Bass-y feedback on cheap BSR turntable
frenchy
console with a BSR changer. (Unit has front fresnel type clear panel
across the front, with colored lights behind it that flash with the
music.)
I don't have any problems with the 78 needle playing my 78s, I can
crank the volume up to 10. But when I switch to the stereo needle, I
can't turn the volume up 1/3 of the way before I start getting
horrible, very bassy feedback. Only happens when the needle is riding
on the record, even on silent parts. If I lift the tonearm, feedback
disappears. Any ideas? This is one of those needles with the two
different sized stylii, larger one for 78s and a smaller one for LPs.
I tried adding some soft material between the record and the
turntable, no effect either. Seems like it is just resulting from the
needle riding on the record, period, even if there's no music.
Thanks!
frenchy
regular stereo LP.
paul @removeppinyot.removecom Paul_P
"frenchy" <mf10...@msn.com> wrote in message
news:75c42cde-524b-49f4...@13g2000prl.googlegroups.com...
Just guessing here,
Check you suspension of the turn table to the cabinet. Is there deteriorated
foam or padding? Are the shipping screws tightened and not released?
Paul
D. Peter Maus
Start by replacing each tube, one at a time. A microphonic tube will
exacerbate mechanical system resonances. Any change in resonances can
produce significant changes in the audio. LP's will have different
rumble resonances than 78s.
You mention that you changed the needle. Did you also change the
cartridge?
I had a similar issue with a Philco. The previous cartridge had
sufficient low end roll off that rumble did not mechanically feedback
through the cabinetry, and turntable structure.
New cartridge, some pretty significant issue with mechanical
regeneration.
Cartridges have damping material between the stylus and the structure
to attenuate rumble, and also mechanical feedback. It's usually not the
cartridge that fails over time, it's the damping material, which changes
resonance points.
There are also resonances within the replacement stylus assembly,
itself. Generic replacements may have resonances damped out at a point
different than the OEM stylus/cartridge complex.
Some tweaks include adding damping material to the head, or to the
arm. There should be foam in the tube. That can be replaced with more
effective materials, including some aerosol foams, now available.
Adding damping materials to the cabinet, itself, may help. But likely
to a limited extent.
Adding damping materials to the turntable assembly, will bear better
fruit. I had really nice results by adding sheaths to the suspension
springs on the base of the turntable.
Adding mass to the base panel the BSR sets on will reduce rumble, and
feedback. Adding mass to the sheet metal assembly will also reduce
rumble in many cases, though not all. This is a cut and try process.
Pressures, counterpressures, and pivot damping, if applicable, will
all have to be re optimized.
Filters, rolling off the rumble frequency at the input of the amp
will produce biggest result but will change the F/R of the system. If
it's been a while since you used the turntable, and I'm talking years,
here, there may have been a shift in low end response over time, anyway.
Capacitors change. Some may need to be replaced.
Richard Knoppow
"frenchy" <mf10...@msn.com> wrote in message
news:75c42cde-524b-49f4...@13g2000prl.googlegroups.com...
Is there a stereo/mono switch on this set? If so do you
play the 78s in mono and the Lps in stereo? If so try
playing the Lps in mono. The problem is mechanical feedback
from the speaker to the turntable probably due to poor
isolation, mono will reduce the modes of vibration that can
couple. The cure in any case is to improve the isolation.
Pads betwen the record and pickup usually won't do it, you
need to put something between the turntable and cabinet.
--
--
Richard Knoppow
Los Angeles
WB6KBL
dick...@ix.netcom.com
Bill Noble
mass will aid in damping vibration. You could put thin foam under the 78s
for better decoupling.
"frenchy" <mf10...@msn.com> wrote in message
news:75c42cde-524b-49f4...@13g2000prl.googlegroups.com...
Peter Elem
"frenchy" <mf10...@msn.com> wrote in message
news:75c42cde-524b-49f4...@13g2000prl.googlegroups.com...
The LP needle has a higher compliance, (lower resonance) than the 78 needle
which is why only it has feedback........
D. Peter Maus
The motor is mounted on isolation rubber grommets, to reduce
rumble. These dry out with time, and rumble increases. These
grommets can be reproduced out of many materials, the best being
sorbothane for isolating rumble. They need not be elegant, and may
be cut by hand out of raw material.
Your new stylus assembly may have resonances such that the rumble
produced by the BSR's motor peaks outside of the band of damped
frequencies. Addressing this will make a big difference in the
reproduced audio.
All this talk makes miss the audio from my Telefunken Opus Royale
console. The turntable has needed a new puck, now for a while.
I may get back on that project over the holidays.
That amp has a very rich, but mellow tone. Perfect for background
Christmas music during dinners.
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Bill Noble
the motor is constant at any volume setting - this is feedback from the
speakers in the console, right? so fixing rumble won't contribute, same
with microphonic tubes (since lifting the cartridge makes it go away) - the
BSR changers had a stamped sheet metal TT, and almost no mass - thus they
are perfectly engineered to resonate with the bass notes and create
feedback. More mechanical style isolation to reduce resonance is needed. I
suggested some 78s to add mass to the TT - a disk of lead glued to the
underside of the TT or on top under the mat would be even better. You need
discontinuities in transmissivity to block the acoustic energy - something
light and soft, then something heavy/hard - foam and bricks is one way,
Styrofoam and lead will work, neoprene and lead is a tried and true
solution, and of course moving the speakers elsewhere works too
"D. Peter Maus" <dpete...@worldnet.att.net> wrote in message
news:hg0mtv$8dl$1...@news.eternal-september.org...
D. Peter Maus
> look, guys - the original complaint is related to volume, and rumble
> from the motor is constant at any volume setting - this is feedback from
> the speakers in the console, right? so fixing rumble won't contribute,
Yes, actually, it will. Remember, we're talking about a change in
resonance points with the change in stylus/cartridge. According to
the OP, the only thing that changed was the stylus assembly (or
possibly the cartridge-that wasn't clarified). The problem appeared
with this single alternation. The only thing that changed in the
mechanical transmission realm was the resonance damping of the
stylus assembly. This means that frequencies that were not issues
before, are now. And now because of the many potential resonances
and entry points for the offending vibrations, anything that wasn't
a factor before CAN be a factor now. And changing volume will make
issues that were irrelevant before, very relevant now.
Consider acoustic feedback. Example: You have a dance club, with
a huge acoustic space, large speakers and a microphone at the DJ
station mounted to the console on flex arm. The rumble of the
furnace blower in the building is constant. And has never been a
problem. The rumble of the traffic outside the building is constant.
And have never been an issue before.
The DJ goes out and gets a brand new microphone of the same model
and manufacture, plugs it in and now, when he opens the mic, and the
music is playing, there's huge bass heavy feedback. All the constant
issues are the same. And yet, when he turns up his mic, and there's
music playing, there's bassy feedback that didn't exist before.
Now, this only happens when the music is playing and mic is
mounted on the flex arm. When the DJ picks up the mic and holds it
in his hand, the rumbling bassy feedback goes away. When there is no
music, the bassy feedback goes away.
How does this happen? Well, the new mic has a different roll off
characteristic than the old one. The new mic has a db or two better
response at the rumble frequencies. So, the new mic picks up audio
from the rumble in the building, amplified and blown out through the
speakers, and regenerated by recirculating into the microphone and
through the the system, with the added component of the music's bass
content. Bassy feed back results. All the constants are still
constant. The only thing that's changed is the roll off of the new mic.
Changing anything about the acoustic circuit, can cause constant
elements that were not a problem before to suddenly become a problem.
So, then, to correct the issues, the fundamental causes of the
rumble pickup need to be addressed. Damping, changing resonances,
rolling off frequencies and even changing microphonic tubes become
the solutions. Because it's resonances that case the issues. Not the
full spectrum of the audio.
So, in the act of changing the stylus on the Grundig hi-fi, a
resonance has changed. And issues that were not issues previously,
are suddenly issues, now. And the points of resonance that have
changed, coupled with the many points of entry into the acoustic
circuit make for a complex of issues that need to be addressed one
at a time before the system can be returned to it's previous
performance.
Since the stylus on the record produces the issue, while holding
the arm off the record does not, the issue begins with rumble. Where
clearly rumble was not an issue before, it IS an issue now. That
must be addressed. As must be all the points of resonance in the
acoustic circuit. This would include microphonic tubes which serve
as a point of entry of acoustic energy into the electrical
amplification circuit. Acoustic energy that wasn't a problem before,
because the rumble wasn't an issue before.
> the BSR changers had a stamped sheet metal TT, and almost no
> mass - thus they are perfectly engineered to resonate with the bass
> notes and create feedback.
A point that was also made. Adding mass to the platter will make
a difference, as will adding mass to the sheet metal holding the
arm/platter/motor system. The whole idea is to move the resonances.
It's resonances that give rise to feedback. Not the entire spectrum.
Sorbothane sheets attached to the underside of the platter will
reduce a broad range of mechanical vibrations and drumhead
vibrational modes. Adding mass will help, as well, as you point out.
Adding mass, or vibration dampening to the cabinetry will also
help by reducing resonances and their transmission.
The key is to reduce points of resonance, and desensitize points
of entry to the acoustic circuit so they're not amplified and
regenerated by the electric circuity.
There will be more than one issue that needs to be addressed
before that global solution is achieved.
And bear in mind that this is a Grundig hi-fi console. Certainly
high state of art in its time, but by no means the highly engineered
phonograph systems that would follow in the 70's and 80's. The
system required certain degrees of non-performace to work without
these kinds of issues. Deficient low end performance was a huge part
of that. A contemporary stylus, and or cartridge assembly, would
benefit from more modern materials and techniques of construction
that would enhance both top and bottom end performance. Increasing
sensitivities where the offending rumbles would not have previously
ever been an issue.
frenchy
cushion the entire phono assembly in it's mounts, and more cushioning/
weight between the turntable and record, and the mono vs stereo test.
This is a cheapy solid state unit so it's not a microphonic tube
issue. Definitely seems like simply a rumble issue since it's horrible
at 33 rpm but not noticeable at 78. Then at higher volume it starts
reverberating thru the cabinet starting up feedback, making it worse
and worse. This is no state of the art console - pressed-wood
cabinet, woodgrain decal peeling off of it. I just grabbed it because
the lighting effect is funky : ))
Mark