dbx 224X odd behavior on playback

[Trevor White]

Hi All,

For quite some time now I have been using a dbx 224X NR unit with my Pioneer RT-707 R2R with outstanding results.

Recently however I happened to notice something rather odd. When playing a tape back through the 224X the 'Playback' leds light up and behave normally. But, at the same time the 'Encode' leds on the 224X are activating as though there is a low level signal available on the inputs. It turns out that this is actually the same signal that is being played through the 'Decode' side of the 224X.

I had never seen this before as I had the 224X plugged into the Tape Loop of my vintage Luxman L-430. However I have been using a modern Luxman L-507uX lately, and when plugged into the Tape Loop of this amp there seemed to be this signal coming back on the inputs.

At first I thought it would have to be something in the setup of the Tape Loop on the Luxman L-507uX, so I took the Lux out of the circuit by disconnecting all the inputs and outputs. Amazingly the 224X still showed some input signal when playing back an encoded tape???

It appears that this is something to do with the 224X itself? When the Record-Out is plugged into the old Luxman L-430 this signal is suppressed somehow and nothing shows on the 'Encode' side of the 224X. But when having the Record-Out connected to nothing at all, or to the new L-507ux I get this low level repeat of the playback signal on the 'Encode' side of the 224X.

It does not seem to do any harm, recording via the 224X works correctly with the 'Tape' and 'Source' signals being correctly separated, it is only during playback that this signal leakage seems to occur.

Has anyone seen this sort of behavior before? Any suggestions as to what I can do? As I say, it all seems to work correctly, it just looks odd.

Cheers,
Trevor

PS: I'd love to know just what happens when plugging the Record-Out to the old Luxman L-430 that causes this extra signal to be suppressed/removed whilst the newer Lux does nothing.

 

[Trevor White]

Oh, I should probably mention that the 224X is connected via a dbx 200X Route Selector. I actually have 3 tape decks, 2 RTR and 1 cassette all of which can use the 224X. The 224X is connected to the 'Noise Reduction' loop on the 200X. All fairly normal setup for this type of gear.

Also, if I enable the 'Record Out' function on the Lux whilst it is monitoring the Tape input, and the tape is playing, it has no effect on this unusual low level signal that the 'Decode' side of the 224X is seeing. It's very odd.

As an exercise I might just take the 200X out of the loop and connect the R2R directly to the 224X and see what happens. Perhaps the signal is leaking somewhere in the 200X?

**EDIT**
OK so I directly connected the Amp and R2R to the 224X. No change in this strange behavior. When playing a tape the 'Encode' led's activate along with the 'Decode' led's, although the 'Encode' led's show at a much lower level.

Anyone seen this sort of thing on dbx units?

 

[Trevor White]

Hi All,

So, when reconnecting everything to the 200X I noticed something else very odd. As you can see, there are a LOT of RCA cables involved. When checking the unit out to ensure I had everything connected properly I accidentally bumped the bunch of RCA cables. To my amazement the 'Encode' led's on the 224X actually lit up, just a few you understand. Upon further mucking about I found that any tapping or sharp movement of the cables would cause the 224X to react as though it was receiving some input with the 'Encode' led's activating!

Clearly some dodgy connections, or even dodgy cables as I have found that even carefully securing the cables so that the RCA plugs on the 200X cannot move, and then banging the cables themselves causes the 'Encode' led's to light up. Somehow this physical movement is causing some electrical reaction!!!

Very strange. I wonder if I might have a bad cable that is somehow affecting the 224X and leaking signal, either through bad shielding or bad connections? As you can see in the picture above the cables are all in very close proximity and in some cases actually clipped together. There is certainly something very odd happening.

Cheers.

 

[Trevor White]

Right, so I did a lot more 'testing' today.

I discovered that the input 'Encode' side of the 224X is very sensitive. I found that even by running my fingers along the length of the RCA cable the 'Encode' led's would light up! Clearly my RCA cables were not very well shielded. Even tapping on the cables would produce input artifacts, not good at all.

So I went out today and purchased four half meter higher quality RCA interconnects that had significantly better shielding than those lightweight cables you can see in the picture above. Once I installed those cables between the 200X and the 224X the spurious input behavior disappeared, thank goodness. I could tap on the cables and connectors all I wanted and this produced no weird effects on the 224X.

The lighter weight cables that still connect the Tape Decks and the Amplifier to the 200X are fine and cause no issues for either the Amp or the Tape Decks. The recording and playback results are astounding.

However I still have the odd input 'Encode' signal coming in when playing a Tape. As I noted previously my old vintage Luxman L-430 seemed to remove this when the 'Record Out' RCA cable was connected to the Amp. But I have found that the newer L-507uX does not do this unless I have the 'Record Out' switch on the Amp enabled, AND I have the input selector set to a valid connected input source that is powered up but producing no signal. As I use an external Phono Pre-Amp I can set the Luxman's input selector to the 'Phono' setting and this kills the signal 'feedback' that seems to be occurring.

It's a bit of a pain but does not seem to affect the performance of the Tape Decks or the dbx 224X for either recording or playback. It just looks odd with the 'Encode' led's on the 224X lighting when playing a tape. At least I seem to have found a work around, although just why it is necessary remains a mystery. Apparently the old Luxman did something different with the 'Tape Out' connection irrespective of whether the 'Recording' button was enabled or not, whereas the newer unit leaves the 'Tape Out' connection inactive unless the 'Recording' switch is enabled, AND the selected input source is active!

Anyway, perhaps this may be of some use to anyone else out there that may be using dbx hardware on newer equipment.

Cheers.

 

[PROJECT 2501]

Right, so I did a lot more 'testing' today.

I discovered that the input 'Encode' side of the 224X is very sensitive. I found that even by running my fingers along the length of the RCA cable the 'Encode' led's would light up! Clearly my RCA cables were not very well shielded. Even tapping on the cables would produce input artifacts, not good at all.

So I went out today and purchased four half meter higher quality RCA interconnects that had significantly better shielding than those lightweight cables you can see in the picture above. Once I installed those cables between the 200X and the 224X the spurious input behavior disappeared, thank goodness. I could tap on the cables and connectors all I wanted and this produced no weird effects on the 224X.

The lighter weight cables that still connect the Tape Decks and the Amplifier to the 200X are fine and cause no issues for either the Amp or the Tape Decks. The recording and playback results are astounding.

However I still have the odd input 'Encode' signal coming in when playing a Tape. As I noted previously my old vintage Luxman L-430 seemed to remove this when the 'Record Out' RCA cable was connected to the Amp. But I have found that the newer L-507uX does not do this unless I have the 'Record Out' switch on the Amp enabled, AND I have the input selector set to a valid connected input source that is powered up but producing no signal. As I use an external Phono Pre-Amp I can set the Luxman's input selector to the 'Phono' setting and this kills the signal 'feedback' that seems to be occurring.

It's a bit of a pain but does not seem to affect the performance of the Tape Decks or the dbx 224X for either recording or playback. It just looks odd with the 'Encode' led's on the 224X lighting when playing a tape. At least I seem to have found a work around, although just why it is necessary remains a mystery. Apparently the old Luxman did something different with the 'Tape Out' connection irrespective of whether the 'Recording' button was enabled or not, whereas the newer unit leaves the 'Tape Out' connection inactive unless the 'Recording' switch is enabled, AND the selected input source is active!

Anyway, perhaps this may be of some use to anyone else out there that may be using dbx hardware on newer equipment.

Cheers.

Hey trevor are you well versed in the recording process using the 224x? I'm having problems making a clean sounding recording. I've read the manual but I'm still confused on what to do and what I'm doing wrong. My recordings have a fluctuating volume as if the recording level was being toggled up and down during recording.. which I'm obviously not doing..
I guess what i need to ask of you (if you have the time and are even interested in doing) I need a step by step run through of what to do to record..
Thanks in advance

 

[Trevor White]

Hey trevor are you well versed in the recording process using the 224x? I'm having problems making a clean sounding recording. I've read the manual but I'm still confused on what to do and what I'm doing wrong. My recordings have a fluctuating volume as if the recording level was being toggled up and down during recording.. which I'm obviously not doing..
I guess what i need to ask of you (if you have the time and are even interested in doing) I need a step by step run through of what to do to record..
Thanks in advance

Hi there mate, sorry it has taken a while to respond.

OK, getting the best out of DBX hardware requires careful setup of the recording levels on the DBX hardware. I always play a number of selections from the source material I intend to record so that I can set the Encoding levels correctly. You basically want some loud passages with lots of high frequency content. Like cymbals or sibilant voices. These high frequency sounds are the things that will overdrive the DBX Encoder. I set the Encoder volume so that I almost never see the red LED. The yellow LED's can be pretty well hard on, but you don't want to see the red LED at all, or at least very, very rarely.

Once the Encoder volume is set I then make a test recording setting the tape record levels so that the VU meters hover around the -3db to 0db mark. The occasional peak at +1db or +2db is OK as long as you are using good quality tape. Setting the tape recording volumes will depend a lot on the nature of the music. Older material might be heavily compressed and yield a fairly steady reading on the VU meters, whilst most modern material can have quite large transients. This is one of the great benefits of recording using the DBX Encoder, the effective dynamic range of the tape is greatly increased and you can really saturate the tape and get fantastic results.

So, having set the tape record levels I then prep the input source and my tape and start the recording process. My results are always outstanding.

It is probably worth mentioning that the DBX system really requires your tape deck to be in top notch condition. This is especially true of the DBX Type 1 encoders, but is still a necessity with the consumer grade Type 2 encoders, such as the 224X. You did not mention above what type of recording hardware you are using, but I use open reel tape, primarily with a Pioneer RT-707 that I have fully overhauled and calibrated using proper calibration tapes. Frequency response and a good fairly flat EQ are important to get the best out of DBX Type 2 encoders.

Your description of recording volumes fluctuating up and down is not something I have ever heard with my hardware. I'm presuming the tape deck itself records OK, which only leaves the 224X as a possible source of problems. Sadly these units are not really serviceable. I have changed the four 470uF caps in the power supply of mine, but all the other capacitors have to be left alone as they are what enables the 224X to do its work and the calibration of these units is not straightforward.

All the best, and good luck.
Trevor