Wayne's BA 2018 linestage

6L6

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Joined 2010
Paid Member
All kits currently spoken for.


There may be some spare PCB remaining, once everything is packed, if there are I will happily distribute them to interested people. Don't contact me about that yet, I'll send out a call at the appropriate time.
 

6L6

Moderator
Joined 2010
Paid Member
omsoc-

I realize I didn't answer your question as well as I could; There will be a version of this circuit/PCB in the store in the future. There will almost assuredly not be another run of these little pink boards if for no other reason than there's no mounting holes on them... :)

This will be a project supported in the store and on the site, it's a great circuit and this is just the very beginning of what will come.
 
Hello,


i have a problem with the preamp.


After soldering i checked some voltages and found no voltag drop on R12 (Drop = 0V). The voltage drop on R7/13 is 1,45V, that should be okay. On R15 it is 39V, representing the 0,36mA figure, so this should be fine, too (rails are at +/-21,5V). At the moment the feedback resistor (R16) is not in the circuit, because i adjusted P1. Voltage drop on R6 and R14 are both 1,5V.


With the feedback resistor (R16) installed i found a voltage drop on R11 = 1,2mV, R12 still 0V. But something else changed: the drop on R2 became 26mV, befor it was 15mV, same value as on R1.



After that i checked the base voltages on the transistors: Q7/8/14 in the range of +20V, Q11/9 at -20V; but Q10 at about +16,6V. I expected it to be -20V or so. Can someone give me an hint? Thank you!


Best regards,
Michael
 
Hello,
first of all i want to thank you for your input! After changing Q10 the circuit works as expected. I can now measure an voltage drop over R11/12 of 0,33V, over the diode its 1,85V. Q10 and Q8 are getting quite hot, so i will lower the rails a little.
Best regards,
Michael
 
I'm using my Whammy PSU for the tests of the preamp. It's quite the same as the original design, except i built it as an variable supply and changed one or two capacitor values. Added two pictures...
 

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No, I did not matching. Neither transistors, nor resistors. I wanted to build the circuit as fast as possible to have a basis to experiment with an balanced solution... By the way: I measured a gain of 12db. Can somebody confirm? Because Mr. Colburn says in the BAF video, gain should be 15db.