QUESTION -- For Nakamichi Experts
 

I have two different Nakamichi BX-300 cassette decks. One was made in
1984, and the other one was made in 1986.

While I had the 1984 deck opened up to do some repair work, I opened
the 1986 BX-300 to take a look at a part number. Looking inside the
1986 deck, I immediately noticed an "extra" PC board mounted on the
right side near the back. According to the service manual, this
"extra" PC board is the Input Amp.

The 1984 deck does not have this Input Amp PC board inside it. The
service manual verifies that it was not installed in the 1984 deck.

MY QUESTIONS:

Why was this board added?

What benefit does it have?

Are later BX-300 decks that have this board "better" in any way than
earlier versions?

These may be dumb questions, I know, but curiosity has gotten the
better of me.

QUESTION -- For Nakamichi Experts
 

"EADGBE"
I have two different Nakamichi BX-300 cassette decks. One was made in
1984, and the other one was made in 1986.

While I had the 1984 deck opened up to do some repair work, I opened
the 1986 BX-300 to take a look at a part number. Looking inside the
1986 deck, I immediately noticed an "extra" PC board mounted on the
right side near the back. According to the service manual, this
"extra" PC board is the Input Amp.

The 1984 deck does not have this Input Amp PC board inside it. The
service manual verifies that it was not installed in the 1984 deck.

Why was this board added?

What benefit does it have?


** The dates are very significant - coincides with CD players coming into
popular, world wide use.

Many early CD players generated significant supersonic signals at their RCA
outputs due to inadequate LP filters and the use of oversampling in the D to
A conversion - mainly at the 44.1 kHz sampling frequency and harmonics
going up to 4 or 8 times that frequency.

When transcribing a CD to cassette, these supersonics can be rendered
audible on the recording by beating with the record /erase bias frequency
used in the recorder, which is typically around 50kHz to 70kHz. The
recording would contain low level but annoying whistling noises as a result.

So, Naka's " Input Amp " ( really input filter) is likely there to solve
the problem.

BTW:

Practically all cassette decks contain a notch filter at 19kHz to remove the
residual "pilot tone" that accompanies stereo FM - for the exact same
reason.



....... Phil

QUESTION -- For Nakamichi Experts
 

In article . com,
EADGBE wrote:
I have two different Nakamichi BX-300 cassette decks. One was made in
1984, and the other one was made in 1986.

While I had the 1984 deck opened up to do some repair work, I opened
the 1986 BX-300 to take a look at a part number. Looking inside the
1986 deck, I immediately noticed an "extra" PC board mounted on the
right side near the back. According to the service manual, this
"extra" PC board is the Input Amp.

The 1984 deck does not have this Input Amp PC board inside it. The
service manual verifies that it was not installed in the 1984 deck.

MY QUESTIONS:

Why was this board added?

What benefit does it have?

I don't know for sure (not being a Nak expert by any means) but I'll
offer a guess which may or may not be somewhere close to the truth.

A lot of tape decks have an unfortunate characteristic - when they're
powered off, their line-input circuitry presents a somewhat nasty
electrical load to whatever is driving it. Ideally, you'd want such
an input to behave somewhat like an intermediate-value resistor... one
which is a nice, linear load that doesn't load down the source. Unless
you're careful in your design, the input circuitry may tend to "look"
somewhat like a diode clamping the signal to ground, when the circuit
is powered off.

Many audio preamps and receivers simply feed the "out to tape deck"
jacks by taking the same preamplified signal that they're about to
send to the volume control and feeding it through a small-value
resistor to the "tape out" jacks. If such a preamp is connected to a
powered-down tape deck, the deck's nonlinear input load can cause some
amount of distortion in the audio signal inside the preamp... perhaps
enough to be audible, perhaps not.

This isn't a problem if the audio preamp/receiver drives its "tape
out" jacks through a separate, robust buffer, or if the tape deck has
input circuitry which presents a high-Z, purely resistive load even
when not powered up.

It's possible that the extra board in the later BX-300 decks is an
input buffer, which isolates the deck's internal circuitry from the
signal source and which preserves this isolation even when powered
off. A FET-input op amp, with a high-value input resistor would
probably serve... and I'm sure that there are numerous discrete
circuits which would have the same benefit.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

QUESTION -- For Nakamichi Experts
 

Wow, those are both very different, but very plausible sounding
explanations! Thanks to you both!

For what it's worth, the IC chip that is the heart of the "Input Amp"
is a 4558 op-amp. Does that help explain anything?

QUESTION -- For Nakamichi Experts
 

Wow, those are both very different, but very plausible sounding
explanations! Thanks to you both!

For what it's worth, the IC chip that is the heart of the "Input Amp"
is a 4558 op-amp. Does that help explain anything?

Possibly... at least, the Philips equivalent schematic for the 4558
does not indicate the presence of "clamp the signal to the rail"
protective diodes. I _think_ that the 4558 might present a pretty
benign load on the audio input bus, even if its power was shut down
and both of its DC power rails were grounded.

So, the use of the 4559 on the input board doesn't rule out the
hypothesis I put forward... but neither does it confirm it, or rule
out the possibility that there's another reason for the additional
board.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

QUESTION -- For Nakamichi Experts
 

"EADGBE"


Why was this board added?

What benefit does it have?


** Scan the damn schematic of that board and post it on ABSE

- you useless pommy prick.




....... Phil

QUESTION -- For Nakamichi Experts
 

OK, I have done some circuit tracing and it turns out that both the
1984 and 1986 decks have this Input Amp circuit, just in different
places.

On the 1984 deck, the IC in question is mounted on the main PC board
and happens to sit directly beneath the control (mode) motor. There
is a reflective shield mounted just above this IC in order to shield
it from the motor.

Apparently, this arrangement was not satisfactory enough for Nakamichi
engineers, who then redesigned the physical arrangement of
components. They removed this IC completely from the main PC board
and mounted it on its own PC board in a more remote location, away
from the control motor and whatever interference it may have been
causing.

QUESTION -- For Nakamichi Experts
 

"EADGBE"

OK, I have done some circuit tracing and it turns out that both the
1984 and 1986 decks have this Input Amp circuit, just in different
places.



** YOU ****ING PITA BLOODY TROLL !!

Drop stone dead, ASAP.



........ Phil

QUESTION -- For Nakamichi Experts
 

On 14 Jun, 05:54, "Phil Allison" wrote:
"EADGBE"



Why was this board added?

What benefit does it have?

** Scan the damn schematic of that board and post it on ABSE

- you useless pommy prick.

...... Phil

My my. you're one tetsy fellow areen't you?

Doc

QUESTION -- For Nakamichi Experts
 

"Dr Hfuhruhurr"

My my. you're one tetsy fellow areen't you?



** My - you are a posturing, ****wit paedophile

- aren't YOU ???

Get back to trolling school dunnies - IMBECILE .





....... Phil