I'm guessing at this point that since further counter clockwise only gets more clicks, and fully clockwise runs to zero - that I've started it up at full bias and gotten lucky that I didn't smoke something. Thinking back I've seen many references to zeroing pots with a meter to be sure which direction they go. Seems impatience has (potentially) gotten the better of me.
So max bias on both channels with offset at zero is .04
So max bias on both channels with offset at zero is .04
Finished this morning and playing music now. The F 4 sounds very good. I like it better than my F5 at least for the kind of music I listen to: Have in front of it BA3 preamp and will try it later with tube preamp.
How much will higher bias change the sound. I have it about .16 volt when hot now, on 28v DC power supply, but do not want to go more until I have a thermometer. But as is I am very pleased.
Thanks everyone for the help and thanks Jim for all the guides you are doing.
How much will higher bias change the sound. I have it about .16 volt when hot now, on 28v DC power supply, but do not want to go more until I have a thermometer. But as is I am very pleased.
Thanks everyone for the help and thanks Jim for all the guides you are doing.
And mine is alive too 
. I let it heat up for a couple hours with the lid on before setting the bias to .2. The sinks get pretty warm, but I could probably keep my hands on them indefinitely. Sounds amazing. Now I need to finish the BA-3 pre, but should probably read the build thread a few more times to avoid asking previously answered questions .
. I let it heat up for a couple hours with the lid on before setting the bias to .2. The sinks get pretty warm, but I could probably keep my hands on them indefinitely. Sounds amazing. Now I need to finish the BA-3 pre, but should probably read the build thread a few more times to avoid asking previously answered questions .
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I have my F4 currently running at 400mV across the .47Ω resistor.
The only thing I can say about higher bias level is the bottom end is stronger.
Not bloated or boomy but more authoritative.
When I convert my F4 to balanced I will drop my bias back to 250mV so I don't overload my power supply.
6L6 has some measurements toward the beginning that shows the bias levels in reference to waveform and distortion.
The only thing I can say about higher bias level is the bottom end is stronger.
Not bloated or boomy but more authoritative.
When I convert my F4 to balanced I will drop my bias back to 250mV so I don't overload my power supply.
6L6 has some measurements toward the beginning that shows the bias levels in reference to waveform and distortion.
usual praxis fro "converting" XLR input(gadget) to RCA (SE) one :
route all 3 from pcb to xlr
if using unbal input via RCA , put shorting plug in 1&3 input holes
that way you're having full functionality for both inputs , if needed
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however - using F4 balanced as SE is sort of waste - it's not working as unbal/bal converter , being fully symmetrical ; while pos branch is working , negative one will be simply muted , with it's output serving only as virtual earth to positive output
in that case , it's much better to use amp as plain stereo or to connect two channels in parallel , if load demands
route all 3 from pcb to xlr
if using unbal input via RCA , put shorting plug in 1&3 input holes
that way you're having full functionality for both inputs , if needed
************************************************************
however - using F4 balanced as SE is sort of waste - it's not working as unbal/bal converter , being fully symmetrical ; while pos branch is working , negative one will be simply muted , with it's output serving only as virtual earth to positive output
in that case , it's much better to use amp as plain stereo or to connect two channels in parallel , if load demands
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put picture that I can see how you wired it , and I'll tell how to do it ; most convenient way is to short needed pins ditto on XLR , with U shaped shorting jumper
XLR is :
pin 1 - GND
pin 2 - positive
pin 3 - negative
so - when you put shortie between pins 2&3 , you'll indeed have mono unbalanced , but more importantly - it'll be mono unbalanced paralleled
XLR is :
pin 1 - GND
pin 2 - positive
pin 3 - negative
so - when you put shortie between pins 2&3 , you'll indeed have mono unbalanced , but more importantly - it'll be mono unbalanced paralleled
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