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PostPosted: Tue Oct 02, 2018 5:48 pm 
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Bottle Rocket

Joined: Tue Oct 02, 2018 5:28 pm
Posts: 2
Hi all,

I have just purchased a subway rocket second hand which has been converted to a head. Great sounding amp, very Markish on the contour mode. I've had a Mark V 25 in the past and a few other Boogies, so I'm used to the tone stack and how to set this amps up in general etc.

When I use the contour mode, regardless of gain position (worse with lower gain settings) , I get this really annoying bass thump that accompanies my pick attack when using the neck pickup, mostly playing higher up the neck. I have had this on other tube amps in the past, namely Hughes and Kettner GM36 and JVM did similar thing when using higher gain channels. My Mark V 25 didn't do this, neither did the JP2C I played a little while ago.

I have tried the following:

Different 12ax7's and EL84's
Different cab's
Different guitars and pickup heights. All pickups are 4-5mm away from the string
Running full treble and zero mid/bass on the amp.

The amp is running Mesa and Mullard 12ax7's and tung sol el84's. Internally the amp looks 100% stock besides caps replaced by previous owner and I have done the parallel to series effects loop mod.

The only thing that seems to fix it somewhat is running a EQ in the loop and pulling ALL of the 125-250hz frequencies.

I seem to have found somewhat of a middle ground by pulling all frequencies down with my 10 band EQ and just boosting the whole signal to compensate for the volume drop by doing so. For some reason this sounds like its helping somewhat.

So my question is, is this just the way the amp is voiced? Is it just the way some tube amps compress the bass frequencies?

Will running a 5751 or 12AY7 help at all?

Ta.


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PostPosted: Tue Oct 02, 2018 10:43 pm 
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Mark II

Joined: Sun Aug 07, 2011 12:17 am
Posts: 107
Location: Alkimos, Western Australia
The contour mode really ramps up the bass. Different speakers will emphasise this more than others. EQ pedal set to roll off some lows is actually your only option. Or, maybe use the regular OD setting with the EQ in the loop, scoop some mids and don't boost the low end as much. You can get a pretty good approximation of the contour mode with an EQ pedal scooped on top of the regular OD setting.


Last edited by wildschwein on Wed Oct 03, 2018 10:16 pm, edited 1 time in total.

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PostPosted: Wed Oct 03, 2018 8:20 am 
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Mark III
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Joined: Mon Jan 14, 2013 4:13 pm
Posts: 257
Location: Chicago, IL
Does this happen with multiple guitars as well? If this has been an issue with other amps, it could be the guitar or the way you play.

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PostPosted: Wed Oct 03, 2018 9:59 pm 
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Bottle Rocket
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Joined: Tue Mar 21, 2017 3:19 pm
Posts: 18
Location: Rincon Beach, California, USA
I’ve had this same problem with Princeton Reverbs, especially with a certain Telecatser I have that has a Charlie Christian pickup in the neck. I suspected it was the voltages in the phase inverter circuit (PR is notoriously unstable), but I never confirmed that. The amp worked fine with other guitars.

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PostPosted: Wed Oct 17, 2018 5:46 pm 
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Bottle Rocket

Joined: Tue Oct 02, 2018 5:28 pm
Posts: 2
Ended up selling the amp and getting a rectifier. It was something in the amp that was causing the thump, ie circuit design. The rec has no such issue, even with the bass cranked it doesn't have this weird thump on picking attack.

Thanks for the replies though.


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