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Post by michaelcleary on Apr 21, 2019 9:23:09 GMT -6
Just recorded some guitar tracks in Cubase with two mics, U67 and R121 on an old late 60's vibrolux. Sounds great but i noticed a lot of offset on the negative (bottom) half of the waveforms. why is this? it was the same on both mics and both were tracked thru different preamps. Thanks, mc
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Post by jcoutu1 on Apr 21, 2019 9:25:51 GMT -6
DC offset?
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Post by michaelcleary on Apr 21, 2019 9:38:44 GMT -6
yes, but my question is why would it overshoot to the lower side as opposed to the positive side. Is it because of the complex nature of the vibrolux amp signal? |
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Post by Deleted on Apr 21, 2019 10:11:20 GMT -6
Maybe speaker is wired backwards. It won't be the first time. Last album I mixed guitar player used two amps and one one of them was wired backwards. I told him and he was always fascinated about "stereo" he got. Check DC offset and call amp tech  Brass instruments spikes appear on positive cycles so you can surely tell issues in microphone, cables and gear if they are flipped |
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Post by johneppstein on Apr 21, 2019 13:02:52 GMT -6
Maybe speaker is wired backwards. It won't be the first time. Last album I mixed guitar player used two amps and one one of them was wired backwards. I told him and he was always fascinated about "stereo" he got. Check DC offset and call amp tech Brass instruments spikes appear on positive cycles so you can surely tell issues in microphone, cables and gear if they are flipped I don't see how wiring the speaker backwards would create assymmetrical offset in a single amp.
Could be a tube problem, could be something's wonky with the self-biasing circuit (which is also affected by the vibrato in some of those amps, depending on the exact model), could be a sign that you have a slightly leaky coupling capacitor. There are a lot of possible causes.
Knowing the actual model number would be helpful.
Take it to a tech.
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Post by svart on Apr 21, 2019 13:05:37 GMT -6
Just recorded some guitar tracks in Cubase with two mics, U67 and R121 on an old late 60's vibrolux. Sounds great but i noticed a lot of offset on the negative (bottom) half of the waveforms. why is this? it was the same on both mics and both were tracked thru different preamps. Thanks, mc Not sure what causes it in your case, but it's normal to see it on some sources. |
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Post by michaelcleary on Apr 21, 2019 15:49:27 GMT -6
Maybe speaker is wired backwards. It won't be the first time. Last album I mixed guitar player used two amps and one one of them was wired backwards. I told him and he was always fascinated about "stereo" he got. Check DC offset and call amp tech Brass instruments spikes appear on positive cycles so you can surely tell issues in microphone, cables and gear if they are flipped I don't see how wiring the speaker backwards would create assymmetrical offset in a single amp.
Could be a tube problem, could be something's wonky with the self-biasing circuit (which is also affected by the vibrato in some of those amps, depending on the exact model), could be a sign that you have a slightly leaky coupling capacitor. There are a lot of possible causes.
Knowing the actual model number would be helpful.
Take it to a tech.
1967 vibrolux 2-10". I'll reach out to my tech this week. Thanks mc |
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Post by Deleted on Apr 21, 2019 16:31:22 GMT -6
Maybe speaker is wired backwards. It won't be the first time. Last album I mixed guitar player used two amps and one one of them was wired backwards. I told him and he was always fascinated about "stereo" he got. Check DC offset and call amp tech Brass instruments spikes appear on positive cycles so you can surely tell issues in microphone, cables and gear if they are flipped I don't see how wiring the speaker backwards would create assymmetrical offset in a single amp.
Could be a tube problem, could be something's wonky with the self-biasing circuit (which is also affected by the vibrato in some of those amps, depending on the exact model), could be a sign that you have a slightly leaky coupling capacitor. There are a lot of possible causes.
Knowing the actual model number would be helpful.
Take it to a tech.
If an amp has DC issues offsets signal to the positive side if speaker is wired right and pushed to negative side of wired backwards |
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Post by johneppstein on Apr 22, 2019 12:59:59 GMT -6
I don't see how wiring the speaker backwards would create assymmetrical offset in a single amp.
Could be a tube problem, could be something's wonky with the self-biasing circuit (which is also affected by the vibrato in some of those amps, depending on the exact model), could be a sign that you have a slightly leaky coupling capacitor. There are a lot of possible causes.
Knowing the actual model number would be helpful.
Take it to a tech.
If an amp has DC issues offsets signal to the positive side if speaker is wired right and pushed to negative side of wired backwards Er, NO.
Tube amps don't and can't have DC offset issues at the output - transformers do not pass direct current.
If there's an asymmetry problem in the output waveform it has to be generated somewhere before the output transformer - either the power amp section is somehow out of balance, which could be a weak power tube, a problem in the phase inverter circuit, or a leaky coupling cap between the PI and the power tubes. More likely, however, is a slight leak in one of the coupling caps somewhere in the preamp, throwing off the biasing of the following stage.
If any FX pedals are being used it could also be a DC offset problem in a pedal, even if the pedal is turned off (if it isn't true bypass.)
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