Note:
Sample music files are located further down this page and must be manually
started because, there are two of them, and having them both play at the
same time would be pointless.
The
whole point of a tape recorder is, obviously, it's ability to faithfully
record sound. To challenge the recording ability of the Wollensak 5750,
a full digital recording on CD was used as a "master". This presents some
challenges that the machine was never designed to handle, and was done as
an experiment to see how well the machine can handle modern audio demands.
Overall, it has done a good job.
The
music is the theme - called "Dream Angels" - from the popular divination
program "The Dream Angel Oracle",
available from ClydeSight Productions as a direct download computer file
(a prototype CD cover is shown here.) The theme is available as an
MP3 download for free to Web site visitors, and has proven very popular.
Procedure:
The
source music is an all digital production, made with the Roland XV-5080 synthesizer
and processed through Mark of the Unicorn's Digital Performer software
on a Macintosh G4 computer. The resulting sound is called "The XV Orchestra"
because it has characteristics that go beyond the limitations of the Roland
XV-5080 (thanks to Digital Performer) enhanced through the software's music
studio mixing and filter boards.
The
original digital recording was saved as a raw AIF file sampled at 44Khz.
This was burned to a CD. The CD was then played on a Sony High Density Linear
Converter CD Player (model CDP-261) with the line outputs directly patched
into the line inputs of the Wollensak 5750. For maximum fidelity, the Wollensak
5750 was set to record at 7-1/2 ips on a vintage Scotch® brand - 150
formulation recording tape. This is the tape most users of the Wollensak
5750 would have had available in 1967, when the machine was in production.
For
this Web page, that recording was played back into the computer and captured
as a RAW AIF file, then converted to MP3 format using Apple's iTunes.
It
is important to note that MP3 compression actually lowers sound quality by
removing some of the audio information from the original "raw" -
WAV - file. This is unavoidable due to bandwidth needs.
There
is a popular misconception that because MP3 is so widely used, it actually
improves sound, which is not the case.
Results:
To
understand the recording results it is important to note the Wollensak 5750
operating characteristics:
- Frequency
Response: 40 - 17,000 Hz
- Wow
and Flutter - .25% RMS
- THD
(Total Harmonic Distortion) - 5%
By today's
standards these specifications are rather poor, although they were standard
for 1967. Typical frequency response of a CD is 20 - 20,000 Hz, and THD is
below 1%. Wow and Flutter simply do not exist on a CD, as they are generally
faults of mechanical analog recording systems.
However, the
amplifier circuitry can contribute to flutter or "gurgling" as
is heard on the recording, especially the bell tones. The Wollensak 5750
uses a number of electrolytic capacitors to filter the line (sometimes these
are called
"filter caps") and smooth out the electrical signal being processed
in the amplifier. I was able to identify them (all 14) thanks to a SAMs Photofact
book, which I ws able to purchase from Stereo
Manuals.com.
Electrolytic
capacitors have a dielectric and electrolyte which over time can fail due
to dryness or other conditions brought about by age (much as a battery chemical
will become exhausted even if the battery is stored on a shelf and not used).
The only solution is to replace the capacitor, a time consuming and potentially
expensive process. To accomplish this on the Wollensak 5750 requires "major
surgery",
as the amplifier board is located deep within the machine, and most of the
frame must be removed to free the board for alterations. The author has chosen
to delay this procedure as long as possible for obvious reasons.
The issue
does not occur when the machine is in playback mode of a commercially produced
tape, and a careful check using sensitive headphones reveals the source.
There is a hum when the recording function is engaged, but the hum is different
on each channel. That hum (or pair of hums) is a giveaway of one or more
failing electrolytic capacitors in the recording circuit. Since there are
two circuits, one for each channel in the stereo mix, with different low
frequency hums, harmonic distortion is introduced, which accounts for the "gurgling".
Nevertheless,
the Wollensak 5750 did a fairly good job with the recording. The most noticeable
defects are tape hiss (which is natural to all reel to reel tape recorders)
and the very noticeable harmonic distortion of the bell tones in the music.
The problem is most likely caused by the weakness of the "filter caps" within
the recording part of the circuit board.
Wow
and flutter seem negligible, certainly within the specs of the machine (.25%)
Bass
frequency response in the recording falls short of the original, probably
because the amplifier simply is not designed for it.
Stereo
separation is quite good, although the original file has a bit more "presence".
Hearing
is Believing
Below
are two sound samples. One is the actual recording made by the Wollensak
5750, and the other is the actual source material. Both are presented as
MP3 files because such compression is required for the Internet. It should
be noted that MP3 compression also introduces some levels of distortion.
With some quick mouse movements, it is possible to do an A-B comparison.
However, if both files are played at the same time-- well, now won't THAT
be interesting!
Summary:
For
what it is, the Wollensak 5750 restored/rebuilt tape recorder does an acceptable
job of tape recording.
As
a 40 year old machine, with no adjustments made to the electronic circuits
it does perform quite well.
It
records as well through microphones as it does through direct line input.
The purpose of the machine in the author's case is nostalgic and to play
back vintage pre-recorded stereo tapes, so the recording function is not
that critical. (Why would one record a CD to reel to reel tape, given the
rarity of reel to reel machines?) However, if it is needed for a project,
it can be depended upon for a relatively faithful reproduction. And of course,
if necessary, the filter caps can be replaced.
But
the story doesn't end here. This test was a bit unfair, expecting the Wollensak
to record a high end digital file from a CD when such equipment wasn't even
dreamt of at the time the machine was made.
What
if we turn back time and go into history and try the machine in the way it
was used in 1967? Easy enough, all we need is a stereo system and phonograph.
And of course, ClydeSight Productions has this audio equipment!
For
a selection demonstrating the Wollensak 5750's ability to record material
from a vinyl phonograph record, please click
here.
For a video of
playback performance, please click here.
For a sample of
stereo playback performance of a commercial tape, please
click here.
Please
note that ClydeSight Productions DOES NOT rebuild or sell vintage
reel to reel tape recorders, nor can we help anyone involved in such a project.
The tape recorders shown in these pages are part of a personal collection
and are not for sale. We Do Not recommend
that unqualified or inexperienced persons attempt to restore vintage audio
equipment.
Visit
www.clydesight.com Master Site
Web site copyright ©ClydeSight
Productions - 2007
