Knork Posted January 17, 2011 Share Posted January 17, 2011 (edited) Recently the volume drops suddenly after some minutes of use in my Mesa Boogie V-Twin floorpedal. It's a 3 channel tube preamp, it's got 2 12AX7 tubes. Strange part: the clean channel (not the bypass) is not affended. It can usually be used as the reference volume setting compared to the bypass. Then the other 2, the softer "blues" and the hot "solo" channels would well... boost. But after say 15 minutes there's that volume drop. Tube changing time only or worse? and more general: the pedal has gain and master controls. Why is a passive bass so much more uneven within the 2 boost channels? It's a bit overdriven in the blues but rocketlauncher loud in the solo, while the active bass' 2 volumes are quite even. The latter just gets more bite in the solo channel. All about gain volume? ah it's this: [url="http://www.mesaboogie.com/Product_Info/Out_of%20_Production/V-Twin/v-twin.html"]http://www.mesaboogie.com/Product_Info/Out...win/v-twin.html[/url] Edited January 17, 2011 by Krohurte Quote Link to comment Share on other sites More sharing options...
Dood Posted January 17, 2011 Share Posted January 17, 2011 Hi Krohurte. I'd try at least taking the valves out and reseating them to begin with just in case there is a tarnished contact. Check the switches are working correctly with a multimeter too. I *can* tell you that valve 2 feeds the dirty channel alone and V1 the clean channel, so see if you can try another valve in that position - maybe just swap the two round as they are both the same to see if the problem moves to the clean channel instead. If that doesn't help then it's time to delve a little deeper! The channel switching itself is only controlled by the footswitches, no signal passes through them - so it maybe an 'active switch' (Which are all J175 FETS) that could be messing about. Or - well, I'm loathed to suggest the 'step up' power supply for the valve HT as I'd expect the volume drop to happen on both channels - maybe it could be the power supplying the heaters on V2. There's quite a few possibilities - but at first try the easy stuff, like swapping the valve out! How do you find the V-Twin for bass? I nearly bought one off ebay last year! Rare beasts for sure! Quote Link to comment Share on other sites More sharing options...
Knork Posted January 17, 2011 Author Share Posted January 17, 2011 Yeah the most obvious move is to get new valves. I swapped quite a lot while handling the problem. 3 different pairs but they are all quite used anyway. Next test would be a new power supply. I don't understand the J175 FETS part, since I'm total noob about these things... I [i]LOVE[/i] the v-twin for bass. It's a bit tricky because the settings or rather the amount of overdrive and volume differ a lot for active and passive basses. But a Stingray through this beast to an Ampeg SVT, oh my... Other bass distortion pedals mostly cut a lot of the low ends and/or muffle the bass sound. But since you have lots of knobs to turn and it's a tube pre amp, you can set it to your liking. You can even [i]add[/i] lots of low end and it sounds still very transparent, as opposed to fuzzes like the Big Muff. The only itch is the slight delay when switching channels. Must be a mechanical thing. But I got used to it and arrange my playing to it. Step on it maybe a 32th note earlier or some other trick. No problem. But there'd be an external select option I never tried. It's also quite good for direct recording for its to-power-amp and to-mixing-desk outputs. Quote Link to comment Share on other sites More sharing options...
Knork Posted January 22, 2011 Author Share Posted January 22, 2011 (edited) No it wasn't the the valves. Fresh ones in, same problem. Edited January 22, 2011 by Krohurte Quote Link to comment Share on other sites More sharing options...
Dood Posted January 22, 2011 Share Posted January 22, 2011 [quote name='Krohurte' post='1098507' date='Jan 22 2011, 11:40 AM']No it wasn't the the valves. Fresh ones in, same problem.[/quote] Ahh poop! - Yeah, sorry about the geekiness of my last post. The FETs are basically like 'electronic switches' in the V-t. The foot switches only control those electronic switches, as opposed to a lot of pedals where the audio signal travels through the foot switch itself. I wondered if there was a problem somewhere with them not conducting properly. Only one would need to be at fault. Agreed about the PSU - are you using an official one with the pedal? It's worth just checking that the one you have is the correct voltage AND is capable of supplying enough current to drive the pedal. Quote Link to comment Share on other sites More sharing options...
Knork Posted January 24, 2011 Author Share Posted January 24, 2011 I'm using the official PSU that came with the pedal. But maybe that one's screwed up. It's all in guitar hospital now, so we'll see. I will call the guy there about this faulty FET switch possibility then. Thanks. Quote Link to comment Share on other sites More sharing options...
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