Film-Tech Forum ARCHIVE: 6-channel line level boost

This is topic 6-channel line level boost in forum Film-Yak at Film-Tech Forum ARCHIVE.

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Posted by Steve Kraus (Member # 476) on 05-17-2004, 08:20 PM:

I bought a DVD player with built-in DD decoding specifically to avoid the need for an external decoder or processing receiver. I'm feeding directly into the 6-channel input of a CP500/D. The level is just a tad low even with the fader at max. I don't want to mess with the CP calibration which is perfect (the same input is used for 6-track mag and Dolby level there makes for proper playback level).

Is there some sort of simple pre-amp I can add to the line? I don't want some sort of processing pre-amp as extra gadgetry was exactly what I wanted to avoid. What I want is some sort of simple black box, sort of a reverse pad, that just boosts a few dB, maybe even a simple thing I can build myself around a single IC or set of op amps. Just a few dB is plenty as it's very close to correct as it is...just lacking some oomph. What say you?

Posted by Steve Guttag (Member # 268) on 05-17-2004, 09:39 PM:

Steve there are several routes here...you can go passive (read transformers) or active (Line Amps).

In the line amp category...there is the RDL FP-UBC6 http://www.rdlnet.org/fp-ubc6.htm. It will do it actively and give you as much or as little boost (or even cut) on all six channels.

From RANE there is the BB (balance buddy). It is all passive and takes advantage of the transformer windings to alter the level. Since it depends on a 20K+ input impedance to do its magic, in a CP-500 situation (I think it is a 10K input impedance) it will have less gain and probably do a fine job in your situation.

http://www.rane.com/bb22.html

You would need three BB22s.

Steve

Posted by Steve Kraus (Member # 476) on 05-17-2004, 09:46 PM:

Good solutions but pricier than the source deck I'm coming from.

Posted by Bobby Henderson (Member # 840) on 05-17-2004, 09:58 PM:

Steve, what kind of DVD player did you buy? Is it a DVD-A/SACD type player with the 5.1 outs, or an older DVD-V unit just with the built in DD decoding?

Normally, any DVD player with a full feature Dolby Digital decoder should have an internal setup where you can adjust output levels for each individual channel. My first DVD player was a Sony DVP-S530D, which had a DD decoder and 5.1 analog output. In the player setup, you could go to a menu where you could turn on test tones, adjust levels and even do bass management functions (the basic "small"/"large" settings, etc.).

Anyway, it's just an idea.

Posted by Luciano Brigite (Member # 1104) on 05-17-2004, 10:00 PM:

If you want to build something,I did use this a few times, it worked ok, doesn't empty anyone's wallet and is simple to build.
a metal box is the right thing to have everything inside.
each IC will take care of 2 channels,3 identical circuits for the 6 channels you need.

lousy scan I know.. [Embarrassed]

Posted by Steve Kraus (Member # 476) on 05-17-2004, 10:30 PM:

Interesting; thanks.

Bobby, it's a Toshiba SD-4900. Yes, there is a setup but everything starts at 0dB and you can go minus from there but not plus.

Posted by Mark Gulbrandsen (Member # 72) on 05-17-2004, 10:55 PM:

Since you normally like to do things for on the cheap I would go with Lucianos idea and breadboard it all on one perf board and put it all on one box. Easy...and just a few hours work.
Or you could check out OpAmp labs, but that solution is still at least 300.00 away.

I would stay away from using any transformers... unless you can afford the best (Jensen) then going the transformer route will just add the "sound" of what ever tranny you stick in there... might be ok, might not be. Cheap trannys generally equal poor sound quality!! This whole thing is unbalanced anyway and that simple circuit is by far your cheapest "Best" route. Too bad you don't have a good surplus electronics store near you. Here in SLC I can build that all out of mil spec surplus parts with 1% RN65 dale resistors in there for less than three bucks a set of channels! The only other thing you need is a split supply to run it... Less than 10 bucks worth of parts including the wall wort. Let me know and I can put you in touch with that store if need be.. they do mail orders too. "Isn't this delightful".

Mark

Posted by Luciano Brigite (Member # 1104) on 05-17-2004, 11:23 PM:

Only now that I noticed that there are 2 resistors in the upper part of that schematic that doesn't have any value marked, they're the same as the lower part. (and that schem was drawn about two years ago ,built a few of them and only now I noticed that)
Originally it was intended as an aditional output buffer stage in a
crappy,cheapo LCRS processor a friend and I tried to make for use in small theatres that couldn't afford a real processor.sometimes the output would not excite the amps to a good level, then those stages were added.There is another circuit,using the same IC but with a different gain level (also fixed) and another config. also on the same IC but with a different gain range/config ( adjustable) however I have no clue where those went,along with the rest of the "processor" circuit.
It'd be done with $10.00 or so with all the parts ( I never spent more than that when I built those).I'll look for the other circuit and post here if interested, just let me know [Smile]

Posted by Steve Kraus (Member # 476) on 05-19-2004, 09:43 AM:

Sure, sounds like fun.

Mark: Yep, taking the cheap way here as this is likely just for my own fun plus adding a multi-hundred dollar pre-amp solution to an $80 player isn't logical. Then I might as well just get a consumer receiver and probably pick up DVD-DTS decoding to boot. So let me know about your favorite sources of parts.

Posted by Bill Gabel (Member # 1105) on 05-19-2004, 10:09 AM:

When we do DVD screenings, I patch the DVD player into a Rane SM 26 splitter mixer which then goes into the CP-500. It works very nicely.

Posted by Scott Norwood (Member # 30) on 05-19-2004, 10:21 AM:

How does one determine the proper playback level for DVD and videotape? Are there test tapes/disks with pink noise and/or Dolby Tone? I've never seen a DVD player or Beta/Digi-Beta/HD deck with the ability to produce either.

Posted by Bill Gabel (Member # 1105) on 05-19-2004, 11:07 AM:

Well most post-houses when doing dubs or transfers places a tone on the color bars. So depending on media your going from you zero out on your meters going into the CP. Your right that no decks produce tones.

And I also have Sound One in this building, so I can get all tones for set-ups.

[ 05-19-2004, 12:11 PM: Message edited by: Bill Gabel ]

Posted by Phil Hill (Member # 371) on 05-19-2004, 12:01 PM:

I always use Joe Kane's "Video Essentials" for setting up NTSC DVD video and 5.1 sound systems.

He also has a LaserDisc set-up disc if your so inclined.

>>> Phil

Posted by Mark Gulbrandsen (Member # 72) on 05-20-2004, 08:00 AM:

Yea, Ole Joe is the way to go. I have both the DVD and Laser Disk version. Did he do A CED version [Big Grin]

? Haha, just joking on that last one.....

Mark

Posted by Luciano Brigite (Member # 1104) on 05-20-2004, 09:49 AM:

I tried to scan the other two schems I mentioned in the previous post but my scanner decided to crap it up [Frown]

The differences aren't many ,only 2 different resistor values for one circuit and a slight different arrangemet for another circuit.
the IC is the same, 4558DD.

1st variation:
18K resistor between pins 1-2 and 6-7 changes to 910 ohm
5K6 resistor fom pin 2 / 7 to ground changes to 4K7
This aplies to the schematic I posted before. the other components remais the same.

2nd variation: (this one is different from the other two)

signal input>10K resistor to ground,>1K resistor in series with a 4,7uF electrolitic (positive goes to IC pin)>10K res. with a 200Pf ceramic cap in paralel to ground > pin 3 (5) of IC.

IC pin 1 (7)>10Uf cap>10K resistor to ground > signal output

IC pin 2 (6)>20K trimpot with a 56pF cer.cap in paralel to IC pin 1 (7). cursor of trimpot with a 3K3 res to ground.

IC pins in () are of the other channel.

good luck in understanding this [Big Grin]

Posted by Steve Guttag (Member # 268) on 05-20-2004, 05:59 PM:

Unlike Mark, I'm a big advocate of transformers. While there used to be a day when Jensen was all one should consider for transformers, such is not the case anymore. While there are indeed cheap, shouldn't be used for audio, transformers out there...there are some surprisingly good low-cost audio transformers that are pretty darn flat in the audible spectrum.

The BB22 I mentioned is quite good. Also RDL has a couple lines of audio transformers that are anywhere from VERY good to exceptional. The "very good" ones are actually rather inexpensive ($30/channel).

Jensen is indeed the "gold standard" of transformers and we sell those too but I wouldn't say they are the only or best solution to all situations.

The SM26B mentioned by other is also a pretty cool unit. It can be a 6-channel line amplifier and/or it can be a 6 x 2 mixer. Street price on that one is $329 though.

Steve

Posted by Gordon McLeod (Member # 33) on 05-23-2004, 06:44 PM:

Hammonds line of broadcast tranformers are very good as well