input transformer for pm-1000

[crashandbash]

Ok,
Please take it easy on me guys. I am aware I know nothing so if this is stupid say it nicely. Anyway. I have read lots about guys using different output transformers on the pm-1000 strips. Has anyone attempted finding a different input transformer for different colors ect. Just wondering. I have googled and used the search function. I did not find anything.

Thanks

[ulysses]

Do you mean as an upgrade? If so, I'd see if the Jensen JT-16 will fit (either the JT-16A or JT-16B, whichever is physically more compatible). If you're looking for an available transformer that sounds like the stock part, well that's another question.

[crashandbash]

Looking to add a little different flavor to a couple of the eight I already have. Haven't found a deffinit answer of the ratio of the input transformer.

[Jim Williams]

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

[ulysses]

I believe (through DIY community discussions) that the stock transformer has a 1:1 or 1:2 ratio, though I haven't measured it and the otherwise very thorough service manual doesn't say. That's why I suggested the JT16, which is widely regarded as about the best mike preamp input transformer available, though of course it's only as good as its suitability for the application. I wouldn't be at all surprised if a higher ratio would be better in the PM1000, but then you'd probably want to screw around quite a bit with the gain control so that the headroom and the labelling on the trim control both remain useful. The PM1000's input trim control is a multi-deck switch that includes some pre-transformer padding, a feedback resistance for the mike preamp, and a preamp bypass. Changing the transformer's ratio will change the gain, probably change the max input level before saturation, reduce the amount of gain needed from the amplifier circuit, and increase the amount of pre-transformer trimming needed for line-level devices. Still, it's probably worth looking into.