Gearslutz.com - View Single Post - input transformer for pm-1000

Jim Williams · 16th April 2007

First, measure the step up gain of the transformer. Apply a -40 db signal and measure the signal on the secondary side of the transformer. If it's a 20 db gain, use a Jensen JK-115KE, if it's 10~13 db gain, use the JT-13KC. Skip the JT-16, that's a low turns ratio transformer designed for very low noise front ends, which the Yamaha is not. Then replace that .47 uf tantalum cap that follows the transformer with a 10 uf Panasonic FM with a Wima MKP-2 .01 uf 630 v bypass. Also you will need to adjust the resistor loading on the 2SC1000 transistor. Use 150k ohms for the JT-115, use the network supplied with the JT-13 or the secondary will not be tuned correctly.

Jim Williams
Audio Upgrades

16th April 2007	#4
Jim Williams Voiding warranties Joined: Feb 2004 Location: beautiful Carlsbad, CA Posts: 10,039	First, measure the step up gain of the transformer. Apply a -40 db signal and measure the signal on the secondary side of the transformer. If it's a 20 db gain, use a Jensen JK-115KE, if it's 10~13 db gain, use the JT-13KC. Skip the JT-16, that's a low turns ratio transformer designed for very low noise front ends, which the Yamaha is not. Then replace that .47 uf tantalum cap that follows the transformer with a 10 uf Panasonic FM with a Wima MKP-2 .01 uf 630 v bypass. Also you will need to adjust the resistor loading on the 2SC1000 transistor. Use 150k ohms for the JT-115, use the network supplied with the JT-13 or the secondary will not be tuned correctly. Jim Williams Audio Upgrades