Marantz 3600 Pre Amplifier
Today were showcasing the Marantz 3600 Pre-Amplifier that came in for a restoration. The 3600 has long been considered one of Marantz’s finest solid state pre-amp pairings using original quality films and a simply straight forward gain stage pre-amp.
Power Supply & Time Delay Circuit
The 3600 is unique I think in the fact it utilizes a RC4194 9 pin device as a early voltage regulator IC determining its -/+ 18V supply and a 470MFD filtering stage. The RC4194 is a unique dual tracking voltage regulator IC with an adjustable output of up to 42V+/- at 200mA within .04% for balance/unbalanced rail voltages.
The large axial 470MFD capacitors were replaced with high quality long life Vishay 470MFD axial capacitors. Often times, as is reflecting int his restoration I will opt for radial construction with appropriate lead dressing versus an axial package. Many older axial electrolytic are inferior to their radial constructed counterparts and I think this still holds some sway on electrolytic axial of today to a degree. The remaining axial were replaced with radial electrolytic with each leg dressed in shielding. low impedance long life Nichicon PW’s replaced the 100MFD elecotrlytics. The rectification network was upgraded to modern Ultra-Fast (UF) type UF400# series diodes and new X1Y2 Vishay Safety capacitors installed. The Time Delay circuit electrolytic were upgraded to low impedance long life PW’s capacitors along with the 1/2W 1K resistors to a KOA 1/2W resistor. The original 2N4250 small signal transistors were upgraded to modern low noise TO-92/L Fairchild devices.
The AF Main stage works through a series of tiered IC’s. First is the UA749 Fairchild IC which is a single package dual inline high gain amplifier consisting of a 3-stage Class A PNP output. Further down we encounter two 8DIP single inline OPAMPs the LM301 which features a low current drain/overload protection tied to a 30pf buffer.
The axial in this stage were again mounted below the chassis using appropriate leg shielding using Nichicon FG Fine Gold audio capacitors. The .22MFD films were upgraded to a high quality polypropylene MKP film capacitors mounted below as well. Remaining electrolytic’s were replaced with audio grade KT Nichicons and all films replaced with high grade polypropylene map .1-.01 film capacitors.
The Front Control Tone Control uses X4 10MFD axials which were replaced with 10MFD (FG) Fine Gold Nichicon radials with proper shielding
The RIAA EQ stage employs a simple PNP differential stage gain amplifier. The electrolytic’s were replaced with a audio grade KT Nichicon’s and high grade polypropylene 1MFD MKP film capacitors. As above the 2N4250 were upgraded to modern low noise TO-92/L Fairchild devices.