Leader LAG-120B Teardown & Testing - diyAudio
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Old 27th October 2012, 12:16 AM   #1
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Default Leader LAG-120B Teardown & Testing

I recently picked up a Leader LAG 120B Audio Signal Generator off ebay (from none other than Joe D'Appolito himself!) and wanted to share my thoughts on it.

The 120B service manual, supplied by Leader, is attached below with some pictures.

First off, Leader brand gear seems pretty well built. I have a bench power supply, and 100Mhz analog oscope made by them and see the quality on par with old Tektronix or HP.

The LAG-120B is built very well, with sturdy controls and strong, all metal chassis. The signal section of the circuit board is shielded, and the main dial has a very nice feel. Circuitry is simple, but seems well done for the goal of making a basic wave generator. Personally, for what most of us on diyaudio do, I'd much rather have a basic generator like this than a cheap "do-it-all" function generator. At least, I think both deserve a place on the bench.

This particular unit is very clean, and seems to work perfectly. My oscope is old, and hasn't been calibrated in many years so I'll wait until I can test the LAG at work and run through the calibration procedure before giving it a clean bill of health. But, the sine wave output looked very good, with no DC offset, and the frequency dial was just within spec (~25Hz off at 1Khz).

The power up output noise is pretty bad, to be expected, but it settles quickly enough. Power off is more controlled. That's all for now until I can do some real testing.

*Note: The 120B is functionally the same as the 120A but the circuitry is pretty different.
Attached Images
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File Type: jpg IMG_1126.JPG (180.2 KB, 162 views)
Attached Files
File Type: pdf LAG 120B SERVICE MANUAL.pdf (661.4 KB, 255 views)
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Old 27th October 2012, 12:23 PM   #2
PChi is offline PChi  United Kingdom
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Thanks for posting the manual and pictures. I like the picture of the frequency adjustment variable capacitance and gears.
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Old 1st November 2012, 08:51 PM   #3
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The LAG 120 Is a Incredible Audio Generator...Small in size,,BIG in features...Low Distortion,,,,Easy To Use..Very Reliable and Low In Cost( Around $420 in 1982) I owned The Lag 126(120's Big Brother) and the 120 was very close in features to my 126!! Sure I had a Tone Burst Feature( Great For Checking Out Speakers,), But At What Price??? $530 more!! The Distortion was Less ,,,Big Deal!!! Your 120 is great for experimenting and Testing Audio Gear!!! Please Take Good Care of Your 120 as it is a Great Piece Of Test Equipment!!Great Article You posted,,Many Thanks From MROHM1970.
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Old 2nd November 2012, 08:36 AM   #4
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MR OHM 1970 Back Again!! I had To Comment on Those Pictures You Took of the LAG-120B..A beautiful and Neat Layout of the P.C. Boards...Is This Pride in Workmanship Or What??? I had a LAG-126 and LMV-181 and LMV-186 (A.C.Millivoltmeters) and These Guys Lasted Me a LONG LONG TIME!!!
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Old 3rd November 2012, 03:59 AM   #5
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It is a neat layout, but they made the board bigger than necessary. It could have been a much more compact unit, really.

Also, I picked up a second one in slightly worse physical condition (poor packing and UPS had a hand in that) but it works as good as the one pictured above. Hurricane Sandy put a damper on my plans this week, but I'm going to try and get one or both of these into the lab next week for some testing.
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