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Twin Tube Classic + Avalon DI = Crazy Ground Hum Dual-Channel Preamps
Old 6th November 2018
  #1
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Twin Tube Classic + Avalon DI = Crazy Ground Hum

Got a very minor problem that I'm wondering if anyone can solve, or at least explain.

I recently picked up a used Seymour Duncan Twin Tube Classic in good condition to add real tube overdrive to a mostly ITB setup. When I plugged it directly into the interface, the signal came in clean and sounded... good! But it was quite low level, since the output of the pedal is intended for instrument inputs.

So, obviously, the solution should be to use an active DI, right? I plugged it into an Avalon 2022--which has an instrument input that works great for electric guitars and bases and provides clean gain--and the union of the two immediately caused a surprisingly loud and constant ground hum that didn't change at all with toggling of lead and rhythm channels or the bypass switch, or volume and gain modulation on the pedal. Of course, changing the gain on the Avalon changed the level of the hum accordingly, but the signal was well beyond unusable at the Avalon's lowest gain.

I looked up the Twin Tube Classic manual, which said the pedal should only be used with grounded outlets, but it came with an ungrounded power supply, and when I looked up appropriate power supplies online, ALL of them were ungrounded. I thought maybe the seller of the pedal had swapped in a substitute, but I'm 99% sure that this is the power supply that came with the pedal from the factory.

Again, testing the pedal with the interface suggests it's in well-working condition, but the Avalon--which has been a stellar performer for about ten years, and still is except for this--doesn't like it. What gives?

Anyone?
Old 6th November 2018
  #2
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jwh1192's Avatar
Quote:
Originally Posted by BigAC View Post
Got a very minor problem that I'm wondering if anyone can solve, or at least explain.

I recently picked up a used Seymour Duncan Twin Tube Classic in good condition to add real tube overdrive to a mostly ITB setup. When I plugged it directly into the interface, the signal came in clean and sounded... good! But it was quite low level, since the output of the pedal is intended for instrument inputs.

So, obviously, the solution should be to use an active DI, right? I plugged it into an Avalon 2022--which has an instrument input that works great for electric guitars and bases and provides clean gain--and the union of the two immediately caused a surprisingly loud and constant ground hum that didn't change at all with toggling of lead and rhythm channels or the bypass switch, or volume and gain modulation on the pedal. Of course, changing the gain on the Avalon changed the level of the hum accordingly, but the signal was well beyond unusable at the Avalon's lowest gain.

I looked up the Twin Tube Classic manual, which said the pedal should only be used with grounded outlets, but it came with an ungrounded power supply, and when I looked up appropriate power supplies online, ALL of them were ungrounded. I thought maybe the seller of the pedal had swapped in a substitute, but I'm 99% sure that this is the power supply that came with the pedal from the factory.

Again, testing the pedal with the interface suggests it's in well-working condition, but the Avalon--which has been a stellar performer for about ten years, and still is except for this--doesn't like it. What gives?

Anyone?
i had an Avalon 2022 for years ... if i plugged a stereo keyboard in a got a wicked hum ... took it in to Avalon and they put a very large ground wire between the two channels ... that hum never fully went away ...

i wonder if your 2022 is doing the same thing .. but with one channel .. do you have anything stereo to see if you get the same effect i did ??? might start you troubleshooting in the right direction
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