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I bought this Symetric SE400 Dual Parametric EQ back in 2003 (on ebay for $102) when the core of my band reformed for a few years to take another crack at putting some tunes together and doing an album, this time produced by ourselves. I had been working at BGW Systems when they went bankrupt, worked for a spell at Marshall Electronics in their Microphone Division in El Segundo, later worked at Westlake Recording Studios running their repair shop, and later still landing the gig at CenterStaging, LLC in Burbank where I still hang my hat.
The living room at my apartment in
Gardena, CA got turned into a music room, and I bought a Yamaha 02R Digital console, it having four ADAT Digital I/O cards, which eventually got routed thru Motu 324 interface into my DAW for recording. I made use of this equalizer in my bass channel for a while.
I had done some clean-up work on the EQ when I was using it with a GK 1001RB bass amp at my church, and now using it with my restored Ampeg SVT4-Pro. This past week, I pulled the unit apart, having bought replacement caps for all the cards inside. While taking photos of the boards for my records, I found a few date codes. Latest one was on the side of the Gain pot of the I/O board, being 9230 (1992, 30th week). Date code on the NE5534A was 8130 (1981, 30th week), and on the frame of the power xfmr 8838 (1988 38th week). I’m guessing this was built in maybe 1993. The date on the schematic of the Symetrix 528 Mic Preamp Channel Strip was July 7, 1993.
I’ve never found any schematics for this SE400, and from what I’ve read on the internet, nor has anyone else. Symetrix offered no help, it being long out of production. When I had the unit apart this past January, armed with the schematic of the 528, I found the parametric EQ circuit very similar to it, though with one less op amp stage in the EQ bands. This past week I finished creating the schematic for the I/O module, then loaded my copy of Protel DXP onto the laptop at work, having it on my DAW at home. So, for the past couple days, I’ve drawn up the schematic for the SE400 Dual Parametric Equalizer, just for fun, and have attached those two pages here.
Symetrix SE-400 Parametric EQ Ch 1.pdf
Symetrix SE-400 Parametric EQ Ch 2.pdf
This past weekend, I took photos of the modules prior to re-capping the modules, and made use of the I/O foil pattern to aid in creating that schematic. As the electrolytic caps in this unit appear to be nearly 30 yrs old, and had polarized caps in the signal path, I replaced those with Nichicon MUSE Nonpolar parts. I forgot to order 1000uF/35V axial buss caps for the power supply board, and now after seeing DC voltages on the buss caps, I’d say replacing those will make more sense. The power xfmr secondary is 37.4VAC CT, and rectifying those 18.7VAC lines and charging them up, finding +23.1VDC and -22.5VDC on the buss caps, those seem low. I don’t recall hearing hum in the unit, but fresh caps should yield higher equal levels.
I did replace the green ‘chicklet’ mylar caps while I was at it, using metalized polypropylene parts from Wima and Kemet. I’ll later have a look at those parts on the network analyzer.
When I did maintenance on this unit, along with my Symetrix 501 Compressor/Limiter as well as the CL-100 Compressor, I had lifted the audio circuit off of the chassis, floating them, with bypass ceramic caps (0.1uF/500V) to chassis, so the chassis’ were at AC Ground for the RF shield, and got rid of the HF buzz I was getting with the GK 1001RB patched into their loop. Some of that buzz was also from the nearby cheap light dimmer switch on the wall adjacent to the bass rig on stage.
Patched into the Ampeg SVT4-Pro, it’s dead quiet.
The living room at my apartment in
Gardena, CA got turned into a music room, and I bought a Yamaha 02R Digital console, it having four ADAT Digital I/O cards, which eventually got routed thru Motu 324 interface into my DAW for recording. I made use of this equalizer in my bass channel for a while.
I had done some clean-up work on the EQ when I was using it with a GK 1001RB bass amp at my church, and now using it with my restored Ampeg SVT4-Pro. This past week, I pulled the unit apart, having bought replacement caps for all the cards inside. While taking photos of the boards for my records, I found a few date codes. Latest one was on the side of the Gain pot of the I/O board, being 9230 (1992, 30th week). Date code on the NE5534A was 8130 (1981, 30th week), and on the frame of the power xfmr 8838 (1988 38th week). I’m guessing this was built in maybe 1993. The date on the schematic of the Symetrix 528 Mic Preamp Channel Strip was July 7, 1993.
I’ve never found any schematics for this SE400, and from what I’ve read on the internet, nor has anyone else. Symetrix offered no help, it being long out of production. When I had the unit apart this past January, armed with the schematic of the 528, I found the parametric EQ circuit very similar to it, though with one less op amp stage in the EQ bands. This past week I finished creating the schematic for the I/O module, then loaded my copy of Protel DXP onto the laptop at work, having it on my DAW at home. So, for the past couple days, I’ve drawn up the schematic for the SE400 Dual Parametric Equalizer, just for fun, and have attached those two pages here.
Symetrix SE-400 Parametric EQ Ch 1.pdf
Symetrix SE-400 Parametric EQ Ch 2.pdf
This past weekend, I took photos of the modules prior to re-capping the modules, and made use of the I/O foil pattern to aid in creating that schematic. As the electrolytic caps in this unit appear to be nearly 30 yrs old, and had polarized caps in the signal path, I replaced those with Nichicon MUSE Nonpolar parts. I forgot to order 1000uF/35V axial buss caps for the power supply board, and now after seeing DC voltages on the buss caps, I’d say replacing those will make more sense. The power xfmr secondary is 37.4VAC CT, and rectifying those 18.7VAC lines and charging them up, finding +23.1VDC and -22.5VDC on the buss caps, those seem low. I don’t recall hearing hum in the unit, but fresh caps should yield higher equal levels.
I did replace the green ‘chicklet’ mylar caps while I was at it, using metalized polypropylene parts from Wima and Kemet. I’ll later have a look at those parts on the network analyzer.
When I did maintenance on this unit, along with my Symetrix 501 Compressor/Limiter as well as the CL-100 Compressor, I had lifted the audio circuit off of the chassis, floating them, with bypass ceramic caps (0.1uF/500V) to chassis, so the chassis’ were at AC Ground for the RF shield, and got rid of the HF buzz I was getting with the GK 1001RB patched into their loop. Some of that buzz was also from the nearby cheap light dimmer switch on the wall adjacent to the bass rig on stage.
Patched into the Ampeg SVT4-Pro, it’s dead quiet.
Attached Files
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