Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dsones on October 11, 2025, 10:33:51 am
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Considering a Vox AC15CH head. Does anyone know how the built in attenuator works? I read the Vox description but it is very vague. I saw a picture of the inside of the amp and it looks like there are just three cement resistors. Is the description just for sales? Thanks.
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https://assets.yoreparo.com/attachments/aeFpEBIg0NXGanzPVC3HTWqTQX0nYwLgg7VoQR48.pdf (https://assets.yoreparo.com/attachments/aeFpEBIg0NXGanzPVC3HTWqTQX0nYwLgg7VoQR48.pdf?utm_source=chatgpt.com)
Page 9 of the pdf
Franco
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Thanks that helps even though I don't fully understand the schematic. So it looks like there is much more going on for attenuation than just resistors. I have a weber minimass and bugera attenuator that work but color the tone to much. I'm hoping the voc ac15ch head attenuates without changing the tone so much. I've seen a couple you tube videos that touch on the attenuator sound and it seems the sound/tone stays the same regardless of the attenuation. I don't have a local music store that carries the head.
Thanks again
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Looks like it's just resistors and switching. It's running imaginary speakers in parallel/series with the existing speaker to create a similar load to the power section. Likely the loss of tone at certain frequencies is due to the speaker not being pushed as hard.
Rob Robinette has a similar mod on his website. I think some of the more expensive attenuators are limited in part by inductance, which would better recreate the response of an actual speaker.
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Thanks