dbx 160xt mods (schematic?)

[matthias]

Hi,

I want to do some mods on my dbx 160xt

I think the power supply is not very good... +/- 24V is connected unregulated to some transistors at the output stage.. the power supply caps for the regulated +/-15V are far too low...
maybe some of te lf35x opamps could be changed to some better types with more modern specs.
replace the transformer with a potted toroid...
does anyone have the user-manual containing the schematic??

I've found a scanned copy here, but schematic section is unreadable :( http://classes.berklee.edu/mpe/pdf_f.../dbx_160xt.pdf


I hope you can help me...


mat

[StefanM]

Yes all psu caps can/should be changed for higher values. In fact that's all I modded so far.
Contact Jim Williams for serious upgrades...

Sorry I only have the unreadable schematic too.

Stefan

[matthias]

do you know the output voltage of the transformer...
I measured a 21 AC...

I think i'll build a new power supply... but maybe the +/- 24V is only for the unbalanced out, then it would be enough to enhance the internal ps...

I hope someone can help us out with a schematic...??

[StefanM]

Looking at that almost unreadable schematic I think the unregulated 24v is in deed for the unbalanced stuff only (btw this is what you want to connect to if your are after the "classic" dark & mushy dbx sound...)

If you are upgrading the internal psu it might be worthwhile to loose the 7x15 regulators and replacing them with 337/317 (and needed peripherals) for cleaner supply rails.

I did not measure transformer secondaries.


Stefan

[matthias]

I changed the transformer to a 2x 18v toroid
the comp is still working fine, I traced the unregulated ps lines ... and if you don't use the unbal output a rebuild of the ps is not necessary..

anyway I still don't have a schematic..

next step would be changing some caps and opamps... I think some better types than 4580 and lf351 could be useful...


mat

[CapstanGreg]

I once asked this question several years ago and I got this response from the Moderator:

"It's like putting a band aid on head wound"

I had a couple XTs, and instead of modding them, I sold them and bought a better compressor. Haven't regretted it since. But then again, I didn't like the XTs in the first place.

[StefanM]

Agreed Greg, if you don't like the sound of a 160 use something else. That is why I didn't mod mine to the max (I have enough other comps) - but I could not resist "bettering" the psu...guess that is a special form of gearslutism.

Cheers,
Stefan

[Matt Syson]

Replacing the mains transformer with a low radiated field torroidal would be a good move but other than increasing the capacitance of the main reservoir caps further mods should be unnecessary unless you want to destroy the 'character' of these units.
I had a pair of 160's racked together and the standard mains transformer from one (left) radiated into the other.....About -75dB if I remember correctly.
Matt S

[matthias]

I really like the sound of the 160xt... and I think it sounds quite similar to the old 160 units (I compared it with the dbx162)

but I just want to clean the signal path a bit .. interstage/coupling caps and opamps ...

but without a schematic I don't know where to start...

[dkelley]

don't know if this is useful to anybody, but I own the 903 compressors which are supposed to be 160xt permanently set to over easy mode. PSU is the standard 900 lunchbox psu, so there's no psu diagram in here, but here's a link (below) to the 903 user manual which includes a fairly readable full schematic as well in case it's helpful for any other mods people may be interested in.

for the record, my 903 comps sound MUCH cleaner and quieter than the only 160xt I've ever used, maybe the superior 900 PSU. Anyway, I have no interest in modding mine.

ftp://ftp.dbxpro.com/pub/PDFs/discon...s%20Manual.pdf

Cheers,
Don

[Sean Sullivan]

Does anyone have a condensed version of the schematic? The one available from DBX is 7 pages long and it's hard to read...some scans are vertical, others horizontal, most are crocked or have creases in the scan

I was going to upgrades the power supply caps to 1000uF or 2200uF/35V and the small to 220uF/50V and bypass them all, and I believe those are C3-C6. I'd like to replace the VCA with a THAT 2180A, which I believe is a DBX 1252 (U11). I'm pretty sure the LM353N (U1) is the input op-amp but I'm not sure what the output op-amp is (U4?). I'd also like to know where the coupling cap is, as with the other compressors I've re-worked it seems replacing that makes a huge difference.

If anyone can help me out, it be appreciated. I like the compression characteristics of the 160XT on a lot of sources, but it's a little muddy for bluegrass. So if I can clean it up a little bit, that be great because I love them on banjo and mandolin. I do have to say compared to the 160A and 160X these are the best build quality of the bunch.

[Proggm]

You will find everything you need here (even the parts list)

dbx® Professional Products

[Sean Sullivan]

Thanks, the schematic is just difficult to read because it has a really sloppy scan job, but I think I print it out and lay out the seven pages on a table I can figure it out.

[Sean Sullivan]

"These circuits can be inproved by replacing the cross coupled 1N4148 diodes with green LED's"

I also found that little snippet from Jim. I guess he's talking about those little 3mm LEDs?

[Sean Sullivan]

Moving along, here's what I'm going to do:

LM353 to LM6172
5534's to LT1357
VCA to THAT 2180
Replace coupling capacitor (C14? I'm 95% sure) with Wima 4.7uF MKS-2, bypass with MIT .01uF PPMFX
Increase size of power supply capacitors, bypass with WIMA MKS-2 .01uF 250V

With the new op-amps I'm sure I'll have to do some power supply decoupling caps for the op-amps (it looks like they are already installed by DBX) and a small cap across the feedback resistor of the opamps.

If anyone wants to explain changing the diodes to LEDs I'll give that a try.

[Jim Williams]

Originally Posted by Matt Syson

Replacing the mains transformer with a low radiated field torroidal would be a good move but other than increasing the capacitance of the main reservoir caps further mods should be unnecessary unless you want to destroy the 'character' of these units.
I had a pair of 160's racked together and the standard mains transformer from one (left) radiated into the other.....About -75dB if I remember correctly.
Matt S

One needs to place these into the racks carefully. The power transformers on dbx stuff is on the left side. Everyone else mounts the iron on the right side. That places the iron right over the I/O connectors for most other gear. Avoid mounting dbx rack gear above or below sensitive analog inputs or hum fields can be generated.

Once I measured a dbx160X I modified in a studio that showed .5% THD, way above the unit's specs. It turned out to be an Eventide H3000 mounted on the same rack, a couple feet away. The switcher noise from that unit destroyed the analog specs of any analog gear near by. When it was shut off, THD returned to normal. The H3k was removed and ended up on the floor 20 feet away from anything else. That was the only way it could be used without spectral contamination.

Any carefully loaded control room will pay for a tech and an AP system to determine if everything is working well with others. Otherwise, it's hit and mostly miss. That requires every piece to be independently speced and then compared to results from the rack after mounting.

Jim Williams
Audio Upgrades

[Jim Williams]

Originally Posted by upinflames

If anyone wants to explain changing the diodes to LEDs I'll give that a try.

The 160X doesn't use them, It uses a low leakage 10 uf cap off pin 4 for RMS timing. The XT went with the "non-linear capacitor" circuit. It uses a couple of caps and an opamp to emulate a fast and slow timing capacitor at the same time.
A couple of 1N4148 diodes are used. Replacing them with 3mm green led's helps as it places the diode conductance at over 2 volts, it's under 2 volts with the silicon diodes. Remember to use a Sharpie to black out the LED's as they can conduct leakage current from external light sources.

Jim Williams
Audio Upgrades

[Sean Sullivan]

Thanks for the explanation Jim. I'll swing by Radio Shack and get some 3mm LEDs. I don't think Mouser/Digikey sells them. If I could just find some diodes to use in place of those Panasonic EXC-ELSA39 that Digikey is out off I'd be on my way to completing all these projects!

[Jim Williams]

The non-linear capacitor circuit also benefits from the use of a very low noise fet input opamp. An Analog Devices AD8510/12A is ideal for that. The 353's are too noisy and add THD to the mix.

Jim Williams
Audio Upgrades

[Sean Sullivan]

Thanks Jim, no luck finding the LED's at my local electronics supply store, but I'll get some off eBay or something.

Do you suggest the following, Jim:
Replace LF353 (op amp 1) with AD8512
Replace LF351(op amp 2) with AD8510
Replace 5534 (op amp 3 and 4) with LT1357
Replace VCA with THAT 2180A

Increase size of power supply capacitors and bypass with WIMA .01uF MKS-2 250V (C3 through C8)
Replace coupling capacitor (I believe it's C14) with WIMA 4.7uF MKS-2, bypassed with MIT .01uF PPMFX
Replace 1N4148 diodes (CR1 and CR2, right?) with 3mm green led's

[12Bass]

IMO, OPA211/2211A sound better than LT1357/58. Coincidentally, I've got a pair of THAT 2181As (lowest distortion, trimmable) which are going to replace the original THAT 2155s in my RNC. The OPA275 was already replaced with an LM4562, but that's going to be changed to a pair of OPA211s on a BrownDog adapter. I'm using two singles because, in testing, I've found them superior to one dual op amp.

[Jim Williams]

That is interesting as BurrBrown advertises the OPA2211 as a dual-single design. The dies are seperate inside the epoxy. Unlike all other duals, that part uses two seperate dies with seperate power feeds to each die. The other duals are laid out on one die.

BB touts the channel seperation is superior in the 2211 and claims even if one side is driven to clipping, the other die is un-effected. That doesn't happen with the other duals.

Jim Williams
Audio Upgrades

[Sean Sullivan]

I have a pair that I'm going to upgrade, so I could try both. But, the BB is more expensive.

Hey Jim/anyone, can anyone confirm that I read the schematic correctly and I'm replacing the right components?

[Jim Williams]

Mine are blurry too. Try a National LM6171 in place of the 5534 output opamps. noisier, but they drive 150 ohm loads.

Jim Williams
Audio Upgrades

[The Beatsmith]

couple of novice questions:

- what is the outcome of these mods, soundwise?

- is there someone in the UK that could do this for me?

[Sean Sullivan]

Increase bandwidth and slew rate, lower total harmonic distortion. Everything Jim does at Audio Upgrades and recommends is an attempt to make things as transparent as possible. That's something I really appreciate. I have a C414B-ULS that he's modified that is my favorite vocal, bass, and electric guitar microphone. And I've used all the standards (U47, U67, U87, C12, ELUX 251, C800G on vocals/Royer R-121, Coles 4038, AEA R84 on guitar/FET47 on bass) and it beats them all for me. I primarily record bluegrass, and the instruments the players play are often some of the best in the world, and I don't want anything messing with what's coming off the instrument.

I also have an Aphex 651, which along with a GML is one of the most transparent compressors I've ever used. The Aphex cost me $100 on eBay, the upgrade was $140, so total it cost me $240. That's 20 time less than a GML, but the GML isn't 20 times better.

If you payed for the shipping, Jim Williams will modified a DBX 160XT for you. His website is audioupgrades.com and it has a price list. If there is something you want modified that isn't listed, just ask him.

[12Bass]

Originally Posted by Jim Williams

That is interesting as BurrBrown advertises the OPA2211 as a dual-single design. The dies are seperate inside the epoxy. Unlike all other duals, that part uses two seperate dies with seperate power feeds to each die. The other duals are laid out on one die.

BB touts the channel seperation is superior in the 2211 and claims even if one side is driven to clipping, the other die is un-effected. That doesn't happen with the other duals.

Read that in the OPA1612 data sheet. However, as much as I wanted the duals (OPA2211A/OPA1612) to sound as good as the singles (OPA211/OPA1611), they didn't. Using two singles gave better channel separation and sounded a bit clearer and somehow more "direct". It sucks because it is easier and cheaper to use duals.

[Jim Williams]

Maybe it's a dynamic response difference due to the shared power rail pins. A pair very large el caps there should fix that.

Sonically I'm a bit dissapointed in the BB 16xx series opamps. They just don't sound quite open enough for me, I feel like something is missing that I hear with other devices. Better than the AD8599/8597 but I still think the LME's sound more true for those audio classes of opamps. The best one's I use are not audio designed parts but are wideband stuff.

Jim Williams
Audio Upgrades

[Sean Sullivan]

So, I finally have some extra money and I was going to go forward and order some parts for my DBX 160XT's

However, I don't think C14 is the coupling capacitor, as it is a .1uF electrolytic.

C45 is a .047uF "green chicklet" film capacitor...honestly, I'm not really sure where to look! There isn't any cap rated a 4.7uF.

[Sean Sullivan]

Figured it out, it's actually C16.