sweetbeats
Reel deep thoughts...
So my Dad gave me a couple of these...he got them at a garage sale some time back for $5 or $10 apiece.
I was at his place looking through his varied collection of audio stuff and came upon them. He asked if I could use them and I said "I'm sure I can figure something out..." and he said "take 'em!" So I did.
For those of you that don't know, the dbx 119 (also very similar to the 117) is a compander originally designed for the home hifi environment, primarily to expand the dynamic range on compressed pre-recorded performances. Think of the classical music enthusiast back in the day who had a nice listening system, but wanted to experience the original dynamic range which was compressed to maintain the limits of the vinyl pressing. Well now he/she could pipe their playback through the 119, expand the compressed pre-recorded audio and experience a dynamic range closer to the original performance. dbx included the ability to compress as well as expand with the 119, hence "compander".
Anyway, the neat-o thing with the 119 is that it utilizes the very same proprietary VCAs as a well-known highly desirable vintage dbx dynamics processor.
I'm not sure yet how I'm going to use these things, but "I'll figure something out."
One of them is in better shape than the other, and I started doing some digging around to find there are some mods that can be done to "improve" things. I was planning on recapping one of them, and then started thinking of modifying by upgrading the audio driver opamps and some other things.
Fortunately the one in better condition also has better stock opamps. I say this is fortunate because two of the five opamps are "internal" drivers for the VCAs, and you don't want to mess with those unless you can recalibrate the thing. I can't. So its safe to assume that the "better" opamps that I'm not going to replace provide for better processing. The one I'm leaving alone has 741 chips in it. The one I'm modifying has LM301 chips in it. As I said, there are five of them: input audio driver, output audio driver, Threshold LED driver, and the aforementioned VCA process drivers. I'm replacing the two audio drivers with 5534s.
Since the 119 audio circuit runs at unity gain, a compensation cap is required for the 5534 to maintain stability at unity gain. I will also bypass the power rails at each opamp. Also, each opamp uses a 33pF ceramic in its feedback loop and these all look like they're heat-stressed so I'm going to replace those.
Other things I'm gonna do:
Here it is:
The guts:
The proprietary VCAs are in the silver boxes. Very few electrolytic caps...and if I'm reading the schematic correctly there are NO ELECTROLYTIC CAPS IN THE AUDIO PATH.
All the caps are related to the power supply, except for two, and they are for timing of two of the VCAs.
Its a really elegant and simple design with very nice quality components...and those two big knobs on the control surface are nice heavy chunky metal.
Anyway, stay tuned.
I was at his place looking through his varied collection of audio stuff and came upon them. He asked if I could use them and I said "I'm sure I can figure something out..." and he said "take 'em!" So I did.
For those of you that don't know, the dbx 119 (also very similar to the 117) is a compander originally designed for the home hifi environment, primarily to expand the dynamic range on compressed pre-recorded performances. Think of the classical music enthusiast back in the day who had a nice listening system, but wanted to experience the original dynamic range which was compressed to maintain the limits of the vinyl pressing. Well now he/she could pipe their playback through the 119, expand the compressed pre-recorded audio and experience a dynamic range closer to the original performance. dbx included the ability to compress as well as expand with the 119, hence "compander".
Anyway, the neat-o thing with the 119 is that it utilizes the very same proprietary VCAs as a well-known highly desirable vintage dbx dynamics processor.
I'm not sure yet how I'm going to use these things, but "I'll figure something out."
One of them is in better shape than the other, and I started doing some digging around to find there are some mods that can be done to "improve" things. I was planning on recapping one of them, and then started thinking of modifying by upgrading the audio driver opamps and some other things.
Fortunately the one in better condition also has better stock opamps. I say this is fortunate because two of the five opamps are "internal" drivers for the VCAs, and you don't want to mess with those unless you can recalibrate the thing. I can't. So its safe to assume that the "better" opamps that I'm not going to replace provide for better processing. The one I'm leaving alone has 741 chips in it. The one I'm modifying has LM301 chips in it. As I said, there are five of them: input audio driver, output audio driver, Threshold LED driver, and the aforementioned VCA process drivers. I'm replacing the two audio drivers with 5534s.
Since the 119 audio circuit runs at unity gain, a compensation cap is required for the 5534 to maintain stability at unity gain. I will also bypass the power rails at each opamp. Also, each opamp uses a 33pF ceramic in its feedback loop and these all look like they're heat-stressed so I'm going to replace those.
Other things I'm gonna do:
- Recap with good quality Nichicon 105C parts with an increase in filter capacitance
- Add HF bypass caps to the filter caps
- Replace the discrete rectifier diodes which look DINKY on this thing...I'm putting in IN4007 parts...overkill...but its what I have here...
- Cosmetic detailing including sanding and refinishing the REAL WOOD side panels
Here it is:
The guts:
The proprietary VCAs are in the silver boxes. Very few electrolytic caps...and if I'm reading the schematic correctly there are NO ELECTROLYTIC CAPS IN THE AUDIO PATH.
All the caps are related to the power supply, except for two, and they are for timing of two of the VCAs.
Its a really elegant and simple design with very nice quality components...and those two big knobs on the control surface are nice heavy chunky metal.
Anyway, stay tuned.
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