dbx rms 208 module for 160VU

[jrmintz]

Hi all,

I'm looking for one of these modules for a friend. Anyone know where they can be obtained?

Thanks

:thumb: :thumb:

 

[SSLtech]

I understand that they can be rebuilt, but they're as rare as hen's lips to purchase. Run a search from (I think) Joe Malone, who once commented on repairing them.

keith

 

[jrmintz]

Thanks, Keith

:thumb:

 

[JLM Audio]

If it is the 208 that has failed hopefully this will help

Cut the clear sealer around the edge of the module with a sharp blade. Unsolder the pins and remove the module. Turn it over and there should be a small PCB held in under the can by 2 blobs of hot melt glue and one wire soldered to the tin can.

Like so

Remove the hot melt and desolder the wire and you should now have the PCB in your hands that has a couple of standard LM301AN ICs and a CA3083 transistor pack DIP on it. Have only ever seen the LM301AN & CA3083 fail. BC453C has always been ok. Do not forget to put the grey cardboard back in the tin can before placing the PCB back into it or the bottom of the PCB will short out on the tin can.

 

[jrmintz]

Thanks very much Joe, that's great!

:thumb: :sam: :thumb: :sam:

 

[SSLtech]

Joe da man! :razz:

 

[q2audio]

I have a 160 "VU" on my bench right now with an aggravating problem.

The original problem was the threshold, ratio and output gain controls all causing major deflection of the VU meter with no input signal. I happen to have a parts unit so I pulled the RMS converter and that solved most of the problem (this swap required trimming R65 with R66). But, I still have an annoyance that I can't figure out. When the output gain is turned to +20, the VU meter deflects up to -40 from it's normal position (fully to the left). This is with no input signal applied - input terminated or unterminated makes no difference. With the output gain at +20 the output is at -60dB relative to "0"on the meter, so I think the problem is in the metering circuit. I have swapped nearly every IC, checked the value of the related resistors, swapped the VCA and the VU meter.

So far I've spent about 8 hours probing this thing and this isn't fun anymore!

Does anyone have any insights??

I tried to repair the RMS detector, replaced both the LM301's and CA3083. Still causes crazy deflection of the meter with any knob turned. I didn't replace the transistor or any of the caps/resistors. Ain't nothin' ever easy??? I need to replace the transistor next. I'm getting tired of desoldering and removing this thing from it's can.

 

[thermionic]

The 208 I had was potted solid - no chance of removing the compound. It was also from a compressor made in 1971, and I believe it was fully discrete (the various reverse-engineered schematics I was given were all discrete - I didn't trust them because, on each occasion, the person who gave me the drawing asked me to contact them once I'd built it...).

I bought a new 208 from these people:

Taken from DBX site:

Many people still own the older dbx Consumer products. If you need service for these items, call:

Musician's Service Center • 379 Meridian Ave, San Jose, CA 95126

Ph :408-297-7532 • Fax:408-286-4861 • website: www.musicianservice.com • email: [email protected]

They'll sell you one, but don't expect it to be cheap... I can't see it being difficult to fashion a newer type of circuit, I guess it comes down to how bothered you are about authenticity.

The 208 I bought performs perfectly btw, and the various test pins in the compressor tally between the pair, i.e. the unit with old 208 and new 208.

I reckon their 208 is authentic, but it cost me $150 USD IIRC...


Justin

 

[matthias]

the rms 208 is also used in the dbx 117 and dbx119
that could be a much cheaper source, than a spare part.

I have a pic of the dbx 160 and there's a rms 209 used instead of the 208.

does anyone have some more information about all that?

thanks,
mat

 

[q2audio]

Does anyone have a schemo of either the 208 or 209? Thanks.

 

[thermionic]

Matthias just reminded me that I posted the schematics at another group here: http://gearslutz.com/board/showthread.php?t=38317

I didn't try the schematic as I needed to sell the compressor ASAP, so I fitted a factory unit (it was a fairly valuable comp, so I wanted it to look original).

If I get some time, I might try it, failing that, anyone here want a try?


Justin

 

[q2audio]

I will check that schematic against my module if I can find the time in the next few weeks.

I have tried to fix this module (replaced all IC's and the transistor), but it still has the same problem: VU meter is pegged to the right with no input signal. I have not tested it further. I assume there is an incorrect DC level coming out of the RMS detector. When time permits, I'll post what I find.

 

[pucho812]

the 208 is the RMS detection circuit correct :?

 

[tomelectro]

I had a unit where a bad cap was pulling down the +15v power rail to +14.75v, which hardly seemed significant, but it turned out that it was enough to completely throw off the RMS detector (the spec called for 15v +/- .1v). Fwiw, I've seen a lot of little problems in these things go away with a re-cap.

 

[q2audio]

I did a complete recap. I will check the supply voltage, thanks for the tip. I would not think that 0.25V would cause a problem either. These things are incredibly touchy!

 

[Jim Zuehsow]

[quote author="matthias"]the rms 208 is also used in the dbx 117 and dbx119
that could be a much cheaper source, than a spare part.

thanks,
mat[/quote]

Don't forget all those dbx 157 noise reduction units you can buy on ebay for 15-20 bucks. They have a pair of rms detectors and 202 style vca modules.

Jim

 

[matthias]

can you remember any of the numbers on the metal cans..??
soemthing like 208 209 77 or 75

 

[q2audio]

I found a fix for the problem I was having. The problem was this: with no signal applied, meter in "output" mode, the meter would move when the "output gain" knob was turned toward "+20". This ended up being R36 which is a "trim" resistor for the RMS module. After 'trimming' per the set up instructions, problem solved.

Now, onto a new problem (same unit!): audio applied, when in the 1:1 ratio and threshold is rotated CCW, the unit EXPANDS! (the audio expands, not the actual unit)... my head hurts...

 

[matthias]

have you recalibrated the whole unit after you changed r36 ?

in my unit r36 is 6k8 in the other unit 100k

 

[q2audio]

Yes, I recalibrated the entire unit.

I just discovered today that dbxpro.com has schematics and set-up info for a lot of their old products.