Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
carvin XV-112 X-AMP problem
Hi guys,
Dont know if this is the right group, but i'll try anyway - got a carvin X-Amp model XV-112. this thing is a hybrid valve/op-amp type thing (3x12AX7, 4xEL34) 100w output. whenever you turn the gain (either the clean channel or the lead channel) up past about 5, the amp lets out a really high pitched squeal & any signal level (like a guitar input) drops out to almost nothing, so all you hear is the squeal. if the eq is set with the highs boosted, it's much worse.. anyone got any ideas what might be wrong with it? tried changing valves, but that makes no difference.. cheers, tc. .. |
#2
|
|||
|
|||
"timbo" got a carvin X-Amp model XV-112. this thing is a hybrid valve/op-amp type thing (3x12AX7, 4xEL34) 100w output. whenever you turn the gain (either the clean channel or the lead channel) up past about 5, the amp lets out a really high pitched squeal & any signal level (like a guitar input) drops out to almost nothing, so all you hear is the squeal. if the eq is set with the highs boosted, it's much worse.. anyone got any ideas what might be wrong with it? tried changing valves, but that makes no difference.. ** Have all the 12AX7s got their metal covers on ? ............ Phil |
#3
|
|||
|
|||
In article , Phil Allison wrote:
"timbo" got a carvin X-Amp model XV-112. this thing is a hybrid valve/op-amp type thing (3x12AX7, 4xEL34) 100w output. whenever you turn the gain (either the clean channel or the lead channel) up past about 5, the amp lets out a really high pitched squeal & any signal level (like a guitar input) drops out to almost nothing, so all you hear is the squeal. if the eq is set with the highs boosted, it's much worse.. anyone got any ideas what might be wrong with it? tried changing valves, but that makes no difference.. ** Have all the 12AX7s got their metal covers on ? no, they don;t have metal covers - doesn;t seem to be any provision for them either.. would that help? cheers, tc. .. |
#4
|
|||
|
|||
"timbo" Phil Allison wrote: got a carvin X-Amp model XV-112. this thing is a hybrid valve/op-amp type thing (3x12AX7, 4xEL34) 100w output. whenever you turn the gain (either the clean channel or the lead channel) up past about 5, the amp lets out a really high pitched squeal & any signal level (like a guitar input) drops out to almost nothing, so all you hear is the squeal. if the eq is set with the highs boosted, it's much worse.. anyone got any ideas what might be wrong with it? tried changing valves, but that makes no difference.. ** Have all the 12AX7s got their metal covers on ? no, they don;t have metal covers - doesn;t seem to be any provision for them either.. would that help? ** What you are describing is high frequency oscillation due to positive feedback which is in turn due to stray capacitance coupling the signal at the output of the amp (likely at plate voltage levels) back into the sensitive first input stage. This is quite common in guitar amps due to the ridiculous amounts of gain and high frequency boost that is available at high knob settings. I have measured a "Marshall Master Model" as having a max sensitivity of ** 60 uV ** at the ( 1 Mohm ) input to give 100 watts output at 6 kHz. This is over 160 dB of power gain !!! Wiring layout, grounding and shielding of the input circuitry are all crucial if such oscillation is to be avoided. Take your amp to a tech who specialises in tube guitar amps for the squealing to be exorcised. .............. Phil |
#5
|
|||
|
|||
timbo wrote: Hi guys, Dont know if this is the right group, but i'll try anyway - got a carvin X-Amp model XV-112. this thing is a hybrid valve/op-amp type thing (3x12AX7, 4xEL34) 100w output. whenever you turn the gain (either the clean channel or the lead channel) up past about 5, the amp lets out a really high pitched squeal & any signal level (like a guitar input) drops out to almost nothing, so all you hear is the squeal. if the eq is set with the highs boosted, it's much worse.. anyone got any ideas what might be wrong with it? tried changing valves, but that makes no difference.. cheers, tc. . I would suspect filter capacitor problems (dried out, lost capacity). You can temporarily bridge a known-good capacitor, say about 20 uF at adequate voltage, across the existing ones, to see if that makes a difference. If it does, replace them. Cheers, Fred -- +--------------------------------------------+ | Music: http://www3.telus.net/dogstarmusic/ | | Projects: http://dogstar.dantimax.dk | +--------------------------------------------+ |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
on topic: we need a rec.audio.pro.ot newsgroup! | Pro Audio | |||
Some Recording Techniques | Pro Audio | |||
Problem With Alpine Head Unit/Type E Subs (Part 2) | Car Audio |