ToastedMaple
New Member
Good Day Fellow AK Members
Recently, Leestereo completed restoration of my Marantz 2270. Success of this project prompted me to revive a project to restore the Equalizer for my beloved 901 Series II. I have three, sets of 901's. Pity me if you must. The active set have the Walnut Facing kit for Series I/II. I'm restoring another set for my daughter.
For context on the restoration, consider the Bose 901 Active Equalizer as a supplement to your existing tone controls. Without any cross-over for the 9 drivers in each channel, it is an essential component of the 901 sound. Now, after 40+ years, the EQ electrolytics are most certainly suspect, but also the many carbon resistors that shape the tone curve will likely have drifted and affected the equalization curve.
With Leestereo’s analysis in hand, I repopulated the board with higher-value electrolytics, film caps and 1% resistors. Some electrolytics were replaced with bipolar film capacitors for better quality audio. New transistors (there are 5 per channel) were selected for low noise and matched for hFE. Phono jacks were upgraded and respected for modern connectors. Tape lop was left intact. The complete parts list is attached with Mouser PN, analysis and recommendations, again, courtesy of Leestereo's deep experience in vintage restoration.
Most of us won’t need the full range of +18dB boost but I have tinnitus and a bit is most welcome. Bass is superb, tight and detailed and getting better, possibly as the caps (in both my 2270 and the EQ) bed in.
This was my first electronics restoration project. It was daunting to depopulate and re-install nearly 100 components. I am very grateful to Leestereo for his advice, enormous patience with a newbie, and support. I learned a lot about restoration and trouble-shooting as well (after I installed the &^*% transistors backwards!).
This board was not unmolested, prior restoration work, and that posed some additional challenges. Pictures attached of original board, intermediate and semi-final project, as well as parts list, noted above.
Please feel free to pose any questions.
Best Regards, DGC
Recently, Leestereo completed restoration of my Marantz 2270. Success of this project prompted me to revive a project to restore the Equalizer for my beloved 901 Series II. I have three, sets of 901's. Pity me if you must. The active set have the Walnut Facing kit for Series I/II. I'm restoring another set for my daughter.
For context on the restoration, consider the Bose 901 Active Equalizer as a supplement to your existing tone controls. Without any cross-over for the 9 drivers in each channel, it is an essential component of the 901 sound. Now, after 40+ years, the EQ electrolytics are most certainly suspect, but also the many carbon resistors that shape the tone curve will likely have drifted and affected the equalization curve.
With Leestereo’s analysis in hand, I repopulated the board with higher-value electrolytics, film caps and 1% resistors. Some electrolytics were replaced with bipolar film capacitors for better quality audio. New transistors (there are 5 per channel) were selected for low noise and matched for hFE. Phono jacks were upgraded and respected for modern connectors. Tape lop was left intact. The complete parts list is attached with Mouser PN, analysis and recommendations, again, courtesy of Leestereo's deep experience in vintage restoration.
Most of us won’t need the full range of +18dB boost but I have tinnitus and a bit is most welcome. Bass is superb, tight and detailed and getting better, possibly as the caps (in both my 2270 and the EQ) bed in.
This was my first electronics restoration project. It was daunting to depopulate and re-install nearly 100 components. I am very grateful to Leestereo for his advice, enormous patience with a newbie, and support. I learned a lot about restoration and trouble-shooting as well (after I installed the &^*% transistors backwards!).
This board was not unmolested, prior restoration work, and that posed some additional challenges. Pictures attached of original board, intermediate and semi-final project, as well as parts list, noted above.
Please feel free to pose any questions.
Best Regards, DGC
