John Linsley Hood FM tuner article/s - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

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 13th October 2012, 06:57 AM   #11
diyAudio Member
 
Join Date: Jun 2004
Location: La Rochelle
The (very kind) ETI scans have allowed me to debug 2 major faults and got this "Hart Linsley-Hood 400 series tuner system" fired up and running.

A solder bridge between adjacent pins of the fm demod chip (which is actually a HA11225 rather than the stated CA3189), and a failure of a ML ceramic cap in the VCO section which prevented it from operating at all (C61 tranformed into a low value resistance).

After listening this evening, I find the sound to be very good indeed, which is not really what I had been expecting. I have not properly aligned it yet, just followed the quick setting up procedure in the scan, but have been suprised by the level of detail and spaciousness to the sound, as well as the degree of stereo separation. Overall, this gives a sense of closeness to the broadcast, which is quite engaging (can be startling on hearing live hand clapping for example).

I have noted also, that the final 2 ceramic filters were not implemented on the 10.7MHz IF amp board (replaced by wire links), so it only has two instead of the four.

Also, C42 was removed (by the previous owner presumably) from the demodulated output the fm chip, which was to form part of a 160KHz LP filter, before going to the audio section.

I haven't yet looked at the decoder section, as it worked first go, but I will soon.

David.
  Reply With Quote
Old 13th October 2012, 08:13 AM   #12
diyAudio Member
 
Join Date: Feb 2004
Location: Queensland Australia
Just to add to the data base. If you want to chase up other JLH FM designs the list of published articles by JLH in "The Class-A Amplifier Site" includes a three part design from 1991 E&WW. (now renamed "Electronics World") March, April and May. Page numbers are given if seeking them through institutional libraries.
Cheers, Jonathan
__________________
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
  Reply With Quote
Old 14th October 2012, 04:35 AM   #13
diyAudio Member
 
Join Date: Jun 2004
Location: La Rochelle
That JLH list shows a publication titled "FM Radio: Playing a Better Tune Part 1 to 3". It would be interesting to see what references he makes, if any, to his previous fm tuner design (the one from ETI 1987), and if he mentions any improvements or developments.

David.
  Reply With Quote
Old 15th October 2012, 03:56 PM   #14
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
David,
Good to hear that you have managed to get it work!!
VCO/tuning capacitor = contradictory statements? is it PLL or mechanical tuning? Just curious!!
HA11225, probably the last generation of these excellent FM IF system IC's.
Quote:
I have noted also, that the final 2 ceramic filters were not implemented on the 10.7MHz IF amp board (replaced by wire links), so it only has two instead of the four.
I have seen some designs use as many as 4 of these IF CF parts, Pioneer SX-1250 etc, some also have diode switching for both wide and narrow IF filtering option, Hitachi/Sansui hi-end receivers.

Cheers
Rick
  Reply With Quote
Old 16th October 2012, 02:46 PM   #15
diyAudio Member
 
Join Date: Jun 2004
Location: La Rochelle
Hi Rick,

Variable capacitor gangs for tuning in the RF head, VCO (with a varactor) used in the IF demodulation as part of the PLL. JLH has done his own linear VCO here instead of quadrature coil. I put in the two missing IF filters, so there are four in total.

The solder bridge I mentioned is actually a later tweak mentioned by JLH on page 44 ETI August 1990 Stereo decoder update (pins 6 and 7), along with two other changes.

I bypassed the Mute circuit entirely, so that the signal goes direct from demod board into the decoder, rather than through the op-amp in the mute circuitry. The mute board was causing some problems with setting up the AFC levels, but is now OK when gone.

Overall, I'm very happy with the sound and performance of this tuner, quite revealing with good quality live broadcasts.

Cheers
David
  Reply With Quote
Old 16th October 2012, 04:21 PM   #16
BFNY is offline BFNY  United States
diyAudio Member
 
Join Date: May 2004
Location: Saratoga NY
Nice, that PLL detector is an advanced design for a tuner built from plans!

Some of the best high end tuners from this time period had the PLL detector, especially the top Kenwood and Denon models (TU-800). The quad detector was then still the most common, but other top models, especially from Yamaha, still used the ratio detector.

For best results, any detector design really needs to be aligned for lowest distortion with an excellent FM stereo generator.

More FM tuner talk here -
FMtuners : High End FM Tuners
  Reply With Quote
Old 16th October 2012, 04:52 PM   #17
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
Thanks for the info folks. It would be nice to do a side by side comparison against the latest offerings from SiLabs. I have built a Si4735 tuner and it is pretty good. AM is poor as I have some noise issues to contend with, FM is great. I still have to compare its reception quality vs my Pioneer SX-950, connected to my FM antenna on the tower outside. I am in a fringe area, so it is a good means of comparison. I can pickup stations in St. Catherines and I live in Sutton, Ontario, which has to be as much as 80-100 miles away. Better at night and cloudy days!!
I have also done a layout for the newer Si4770 part, still have to fab it, write the code, one of my winter projects.

Take care
Rick
  Reply With Quote
Old 16th October 2012, 07:46 PM   #18
AMV8 is offline AMV8  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: near london
Hi Davidkou
You might be interested to know that I built the JLH tuner when it first came out. I believe some modifications to the original were made by JLH.
I found the tuner had a very pleasant yet revealing sound; great musically and better than the quad FM4 I was using. The only problems I found with the JLH tuner were the lack of presets and lack of tuner sensativity meaning it did not up distant stations.

Don
  Reply With Quote
Old 16th October 2012, 08:10 PM   #19
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
To bad to hear that the FM front end was not very sensitive. Sounds as if the IF section was very well done. If you post me a schematic, I might be able to give you some advise how to improve the front end to get better sensitivity.
Could also be possible that it is not properly aligned, if this is the case, then try to re-align the front end to see if you can make an improvement. I would think that you need a half decent RF SG for this however.

Regards
Rick
  Reply With Quote
Old 17th October 2012, 11:36 AM   #20
diyAudio Member
 
Join Date: Jun 2004
Location: La Rochelle
These days excellent tuners can be cheap, but stereo generators still quite pricey.

Actually, the VCO setup procedure given by JLH was not done by measuring distortion, but rather setting up the VCO coil centre frequency to coincide with the "on tune" signal from the chip's AFC system. ie by voltmeter measuring AFC output level when on tune to a strong signal
and adjusting the coil so that the AFC voltage equals the AFC output level when off station (no signal). The correct adjustment setting for the coil is quite precise, with no margin either way.

Anyway,I used an digitally tuned FM Stereo transmitter that I built up from a kit, and M-Audio USB sound card to generate test tones and phases, while recording tuner output at the same time, with cool-edit pro audio software for FFT analysing. I did a fairly quick and dirty attempt which is probably not optimised, and with 440Hz test tone got 2nd Harmonic -42dB down, 3rd at -57dB, 4th at -51dB, 5th at -61dB. 19KHz pilot at -34dB,Noise floor at -72dB. My problem is that I don't know how much distortion is due to the FM transmitter itself rather than the tuner!

I also set the separation using L-R out of phase test noise, and doing a phase analysis with cool-edit pro.

There is also some interesting software at MpxTool - Modulation Monitoring Software site for fm encoding/decoding etc.

Cheers,
David.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help wanted please - Linsley Hood article index Geoff Everything Else 2 5th March 2013 04:57 AM
John Linsley Hood RIAA Preamp? roger-k Solid State 5 16th March 2007 07:10 PM
John Linsley Hood's "Art of Linear Electronics" Nelson Pass Pass Labs 6 24th October 2005 09:20 PM
John Linsley Hood "Valve and Xstor" amps jackinnj Swap Meet 0 4th July 2002 02:14 AM
Linsley Hood SE 10W amp Asen Solid State 35 8th October 2001 09:07 PM


New To Site? Need Help?

All times are GMT. The time now is 06:27 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2