Bottlehead Forum

Bottlehead Kits => BeePre => Topic started by: dave-tx on December 24, 2013, 07:28:03 AM

Title: Line out mod?
Post by: dave-tx on December 24, 2013, 07:28:03 AM

I was thinking of replacing the balanced outputs with a line-out for recording purposes.  Would there be anything wrong with routing the output of the selector switch (S2B) back up to the I/O area using shielded twisted-pair (one pair per channel)?

Other than a volume/balance issue that I'm debugging (very similar to that in a couple of threads from April 2013), this thing sounds amazing...As in, completely captivating.  And it looks stunning as well.  Next step is the BeeQuiet.

Happy Holidays,
David

Title: Re: Line out mod?
Post by: Grainger49 on December 24, 2013, 10:45:41 AM

A record out is best when isolated by a cathode follower or any other buffer stage.  The impedances of the recording device when on and off are often very different.  This can affect the input to the 300B in the BeePree.

I would advise against it.

Title: Re: Line out mod?
Post by: dave-tx on December 26, 2013, 07:59:38 AM

Thanks, Grainger...I might try play around with a jfet source follower of some sort, but nothing that couldn't be removed in case it behaved poorly.

From the schematics I've browsed online, it appears that most pre-amps stick a buffer in the signal path before the amp stages, is that the reason they can get away with a simply a resistor between the inputs and the line out?  Avoiding that buffer was one of the main design goals in the BeePre, if I recall correctly.

Title: Re: Line out mod?
Post by: Paul Birkeland on December 26, 2013, 07:15:08 PM

If you have the BeeQuiet, you can setup the BeePre pretty easily to be a unity gain buffer without performing any modifications.

Title: Re: Line out mod?
Post by: dave-tx on December 29, 2013, 12:54:05 PM

Quote from: Caucasian Blackplate on December 26, 2013, 07:15:08 PM

If you have the BeeQuiet, you can setup the BeePre pretty easily to be a unity gain buffer without performing any modifications.

I'm assuming by this you mean with both fine and coarse set to 0dB?  Or does the BeeQuiet provide enough resistance that it would be okay to tap an output off S2B?

Thanks,
David

Title: Re: Line out mod?
Post by: Paul Birkeland on December 29, 2013, 01:02:12 PM

The BeeQuiet has roughly 4dB of pre-attenuation.  If you go down to -4.5dB on the fine attenuator, and -0dB on the coarse, you'll have roughly a unity gain buffer.