On Sat, 23 Oct 2004 10:17:57 -0400, "tempus fugit"
wrote:

Hey all;

I've got a Technics tape deck (RS-B18) that is about 20 years old. I had
some problems with intermittent channels (rec and play) and took it apart to
see what I could do. I found a cold solder joint in the signal path and
resoldered it, which (so far, anyway) has fixed the problem.

However, there are a few things I'm wondering about. First, the levels (as
indicated on the meters) are lower in playback than record. IOW, if I record
a cassette with the levels reading around 0, the tape will play back with
the levels at, say -3 or so. It also varies depending on how the noise
reduction and bias is set:

1. No Dolby, CrO2 - levels are pretty much the same
2. Dolby B, Cr02 - levels slightly lower on playback
3. dbx, Cr02 - levels considerably (3 - 6 db) lower on playback
4. any or no noise reduction, Metal - no playback at all (this has been a
problem since I got the deck)

I can post more combinations if need be, but I hope that this will give the
general idea. I also cannot remember if this was the way things were going
before the repair (I think it was though).
Are these type of discrepencies normal, or can/should I adjust things to
equal them out?

I also noticed that the playback was a little dull after the repair (to be
honest, I hadn't used the deck in quite a while, so it may be the way it
always sounded). Would this be a bias setting that I may have inadvertently
moved while repairing? or perhaps it needs some adjustment in another area?

Thanks


It's perfectly normal for you to lose a bit of gain. Meters are far
from exact and you are dealing with an analog process.
Tape formulations are such that they are simply not 100% capable of
capturing all the signal that you give them.
That's why you run a test recording before the real thing on any
type/batch of tape you're going to use.
Also has alot to do with the type of metering you're using too.
Some decks use A weighted some B or even C.
Some use a average weight combination etc...
(Peak, Average and mixed are the 3 basic flavors tho' there are dozens
of variations.)
In fact it's desireable to stay a bit under 0 with most tapes,
especially Chrome and Metal, both of which distort easily with
oversaturation.
As for DBX, it's designed to under record about -3 to -10 dbs to allow
for greater headroom on high or sudden peaks/surges.
There wer attempts in the late70's early 80's to design cassette decks
that would test tone tapes and set the optimum level.
One was the Luxman KXP-102, I had one of these and they produced the
most accurate, clean mids and lows capable out of cassette tapes.
It would run a test tone in three basic ranges(low, mids and highs)
and read the results repeating the tones until the optimumlevel had
been achieved in each zone.
This allowed it to tweak bias and noise reduction until you got the
perfect recording with each tape.(It was less than perfect in
capturing the very highs but was a great deck for instrumental jass
and blues etc...)
Just run a test on whatever type of tape you're using adjusting the
gain untill you get the desired level that gives you highest sound
level without oversaturation.(Think you'll find that you'll be setting
the gain around 7 or so and depending on your type of meters the
signal will show to be around +2 to +4 during record and bang on 0 on
playback.