In a previous post ("tuner repair problems") I outlined some steps that I
had taken to repair a Sansui T-80 AM/FM tuner. In particular I replaced all
of the electrolytic capacitors.

This seems to have fixed the unwanted behaviors. However, quite by accident
(rec'd the wrong part from DigiKey) I replaced the series output cap with a
much smaller value cap. The cap in question was spec'ed at 0.15uF. There
was actually a 0.22uF in there when I started, and the cap I inadvertently
put in was 0.0015uF. It sounded bad. Tinny. Not much volume. I
understand that this cap in conjunction with my pre-amp's input impedence
makes up a high-pass filter. Frequencies below 3.5KHz would have been
attenuated with this tiny cap, hence my tinny sound.

Well, I put the 0.22uF caps back in while I waited for the correct 0.15uF
caps. The sound improved dramatically. I measured the input imepdence of
my amp at 30.2K. As an aside, I also calculated it from the schematic and
it should have been about 44K. Anyways, using the measured impedance, I
should be using a 0.26uF filter cap if I want to roll off at 20Hz. Hmm,
wonder what would happen if I stuck in a 1uF cap (the next higher-size cap I
happened to have in my inventory). Wow. What a difference! The bass is
tight and defined INDEPENDENT of volume. Not only do I not need to use the
loudness button on my preamp at low volume, I can't use it without it
generating more bass than I want! This has made such a huge difference to
the sound of this tuner that whereas before I was thinking of replacing it,
now I definitely will keep it.

Is there any downside (potential harm) to what I've done? I have a subsonic
filter (15Hz) on my amp which I have switched on to avoid any subsonic
damage to my speakers (shouldn't matter if sound below human hearing is
filtered out, right?). The 0.15uF cap in the design spec would start my
bass roll-off at 35Hz. Wouldn't it make sense to size the filter cap in
each component to jive with the pre-amp's impedence? You'd almost think
manufacturers would put in some jumpers and a few ten-cent caps so you could
adjust it to suit.

Dave

In article ifCTf.4051$J43.2587@edtnps90, "Dave" wrote:
In a previous post ("tuner repair problems") I outlined some steps that I
had taken to repair a Sansui T-80 AM/FM tuner. In particular I replaced all
of the electrolytic capacitors.

This seems to have fixed the unwanted behaviors. However, quite by accident
(rec'd the wrong part from DigiKey) I replaced the series output cap with a
much smaller value cap. The cap in question was spec'ed at 0.15uF. There
was actually a 0.22uF in there when I started, and the cap I inadvertently
put in was 0.0015uF. It sounded bad. Tinny. Not much volume. I
understand that this cap in conjunction with my pre-amp's input impedence
makes up a high-pass filter. Frequencies below 3.5KHz would have been
attenuated with this tiny cap, hence my tinny sound.

Well, I put the 0.22uF caps back in while I waited for the correct 0.15uF
caps. The sound improved dramatically. I measured the input imepdence of
my amp at 30.2K. As an aside, I also calculated it from the schematic and
it should have been about 44K. Anyways, using the measured impedance, I
should be using a 0.26uF filter cap if I want to roll off at 20Hz. Hmm,
wonder what would happen if I stuck in a 1uF cap (the next higher-size cap I
happened to have in my inventory). Wow. What a difference! The bass is
tight and defined INDEPENDENT of volume. Not only do I not need to use the
loudness button on my preamp at low volume, I can't use it without it
generating more bass than I want! This has made such a huge difference to
the sound of this tuner that whereas before I was thinking of replacing it,
now I definitely will keep it.

Is there any downside (potential harm) to what I've done? I have a subsonic
filter (15Hz) on my amp which I have switched on to avoid any subsonic
damage to my speakers (shouldn't matter if sound below human hearing is
filtered out, right?). The 0.15uF cap in the design spec would start my
bass roll-off at 35Hz. Wouldn't it make sense to size the filter cap in
each component to jive with the pre-amp's impedence? You'd almost think
manufacturers would put in some jumpers and a few ten-cent caps so you could
adjust it to suit.

It might seem a bit strange to be working on an inexpensive tuner to
such a degree. Most mods to tuners involve getting more sensitivity
and more selectivity. Perhaps there are things to be learned.
It seemed to me a long time ago, that FM had rolloffs, or
perhaps it was TV sound. 50 Hz rings a bell. Today, there
is plenty or too much bass. Many brodcasters are using 3 band compression,
and many songs have way too much low bass compared to listening
to it direct from disk.

greg

"GregS" wrote in message
...
In article ifCTf.4051$J43.2587@edtnps90, "Dave"
wrote:

It might seem a bit strange to be working on an inexpensive tuner to
such a degree. Most mods to tuners involve getting more sensitivity
and more selectivity. Perhaps there are things to be learned.
It seemed to me a long time ago, that FM had rolloffs, or
perhaps it was TV sound. 50 Hz rings a bell. Today, there
is plenty or too much bass. Many brodcasters are using 3 band compression,
and many songs have way too much low bass compared to listening
to it direct from disk.

I bought the tuner so I could screw around with it with the aim of learning
about the various mods without risking destroying an expensive piece of
hardware. The tuner cost me $15 and so far I've got about $30 in it.

Since I got this tuner, I have felt that it lacks bass response as compared
to disk. Now it doesn't.

I live in a mountainous region distant from major cities. It is a radio
signal wasteland, so I am not really concerned about DX'ing/sensitivity. My
cable provider kindly provides me with an fm feed; the stations are nicely
spaced out over the dial, so I am not too worried about multipath or
selectivity.

I listen to a variety of radio stations via cable feed and the quality of
sound varies immensely from station to station. I don't know why but I'd
guess that, like everything else, quality FM signal costs money (to generate
and to reproduce) and how good does Britney Spears need to sound played on
a portable player through cheap headphones or through your average car
stereo. Here in Canada, CBC-2 sounds fantastic. The local stations tend to
sound better than the ones I pull off the cable feed.

Does anyone know what is the effect of fm transmission via cable tv feed?
How is the signal provided to the cable company and what do they do with it
from there?

Thanks for the replies.

In article buDTf.4120$J43.1177@edtnps90, "Dave" wrote:

"GregS" wrote in message
...
In article ifCTf.4051$J43.2587@edtnps90, "Dave"
wrote:

It might seem a bit strange to be working on an inexpensive tuner to
such a degree. Most mods to tuners involve getting more sensitivity
and more selectivity. Perhaps there are things to be learned.
It seemed to me a long time ago, that FM had rolloffs, or
perhaps it was TV sound. 50 Hz rings a bell. Today, there
is plenty or too much bass. Many brodcasters are using 3 band compression,
and many songs have way too much low bass compared to listening
to it direct from disk.

I bought the tuner so I could screw around with it with the aim of learning
about the various mods without risking destroying an expensive piece of
hardware. The tuner cost me $15 and so far I've got about $30 in it.

Since I got this tuner, I have felt that it lacks bass response as compared
to disk. Now it doesn't.

I live in a mountainous region distant from major cities. It is a radio
signal wasteland, so I am not really concerned about DX'ing/sensitivity. My
cable provider kindly provides me with an fm feed; the stations are nicely
spaced out over the dial, so I am not too worried about multipath or
selectivity.

I listen to a variety of radio stations via cable feed and the quality of
sound varies immensely from station to station. I don't know why but I'd
guess that, like everything else, quality FM signal costs money (to generate
and to reproduce) and how good does Britney Spears need to sound played on
a portable player through cheap headphones or through your average car
stereo. Here in Canada, CBC-2 sounds fantastic. The local stations tend to
sound better than the ones I pull off the cable feed.

Does anyone know what is the effect of fm transmission via cable tv feed?
How is the signal provided to the cable company and what do they do with it
from there?

I used to get FM cable stations, but they were basically identical
to the over the air broadcast frequencies. Cable suffers from extra noise
which is generated through the whole system, so during full quieting of
your FM receiver, thee might still be some extra noise present, which
was not part of the orginal broadcast.

greg

On Mon, 20 Mar 2006 18:11:26 GMT, "Dave"
wrote:

Hmm,
wonder what would happen if I stuck in a 1uF cap (the next higher-size cap I
happened to have in my inventory). Wow. What a difference! The bass is
tight and defined INDEPENDENT of volume. Not only do I not need to use the
loudness button on my preamp at low volume, I can't use it without it
generating more bass than I want! This has made such a huge difference to
the sound of this tuner that whereas before I was thinking of replacing it,
now I definitely will keep it.

Sounds like you've just cut treble. Which will sound like a
"loudness" curve at low levels. If this suits your
speakers/room/ears, fine. If you tire of it, you know what to do.

In ifCTf.4051$J43.2587@edtnps90, on 03/20/06
at 06:11 PM, "Dave" said:

[ ... ]

Is there any downside (potential harm) to what I've done? I have a
subsonic filter (15Hz) on my amp which I have switched on to avoid any
subsonic damage to my speakers (shouldn't matter if sound below human
hearing is filtered out, right?). The 0.15uF cap in the design spec
would start my bass roll-off at 35Hz. Wouldn't it make sense to size
the filter cap in each component to jive with the pre-amp's impedence?
You'd almost think manufacturers would put in some jumpers and a few
ten-cent caps so you could adjust it to suit.

No physical harm.

I'm surprised that the response changes so dramatically. Mostly, I
don't expect much from the stations below 50Hz. Are you sure that the
capacitor doesn't interact with the de-emphesis? Anyway, it is personal
preference. In normal decoupling situations increasing the capacitor
beyong a certain point is of little value. Other than some phase shift,
the audible consequence from moving the lower cutoff from 10Hz to 5Hz
is minimal.

As far as FM over cable is concerned, they will usually demodulate and
modulate the station at the cable front end. This process could be very
flawed -- or not.

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13 (Barry Mann)
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-----------------------------------------------------------

"Barry Mann" wrote in message
.. .
In ifCTf.4051$J43.2587@edtnps90, on 03/20/06
at 06:11 PM, "Dave" said:

I'm surprised that the response changes so dramatically. Mostly, I
don't expect much from the stations below 50Hz. Are you sure that the
capacitor doesn't interact with the de-emphesis? Anyway, it is personal
preference. In normal decoupling situations increasing the capacitor
beyong a certain point is of little value. Other than some phase shift,
the audible consequence from moving the lower cutoff from 10Hz to 5Hz
is minimal.

Yes, I was really surprised too. This cap is not involved in de-emphesis in
any way, it is after the output of the MPX demodulator. Changing the cap
lowered my roll-off from 35 Hz to 5Hz, and I cut off the lower half of this
range with my subsonic filter later on anyway. So I really should only
be gaining from 15 to 35Hz which everyone seems to agree is lacking in most
FM signal sources. But the SOUND... it's really night and day. As it's
part of a high-pass filter, I definitely haven't cut any treble as another
poster has speculated.

Sometimes you just get lucky.

Dave