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Old 2nd January 2009, 11:58 PM   #1
losacco is offline losacco  United States
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Default Booz preamp

Anyone familiar with the Boozhoundlabs preamp? Looking for some more detail.
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Old 3rd January 2009, 01:14 AM   #2
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The schematic and build details are listed on his site. What sort of info do you seek?

http://boozhoundlabs.com/transformer-output-pre/

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Old 3rd January 2009, 12:40 PM   #3
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So the 15095 ALtec is being used in place of the Edcor?
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Old 3rd January 2009, 12:59 PM   #4
losacco is offline losacco  United States
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Well I think I might try this as my first build, looks simple. What kinda power supply?
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Old 3rd January 2009, 10:33 PM   #5
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Quote:
Originally posted by burnedfingers
So the 15095 ALtec is being used in place of the Edcor?
Yes, according to the author, the Edcor transformer is not shielded and hummed too much. Another recommendation is to use a larger chassis and place the output transformers on the opposite side from the power transformer.

Quote:
Originally posted by losacco
Well I think I might try this as my first build, looks simple. What kinda power supply?
Do a forum search for typical 6SN7 operation points. Here's a couple of threads:

Optimal operating point for 7N7/6SN7
Optimal operating point for 7N7/6SN7?

A 6SN7 direct coupled preamp & regulated supply for everyone's perusal.

12AY7/6SN7 preamp PSU check

If you cannot get the power supply voltage right on for the desired operating point, I recommend you substitute the 100K plate resistor by a CCS, like an IXYS, which will give you more latitude with the B+ and allow you to control the current.

Enjoy,

-- josť k.
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Old 3rd January 2009, 11:48 PM   #6
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Conceptually I am a fan of this sort of preamp, but there are some real issues with the implementation. The coupling cap is too small by almost an order of magnitude. Moreover, the unbypassed Rk increases ra by way too much -- could be why the cap used is doable, but either bypassing Rk, using an LED, or tying the OPT to the cathode rather than ground might be helpful. I also like a CCS on the plate here.
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Old 4th January 2009, 12:13 AM   #7
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Quote:
Originally posted by dsavitsk
Conceptually I am a fan of this sort of preamp, but there are some real issues with the implementation. The coupling cap is too small by almost an order of magnitude. Moreover, the unbypassed Rk increases ra by way too much -- could be why the cap used is doable, but either bypassing Rk, using an LED, or tying the OPT to the cathode rather than ground might be helpful. I also like a CCS on the plate here.
Yes, with the following op points one could easily use a cheap 2V red LED for cathode biasing and a CCS set for 6.5mA:

Ups =230v
Up= 107v
Ip=6.5mA
Ug=-2v
Rpl=18kOm

Additionally, one could use two 6J5 or 2C22 in place of the 6SN7. Even two 76 tubes could replace the 6SN7, albeit, with different sonics.

Time to experiment...

Enjoy,

-- josť k.
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