Picked up a DBX166 (blackface) from the junk corner cos it comes in a really nice case. As usual with gear for gutting, I first checked power and turns out unit still fully worked -- a bit anaemic or blunt sounding though. So I took a closer look and...
...out of curiosity decided to try the 'PEAKSTOP limiter modification' as described by jef111 in this thread:
https://groupdiy.com/threads/dbx-166xl-schemo.34107/
[Added]This modification turns the Peakstop from a hard limiter/clipper into a soft limiter/clipper.[/added]
It works great. Same circuit. No more distortion from the limiter but still 6dB of limiting available -- plenty for most needs. Unlike the 166XL model, the DBX166 Blackface is still thru-hole. But available schematics are a real pain with component identifier numbers and values all blotted. So the board needed some tracing. Here are the two diodes:
And next is an image for easier spotting of the two diodes on the board and where/how to add the 1K resistor for the peakstop modification. On the PCB it's the only place where two diodes sit side by side. Two leads lifted up and forming junction with the 1K resistor.
Verdict:
Overall usable now and easy enough to implement.
_________
Other things:
The DBX166 Blackface over here came with DBX1252 and DBX1253 chips. I kept them all. No changes cos the four RMS detectors (2xComp and 2xGate) have Rf input bias compensation resistors installed as per datasheet, and cos the 1252 VCAs sound good enough there for a little helper in tracking.
All RMS chips are fed thru HP filters at around 17Hz/18Hz. I kept it that way. Wouldn't want sub dirt to trigger. Actually I even thought about upping the filters to 30Hz or higher, but ultimately left as is. Easy to change later though -- as the case is really nice with slide-open top and bottom.
As for the direct audio path, I matched all and changed a few components (frequency response & CMRR); also LF353 there had to go. As for the VCAs, all resistors in periphery now matched. As for the sidechains, no changes. Unit has stereo link.
Power bypass caps on this unit struck me as unusually low: 10n and 1uf. Careful though, as one of the 1uf is part of the RMS input filter. I kept the 1uf but beefed up all PSU caps.
PSU caps were hot-glued onto the board
. Used a hotgun to preheat them and with it the glue for desoldering.
Some of the ceramic discs came apart (lost a lead) on the slightest touch when desoldering. Changed to C0G.
...And now back to work...
...out of curiosity decided to try the 'PEAKSTOP limiter modification' as described by jef111 in this thread:
https://groupdiy.com/threads/dbx-166xl-schemo.34107/
[Added]This modification turns the Peakstop from a hard limiter/clipper into a soft limiter/clipper.[/added]
It works great. Same circuit. No more distortion from the limiter but still 6dB of limiting available -- plenty for most needs. Unlike the 166XL model, the DBX166 Blackface is still thru-hole. But available schematics are a real pain with component identifier numbers and values all blotted. So the board needed some tracing. Here are the two diodes:
And next is an image for easier spotting of the two diodes on the board and where/how to add the 1K resistor for the peakstop modification. On the PCB it's the only place where two diodes sit side by side. Two leads lifted up and forming junction with the 1K resistor.
Verdict:
Overall usable now and easy enough to implement.
_________
Other things:
The DBX166 Blackface over here came with DBX1252 and DBX1253 chips. I kept them all. No changes cos the four RMS detectors (2xComp and 2xGate) have Rf input bias compensation resistors installed as per datasheet, and cos the 1252 VCAs sound good enough there for a little helper in tracking.
All RMS chips are fed thru HP filters at around 17Hz/18Hz. I kept it that way. Wouldn't want sub dirt to trigger. Actually I even thought about upping the filters to 30Hz or higher, but ultimately left as is. Easy to change later though -- as the case is really nice with slide-open top and bottom.
As for the direct audio path, I matched all and changed a few components (frequency response & CMRR); also LF353 there had to go. As for the VCAs, all resistors in periphery now matched. As for the sidechains, no changes. Unit has stereo link.
Power bypass caps on this unit struck me as unusually low: 10n and 1uf. Careful though, as one of the 1uf is part of the RMS input filter. I kept the 1uf but beefed up all PSU caps.
PSU caps were hot-glued onto the board
. Used a hotgun to preheat them and with it the glue for desoldering.Some of the ceramic discs came apart (lost a lead) on the slightest touch when desoldering. Changed to C0G.
...And now back to work...
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