DBX 224 Type II encoder/decoder need help using it

[pioneernut]

Does anyone have any tips on using a DBX 224 Type II decoder on a RTR. I've been wanting to try using this on new recordings to see what kind of performance it can do, but I'm not sure on the best procedure for recording and for setting the record and playback adjustment pots on the back. Haven't found any manuals for it either. The thing is capable of simulatnious record and playback so it should be easier to use with the 3 head RTR I've got.

Thanks, Mike

 

[goldear]

I've been using dbx on my R2Rs for more than 20 years. There really isn't much to it. DBX doesn't require elaborate setup procedures and calibration the way than all of the Dolbys do.

Just connect your tape deck to the appropriate connections, and your amp to the appropriate connections, plug it in, and turn it on.

There are some level controls on the back, but their settings really only effect the level matching from input to output, and visa-versa, so they truly are not crucial at all. If you had them all set about three-quaters of the way up, they should be perfectly fine. However, if after doing this you find that the Input levels are too low, then turn-up the input. And if the outpust are too low, then turn them up, or visa versa.

As to recordling levels, you will want to turn these down quite a bit from what you are proabably used to recording at without NR. If recording at 3.75 ips, never drive them above about -6dB on the peaks. If you are running at 7.5, Never go above about -3dB. And is perfectly fine to remain well below these levels. If you violate these rules, be prepared to pay for it when your high-end saturates because of the extra 10dB DBX HF boost that occurs durring recording with dbx.

The only other thing that is really important is that you set the bias and EQ settings on your R2R (if you have them) correctly, so that you have as flat of frequency response as is possible. DBX's biggest side effect is that it doubles all frequency response errors, and this is why many people who have tried it dislike the sound. If you don't thave these adjustments, then only uses a tape that is well matched to your machines internal bias settings.

I hope that this didn't scare you off, as there really is nothing to it. I'm just pointing out some of the gotchas that you might experience in the process.

Good luck!

 

[pioneernut]

Great pointers, I'm going to give it shot, but my first trial run last night, I noticed issues with the DBX 224 I got. Found a bad Op-Amp IC where the signal on the right channel is extremely distorted on my scope. The other channel, same test point, is just fine. I ordered the 55 cent part from Mouser and hope to get it fixed next week.

However, I was pleasantly surprised by the overall effect at reducing tape hiss on the good channel. But I need to try it again at a lower level as you suggested, I did notice the highs were little off from the source, but that was after 5 minutes of playin around with it.

Anyway, thanks alot,
Mike

 

[pioneernut]

Goldear,
Just wanted to followup on the my experience with the DBX-224. I replaced two of the LF385N op amps in my unit, one was totally distorted, and the other was weak after replacing the bad one.
Anyway, I finally got to test it, and OH MY goodness I was completely surprised at the sound quality compared to the original source of a CD. I recently went through my RT-701 and alligned the Bias and EQ to match my Maxell UD35-90s and some Quantegy Tapes I had, and I can honestly say this tape deck has very flat Frequency response up to 20khz at 7-1/2ips. On your recommendations I kept the peaks well below the 0 to -3db range so typically it was around -6db. During my testing I never found that the music had a pumping sensation, it sounded as close to original as I think any tape deck could approach.

I only wish I had gotten one 15 years ago.

Thanks, Mike

 

[Nitro]

Works good with cassette too. There even used to be some car audio decoders.

 

[goldear]

Goldear,
Just wanted to followup on the my experience with the DBX-224. I replaced two of the LF385N op amps in my unit, one was totally distorted, and the other was weak after replacing the bad one.
Anyway, I finally got to test it, and OH MY goodness I was completely surprised at the sound quality compared to the original source of a CD. I recently went through my RT-701 and alligned the Bias and EQ to match my Maxell UD35-90s and some Quantegy Tapes I had, and I can honestly say this tape deck has very flat Frequency response up to 20khz at 7-1/2ips. On your recommendations I kept the peaks well below the 0 to -3db range so typically it was around -6db. During my testing I never found that the music had a pumping sensation, it sounded as close to original as I think any tape deck could approach.

I only wish I had gotten one 15 years ago.

Thanks, Mike

I'm glad to hear that is has worked out well for you. The key for having DBX work properly is exactly what I described before. And when it is used on a good deck, that has been calibrated for the tape you are using, it can indeed sound very, very good! :thmbsp:

Unfortunately IMHO, both Dolby and DBX tend to get a bum rap, and it is primarily because the tape decks was not callibrated properly. Both can sound excellent when used properly (ie, with an understanding of their limitations), on a good, and well calibrated tape deck. And no, Dobly doesn't always make tapes sound dull. That effect is usually caused by the deck's dolby circuits not having been calibrated appropriately for the tape that you are using.

But DBX, when used on a good, and well calibrated reel to reel can actually exhibit a wider dynamic range than do CDs.