jjhaz@ont.com Posted February 13, 2002 Share Posted February 13, 2002 This is weird!! I just hooked up a Dynaco ST70 on loan till my NEW ALS Tube amp comes next week a whooping 5 watts per channel. (yea!!!!) Anyway the ST 70 is hooked up to a pair of Cornwall's Original Crossovers. I turned on some music and almost immediately both my friend and I felt like we were in an airplane with our ears popping. (No drugs involved) I have never experienced this type of effect. I took one speaker and changed the wires to be out of phase. The pressure sensation stopped but so did the stereo sound field. Other amps with these speakers in this room have never yielding this ear popping pressure. Ive tried many different CDs and the effect is the same, when wire correctly ears start popping move one out of phase and the ear popping starts. Change both speakers out of phase and the ear popping starts again. The big question "Whats going on here?" Help, Jeff ------------------ Cornwalls Main fronts ALK Networks Heresy Center KLF-C7 Center IW-150 Rears KSW-12 200watt Sub (na) Anthem AVM20 Preamp 5 Adcom 555s Modified By Musical designs all mono BLock Toshiba 9200 DVD Echostar Dolby Satilite. JVC-7800 SVHS VCR ----------------------- Project room Genelec Nearfield Monitors with Genalac Sub Alisis 32 channel board Joe Meek VC1Q Studio channel Art Power Plant Roland R8 Wave/24 24bit and Delta 66 digital recording Aphex Comperesors And so on. Quote Link to comment Share on other sites More sharing options...
JohnA Posted February 13, 2002 Share Posted February 13, 2002 Very high frequency oscillation? Say 15kHz? John Quote Link to comment Share on other sites More sharing options...
jjhaz@ont.com Posted February 13, 2002 Author Share Posted February 13, 2002 john, No it seems to be in the lower register. It seem to build. I've thought maybe standing waves but why with this one tube amp? JEff ------------------ Cornwalls Main fronts ALK Networks Heresy Center KLF-C7 Center IW-150 Rears KSW-12 200watt Sub (na) Anthem AVM20 Preamp 5 Adcom 555s Modified By Musical designs all mono BLock Toshiba 9200 DVD Echostar Dolby Satilite. JVC-7800 SVHS VCR ----------------------- Project room Genelec Nearfield Monitors with Genalac Sub Alisis 32 channel board Joe Meek VC1Q Studio channel Art Power Plant Roland R8 Wave/24 24bit and Delta 66 digital recording Aphex Comperesors And so on. Quote Link to comment Share on other sites More sharing options...
leok Posted February 13, 2002 Share Posted February 13, 2002 Hello jjhaz, Maybe low freq oscillation due to feedback problems. I wouldn't have expected it with the Dynaco, but there are many factors involved. Try a different impedence hookup for the speakers (If they are connected to the 8 Ohm tap, try the 4 Ohm tap). The amp may be experiencing positive feedback at some low frequency and is oscillating. Usually changing something in the output circuit calms things down. Other possibilities: very long speaker wires, grounding problems .. try grounding the amp chassis to the preamp chassis. Good luck. Quote Link to comment Share on other sites More sharing options...
jjhaz@ont.com Posted February 13, 2002 Author Share Posted February 13, 2002 leok, Thanks for the thoughts I'll try changing the ohms setting and reground the amp. Thanks, Jeff ------------------ Cornwalls Main fronts ALK Networks Heresy Center KLF-C7 Center IW-150 Rears KSW-12 200watt Sub (na) Anthem AVM20 Preamp 5 Adcom 555s Modified By Musical designs all mono BLock Toshiba 9200 DVD Echostar Dolby Satilite. JVC-7800 SVHS VCR ----------------------- Project room Genelec Nearfield Monitors with Genalac Sub Alisis 32 channel board Joe Meek VC1Q Studio channel Art Power Plant Roland R8 Wave/24 24bit and Delta 66 digital recording Aphex Comperesors And so on. Quote Link to comment Share on other sites More sharing options...
lynnm Posted February 19, 2002 Share Posted February 19, 2002 I agree with mdeneen. I am old enough to have worked on a lot of old tube equipment and the symptoms described are classic for "motorboating" I think this condition relates to a fault in the input circuit for the power amp which results in a very low frequency signal being generated and amplified but I am reaching WAAAAY back into the murky mists of my memory here. It seems to me that the trigger can be a microphonic preamp tube. In other words the tube does not actually "cause" the motorboating but if the preconditions exist the tube can give the nudge which starts and maintains the low frequency oscillation. ------------------ It is meet to recall that the Great Green Heron rarely flies upside down in the moonlight - (Foo Ling ca.1900) Quote Link to comment Share on other sites More sharing options...
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