New user of old Comteks (72's)... looking for tips n' tricks...
Derek
Just picked up a set of comteks (72's) for my eng rig. Have a couple
of questions regarding them..
- What type of cable is best for patching from transmitter to
antenna? 50ohm? 75ohm? rg-58/59/6?????
- Can these transmitters be tuned to different frequency ranges (ie..
can I take an "A" Tx and turn it into an "H" Tx??)
- Why do the older pr72b Rx's with the recessed (flat style volume
pot) seem to suck so much??
I know these units have been in use for a long time so I'm hoping
someone can share a little experience with these! Thanks!
-d
massman
> Hey rampers,
>
> Just picked up a set of comteks (72's) for my eng rig. Have a couple
> of questions regarding them..
>
> - What type of cable is best for patching from transmitter to
> antenna? 50ohm? 75ohm? rg-58/59/6?????
bag setup!!!
>
> - Can these transmitters be tuned to different frequency ranges (ie..
> can I take an "A" Tx and turn it into an "H" Tx??)
guidance!!!
>
> - Why do the older pr72b Rx's with the recessed (flat style volume
> pot) seem to suck so much??
>
> I know these units have been in use for a long time so I'm hoping
> someone can share a little experience with these! Thanks!
longer.
>
> -d
haophat
treated me well. actually paid themselves off in just a few rentals.
What i did was have a cable made for the input.
I have a SD 302 and I called up Loc snd. they made a cable for me that
takes the tape out and connects to the mini Comtek in.
It works great and its nice and short for my bag setup.
My M72 has a antenna, but I have had clients way across the set and
they can hear clearly. so I am very happy with their performance.
( I had to have the cable made because there is no cable like that
currently, they had to put a pad in there and its all nice and
sleek) Just buying a ta3 to XLR didnt work for me.
As fer the Crystals, just hope there is no interference!
philper
esp w/ decent heasphones. They are serviceable by a knowledgable
tech or by Comtek--maybe have your problematic ones checked out.
Philip Perkins
David Waelder
0e92d36b-8bda-4fa4...@f18g2000vbf.googlegroups.com, "Derek"
<derek....@gmail.com> wrote:
[ship]
>
> - What type of cable is best for patching from transmitter to
> antenna? 50ohm? 75ohm? rg-58/59/6?????
Regarding cable, be aware that Comtek cables need a filter trap in the
connector to keep RF from sneaking back into your mixer or recorder. Cables
purchased from Comtek will have that filter. If you order a custom built
cable from one of the professional suppliers (LSC, Coffey, Trew, Gotham,
Attias) and tell them it's for a Comtek, they will most likely remember to
include the filter. If you build it yourself, you should contact one of
those sources to ask for specifics.
>
> - Can these transmitters be tuned to different frequency ranges (ie..
> can I take an "A" Tx and turn it into an "H" Tx??)
>
The earliest versions of this system had to be sent back to the factory to
be fitted with a different crystal to work at a different frequency.
Later models (dating to the mid-80s, perhaps?) had a plug-in crystal that
could easily be changed out by the operator. They were relatively
inexpensive (maybe $5 or $10 each) so, if still available, one could easily
carry two sets for some frequency agility.
If yours have this feature, you will see a rectangular button on one side of
the unit with a prominent letter, "A" or "B" etc. Simply pull on the button
to remove the two-pin crystal component. Alternate frequencies plug in. If
yours have this capability and you would like additional crystals, you might
contact the parts department at LSC (818-980-9891) or one of the other pro
sources to see if crystals are still available.
> - Why do the older pr72b Rx's with the recessed (flat style volume
> pot) seem to suck so much??
Hard to say. They'll never sound as good as the more modern systems (Comtek
PR216, Lectrosonics IFB) but they should be OK. These receivers needs to be
tuned occasionally. Maybe yours need a little adjustment.
>
> I know these units have been in use for a long time so I'm hoping
> someone can share a little experience with these! Thanks!
>
> -d
David Waelder
rickjohnsonfilms
Thanks to David Waelder for his responses.
Do any of you have the schematic for a Comtek input cable (mixer line
out to Comtek mic level in) that includes the RF filter trap
components?
Thanks,
Rick
Derek Hanson
crystal, but that question was regarding the m72 transmitter which
does not have a pullout style crystal. Would cable length of the
headphones have any impact on reception?
-d
David Waelder
11711519-1247-4462...@w35g2000yqm.googlegroups.com, "Derek
Hanson" <derek....@gmail.com> wrote:
Oh, maybe that's so. As I think back, I only recall seeing the pullout
crystal on receivers, never on the transmitter.
Of course, one can use these older receivers with the BST-75 base station.
That can be set to transmit on a variety of frequencies (only one at a time,
of course) and mates very well with the older receivers.
That makes a nice package if you work from a cart. You can use the BST-75 on
the cart and keep the m72 for bag work.
> Would cable length of the
> headphones have any impact on reception?
Well, yes but as a practical matter, probably not crucial. The cable serves
as the receiving antenna so it must be sufficiently long to function. At 72
MHz, a wavelength is a little over 13 feet and a 1/4 wavelength would be
about 3 1/2 feet. So you would probably want to avoid any really short
headset cables.
For more precise antenna length calculations, go to:
http://www.flysteve.it/antenna.html
David Waelder
Douglas Tourtelot
it. I use the PR72 receivers and a variety of portable transmitters and
base stations. I usually run one main system for the village, but sometimes
two. I sometimes rely on the high output of the base station to cover the
set, or can remote a portable to video village via Cat5. If we go onto an
insert car, I merely rig a portable on the car with the same frequency that
folks are already listening to, and away we go. This is a huge advantage
and benefit of having a large Comtek setup that I could not afford to
replicate with another manufacturer's rig. My philosophy on Comteks probably
varies a bit from most others in that the folks who routinely listen on my
set are not making critical judgments on the actual quality of the sound
that they are hearing. They are paying me to do that.
Comteks are, for the most part, really hard to break, not a lot of money if
left behind and, for me, quite suitable. I can feel okay about giving
"ears" to just about anyone who asks; the actor's kids, the studio teacher,
producer's friends. I have 28 units, plenty on most days<g>!
Just seems to still work for me. Are there higher quality replacements? Of
course. Like others have mentioned, the 216 series from Comtek has a great
rep. The Lectro IFBs are great as well; my boommen listen through those.
But then again, my boommen don't drop their receivers (mostly<g>) and they
rarely leave them on top of a bookcase in the last office down the hall
where they went to make a phone call.
All in all, the Commies work pretty well for me.
Just my $.02.
Hunter
"Orpheus" receivers from Landmark Audio (you'll have to google for the
website, as I'm on my Treo--sorry) for like $50 each. They're
frequency agile, run for days on two AAAs, and are like $50 each! They
sound just fine for most listeners, have about the same range as a 72
series receiver, and did I mention they're like $50 each?
But don't bother getting Landmark's base station transmitter. It's RCA
input only and has way too much hiss.
-H
chrisb...@bellsouth.net
So.. what are you using as a transmitter? Would a comtek 72 series
work?
johnpaul215
sounds like these are what they are talking about. they specifically
mention compatibility with Comtek 72 series transmitters. Some used
ones for about $26. I *just* bought a few to try out. it's nice to
keep the old Comteks around for pretty much anyone that wants a set
(like an investor coming to set or something, or a friend of the
production). Nothing more awkward than a goofy producer swiping the
Scriptie's headphones for somebody investing in the project. Yeah,
been there.
I can't vouch for this seller or anything, but like i said, i just
bought a few to try out.
-johnpaul
Bill White
Derek wrote:
Why do the older pr72b Rx's with the recessed (flat style volume pot)
seem to suck so much??
Hello Derek,
The older PR72b did not support audio expansion like the MRC82C version.
If you use them with the companded version of the M72, it will sound
like crap.
The PR72b was the companion RX to the M72 TX without a compander.
The TX compander board was an optional printed circuit board that could
be retro-fitted (for the brave or foolish only ;-).
Their MRC82C receiver matched with a companded M72 was designed to fill
the market for low-end wireless mikes or camera links. The end-to-end
distortion was typically 1.5% at best. They also had a version of the
MRC82 called a Pro-listener. This featured a low impedance headphone
socket and you could give one of these to your boomie or DoP without
apologizing.
The uncompanded M&2 in combination with the PR72b was always a pretty
basic system which suffered considerably (as did their other models) as
you had no level indication. It was a bit like flying in fog without an
altimeter.
One useful technique was to fire your line-up tone into the TX and watch
the audio level out of the RX. As you wind up the TX level, the RX
output level will 'flatten off' as the TX limiter kicked in. Note that
RX audio level and then reduce the TX input until the RX level falls
back, say 4-6 dB. As the M72/PR72b combo has a fairly poor noise floor
anyway, it is important that the TX is running pretty close to limiting.
A few dB of limiting will not degrade the overall performance as much as
under-deviation which will magnify the noise floor.
Their 'plug and pray' crystal changing was likewise less than perfect.
The receiver front end was nowhere near wide enough to cover 66-88 MHz.
Any frequency change of more than a MHz or two would result in lower
sensitivity unless the front-end was professionally realigned. In my
experience, the manufacturing variation in crystal frequency often
caused discriminator error which raised the RX distortion.
Many of the early M72 versions used the lapel mike lead as an aerial.
The BNC aerial socket version is called M72 OPTION 7.
Good luck and best wishes,
Bill White
Microphone Magic
Sydney Australia
http://microphonemagic.tv
Derek Hanson
So far so good, I've gotten my system to work as well as I had hoped
for and seems to be doing fine providing basic ifb function, I've got
the Tx modulated pretty hot and the noise on the Rx's is acceptable.
I found that the older unit I initially thought "sucked" more than the
others sucked much less when I swapped crystals with one of the other
crystals, so I guess that was the culprit. Picking up some cheap
headphones that have straight cables also helped (was using coily
cable 7506 to test previously). The flat knob receiver does seem to
have a lot more gain than the other version.. Now we'll just see how
well the "A" crystals do in Chicago, which is anyone's guess. Thanks
to all who gave advice.
-d