SWR 750X active input "splat"

[psycle_1]

Working on an SWR 750X. Replaced the preamp tube, original was dead. When testing the active input, i get an audible "splat" on the attack of the E and A strings on my bass. When using the passive/active input, it sounds great, no splat. When I pull the preamp tube, the splat disappears from the active input. Checked preamp out to another power amp, splat is still there so I know it's isolated to the preamp section. Splat is also present in Tuner Out and XLR out on all settings (Line, Direct, Direct+FX). Bass has active EMG's running at 18v. Batteries are at 17.9V, so it's not the bass itself clipping.

If this was my personal amp, I wouldn't sweat it but since it's for a client, I want to make sure it's 100%. I've attached the preamp schematic for reference. Any ideas? Thanks!

[glebert]

Did you try a different preamp tube? If you turn down volume on the bass does the splat go away? An 18v bass preamp can put out a considerable signal swing.

[psycle_1]

Did you try a different preamp tube? If you turn down volume on the bass does the splat go away? An 18v bass preamp can put out a considerable signal swing.

Different known good preamp tubes didn't change anything. It goes away slightly when turning bass volume down, but I would think if it was an output level issue from my bass the splat would be even more exaggerated using the passive/active input.

I did find the tips on the input jacks are not shorting to ground when unplugged as they should. Going to ground the passive/active tip input and check the active input again for attack splat.

[psycle_1]

Confirmed, shorting plug in passive/active input makes the splat on active input disappear. Time to see if I can repair the tip connection on the cliff jacks.