Symetrix 551E and 552E MODS.

The Symetrix 551E and 552E are very well built EQ's and sound good stock. Some improvements can be made. Better psu filtering. Better input and output IC's. Eq shift on the high band so you can get some "air". The other capacitors do not need to be changed unless you like the sound or prefer polypo caps or styrene caps (Not much difference, IMO)
PSU MoD: - Add heatsinks to the regulators.
- Replace c3 and c4 (AC inlet board) with 1500uf caps (MAL215031152E3)
- Bypass c1, c3, c56, and c57 with .1u film caps (near the 15v regulators on main board)

IC MoD: - Replace SMT chips U1 (input) and U7 (output) with better ic's (OPA2132, opa2134, OPA2107, LT1358, or LME49860NA (My fav))
(optional) - Replace all 16 ic's with a better dual op amp. While the standard IC mod only effects the sound of the input and output, This optional mod effects the sound of each band as well as the input and output. It turns this EQ into a decent piece of equipment.
Note: Use a soldering iron designed for surface mount parts. If you use a standard soldering iron be careful to not burn off the pads or your screwed.

Capacitor "AIR" MoD: - Band 5
- Replace c48 (680pf) with a 620pf Polypro cap and Replace c51 (2200pf) with a 2000pf polypro or styrene cap to shift freq up to around 25khz max
- Remove c48 (SMT PARTS, Be careful. You can solder to the underside of the board) like this:

Capacitor Extended MoD:Bands 1-5
- Replace c7 and c8 with a .47u polypro
- Replace c24, 30, 36, 42, 48 with 680pf polypro or styrene caps (Remove old SMT caps first, Be careful. You can solder to the underside of the board on the switch) like this:
- Replace c25, 31, 37, 43, 49 with 6800pf polypro or styrene caps
- Replace c26, 32, 38, 44, 50 with 68nf polypro caps
- Replace c27, 33, 39, 45, 51 with 2200pf polypro or styrene caps
- Replace c28, 34, 40, 46, 52 with 22nf polypro caps
- Replace c29, 35, 41, 47, 53 with 220nf polypro caps

Here are some images:

Disclaimer: I encourage people to DIY and I'm here in a informative role.


ModDefecation is about making equipment sound better, providing knowledge and support, repairing that awesome piece of gear, and custom builds. Send me you questions or Ideas.