History* I purchased this Spectral DMC-10 preamplifier, serial number 10491, new in 1983 from Straight Gain Electronics, Toronto ON. I was very impressed with this preamplifier's sound quality; it performed extremely well with my Oracle Premier turntable originally fitted with a Kiseki Blue MC phono cartridge.
Figure 1. Spectral model DMC-10 Preamplifier - photo taken after repairs completed.* I enjoyed listening to my audio equipment throughout 18 years of worldwide assignments in Canada, Japan, UAE and UK. Although it was in full working condition, sadly I had to put my audio equipment into storage in 2001 due to shortage of living space.
* In 2022 I brought my preamplifier out of storage and powered it up for the first time in 20 years. Although it was basically working and usable, there was something wrong with it.
Failure Issue* Initially I noticed an increase in hum noise, later followed by the protection monitor LED illuminating Red. At this stage the preamplifier's power supply had become hot and the unit inoperative.
* The heavy current load on the power supply was finally traced to two of the bypass capacitors leaking. Although the leaking capacitor's electrolyte had spilled onto the printed circuit board, fortunately the damage was mostly on surface, and I was able to fully clean the affected area.
* As a precaution considering the age of this unit, I felt it best to replace all electrolytic capacitors with new.
Summary of Electrolytic Capacitors replacement
Table 1. Capacitor replacement summary.Internal view of replaced components
Figure 2. New bypass capacitors (left side), new power supply capacitors (right side).
Figure 3. New power supply capacitors (center),
protection circuit axial capacitors replaced by radials (right side).Parts replaced
Figure 4. Original components replaced.* Left bin: Power Supply capacitors qty 16.
* Center bin: Bypass capacitors qty 24 (two of these were leaking).
* Right bin: Protection circuit; Bipolar axial capacitors qty 2, axial capacitor qty 1.
Final notes* The reason for this writing is to share my experience repairing a Spectral DMC-10 preamplifier. It's not an endorsement of any component supplier, just to share what worked for me.
* Other than replacing all electrolytic capacitors and adjusting the internal trim-pots for DC offset, output bias current, and gain balance as per the DMC-10 Operation and Maintenance Manual, I did not make any modifications or changes to the circuitry. With the excellent specifications of this unit (Fig. 5), I did not see the need for any changes.
* At time of this writing all repairs have been operating without issue, now enjoying listening to my repaired DMC-10 preamplifier with my rebuilt Oracle Premier turntable fitted with new Phasemation PP-2000 MC cartridge - this setup looks like new and sounds better than ever!
Appendix
Figure 5. Spectral DMC-10 Specifications - from brochure scan.
