Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Equipment & Tools From test equipment to hand tools

Boonton 1120/1121 Distortion Analyzer tweaks
Boonton 1120/1121 Distortion Analyzer tweaks
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th March 2020, 04:14 AM   #161
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Boonton 1120/1121 Distortion Analyzer tweaks
I had trouble finding them as well. i had to search for "j108 fet" to get any useful hits.

The confusion is sj108 vs. J108, originally a Siliconix proprietary part that National knocked off. The National parts have a lot lower rDS on than the Siliconix parts.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 26th March 2020, 04:37 AM   #162
SyncTronX is offline SyncTronX  United States
diyAudio Member
 
SyncTronX's Avatar
 
Join Date: Oct 2008
Location: New Projects Enter the Queue Oh My!
Was that Mr. Pease again, helping National making that fet with lower rDS on?

making it better.
__________________
-- Sync
  Reply With Quote
Old 26th March 2020, 09:29 PM   #163
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Boonton 1120/1121 Distortion Analyzer tweaks
No. He was in the IC group.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 27th March 2020, 07:04 AM   #164
slbender is offline slbender  United States
diyAudio Member
 
Join Date: Aug 2004
Location: Queens, New York
Quote:
Originally Posted by 1audio View Post
The FETs are obsolete mostly due to the package. Variations are available in SMT. I bought 100 on eBay recently and they test way better than the ones in the older unit I have. Now that I have a Metcal desoldering tool I'm almost ready to swap out 30 FETs. But not quite. . .

I'm looking at ways to sort that are not too difficult. So far what works well is to mount a socket with gate shorted to source through a 5K resistor and then apply 5V AC through 600 Ohms across source-drain and measure the voltage there. Lower is better and use the lowest in series with the lowest value resistors (5K) in the attenuator networks.

I have several of those little all purpose part testers with either multiline or graphical displays, based on microcontrollers, that cost around $15 each. They do R's, Caps, Transistors, and Jfets, using a single voltage and I guess a constant current, probably 5 volts and 1 mA. or similar. Different sets give several different values or parameters on the readout, but all let you select or match parts, for polarity and hfe and likely use 1 mA., or 5 mA. and another voltage, so I suppose their test is somewhat like what you suggested.

Either way, one could select for a particular parameter, high or lower. On caps it gives ESR values and that allows best / mediocre / bad selection, along with uF., very good for grading and matching tantalum caps, and electrolytics. I didn't have any J108's, but previously I matched and tested 2SK170's, and noted that the three testers all give very similar results.

I just ordered a handful of those National J108's just to have them. Reading through the Boonton 1120 and the 1121A manuals it appears that the source (Oscillator) card #112077-00A is, as far as I can tell, the same in my 1120/S10, the 1121, and in the 1121A, all three using the thru pin J108's. I note that on the A6 Oscillator board Q1 is a PN4391A in the 1121A, not sure if it is the same in both my sets, ( yes it is, I just looked!). All the rest of the Jfets Q2 - Q24 are J108's, I wonder if they are matched in some way - for a particular parameter?

All the other cards in the 1121A, use surface mount parts MMBF4391LT1 and MMBJ108's Jfets on other boards that were converted to all smt parts. Maybe there are some minor differences that I did not pick up on, but really the only difference between the 1120/S10, the 1121, and the 1121A seems to be conversion of thru pin parts to smt parts, and that the -5 volt regulator is no longer a TO-3 on the heatsink, but another flat pack type on the inside. Functionally, the differences must be in the software (firmware) as the hardware is quite a constant thing.


Steven
__________________
--
Steven L. Bender, Designer of Vintage Audio Equipment
  Reply With Quote
Old 27th March 2020, 11:40 PM   #165
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
Boonton 1120/1121 Distortion Analyzer tweaks
the parameter you are checking for is the on resistance. A 5K resistor tied between source and gate will turn the jfet on and is approx what is used on the PCB. Then you can measure with DC or AC but AC is what its used with. And its easy to measure small AC levels. The on resistance is 5 Ohms or less. There seems to be a correlation between on resistance and distortion so I'm opting for the lowest on resistance.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 2nd April 2020, 06:44 AM   #166
slbender is offline slbender  United States
diyAudio Member
 
Join Date: Aug 2004
Location: Queens, New York
Default Regarding the Jfets...

Quote:
Originally Posted by 1audio View Post
the parameter you are checking for is the on resistance. A 5K resistor tied between source and gate will turn the jfet on and is approx what is used on the PCB. Then you can measure with DC or AC but AC is what its used with. And its easy to measure small AC levels. The on resistance is 5 Ohms or less. There seems to be a correlation between on resistance and distortion so I'm opting for the lowest on resistance.
I have been doing a lot of figuring the past few weeks, stuck in the house due to the CoronaVirus being so prevalent here in Queens, everything outside is basically shut down. Thinking about these Boonton units - they really screwed up the power supplies in these sets!

First some background. There are three main voltages, +15, -15, and +5 volts. For whatever reasons the +/-15 are derived from a 4A full wave Bridge followed by a 4,700 uF. / 35 volt Cap feeding both the + and - regulators a 7805 and 7905, with some zeners and feedback Op Amps on the pin to ground so they float. That is OK, and that one cap lowers the AC ripple just enough to give fairly low ripple to ensure the 1 Amp 7805/7905 pair work well enough.

However, the main +5 Volt 3 Amp power comes from U4, an even older technology, obsolete type LM323K in a TO-3 case, on the external side of a large heatsink, which is powered from a SDA-980-1 a 25 Amp bridge, and C18 a 26,000 uF. /16 Volt cap (according to the 1120 manual parts list).

On the hand written 1120 schematic it's even worse, one zero was apparently dropped, on there, making the power supply a 25 Amp Bridge, followed by a 2,600 uF. / 35 Volt cap... Inside the set (in reality) - is a 4,700 uF. +/-20% 35 Volt cap (which might be functionally as low as 3,800 uF. and still be within tolerance, circa 1985... over three decades ago). That is what lowers the ripple inside the Boonton 1120 and 1120/S10 sets, but not enough! No wonder those P.S. caps overheat and keep failing!!!

This "U4" LM323K 5 Volt / 3 Amp regulator needs at least 22,000 to 27,000 uF. upstream on the input side to have sufficiently low ripple in order to operate properly and with best efficiency. I'd recommend a 33,000 uF. / 35 Volt part for C18 if I was refurbishing the set. Yes, that external heatsink gets pretty warm, and it is from that LM323K goin' bonkers!!! This is a Factory Error inside EVERY BOONTON SET.

It gets no better in the 1121, or 1121A which uses C113, a mighty 6,800uF. / 50 Volt cap that is feeding the equivalent of the 323K, an updated LM1085-5 a flat pack, low-dropout modern 5 Volt / 3 Amp regulator, that too should also see 22,000 to 27,000 uF. upstream!!!

My 1120/S10 will have a new 33,000 uF. / 35 Volt C18 cap installed in a few days, when those parts arrive. I wonder if the loopback residual distortion of 0.0022% will be improved, before any other upgrades on the plug-in cards are involved? (still waiting for my extender card to arrive!).

I'll let ya know!


Steven
__________________
--
Steven L. Bender, Designer of Vintage Audio Equipment

Last edited by slbender; 2nd April 2020 at 07:01 AM. Reason: Left out a word.
  Reply With Quote

Reply


Boonton 1120/1121 Distortion Analyzer tweaksHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Boonton 1120 and 1121 filter cards 1audio Everything Else 3 4th December 2016 04:33 PM
FS: Boonton 1121 audio analyzer jackson7575 Swap Meet 0 1st September 2011 01:23 PM
Improve this Boonton 1120 Output Stage jackinnj Everything Else 9 13th November 2007 07:04 PM
boonton 1120 manual azaz Everything Else 2 13th November 2007 06:26 PM
Boonton 1120 audio analyzer Matyeo Swap Meet 1 8th April 2007 04:57 PM


New To Site? Need Help?

All times are GMT. The time now is 05:05 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki