid bit higher, for example, a tuner with 0,02% distortion and a generator with 0,05% ? Using a spectrum analyzer (in my case I plan to use PC based software with a high end sound card), even if there is distortion present that is not originated by the tuner, one would still be able to lower distortion up to spec because the distortion caused by the generator is in the same order of magnitude of the tuners, provided the spectrum analyzer's scale and graph is up to it. Totally different scenario from using a generator with say 0,5% distortion, which is not so uncommon.
Is my theory correct or do you really need a 0,01% distortion generator for this type of thing ?
Thanks to all.
 
@KentTeffeteller
I think these tuners are ok with just following the service manual indications, which mention a signal generator, oscilloscope, a distortion analyzer and a good volt meter (VTVM but I think a good modern one is enough). They are a Technics ST G7 and a Pioneer F93. I'm not into tuner design but I think these are PLL with a varicap, whatever the implications are ... :) From the comments around they seem less of a hassle to tune.
 
I realize my comment is based on other posts and not on even mentioning valid arguments, so I'd like to avoid that, sorry about that. So why does PC based doesn't do it ? BTW the ST1000A, which is what most use as the other later model is rare and expensive, doesn't have very good specs for more modern tuners.
 
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For example the max THD for the ST-1000A is 0.2% in stereo!
Why ask for advice when you're determined to do it your way? To do the job properly requires an FM signal generator (there are analog FM generators & digital FM generators). You'll also need a good scope followed by experience & expertise. As they say in baseball, you are 0 for 4. This is not a DIY job. You might as well try alignment with your I phone.
 
"Why ask for advice when you're determined to do it your way?"
I'm not, otherwise I wouldn't post this thread. Just presenting my thoughts and asking help on if they're wrong and why.
So why is 0.2% not a problem ?
 
"Why ask for advice when you're determined to do it your way?"
I'm not, otherwise I wouldn't post this thread. Just presenting my thoughts and asking help on if they're wrong and why.
So why is 0.2% not a problem ?
How many people do you need to tell you it can't be done your way? If you want to be placated, forums are not the place. There's nothing wrong with 0.2%. There's a lot wrong with your understanding of alignment. Why not google FM tuner alignment? Google is your friend.
 
Hey, like the saying goes, the only bad question is the one not asked. I'm not asking for a PhD doctoral thesis explanation. Just a simple why it can or can't be done, that's what the forums are for, sharing information no ?
I also would like to know what's the problem with following the instructions on the service manual, cause that seems like nonsense to me. Is there another way ?
 
Your biggest problem is getting a suitable FM stereo generator. Not only does it need a low THD oscillator, but that low THD has to be preserved during the modulation.

I've pondered this same issue and here's the best way I can describe the problem. I may be completely wrong, so hopefully somebody smarter will pipe up. You'd think the DUT THD and the generator THD would be unlikely to cancel out or add. You'd think even with a highish generator THD you could still find the trough of adjustment and get pretty close. Not well enough. Consider the S-curve display that you optimize and center in the process of alignment. By twiddling the transformer core you can bend the curve in both direction. Now think about the THD of the generator, which is basically a similar warpage. It turns out they can in fact, cancel, and you get a bad alignment.

IMO, most service manual alignment procedures make a lot of assumptions that you know what you're doing. They often have omissions and outright errors. It takes a few years of doing this before you can claim competence. There's a summary for the Sansui 2000X and Yamaha CR-620 on my site you might find useful. You should also read the manual for the Sencore SG-165, even if you don't have one. It's a really good summary. Note that ceramic filters simplify things greatly. Adjusting the multiple transformer IF on the old Sansui's isn't for the faint of heart.
 
Use a Sound Technology generator on a TOTL tuner, or outsource the job, PC based won't do.

PC based solution using modern 24 bit cards will work. They allow measurement of audio signal distortion down to -150 dB. Of cause signal generator (actually FM modulator in RF generator) should be up to the task. RF generators may not have best internal audio signal source, so PC can be used to generate stereo multiplex signal too - software is available for that too and works with audio cards suppporting 192 kHz sampling rate.

Of cause standalone device is much more convenient. You can find good stereo FM generator on e-bay for $600-800. Panasonic models are good. There are some other brands too. For your purpose, I would use only fully digital models.

If you need RF section alignment too, then things get complicated rather quickly. Proper tool for that is RF spectrum analyzer with tracking generator. This is probably another $1500.
 
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Is it under modulation low distortion enough, I highly suspect it is marginal unless that Sound Card is extremely fine and suited for audio processor use in software like Stereo tool. Most consumer PC audio cards are not up to that level. TOTL tuners need TOTL test equipment in good calibration to align correctly, not sort of solutions. Again, use what the tuner manufacturer recommends or better or OUTSOURCE IT if you expect it to perform right. I lack this caliber of test equipment at home, I take it to work to align or outsource it. PC consumer sound cards on average are NOT SUITED to generate multiplex signal with suffficient accuracy without tilt for FM work. ESI Juli or AudioScience are about the only cards I'd trust to do that dependably.
 
Conrad, Kent & for_p1 have formulated good info. I would strongly suggest some research on FM alignment & then their cogent responses will make sense to you. Other than that, we're going in circles for no reason.
 
Thanks all for your answers.
@KentTefferteller
I got a Lynx L22 :) It's amazing what people almost through out when doing upgrades. Granted PCI (which the L22 is) is now non existent in more than 90% of newer motherboards and that makes it impossible to use more modern PCs with those cards, but it's such a waste. Ironically the newer PCie version of the L22 (the E22) has practically the same specs!

Most Panasonic and Leader generators around the bay are at about 0,05% distortion. Still too close if the distortions can cancel out like ConradH mentions.
 
Is it under modulation low distortion enough, I highly suspect it is marginal unless that Sound Card is extremely fine and suited for audio processor use in software like Stereo tool. Most consumer PC audio cards are not up to that level. TOTL tuners need TOTL test equipment in good calibration to align correctly, not sort of solutions. Again, use what the tuner manufacturer recommends or better or OUTSOURCE IT if you expect it to perform right. I lack this caliber of test equipment at home, I take it to work to align or outsource it. PC consumer sound cards on average are NOT SUITED to generate multiplex signal with suffficient accuracy without tilt for FM work. ESI Juli or AudioScience are about the only cards I'd trust to do that dependably.

I use PC and sound interface to check all audio frequency gear. Of cause this is not internal audio interface I use, but pro level external audio codec. $300-500 will buy you a good device capable to reliablyregister distortions in very fine gear and is bested only by top of the line measurement equipment like made by Audio Precision.

Here we are talking about RF things, and there standalone gear is the only option today. Though some products on the market come close (I am talking about Red Pitaya and similar devices). But those which 16 bit A/D and D/A needed for precise measurement are still too expensive).
 
"But those which 16 bit A/D and D/A needed for precise measurement are still too expensive."

Which is why I keep saying that it's not a DIY job. There may be more shoemakers in audio than actual shoemakers world wide. Many piss away $100s & $1000s of dollars on tweaks which only alpha bats can possibly hear. Advocate pro alignment & @ minimum a multi element Yagi antenna sans rotor, & the great unwashed cry too expensive & too difficult.
 
Of course to properly measure/set the FM distortion you should have something like 10X or better, not so easy to make an FM RF SG sub 0.1% THD.
One usually uses a mono (L+R) signal with 75KHz deviation to test/set THD.
I am actually putting one together a tester using a old HP 11715A AM/FM test source that was designed for testing HP8901A/B,8902 modulation analyzers and FM broadcast receivers. There is a 11715A test procedure to measure THD in the service manual.
Distortion:
<0.025% THD (<–72 dB) for Carrier Peak Modulation frequency deviation rate
12.5 MHz 12.5 kHz <10 kHz
100 MHz 100 kHz <100 kHz
400 MHz 400 kHz <100 kHz
Flatness:
dc to 100 kHz rates: ±0.1%
dc to 200 kHz rates: ±0.25%

I also have a HP8656B, but its FM THD is in the order of 0.1%, good enough for most except some TOTL tuners.
 
Hello
Jauk if this is your first time doing Fm alignments, I really really dont recommend you start with 2 so sophisticated and low distortion tuners. Practice on something cheaper and easier.
Practice measuring the tuner and see if you reproduce the specs first. Trust me just this will challenging using your tools .
Study the schematics and the service manuals. BTw it isn't uncommon that these will have errors or omissions. I glanced at the SM of both. The pioneer has 35 steps ! And you will need repeat several to converge.
Next read FM books you need to understand how each part works and how changes in one part impact the other ( RF, IF, MPX etc) plus there is an order to alignment. You can easily get lost and improve one part yet the total THD is going up. Also you can go in the wrong direction sometimes and need to be able to reverse what you did hence measuring the starting point.
Finally be aware that some specs are inflated or not exactly achievable. That FM tuner specs can sometimes only be reached with hand matched IF filters which was not done in production units but was done for the benchmarking units. Or if measured inside a faraday cage well you get the idea.

Now instruments. The G7 claims 0.02% in stereo and the F93 claims 0.04% in stereo. So this really limits the FM stereo generators you can use. there are probably less than 10 units and all discontinued. Only a few models of the brands Kikusui, meguro, sencore sg80, ST-1020A not the 1000A, panasonic will go low enough.
I do suggest a spectrum analyzer, these are not suggested in SM but more common today and allow you to "see" things differently and can see the impact of each adjustment as you turn the pot.

Good luck and dont get discouraged. But be prepared this is perseverance work.
Paba
 
Great advice. Learn alignment basics on average radios and cheaper tuners, work your way up as you gain skills and better test equipment.
 
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