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Active Bass and K250 preamp damage [message #27964]

Wed, 20 January 2021 07:45

stevem
Messages: 4735
Registered: June 2004
Location: NY

Senior Member

Well over a year ago now while at rehearsal and using one of my basses with a 18 volt active preamp I damaged my selectone channel in one of my K250 heads when it started to produce a ton of hiss.

Just over the weekend I got to look into the issue and had to replace the 14 pin duel section IC chip to fix it.

So you folks with active preamps in your guitars and or using stomp boxes that can add to signal input levels in to the amp beware of driving these 250 and K150 heads with too much signal into them!

These amps where not made to need that hot a input signal level to drive them to full output wattage.

[Updated on: Wed, 20 January 2021 07:48]

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Re: Active Bass and K250 preamp damage [message #29239 is a reply to message #27964]

Sun, 05 May 2024 19:49

Default
Messages: 2
Registered: May 2024

Junior Member

I occasionally run a 9v Stingray thru my 250, rarely above 9oclock on the volume and into the "passive" input. SO FAR no issues, but I'm also not playing for long as I'm just messing about. I do find that even with my passive basses it seems like I'm "overdriving" the head, as the tone seems to shift and not be quite as good past a certain volume, but Im also new and may be dialing things in wrong.

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Re: Active Bass and K250 preamp damage [message #29241 is a reply to message #27964]

Tue, 07 May 2024 06:48

stevem
Messages: 4735
Registered: June 2004
Location: NY

Senior Member

In 72 due to complaints from guitar player a circuit change was put in place on the 250 and 150 amps to provide more gain.

This worked great for the guitar player, but I find that for bass I like the pre 72 non mod better , there more dynamic range for bass use and as such less chance of driving the amp into clipping

If you have one of these amps it's all of 5 bucks worth of parts to put it back to it original production form.

Another thing that helps when you have a active bass with hot output is to run the volume on the bass down to 3/4s or less and turn the amp up more.

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