rowdy yates wrwer wrote:
Morning men. Is there a known issue with the Tanberg 3008-A preamp?
Any possibility of a language problem in silk screening the phono
inputs? A mix-up? A faux pas? From the schematic, and from a signal
trace, I see the input labeled MM (moving magnet) has an elaborate
selective loading scheme you sometimes see on MC inputs. Separate
loading for each channel even. (any idea why someone would do that?)

Because MM cartridges generally sound very different with different
loading. There are a few, like the Decca ones, which are even specified
for something other than 47k loading.

If you measure the input resistance with a meter, you'll find it's adjustable
but probably in the 25-75 kohm region. (I am assuming most of the load is
from the shunt resistance).

This is a very nice thing to have.

The input labeled MC (moving coil) has a much more standard input in
terms of circuitry.

Yes, but what is the input impedance? I bet it is a whole lot lower
than the MM input Z. Again, measure the resistance and assume that the
resistance is the dominant part of the load.

I repaired my channel (problem was not part of the
riaa inputs) and when I hooked up a turntable to the MM input it
sounded terrible, no bass, squawky- something definitely screwed. I
called Grado and talked to the engineer who designed the Signature
8MZV cartridge and was told it is definitely a MM device. If I plug it
into the input labeled MC it sounds fine. (he says, "so leave it
there,..". That's the way they approach these things in NY- out here
we have science!) I was wondering if anyone had come across this
before in the Tanberg line. Thank you for your time.

What load impedance does it call for on the data sheet? What load
impedance is the MM input on the Tandberg strapped for? What load
impedance is the MC input strapped for?

No bass and sqawky would tend to make me thing the load impedance is
too high and the cartridge is ringing.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

rowdy yates wrwer wrote:
On 5 Jan 2005 18:43:26 -0500, (Scott Dorsey) wrote:

rowdy yates wrwer wrote:
Morning men. Is there a known issue with the Tanberg 3008-A preamp?
Any possibility of a language problem in silk screening the phono
inputs? A mix-up? A faux pas? From the schematic, and from a signal
trace, I see the input labeled MM (moving magnet) has an elaborate
selective loading scheme you sometimes see on MC inputs. Separate
loading for each channel even. (any idea why someone would do that?)

Because MM cartridges generally sound very different with different
loading. There are a few, like the Decca ones, which are even specified
for something other than 47k loading.

That's what Grado said, 47k.

47k is the standard. The Grado might like something a little bit lower
in actuality. Try it and see.

If you measure the input resistance with a meter, you'll find it's adjustable
but probably in the 25-75 kohm region. (I am assuming most of the load is
from the shunt resistance).

This is a very nice thing to have.

Why would you want a separate adjustment for L and R channels?

Because it's cheaper to build that way rather than using coupled switches.


The input labeled MC (moving coil) has a much more standard input in
terms of circuitry.

Yes, but what is the input impedance? I bet it is a whole lot lower
than the MM input Z. Again, measure the resistance and assume that the
resistance is the dominant part of the load.

I do this with the TT plugged in and the whole thing powered up?
Flipping the switches, I measure 33k or 56k or 114k ohms at the MM
input to the first xistor base without the TT plugged in and 550ohms
with it plugged in. Flipping the switches doesn't make any difference
in the sound. It sounds tinny.

You have only three options? You should have at least four possible
combinations of switches if you have two switches. Or nine combinations
with three. The manual should tell you what combinations to switch to
get a given load.

But if changing the switches does not make any change in sound, you
have something wrong elsewhere.

All of those numbers sound quite reasonable.

The MC input shows 1.9k plugged or unplugged. It has a ferrite bead in
series with the input jack, then a 150ohm R to ground, then a 100p cap
to ground then the first transistor.

Something does not sound right here. The cartridge itself is almost a
dead short (550 ohms as you measured before) and it should really drop
the measurement way down if you are measuring in parallel.

Also, if you are measuring across a 150 ohm resistor, through a ferrite
bead, you should be seeing 150 ohms or less. 1.9k is way too high here,
and is also kind of high for an MC cartridge.

I repaired my channel (problem was not part of the
riaa inputs) and when I hooked up a turntable to the MM input it
sounded terrible, no bass, squawky- something definitely screwed. I
called Grado and talked to the engineer who designed the Signature
8MZV cartridge and was told it is definitely a MM device. If I plug it
into the input labeled MC it sounds fine. (he says, "so leave it
there,..". That's the way they approach these things in NY- out here
we have science!) I was wondering if anyone had come across this
before in the Tanberg line. Thank you for your time.

What load impedance does it call for on the data sheet? What load
impedance is the MM input on the Tandberg strapped for?

Don't have the Data Sheet.
R's on the load switch positions are 120k, 27k, 39k. There's some caps
involved too.

You sure that 2.7k number is right?

What load impedance is the MC input strapped for?
Umm, not sure. 1.9k I think. See above.

From your circuit description, it should be 150 ohms, but you are measuring
something way higher, which is a sign something is wrong there.

No bass and sqawky would tend to make me thing the load impedance is
too high and the cartridge is ringing.

Grado said the cartridge wants 47k. A third party said the 8MZV isn't
really a MM it's something called a moving-iron. Kind of a cross
between MM and MC. I'm not sure I'm measuring all this right. Thanks
again.

Right, but the cartridge still wants to see 47k. If the cartridge has a
47k load and it sounds tinny, something is wrong. Your problem is to find
out if it is wrong in the preamp or in the cartridge/arm combination.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Wed, 05 Jan 2005 21:35:23 GMT, rowdy yates
wrote:

Morning men. Is there a known issue with the Tanberg 3008-A preamp?
Any possibility of a language problem in silk screening the phono
inputs? A mix-up? A faux pas? From the schematic, and from a signal
trace, I see the input labeled MM (moving magnet) has an elaborate
selective loading scheme you sometimes see on MC inputs. Separate
loading for each channel even. (any idea why someone would do that?)
The input labeled MC (moving coil) has a much more standard input in
terms of circuitry. I repaired my channel (problem was not part of the
riaa inputs) and when I hooked up a turntable to the MM input it
sounded terrible, no bass, squawky- something definitely screwed. I
called Grado and talked to the engineer who designed the Signature
8MZV cartridge and was told it is definitely a MM device. If I plug it
into the input labeled MC it sounds fine. (he says, "so leave it
there,..". That's the way they approach these things in NY- out here
we have science!) I was wondering if anyone had come across this
before in the Tanberg line. Thank you for your time.

-- It seems that you are, as Scott pointed out, simply getting weird
values in your Tandberg phono preamp section. I would check every
component in the circuitry, paying attention to capacitors and all
contact areas and finally I'd quality resolder everything. Check
whether all the connectors are corrosion-free and clean too, turntable
and cable included. A quality contact cleaner could be helpful but
apply it with cotton swabs rather of spraying everything.
Moving iron cartridges are variant of moving magnet, the "iron" being
an induced piece of ferromagnetic metal, yet somewhat lighter than the
magnet materials itself (lower mass, sometimes tubular, but it yields
magnetic properties close to real magnets). Almost all MM cartridges
including this one commonly have 47 Kohm impedance or closely
thereabout.

Edi Zubovic, Crikvenica, Croatia