How to change deemphasis from 75uS to 50uS for Fisher FM100

DC88 · 22nd July 2008, 02:07 PM

Hi, can anyone tell me how to change the deemphasis for FM100. I got the FM tuner from US and will use in Hong Kong. I need to change the deemphasis from 75u to 50u.

oshifis · 22nd July 2008, 03:44 PM

You need to find the two deemphasis capacitors around the stereo multiplex decoder IC. They are in the order of a few nanofarads. Change them to 2/3 of their original value (e.g from 2.2nF to 1.5nF; these are typical values).

kevinkr · 22nd July 2008, 03:52 PM

FM-100 is a vacuum tube tuner and has no stereo decoder IC..

Is it a FM-100 or a 100B?

www.vintagemanuals.com has manuals for several versions of this tuner..

Changing a pair of capacitors after the multiplex demodulator stage and before the output amplifier is all that is needed. I am sketchy on the details as it has been a while since I last worked on one.

Very nice sounding tuner, better RF performance than the FM-50B (I have one) and less complexity than the FM-200..

DC88 · 23rd July 2008, 12:05 PM

Thanks for your reply. I have the schematic for FM1000. Which cap should I change?

kevinkr · 23rd July 2008, 01:26 PM

Change C225 and C226.. Can't make out the values, but they should be approximately 2/3 of the existing values...

rtsang · 23rd July 2008, 02:30 PM

The FM100B multiplex section is the same as the FM1000.

I also have a FM100B and FM200B. I think the FM200B have a better reception, but soundwise, both are very good and for my peference, I prefer them to the McIntosh tuners.

I would also like to change the deemphasis, if possible.

Raymond

kevinkr · 23rd July 2008, 06:02 PM

Quote:

Originally posted by kevinkr
Change C225 and C226.. Can't make out the values, but they should be approximately 2/3 of the existing values...

Quote:

Originally posted by rtsang
The FM100B multiplex section is the same as the FM1000.

I also have a FM100B and FM200B. I think the FM200B have a better reception, but soundwise, both are very good and for my peference, I prefer them to the McIntosh tuners.

I would also like to change the deemphasis, if possible.

Raymond

See above

DC88 · 24th July 2008, 11:51 AM

Thanks! Kevin,

The value is 2200uuf.
I will replace it with 1500uuf.

Derek

kevinkr · 24th July 2008, 02:02 PM

Quote:

Originally posted by DC88
Thanks! Kevin,

The value is 2200uuf.
I will replace it with 1500uuf.

Derek

That should work fine..

22nd July 2008, 02:07 PM	#1
DC88 diyAudio Member Join Date: Aug 2004 Location: Hong Kong	How to change deemphasis from 75uS to 50uS for Fisher FM100 Hi, can anyone tell me how to change the deemphasis for FM100. I got the FM tuner from US and will use in Hong Kong. I need to change the deemphasis from 75u to 50u.

22nd July 2008, 03:52 PM	#3
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	FM-100 is a vacuum tube tuner and has no stereo decoder IC.. Is it a FM-100 or a 100B? www.vintagemanuals.com has manuals for several versions of this tuner.. Changing a pair of capacitors after the multiplex demodulator stage and before the output amplifier is all that is needed. I am sketchy on the details as it has been a while since I last worked on one. Very nice sounding tuner, better RF performance than the FM-50B (I have one) and less complexity than the FM-200.. __________________ www.kta-hifi.net

23rd July 2008, 01:26 PM	#5
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Change C225 and C226.. Can't make out the values, but they should be approximately 2/3 of the existing values... __________________ www.kta-hifi.net

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22nd July 2008, 03:44 PM	#2
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	You need to find the two deemphasis capacitors around the stereo multiplex decoder IC. They are in the order of a few nanofarads. Change them to 2/3 of their original value (e.g from 2.2nF to 1.5nF; these are typical values).

23rd July 2008, 02:30 PM	#6
rtsang diyAudio Member Join Date: Aug 2005	The FM100B multiplex section is the same as the FM1000. I also have a FM100B and FM200B. I think the FM200B have a better reception, but soundwise, both are very good and for my peference, I prefer them to the McIntosh tuners. I would also like to change the deemphasis, if possible. Raymond

24th July 2008, 11:51 AM	#8
DC88 diyAudio Member Join Date: Aug 2004 Location: Hong Kong	Thanks! Kevin, The value is 2200uuf. I will replace it with 1500uuf. Derek

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