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| 100v Line Audio Distortion |
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| Arlen Moulton2:
Hi All, I was recently gifted a TOA VM1120 100v and 70v line amp, it's one of their earlier models with a transformer output stage rather than direct coupling to the transistors. It's a 120w rated amp but I've been testing it with a 30w speaker, 16w speaker and 6w speaker (all set to 100v) but I've noticed what I'd class as an unreasonable amount of distortion to the sound, when bass notes hit they make a "pop" noise and the whole amp chassis judders, almost like an electromagnet is being energised. It seems to me like the output transformer core is being saturated, this happens above 25% volume (sound is crystal clear and rich below 25%) and is worse on the 100v tap than the 70v tap. I've noticed adding more speakers in parallel also reduces the problem but it's still there. Does anyone have any ideas what the cause might be, or whether this is what these amps are always like? Thank you in advance. |
| Benta:
Please clarify "all set to 100 V". Are your speakers real 100 V line speakers? |
| dmills:
That's probably core saturation right enough. 100V amps in general are not normally designed to do bass, these are really paging system amplifiers, so think in terms of a couple of hundred Hz and up, the better ones have an HPF to enforce this given the limits of both the output iron and (sometimes more significant) the speaker transformer iron. |
| bob91343:
An oscilloscope would come in handy. |
| Arlen Moulton2:
--- Quote from: Benta on November 22, 2020, 07:20:19 pm ---Please clarify "all set to 100 V". Are your speakers real 100 V line speakers? --- End quote --- Yes, I have an Eagle PA speaker which can run either 8Ohm, 70v or 100v. I also have a pair of Bosch 100v ceiling speakers and another PA speaker with an RS Components matching transformer fitted. |
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