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Just built this the other day. When biasing I was unable to get Q3 below 6.4v. The recommendation in the build guide was to shoot for 5v. It sounds fine to me but I don’t know what it would sound like at 5v to compare. I was able to get Q1 and Q2 right at 5v.
I have a couple dozen 2N5457’s (bought from legitimate sources…here and SB). I also have a DCA55. Is there a way I could test what I have against the one I used to try to select one that will bias correctly? My knowledge of the DCA55 only extends as far as testing Ge transistors for gain and leakage…and double checking pinouts.
I would prefer to not attempt to desolder the trimpot or add a resistor in series somehow…or randomly plug in the other 2N5457’s trying to get it in the 5v range.
Any suggestions would be appreciated.
It’s not absolutely crucial to bias at 5v all FETs vary wildly even from the same batch
You can experiment with Q1 and 2 and bias them slightly higher than Q3 to around 6.5v to 6.7v to see if that makes a difference but my personal opinion is if it sounds good leave it
I biased mine higher than 5v when I built it
If you really want to try some additional series resistance you could simply tac a resistor on the underside of the board between TR3 lug 1 and Q3 drain obviously removing Q3 first, I’d start at 2K
Thanks for the suggestions. I messed with the bias of 1 and 2 a little bit but didn’t try them both slightly above Q3. I will start there.
And, you are right, not too tough to tack that resistor on the bottom of the board…my mind went straight to putting a higher value trimmer in there and was not looking forward to that. Not of a fan of having to desolder…
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