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John East Uni-Pre Squealing with treble cranked
- Thread starter edwinhurwitz
- Start date
The easy answer: decrank the treble... Maybe having the treble cranked is inducing microphonic feedback? If you need more top end maybe use brighter strings
Except that it never used to do this. I’m looking for a fix, not a workaround. I can’t imagine anything is feeding back when playing into only IEMs and no amp or PA.
Not yet. He has been unresponsive when I’ve tried to reach him before.
I don't know much about John East preamps, but generally speaking, when you get squealing, it's often because an (unshielded) output wire is too close to an input wire, coupling a bit into it and causing feedback. Like a microphone too close to a speaker. I would try to reroute the internal wiring, or use a shielded output wire to cut down on parasitic coupling.
Do you have an active/passive switch? These can also be problematic because they bring input and output wires close together.
Do you have an active/passive switch? These can also be problematic because they bring input and output wires close together.
I've never seen a pre-amp (inside an amp or instrument) that didn't add noise when boosting the treble at max.
+18dB at treble on a bass will sound noisy with whatever circuit.
this said, if it's not just noisy, but 'squealing', that might be a grounding problem. when I suspect one, I usually take off the control cavity cover, touch the strings with one hand and touch backs of the pots with another one. if it stops at me touching some specific thing -- that's the culprit.
or indeed the hot wire, as Jerry suggested. I've also faced it.
p.s. and yes -- it's much easier to hear this in IEM than in a cab, a bass cab cuts the higher frequencies. try some LPF in your chain.
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18 dB is a LOT of treble boost - that's about 12 dB more than I EVER use. One of my criticisms of active basses is that a lot of them have way more treble boost than I would ever use - they get noisy and brittle sounding up there.
Most string musical instruments have an upper mid peak at somewhere around 3 kHz, and a rolloff above that inherent in their design - violins, acoustic guitars, pianos, etc, all have it done acoustically - the top or sounding board resonates, then rolls off a lot of stuff up there. Electric instruments do that peak and rolloff electrically. Undoing that rolloff with a lot of electrical treble boost takes you into territory that, for hundreds (perhaps thousands) of years, people have avoided when making musical instruments.
Most string musical instruments have an upper mid peak at somewhere around 3 kHz, and a rolloff above that inherent in their design - violins, acoustic guitars, pianos, etc, all have it done acoustically - the top or sounding board resonates, then rolls off a lot of stuff up there. Electric instruments do that peak and rolloff electrically. Undoing that rolloff with a lot of electrical treble boost takes you into territory that, for hundreds (perhaps thousands) of years, people have avoided when making musical instruments.
Also had this issue with a bass that I built for @rogerbmiller. It was a Nordy Big Blade Man (or possibly a Big Split Man) pickup and 3B preamp. He got the bass and it was shrieking as you mentioned. Basically, that internal gain pot was just too high for these rather high-output pickups. A slight dial back and it was no longer a problem.
There is no harm trying to move wires internally, as suggested above, but this could be the fix that is very easy to at least try.
It's odd that it wasn't doing it and now it is, but there's no cost or harm in making an attempt at reducing the gain at the trim pot.
Another thing to check would be your battery voltage. As the battery gets weaker, its internal resistance increases. Its voltage becomes less stiff, easier to move up and down by the load presented by the circuit, which varies with the signal. This can make the circuit more prone to oscillation, even though it still works at, say, 6V instead of 9V. I found this the hard way...
This. I was going to joke with the OP that I would hate him with the treble cranked on my in-ears even without the squealing.
I have no input on the audio issue, but that photo is epic. Must have been a great show!
Yeah, I would never turn it up that high, but it starts squealing about half way up.This. I was going to joke with the OP that I would hate him with the treble cranked on my in-ears even without the squealing.
Did you move the treble pot in the cavity,, Did you crank that, What pickup is squealing on. Then look at the pickup gain adjustment inside/ I keep those just past unity which is zero. Make sure sure non of the user replaceable square cap is pushed in all the way.
I had the same issue (squealing with the treble cranked). Reducing the internal gain trims sorted the issue for me. Thanks!
Update:
It’s fixed. I reconnected all the wires and it went away. I’m suspecting a ground wire that looked good but wasn’t.
There are things I like about the screw terminal setup, but at the end of the day, I’d rather solder the wires to the board. It seems stronger to me.
I really appreciate all of the input from everyone!
It’s fixed. I reconnected all the wires and it went away. I’m suspecting a ground wire that looked good but wasn’t.
There are things I like about the screw terminal setup, but at the end of the day, I’d rather solder the wires to the board. It seems stronger to me.
I really appreciate all of the input from everyone!
