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Donesigneduptwice

GenzBenz Shuttle distortion problem

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Just noticed a problem with my Genz-Benz Shuttle 3.0. It's been sitting up for about half a year, since our local open jam shut down. Had a buddy stop by and want to jam a bit. So he plugged up his guitar to a handy Fender, and I plugged up my bass into my Shuttle with a 1x10 cab.

 

I immediately noticed that as a note decays in level a fuzzy, buzzy distortion is apparent till the note falls off completely or is muted. I initially thought it might be my bass's active preamp battery (it has been 6+ months since playing); no dice. It still does it. So I plugged my trusty ES335 in to make it as simple and passive as possible, but it still does it. Things sound fine at a decent volume, but as it decays, the sound just fuzzes out... and not a pretty fuzz.

 

I plugged a Line 6 POD in to both the effects return and the aux in, to attempt to bypass the internal Genz preamp, but it still does the fuzz. At this point I'm wondering if there might be a capacitor going bad in either the power supply or the power amp section. Any thoughts?

 

BTW, to eliminate the speaker being blown, I plugged a pair of phones up and got the same, albeit somewhat lower level. That tends to lean me toward PSU rather than amp section, but I'm not an electronics expert... by any means. I tend to zap myself if I mess with amplifier caps. :D

 

Thanks,

 

DoneSignedUpTwice

 

Pedulla Rapture 5

Genz-Benz Shuttle 3.0 1x10

other misc detritus of a life near music

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If you can hear it through phones, the issue is probably in the preamp. Beyond that, I have no clue.

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Here are my thoughts, for what they're worth. The Shuttle 3.0 doesn't appear to have an actual preamp out or power amp in. I don't see an easy way to isolate the preamp from the power amp. I would try all possible ins and outs, including the direct out in both pre and post modes. I don't think that the level or ground switches would make a difference, but try them, too, just in case. Take notes on everything you try. You say that you're not a technician, so I recommend that you not try to work on it yourself, but the notes should be helpful to whoever does.

 

I agree that it sounds like the problem is in the power amp or possibly the power supply, but I'm not familiar with class D amplifier architecture. Taking an output from the direct out, post EQ, should isolate most of the preamp section. If that signal is clean, then you know that the problem is downstream (i.e., somewhere between there and the speaker output). If it's not, then try it in the pre mode. If it's still distorted, then you know that it's upstream from the tone controls. If it's clean at that point, then it's likely in the tone stack.

 

Anyway, none of this matters much, as you're not going to try to work on it yourself, right? Gather all of the information you can, then take it to a technician.

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Here are my thoughts' date=' for what they're worth. The Shuttle 3.0 doesn't appear to have an actual preamp out or power amp in. I don't see an easy way to isolate the preamp from the power amp. I would try all possible ins and outs, including the direct out in both pre and post modes. I don't think that the level or ground switches would make a difference, but try them, too, just in case. Take notes on everything you try. You say that you're not a technician, so I recommend that you not try to work on it yourself, but the notes should be helpful to whoever does. . . .[/quote']

The OP mentioned that he tried headphones and got the same symptom. Wouldn't that take the power amp out of the equation?

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The OP mentioned that he tried headphones and got the same symptom. Wouldn't that take the power amp out of the equation?

 

I don't think so. Headphones can't be pushed by a preamp alone. Their impedance is too low, and they need more power than a typical preamp can deliver, though usually only a few watts.

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I don't think so. Headphones can't be pushed by a preamp alone. Their impedance is too low' date=' and they need more power than a typical preamp can deliver, though usually only a few watts.[/quote']

I stand corrected. I thought the headphone amp was a dedicated amp built into the preamp.

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I stand corrected. I thought the headphone amp was a dedicated amp built into the preamp.

 

That is possible. I am not familiar with the internal architecture of the amp. But it could also (more easily and more cheaply, I think) be an attenuated output from the main amp.

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If Agedhorse still posts on the live sound forum, I would consider DMing CraigV and asking if you could post your question on the CVLS forum. Agedhorse would likely have a good handle on the issue as he likely had a big hand in that amp design. He is over at Mesa now, IINM.

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IIRC the GB Shuttle is a hybrid tube pre/solid state power amp, and hybrid amps have their own set of oddities. This could be one of several possible issues including a bad pre-amp tube [my first guess], FET, capacitor, erratic solder joint...or a ghost in the machine. There is also no transformer in the circuit, so the Class D amp does all the 'heavy lifting' up to 600W.

Have you lowered the gain level on the preamp and or adjusted the 'shape settings'? If you see the same issue at all settings on the preamp, then the 12AX7 is likely not the culprit...but swapping it is probably the easiest cheapest 'test' you can do without risking life and limb.

 

Based on your comment about getting cap-zapped, I suggest, along with my colleagues here, that you take this to a reputable qualified tech.

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