DBX Expander

I agree as well. The DBX does to much pumping of the signal.
Although the ONE BAND DBX seemed to not do as much pumping as the others. Teac use to make an outboard noice reduction device for their machines as well which may have lowered the noise another 5 or 6 db without the pumping affects. If your a tweaker, you can try replacing the resistors and or the caps in the recording board, which is what I did to my Teac and had noticed a definate improvement in lower noise.But this is very time consuming indeed.

Well, I totally disagree with the 2 comments above. I have demo-ed properly adjusted DBX DS Series expanders for at least 15 "vinyl people" - and only ONE did not hear a dramatic improvement in A/B auditioning. Yes, they will "pump" if you overdo the levels - so don't overdo it.

If you bi-amp vertically, you can also just use them on the mids and highs, eliminating any bass pumping - but I have not found this to be an issue. Factors to consider here are the Damping Factor of you amps, and also the speakers themselves. Mine are sealed box bass cabinets, and pumping has not been a problem. Transmission line and ported cabinets may be more of an issue.

I consider the DBX an absolutely essential part of my system. Many of the recordings of the '70's and '80's were run through STACKS of DBX, or similar, equipment in the studio - EQ, compression, and peak limiting AT A MINIMUM! Proper use of one more quality device that attempts to reverse the "processing" on the output side does "color" the sound (that's what it's supposed to do) but not detrimentally IMO - just the opposite. They DO include op-amps in the circuit, but again, nobody who has heard mine can point out any negatives. One guy who is a hard core minimalist simply decided he liked the sound without the 3BX better, but admittedly had no rational explanation. Then on a 2nd visit, he was pretty much neutral on the 5BX. Quite a few people have bought 3BX's immediately after hearing mine.

That being said, a DBX will not elevate a cheaper, worn out, or misalignes RtR to the level you're looking for.

Unless you have much money to burn, try a 3BX-DS first. The DS version is the ONLY one to consider - the older ones are not as good. It should only cost around $200 to $225 plus shipping, on Ebay. There are lots around and they're affordable. If you don't like it, you can very easily resell it for what you paid.
A mint 5BX may cost you close to $1500 or more, so it's a bit riskier to start out with - especially if buying from an Ebay dealer and/or shipping via UPS or Fedex is part of the equation! The 5BX's Impact Restoration circuit is better, but the 3BX-DS's Dynamic Range Expansion is better IMO. So it's kind of a toss up anyway. I know someone who uses one 3BX on each channel and the results are superb.

I think Opalchip has a great point, first spend the money to get your R2R serviced and tuned up, including a check of its performance against the original spec. Heads could be dirty, worn, mis aligned. I have a number of broadcast tapes, all sound better then the vinyl. Only after making sure the R2R is okay would I move on to DBX.

DBX is no substitute for properly functioning equipment.

A 1 band DBX will be more prone to audible "pumping" than a multi band DBX, particularly with noisier recordings (tape recordings are often more prone to "hiss" than other sources).

THe secret with the DBX expanders is to have the levels adjusted properly and to not overdue it.

You may need to adjust the levels differently for different input sources with different inherent levels or even recording by recording.

When properly applied and adjusted, a properly functioning 3BX can help deliver more lifelike dynamics into otherwise compressed and artificial sounding recordings.

I've never detected any inherent coloration from the DBX itself, but of course interconnects used can make a difference so these have to be considered as a factor in the resulting sound.

I've not heard the DBX, but agree with an r2r tuneup. I recently bought a very lightly used Revox cassette deck with a boogered up $4.00 balance trim pot and am incurring additional expenses for parts and the attendant labor charge for new pinch rollers, capstan shaft resurfacing, align/clean/lube. The heads are out of spec and will also be replaced. At $260, the heads parts cost accounts for about half the total outlay. For comparison, my speaker cables cost more than this tuneup.

A certified Revox tech is doing the work.

The worth of a properly reconditioned tape source is up to you, but if you're serious about using and holding on to a classic machine, you ought to consider the expenditure. The experienced service shops for tape gear will likely become nearly extinct in our lifetime...