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SFL-2 Bias Question...Helllp

I recently bought replacement tubes and I need to optimize or bias my SFL-2 preamp, which should be performed with new tubes.

My question for all you SFL-2 owners is this; Have you performed this procedure yourself and was it difficult? Which TEST cd did you use, (test cd which contains "1kHz mono test tone" recorded at a level of 0db required).

I contacted Sonic Frontiers and they of course suggested to me that I should ship them the unit to perform this procedure. I'd like to attempt it myself.

I'm a novice at this sort of thing...should I go for it?

Any comments or advice appreciated.
equinox

Showing 1 response by kana813

kana813
956 posts
 
As Newbee points out, if you are using RCA connection the trimpot position doesn't matter, but for XLR the easiest way is as follows:

1. Disconnect cable from preamp to power amp.

2. With the preamp warmed up for 20 minutes, play a 1 kHz sine wave from a test CD or signal generator.

3. Use a voltmeter set to AC, and measure voltage from pin 1 to pin 2 on left channel XLR output.

4. Adjust volume on preamp so voltage output is approximately 1V.

5. Measure voltage from pin 1 to pin 3.

6. Adjust left phase balance pot until pin 1-2 voltage equals pin 1-3 voltage - check 1-2 after adjusting 1-3 and adjust again as necessary.

7. Repeat for right channel.

This procedure also applies to the SF Line series preamp.

The bias tool that comes with SF Power series amps
is perfect for adjusting the pots, otherwise you'll need a long shank small blade screwdriver.
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